国際化推進共同研究概要
No. 1
21EA-1
タ イ ト ル： Dynamical mechanisms of stratospheric control on the tropical
troposphere and ocean
研 究 代 表 者： UEYAMA Rei

所内世話人： 江口 菜穂
研究概要：

2019 年 9 月初旬、南半球極域で成層圏突然昇温（SSW）イベントが発生しました。 このイベントは、南半球極渦の崩壊には至りませんでしたが、成層圏の南北循環を大幅に強化し、熱帯湧昇を増加させ、熱帯下部成層
圏の気温を低下させました。 本研究課題から、この SSW によって太平洋と大西洋での熱帯暴風とサイクロンの発達を含む、熱帯対流活動が強化されたことがわかりました。特に大西洋上で急速に発達した熱帯低気圧
Dorian が SSW 前後で急速に発達する様子を、高鉛直分解能な雲データを用いて、明らかにしました。

Dynamical Mechanisms of Stratospheric Control on the
Tropical Troposphere and Ocean
Rei Ueyama (NASA Ames Research Center)
I. Abstract
In early September 2019, a large stratospheric sudden warming (SSW)
event occurred in the southern hemisphere (SH) polar region. This event did notlead to a breakdown of the SH polar vortex, but significantly enhanced thestratospheric Brewer-Dobson circulation with increased tropical upwelling andthus decreased temperatures in the tropical lower stratosphere. In thisobservational study, we find that tropical convective activity was enhanced dueto this SSW, including the development of tropical storms and cyclones over the
Pacific and Atlantic ocean basins.
II. Introduction
Stratospheric sudden warming (SSW) events have been known toincrease the stratospheric mean meridional circulation (also known as theBrewer-Dobson circulation) with enhanced upwelling in the tropics. Cooling of
the tropical lower stratosphere associated with enhanced tropical upwelling
destabilizes the tropical tropopause layer (TTL) and supports the developmentof deep tropical convection and cyclones (Kodera et al., 2015; Eguchi et al.,2015). A statistical relationship between northern hemisphere (NH) SSW eventsand tropical cyclones in the summer southern hemisphere (SH) has been
demonstrated recently in large ensemble mean numerical experiments (Yoshida
and Mizuta, 2021). They showed that SSW-induced cooling of the tropicalstratosphere results in increased convective precipitation over tropical cyclone
genesis regions (e.g., South China Sea, eastern tropical Pacific, Caribbean Sea).
In this study, we demonstrate how and to what extent tropical cyclone
activity was impacted by the strong SSW in September 2019.
III. Method/Data
We analyzed JRA-55 reanalysis data, NOAA outgoing longwave radiation(OLR) data, surface precipitation measurements from Global Precipitation
Climatology Project (GPCP), and satellite-derived global convective cloud top
altitudes (Pfister et al, 2022). Our approach for calculating the convective cloud
top altitudes is based on the assumption that rainfall, properly thresholded, candefine the area where convection is occurring. These rainfall data, coupled with
the infrared satellite information, can then define both the regions where themass-transporting convective cores occur, and their altitude.
IV. Results
The longitudinal variation in upwelling along 10°‒20°N associated withthe 2019 SSW is illustrated in Figure 1. Tropical temperatures decreased in theupper stratosphere at the end of August 2019, coincident with the start of theSSW. At this initial stage, cooling in the tropical stratosphere has not yet reached
down to the 100 hPa level. During this time, anomalously low temperatures arelocated over limited areas of South China Sea and the Pacific where convection isactive (as indicated by low OLR values). Tropical stratospheric cooling extends
downward to the tropopause level in early September over the ascending branchof the Hadley circulation. At this time, upwelling in the troposphere also
increases (Fig. 1b). Furthermore, longitudinal variations in 100 hPa
temperatures appear to correspond to variations in convective activity in thenorthern tropics (10°‒25°N).

Figure 1: (a) Top panel shows the 3-day (27-29 August) mean heightlongitude section of anomalous temperature (color shading) and pressure
velocity averaged over 10-20°N. Bottom panel shows the 3-day mean OLR
field in the northern tropics. (b) Same as (as) but for 2-4 September mean.
The longitude-time section of anomalous OLR and relative vorticity at 850
hPa averaged over 15°-25°N shown in Figure 2 illustrates a coherent and rapidchange in convective activity around 1 September. Convection organizes into
tropical disturbances and cyclones, which move westward over the Pacific andAtlantic Ocean sectors in September.

Figure 2: Longitude-time section of anomalous OLR and relative vorticity at
850 hPa averaged over 15-25°N.
A clear example of the impact of stratospheric temperatures on tropical
cyclone activity was seen in the case of hurricane Dorian, which generated over
the Caribbean Sea on 24 August. The relationship between tropical stratosphericcooling and the development of hurricane Dorian is illustrated in Figure 3. Whilethe cyclone initiation occurred prior to the development of SSW, hurricane
intensity increased from category 4 to 5 between 1 and 2 of September,coinciding with timing of rapid cooling of the tropical lower stratosphere over
the Caribbean Sea. At this time, strong enhancement in the upwelling isobserved at the 125 hPa level. There is remarkable agreement between thetemporal variations in 125 hPa pressure velocity and in the occurrence of deep(>14 km) convective cloud top height throughout this period. The distribution of
convective cloud top height indicates that the enhanced upwelling occurred inassociation with the increase in clouds reaching the TTL (cloud top pressure
higher than 140 hPa). It is also worth noting that the diurnal cycle in cloud top
height is significant before 29 August, but non-diurnal variations increase inearly September.

Figure 3: Time-height sections of (a) temperature anomalies and (b)pressure velocity anomalies at 125 hPa averaged over the Caribbean
region (80W-60W, 20-30N). (c) Convective cloud top occurrence fraction
over the same domain as (a) and (b).

V. Discussion/Summary
In this study, we found that the SSW event in September 2019 was
associated with an increase in deep tropical convective activity along theascending branch of the Hadley circulation in the NH over 10°‒25°N. Here weshowed an example of the SSW impact on the intensification of a tropical cyclone
over the Caribbean Sea. Similar examples were also found over other ocean
basins in the northern tropical latitudes such as the Pacific, India and African
sectors. This impact of SSW on deep convective activity and tropical cyclones
along the ascending branch of the Hadley circulation is similar to that found inassociation with other strong SSW events in the northern polar regions (e.g.,January 2009 and 2010; Kodera et al., 2015). We have shown that the influenceof stratospheric cooling first manifests itself on the deep convection penetrating
into the TTL. The difficulty in simulating the intensification of hurricane Dorianin many models (Ryglicki et al., 2021) may be related to model deficiencies insimulating the connection between tropical deep convection and the large-scale
stratospheric circulation.
VI. References
Eguchi, N., K. Kodera, and T. Nasuno, 2015: A global non-hydrostatic model studyof a downward coupling through the tropical tropopause layer during astratospheric sudden warming, Atmos. Chem. Phys., 15, 297-304,
doi:10.5194/acp-15-297-2015.
Kodera, K., B. M. Funatsu, C. Claud, and N. Eguchi, 2015: The role of convective
overshooting clouds in tropical stratosphere-troposphere dynamical coupling,
Atmos. Chem. Phys., 15, 6767-6774, doi:10.5194/acp-15-6767-2015.
Kodera, K., N. Eguchi, R. Ueyama, Y. Kuroda, C. Kobayashi, B.M. Funatsu, and C.
Claud, 2019: Implication of tropical lower stratospheric cooling in recent trends
in tropical circulation and deep convective activity. Atmos. Chem. Phys., 19, 26552669, doi:10.5194/acp-19-2655-2019.
Pfister, L., Ueyama R., Jensen E., and Schoeberl, M., 2022: A method for obtaining
high frequency, global, IR-based convective cloud tops for studies of the tropical
tropopause layer, in preparation.
Ryglicki, D. R., Velden, C. S., Reasor, P. D., Hodyss, D., & Doyle, J. D., 2021:
Observations of Atypical Rapid Intensification Characteristics in Hurricane
Dorian (2019), Monthly Weather Review (published online ahead of print 2021).
https://journals.ametsoc.org/view/journals/mwre/aop/MWR-D-200413.1/MWR-D-20-0413.1.xml.
Yoshida, K., & Mizuta, R., 2021: Do sudden stratospheric warmings boost
convective activity in the tropics? Geophysical Research Letters, 48,e2021GL093688. https://doi.org/10.1029/2021GL093688.

VII. List of Publications• Kodera, K., Eguchi, N., Ueyama, R., Funatsu, B., Gaetani, M., and Taylor, C.
(2021), The impact of tropical tropopause cooling on Sahelian extreme
deep convection, J. Meteor. Soc. Japan, 99,
https://doi.org/10.2151/jmsj.2021-055.
VIII. Research meeting and discussion
Several virtual meetings (participants: Rei Ueyama, Nawo Eguchi, and Kunihiko)were help to discuss the relationship between sudden stratospheric warmings
and tropical cyclones, and NICAM simulation results of the stratospheretroposphere exchange mechanism.
IX. Additional information
Rei Ueyama is still on a reduced work schedule due to COVID-19 caregiving.
NASA has granted excused leave to employees with COVID-19 caregiving
responsibilities through the end of January 2022. All travel is still restricted someeting in person was not possible this past year. However, we have maintained
communication via email and virtual meetings. We have used the funds topurchase a data server for storing and archiving our research data.
X. Other members of the joint research team
Nawo Eguchi
RIAM, Kyushu University
Kunihiko Kodera
Meteorological Research Institute国際化推進共同研究概要
No. 2
21NU-1
タ イ ト ル： Numerical simulation of EC and EBW in QUEST
研 究 代 表 者： BERTELLI Nicola

所内世話人： 出射 浩
研究概要：
QUEST では 3 年間で閉じ込め磁場を 0.25 T から 0.5 T に増強する計画を進めている。
0.5 T では現在、非誘導電流立ち上げ実験に用いられている 28 GHz ECH システムを用い、第二高調波中心加熱が行えるようになる。加えて内側に基本波加熱共鳴層が存在する。低密度、高密度プラズマにおける 0.5 T 実験時の基本波加熱・第二高調波加熱による入射ビームの１回通過吸収が評価された。有効なアップシフト共鳴で高効率な電流駆動が見込める。また、Petra-M により有限要素シミュレーションも進められている。

21 NU-1

Numerical simulation of EC and EBW in QUESTBERTELLI Nicola(Princeton University, U.S.A)
Extra-ordinary mode fundamental ( 1st ) and second ( 2nd ) harmonic heating scenario
has been considered for the 0.5 T ECHCD experiment, based on the ray tracing analysis.
Figure 1 shows ray trajectories at top view and transmitted power evolution along ray
propagation with parallel refractive indexes N//a = 0.15, 0.25 and 0.35 in low density
plasma. Bulk (with Teb0 = 0.5 keV ) and highly energetic (with Teh0 = 60 keV ) electroncomponents are taken into consideration in the ray tracing. The incident ray from the low
field side (LHS) starts to be damped as third harmonic absorption of the energetic electron,and is damped as 2nd harmonic absorption of energetic and bulk electrons. In addition, it
is damped as 1st absorption when it come closer to the Doppler shifted resonance, andreflected back outside due to the cutoff. The total single pass absorption reaches to 8090 %.

(a)

(b)

Fig.1 (a) Ray trajectories at top view and (b) transmitted power evolution along ray
propagation with parallel refractive indexes N//a = 0.15, 0.25 and 0.35 in low density
plasma. At the top view of (a), fundamental (1st ), second (2nd ) and third (3rd )resonance field radii are shown.
In high density case, it reflected back outside before coming to the 1st absorption area.

Figure 2 shows ray trajectories at top view and the transmitted power evolution along ray

propagation with parallel refractive indexes N//a = 0.15, 0.25 and 0.35 in high density
plasma. Here two (bulk and highly energetic) electron components are also considered asin the low-density case. The ray is strongly damped as 2nd harmonic resonance in theabsorption area of the bulk electrons. The resonance area for the energetic electrons
strongly shifts to the high field side (HFS) due to the relativistic effect and expands toboth of the HFS and LHS sides due to the Doppler shift effect. The strong damping resultsfrom the up-shifted resonance absorption of the highly energetic electrons due to the
Doppler shift effect as well as the bulk electron absorption. The non-inductive plasma
current driven by the ECHCD will be evaluated with the Fokker-Planck code.

(a)

(b)

Fig.2 (a) Ray trajectories at top view and (b) transmitted power evolution
along ray propagation with parallel refractive indexes N//a = 0.15, 0.25 and 0.35

Full 3D NSTX-U device geometry including realistic antenna geometry and 3D scrapeoff-layer (SOL) plasma is also modeled to simulate NSTX-Upgrade plasmas using PetraM finite-element-method (FEM). The antenna geometry and the 3D NSTX-U geometry
are from the NSTX-U CAD models. Petra-M code is a state-of-the-art genericelectromagnetic simulation tool for modelling RF wave propagation based on MFEM
[http://mfem.org], open-source scalable C++ finite element method library. In Kyushu
University, a commercial software of COMSOL has been prepared for FEM simulations.

国際化推進共同研究概要
No. 3
21NU-2タ イ ト ル： Design of Electron Cyclotron Emission Diagnostic for Electron
Temperature and its Fluctuation Measurements
研 究 代 表 者： SUNG Choongki

所内世話人： 文 贊鎬
研究概要：
トカマク装置 PLATO における新プラズマ診断法として電子サイクロトロン放射（ECE）と相関 ECE(CECE)計測の実現可能性を調べた。
実際 PLATO の放電パラメータの代わりに、持永らによる輸送研究の平衡値で放物線状の空間分布を仮定した。即ち、𝐵𝐵𝑇𝑇 = 0.3 T、𝑇𝑇𝑒𝑒 = 130 eV、𝑛𝑛𝑒𝑒= 1×1019 m−3 の値を用いて最初にプラズマのアクセス可能性を決定した。また、アクセス可能な周波数の総光学的厚さ（𝜏𝜏𝑚𝑚）を計算した。PLATO プラズマは、

基本波 O モードと第 2 高調波 X モードの両方でアクセス可能なすべての周波数にわたってアクセス可能な外層の深さが薄く、光学的厚さが 𝜏𝜏𝑚𝑚 < 1 の低密度であると判断した。これは、ECE/CECE が現在 PLATO の診断法として実行可能ではないことを示した。一方、アクセシビリティと𝜏𝜏𝑚𝑚値を改善するために必要な𝐵𝐵𝑇𝑇と𝑇𝑇𝑒𝑒値をシミュレーションした。
その結果、PLATO トカマクは ECE/CECE 測定には𝐵𝐵𝑇𝑇を約 1.1 T まで、𝑇𝑇𝑒𝑒を最大 1 KeV ま

で増やす必要があることが分かった。従って、ECE/CECE 測定のためには、デバイスアッ
プグレードして𝑇𝑇𝑒𝑒と𝐵𝐵𝑇𝑇を増やす必要があると考えられた。

CECE Feasibility for PLATO Tokamak
Pocholo Nebres, Choongki Sung
Fusion and Plasma Dynamics Laboratory, KAIST, Daejeon, ROK
Correlation electron cyclotron emission or CECE, is a plasma diagnostic technique which allows for themeasurement of small amplitude (~1%) temperature fluctuations which can be masked by thermal noise, in
addition to the ability to measure local electron temperature. These small amplitude fluctuations are often believed
to be related to turbulent transport in fusion plasmas [1]. This study aims to determine the feasibility of CECE for
use as a diagnostic system for the PLATO tokamak.
For the study, a simulation was done using code written in Python. The accessibility of the plasma created in thesimulation is first checked. The total optical depth of the accessible frequencies for the fundamental ordinarymode and 2nd harmonic extraordinary mode is then determined to check whether the plasma has sufficient optical
thickness for use in CECE or not.
The ordinary mode cyclotron frequencies are cut off when the cyclotron frequency is less than the plasma
frequency (𝜈𝜈𝑐𝑐 < 𝜈𝜈𝑃𝑃 ). As such, only the cyclotron frequencies greater than or equal to the plasma frequencies canbe detected in CECE, assuming that the detector views the plasma from the outboard edge. For the extraordinarymode frequencies, the signal cutoffs occur when the frequency is greater than the hybrid frequency 𝜈𝜈𝐻𝐻 and lessthan the right-hand cutoff 𝜈𝜈𝑅𝑅 (or 𝜈𝜈𝐻𝐻 < 𝜈𝜈 < 𝜈𝜈𝑅𝑅 ). The signal also experiences a cutoff when the frequency is lessthan the left-hand cutoff frequency 𝜈𝜈𝐿𝐿 [1].
The plasma parameters used for the calculations are: 𝐵𝐵𝑇𝑇 = 0.3 Tesla, 𝑇𝑇𝑒𝑒 = 130 eV, and 𝑛𝑛𝑒𝑒 = 1 × 1019 m−3 .
These values are the literature values for a simulation of equilibrium conditions by the PLATO team [2]. A
parabolic decay of off-center values has been assumed to account for the spatial variation of the plasma
parameters. Plasma center values have a factor of 1.0 to reflect the literature values.

The accessibility was first determined. CECE feasibility was then determined by using the total optical depth of
the accessible region for the ordinary and extraordinary mode waves. The desired optical depth should be τ𝑚𝑚 ≫ 1
so that the measured temperature is the blackbody/local electron temperature [1].
Plasma parameter values and center frequencies are shown in Table 1 and Table 2, respectively.
Tab. 1 Plasma Center Parameters130
Te (eV)ne (m−3 )1 × 1019
0.3
BT (Tesla)
Minor Radius (a; mtr)
0.18
0.7
Major Radius (R 0 ; mtr)

Tab. 2 Plasma Frequencies at 𝑟𝑟/𝑎𝑎 = 0 (in GHz)
8.4
29.6
νc
νH
16.8
28.4
2νc
νP
25.2
24.2
3νc
νL
32.6
νR

Tab. 3 Optical Depth 𝜏𝜏𝑚𝑚 Data for 𝑚𝑚 = 1 and 𝑚𝑚 = 2
Fundamental Ordinary Mode (m = 1)
𝜏𝜏𝑚𝑚 Range
0.0002 → 0.0027
Accessible Frequencies
6.68 → 6.72 GHz
Accessible 𝑟𝑟/𝑎𝑎
0.97 → 1.0
2nd Harmonic Extraordinary Mode (m = 2)
𝜏𝜏𝑚𝑚 Range
0.002 → 0.023
Accessible Frequencies
13.36 → 13.52 GHz
Accessible 𝑟𝑟/𝑎𝑎
0.94 → 1.0

Figure 1 shows the accessibility plot for the plasma parameters used in the simulation. The accessible frequencies
for the ordinary and extraordinary modes are marked along with the frequency range that can be detected. The xaxis is the plasma 𝑟𝑟/𝑎𝑎 parameter, ranging from -1 to +1, with 𝑟𝑟/𝑎𝑎 = 0 as the plasma center and – and + indicate
high and low field side, respectively. Only the low field side is shown starting from 𝑟𝑟/𝑎𝑎 = 0.8 − 1.0 since theaccessible window for both modes is very narrow, only to within 6% distance from the plasma outer layer. In theaccessible frequency range, the total optical depth range for the ordinary mode fundamental frequencies is τ𝑚𝑚 =0.0002 − 0.0027 while for the 𝑚𝑚 = 2 extraordinary mode frequencies the total optical depth range is τ𝑚𝑚 =0.002 − 0.023. Optical thickness values of less than 1 are defined as optically thin [1]. These are summarized inTable 3.

The small 𝐵𝐵𝑇𝑇 value contributes to the small accessible window as it is directly proportional to the cyclotron
frequency. The high electron density also produces a high plasma frequency. These two factors generate a plasma
with large cutoff regions and small accessible windows.

Fig. 1 Accessibility plot for the simulated PLATO plasma. Only the low-field side accessibility is presented due to the narrow
accessible layer (last ~6% outer layer depth of the plasma).

The total optical depth for either mode is much less than 1 for the simulated parameters, indicating that the plasma
is optically thin at the accessible outer layer regions. For optically thin plasmas, additional consideration must be
taken to account for the refraction of the ECE ray through the plasma [1], since the signal is not well-localizedcompared to an optically thick case where the intensity observed is directly related to the local electron
temperature. Since the absorption coefficient and the total optical depth are position-dependent (ω𝑝𝑝 and Ω(𝑠𝑠)),
regardless of the frequency and position that could be observed, the optical depth will be less than 1, signifying
an optically thin plasma. The plasma created in PLATO using the simulated conditions is called an ‘over-dense
plasma’.
The plasma parameters can be changed such that there is full accessibility on the low field side for both the Xand O-mode frequencies. Increasing the 𝐵𝐵𝑇𝑇 to 1.1T allows for full accessibility of the plasma across all
frequencies. The increased 𝐵𝐵𝑇𝑇 shifts the cyclotron frequency of the plasma and its harmonics upward to above thecorresponding cutoffs as shown in figure 2. Since the absorption coefficient and the total optical depth are directly
proportional to 𝑇𝑇𝑒𝑒 , increasing the temperature will also increase 𝜏𝜏𝑚𝑚 . Figure 3 shows the total optical depth plot ofseveral 𝑇𝑇𝑒𝑒 values with 𝐵𝐵𝑇𝑇 = 1.1T and the density kept at the original value of 𝑛𝑛𝑒𝑒 = 1 × 1019 m−3 . “Opticallythick” is defined as having 𝜏𝜏𝑚𝑚 ≫ 1 [1], but a value of at least 𝜏𝜏𝑚𝑚 = 2 is usually acceptable for use in CECE. For
ECE, a value of at least 𝜏𝜏𝑚𝑚 = 1 is also acceptable. Increasing the 𝑇𝑇𝑒𝑒 to 1 KeV increases the optical depth of theplasma to around 𝜏𝜏𝑚𝑚 = 1 for the fundamental O-mode wave from the center of the plasma to around 𝑟𝑟/𝑎𝑎 = 0.35.
This mode is acceptable for use only in ECE, since the optical depth is around 1. For the 1 KeV 2nd harmonic Xmode wave, 𝜏𝜏𝑚𝑚 ranges from 2 ~ 3 from the plasma center to 𝑟𝑟/𝑎𝑎 = 0.5. The 2 KeV fundamental O-mode wave
is optically thick with 𝜏𝜏𝑚𝑚 = 2 − 2.3 from the plasma center to 𝑟𝑟/𝑎𝑎 ~ 0.35 and the 2 KeV 2nd harmonic X-mode
and the 5 KeV fundamental O-mode waves are optically thick, with 𝜏𝜏𝑚𝑚 ranging from 2 − 6, in the low-field sideof the plasma up to around 𝑟𝑟/𝑎𝑎 = 0.7 from the center of the plasma. The 5 KeV 2nd harmonic X-mode wave has
acceptable optical depth, with 𝜏𝜏𝑚𝑚 ranging from 2 − 14, at up to around 𝑟𝑟/𝑎𝑎 = 0.8 from the center of the plasma.
Increasing the magnetic field and temperature parameters to 𝐵𝐵𝑇𝑇 = 1.1 Tesla and 𝑇𝑇𝑒𝑒 = 1 KeV are sufficient toenable ECE and CECE diagnostics in PLATO.

Fig. 2 Accessibility plot for the first three harmonics when 𝐵𝐵𝑇𝑇 is increased to 1.1 Tesla and all other parameters are maintained.
All frequencies are accessible; no frequency is cut off. The following plasma parameters were used: 𝐵𝐵𝑇𝑇 = 1.1 T, 𝑛𝑛𝑒𝑒 =1 × 1019 m−3 , and 𝑇𝑇𝑒𝑒 = 130 eV.

Fig. 3 Total optical depth 𝜏𝜏𝑚𝑚 vs. 𝑟𝑟/𝑎𝑎 plot for several values of 𝑇𝑇𝑒𝑒 . The absence of discontinuities in the plot indicates fullaccessibility of the harmonic frequencies. The following values were used for the 𝐵𝐵𝑇𝑇 and 𝑛𝑛𝑒𝑒 parameters: 𝐵𝐵𝑇𝑇 = 1.1 Tesla, 𝑛𝑛𝑒𝑒 =1 × 1019 m−3 .

The current PLATO parameters produce an over-dense plasma which makes it not suitable for ECE and CECE
measurements. The researchers would like to suggest to the PLATO team to consider increasing the toroidal
magnetic field and the plasma temperature in any planned future upgrades to PLATO, so that CECE diagnostic
can also be employed as one of its diagnostic techniques.

REFERENCES[1] Hutchinson, I. (2002). Principles of Plasma Diagnostics (2nd ed.). Cambridge: Cambridge University Press.
[2] Mochinaga, Shota, et al. "Transport Simulation of PLATO Tokamak Plasma Using Integrated Code TASK."
Plasma and Fusion Research (2021): 1403093-1 to 6.

国際化推進共同研究概要
No. 4
21NU-3タ イ ト ル： Plasma start-up and sustainment in spherical tokamak configuration
by RF
研 究 代 表 者： SHEVCHENKO Vladimir

所内世話人： 出射 浩
研究概要：
令和３年２月２−４日の３日間で国際 WS を遠隔開催した。英国から５名、米国から２名、国内から９名の参加があった。英国、米国、国内からの参会者が参加できるよう、日本時間で 21時からとなった。QUEST 実験の最近の進展・検討に加え、国内外実験の進展・検討、新たなシミュレーション解析などが議論された。英国から３件、米国から２件、国内で８件の研究成果発表があり、主に非誘導プラズマ電流立ち上げに関し、活発な議論があった。

RF-only ST plasma start-up, ramp-up and sustainment
Hiroshi Idei
Vladimir Shevchenko
A Summary of the Workshop which was held remotely via Zoom on 2-4 February
2022 and was as following:
10th Workshop Agenda, RIAM 2022

2 February
JST 21:00 / GMT 12:00 / EST 7:00 [ + 10 min. ]Vladimir Shevchenko / Hanada
WS purpose and agenda
JST 21:10 / GMT 12:10 / EST 7:10 [ + 40 min. ]Vladimir Shevchenko
ECRH Technology on ST40
JST 21:50 / GMT 12:50 / EST 7:50 [ + 30 min. ]Erasmus du Toit
Overview of ECRH and EBW modelling for ST40
JST 22:20 / GMT 13:20 / EST 8:20 [ + 40 min. ]Simon Freely
Microwave current drive studies at UKAEA
3 February
JST 21:00 / GMT 12:00 / EST 7:00 [ + 30 min. ]Hitoshi Tanaka
LATE - Recent result and future plan
JST 21:30 / GMT 12:30 / EST 7:30 [ + 30 min. ]Nicola Bertelli
Update of the 3-D full wave Petra-M simulation modeling of NSTX-U
HHFW
JST 22:00 / GMT 13:00 / EST 8:00 [ + 30 min. ]Akira Ejiri
Plasma current start-up by using the lower hybrid wave and its
modeling on TST-2
JST 22:30 / GMT 13:30 / EST 8:30 [ + 30 min. ]Yongtae Ko
Development of a capacitively coupled combline antenna for offmidplane launch of lower-hybrid waves in TST-2
JST 23:00 / GMT 14:00 / EST 8:30 [ + 30 min. ]Masayuki OnoAccessibility enhanced ECH and ECCD for plasma current start-up
and ramp-up
4 February
JST 21:00 / GMT 12:00 / EST 7:00 [ + 30 min. ]Hiroshi Idei
Recent Topics on 28-GHz ECHCD in QUESTJST 21:30 / GMT 12:30 / EST 6:30 [ + 30 min. ]Shin Kubo
Study of excited EBW detection by sub-Tera-Hz scattering in the
QUEST
JST 22:00 / GMT 13:00 / EST 6:50 [ + 20 min. ]Makoto Hasegawa
Long-time operation with high temperature wall (<400 C) on QUESTJST 22:20/ GMT 13:20 / EST 7:10 [ + 20 min. ]Qilin Yue
Preliminary results of Hydrogen Recycling with Fast Ejecting System
of Targeted Sample (FESTA) on QUESTJST 22:40 / GMT 13:40 / EST 7:40 [ + 20 min. ]Kengo Kuroda
Improved results of CHI discharge on remodeled system in QUESTJST 23:00 / GMT 14:00 / EST 8:00 [ + 10 min. ]Vladimir Shevchenko / Hanada
ClosingThe presentation summaries are as following:
Vladimir Shevchenko:

ECRH Technology on ST40
Two 1 MW gyrotrons have been ordered for ST40. These gyrotrons can operate either at 105
GHz or 140 GHz with RF pulse duration up to 2 seconds. Transmission lines as well as
gyrotrons are designed and manufactured by GYCOM Ltd., Nizhny Novgorod, Russia.
Transmission lines are based on corrugated cylindrical waveguide elements 63.5 mm indiameter. During operation these lines are kept under vacuum higher than 10-4 mbar. An input
HE1,1 mode is formed by mirrors in a matching optics unit. Each transmission line includes amiter bend combined with a directional coupler, two waveguide switches, a universal quasioptical polarizer, several miter bends, expansion joints, vacuum pumping ports, a dielectric
waveguide isolation (DC-break) and a vacuum gate. Some elements of the transmission line
are cooled by water. Corrugated waveguides are manufactured from aluminum in sections of
1 m long. These sections are connected to each other and to other transmission line elementsby special connectors, ensuring elements alignment and vacuum tightness.
During assembly any part of the transmission line can be connected to a short-pulse load toconfigure operating regimes of the gyrotron and to check performance of individual elements.
The short-pulse load can operate with pulse durations not exceeding 100 ms. For full pulse
length measurements RF power from any gyrotron can be directed to a shared long-pulse
dummy load using two waveguide switches.
The lower field side launcher is designed to study a wide variety of ECRH and CD scenarios
including conventional ECRH at second EC harmonic using extra-ordinary (X2) or ordinary(O2) modes at both 140 and 105 GHz. It also allows excitation of the EBW mode by launchingof a fundamental O mode (O1) with further mode conversion into an X mode (X1) at the mirrorpolarizer attached to the central post. The slow X1 mode experiences a subsequent mode
conversion into EBW mode at the upper hybrid resonance and then EBW propagates back to
the EC resonance. This scheme allows experimental studies of non-inductive plasma start-up,
current ramp-up and sustainment.
Erasmus du Toit:

Overview of ECRH and EBW modelling for ST40
A dual-frequency ECRH system is currently under development at ST40. The system will
employ two GYCOM gyrotrons with a maximum output power of 1 MW each and a pulse
length of 2s. Both gyrotrons can be tuned to operate at either 105GHz or 140GHz, which allows
for a study of non-inductive plasma start-up, current ramp-up and sustainment.
Operations in 2022 will use a fixed low field side (LFS) launcher that allows the study of
conventional ECRH at the 2nd EC harmonic using extra-ordinary (X2) or ordinary (O2) modes.
Both frequencies available have good accessibility to the 2nd harmonic resonance, whilemodelling shows that good absorption is expected across a range of densities, as shown infigure 1.

Plasma start-up and current drive will be studied in later experiments using electron Bernstein
waves (EBWs), by using the LFS launcher in an O-X-B successfully demonstrated on MAST 1.
An O-mode beam is launched from the LFS and converted to X-mode via a grooved mirror
polarizer located on the centre post. The X-mode propagates back into the plasma andundergoes mode conversion to EBWs at the UHR, which are subsequently absorbed.
Modelling results show strong absorption of EBWs across a range of parameters, with current
drive efficiencies up to 0.15A/W expected.

Figure 1 – Topology plot for ST40 plasma (left) shows the locations of the fundamental and 2nd harmonicresonances for 𝐵𝐵 = 2.4𝑇𝑇. The region where the fraction of power absorbed is greater than 70% is shown for arange of densities and magnetic field strengths for 105GHz (middle) and 140GHz (right) at 𝑇𝑇𝑒𝑒 = 2.5𝑘𝑘𝑘𝑘𝑘𝑘.

Simon Freely

Hitoshi Tanaka

LATE - Recent result and future plan
The primary objective of LATE (Low Aspect-ratio Torus Experiment) is to study on
non-inductive formation of spherical tokamak by using ECH/ECCD. For production of overdense plasmas, O-mode microwave is injected obliquely to the toroidal field from outboard
side to excite EBW.
Recently, by using a newly developed five-pin probe antenna and two-dimensional (2D) mechanical probe driving system, the 2-D wave pattern of phase and amplitude has been
directly measured for an over-dense ECR plasma with 1.5 GHz microwave. In the case of Omode injection, an EBW-like wave pattern has been detected for the first time, in a localized
region near the upper hybrid resonance layer. The pattern has a short wavelength of about 2
mm and is also electrostatic and backward. By adjusting the toroidal magnetic field, it is foundthat both the position and size of the EBW region have changed, which suggest the localized
condition of efficient O-X-B conversion and high collisional damping rate of EBWs.
In May 2021, the LATE device and all the diagnostics were disassembled and moved
to Uji campus (~10 km away from Yoshida campus) because of repair work of Plasma Wave
Experiment Building. The construction period is from August 2021 to February 2022. New 66
ports in total will be added to the original vacuum vessel. Assembling and installation will bestarted from April after movement of all the materials to the renovated experiment building.

Nicola Bertelli:Update of 3-D full wave Petra-M simulation modelling of NSTX-U HHFW
In this work we present recent updates of 3-D full wave Petra-M finite-element-method (FEM)
simulations for NSTX-Upgrade plasma. Petra-M code [1] is a state-of-the-art genericelectromagnetic simulation tool for modelling RF wave propagation based on MFEM
[http://mfem.org], open-source scalable C++ finite element method library.
This paper shows the full 3D NSTX-U device geometry including realistic antenna geometry
and 3D scrape-off-layer (SOL) plasma. The antenna geometry and the 3D NSTX-U geometry
are from the NSTX-U CAD models.
These 3-D simulations show a strong interaction between FWs and the SOL plasma. Cavity
modes in the SOL plasma appear in all simulations. A scan can of magnetic field (B = 0.6 T,
0.75 T, and 1 T) shows was performed and the cavity modes in the SOL plasma tend to decreasefor higher magnetic field. A scan in the SOL electron density (ne = 1 x 1018/m3, 2 x 1018/m3,
and 5 x 1018/m3) was also performed. In this scan, the cavity modes increase with higher
density. In general, these results are consistent with the 2D full wave simulations performed
by AORSA [2] and FW2D [3]. Further studies in Petra-M are necessary to try to quantify the
HHFW losses in the SOL plasma. An evaluation of the scattering matrix (S-matrix) in vacuum
and three plasma cases (corresponding to the density mentioned above) were shown. In thevacuum, S-matrix is symmetric as expected unlike the plasma case due to the plasma absorption.
The S-matrix evaluation is the first step to be able to quantify the HHFW antenna performanceand compared it with the measurements.
[1] S. Shiraiwa et al., EPJ Web of Conferences 157, 03048 (2017).
[2] N. Bertelli et al., Nucl. Fusion 54, 083004 (2014).
[3] E.-H. Kim et al., Phys. Plasmas 26, 062501 (2019).
Akira Ejiri:

Plasma current start-up by using the lower hybrid wave and its modelingon TST-2
In the TST-2 spherical tokamak, non-inductive start-up by lower-hybrid waves (200 MHz) has
been studied and a plasma current of 27 kA was achieved. A model for lower hybrid wave
induced transport to reproduce the hard x-ray (HX) behaviors has been constructed. The model
consists of (1) orbit tracing (in Rin- Rout- Vpara space) under RF heating and collisionalslowing down, self-inductive field, and (2) X-ray emission models. The experimental HX
spectral shape are well reproduced by the model. Responses of RF power turn off (rapid HX
decrease, Ip decay, ne increase) are qualitatively reproduced, but the remaining HX after theturn off cannot be reproduced. The effect of self-inductive field is found to be nonnegligible.
Responses of additional gas puff were investigated, and the plasma current response seems tobe affected by both decreases in the fast electron loss and fast electron population. Movabletarget was inserted into the SOL and HX from the target was measured, and the existence offast electrons at the outboard side SOL is indicated. Opposite directed electrons are alsosuggested.

Yongtae Ko:

Development of a capacitively coupled combline antenna for off-midplanelaunch of lower-hybrid waves in TST-2
Summary: In the TST-2 spherical tokamak device, non-inductive plasma start-up andoptimization of the current drive have been studied using lower hybrid wave with frequency of
200 MHz. LHCD has been achieved by using two antennas, one on the outer-midplane and theother on the top side. However, with the increase in plasma density, the accessibility of waves
launched from the outer-midplane is restricted to the outer region, and the electron distribution
cannot be controlled. The wavenumber spectrum of the top launch is ideal, but most of theelectrons are lost as fast electrons in the region where the wave absorption is r/a > 0.7. In theouter-midplane launch, the wave propagates to the magnetic axis, but the phase velocity is large
and the heating of thermal electrons is not achieved. The optimal launching scenario isinvestigated using the ray-tracking code GENRAY and the orbit-averaged Fokker-Planck code
CQL3D. Calculations showed that the wave propagates through the center of the plasma andthe phase velocity resonates with that of the thermal electrons when the wave of n_parallel~13
is launched from the off-midplane. In terms of the dependence of the electron density,
equilibrium current and temperature, there was no significant change in the driving current andwave absorption. Thus off-midplane launch is attractive. The synergy of conventional outermidplane launch and off-midplane launch is expected to further optimize the current drive andextend the operation regime. To prove above off-midplane antenna is designed and will be
installed by May 2022.
Masayuki Ono:

Accessibility enhanced ECH and ECCD for plasma current start-up andramp-up
An efficient solenoid-free start-up and ramp-up scenario utilizing the low-field-side launch(LFSL) I-X-mode is proposed [1]. The I-X wave accessibility density limit improves
significantly at higher BT0 as accessible density goes up as 𝑓𝑓2 (or as 𝐵𝐵2T0) that enables thecurrent start-up and ramp-up to 10 MA with 10 MW in a reasonable plasma density of ~ 0.5 –1.0 x 1019/𝑚𝑚3 with a very high ECH/ECCD efficiency at 170 GHz for 𝐵𝐵T0 ~ 5 - 6 T in SustainedHigh Power Density (SHPD) facility. The high ECCD efficiency is due to the strong waveparticle interactions at the Doppler broadened ω = Ωe resonance, due to the strong cyclotroninteraction of X-mode polarization, together with absorption on uni-directional passing
electrons which results from the wave accessibility constraint. The quasi-linear analysis using
CQL3D shows further enhancements of ECCD efficiency over the linear calculations due tothe generation of less collisional higher energy tail electrons. The current drive efficiency
remains high for a broad range of 𝑛𝑛||# (or injection angle) suggesting that a relatively simple
waveguide launcher could be used. In ST-40, using the 105 GHz gyrotron at BT0 = 2 T, it
appears to be possible to drive ~ 1 MA of plasma current with 1 MW at the plasma density of
8 x 1018/m3. Once the ramp-up to the full plasma current is achieved, the same ECH system
can be switched to more conventional ECH and ECCD such as the O-mode which would permit
the access to high density ~ 2-3 x 1020/𝑚𝑚3 or more advanced EBW-based scenarios for evenhigher density steady-state operations.

[1] M. Ono, N. Bertelli, et al., AIP Conference Proceedings 2254, 090001 (2020).
Hiroshi Idei:

Recent Topics on 28-GHz ECHCD in QUEST
Recent two topics on 28-GHz ECHCD in QUEST are reported. One is related to a new 28GHz CW gyrotron. The gyrotron has been assembled by last year, and it is tested in this year
at Univ. of Tsukuba. The designed output of 1.2 MW is achieved with cathode voltage andcurrent of Vk = 80 kV and Ik = 50 A. To apply it to QUEST experiment, the performance at
Vk = 70 kV and Ik = 25 A is checked, and reasonable output of 0.6 MW is attained with theefficiency of 38 %. It will be operated at a power level of 400 kW with CPD configuration in
CW. The 480-kW output is also attained with a high efficiency of 42 % with the CPD at Ik =15A. It enables us to operate one more gyrotron used currently with Ik = 10 A also in the CPD
configuration. The EC plasma ramp-up experiment with two different parallel indexes to themagnetic field will be conducted to obtain high plasma current and bulk electron temperatureby using two 28-GHz systems. The other topics is related to doubling of the toroidal magnetic
field in QUEST. New 100 kA power supply system, composed of lithium capacitor modules
and DC-DC converters, is developing to excite 0.5 T in QUEST. The fundamental ( 1st ) andsecond ( 2nd ) harmonic X-mode heating scenario is considered for the 0.5 T ECHCD
experiment, based on the ray tracing analysis. The incident ray from the low field side (LHS)
starts to be damped as third harmonic absorption of the energetic electron and is damped as 2nd
harmonic absorption of energetic and bulk electrons. In addition, it is damped as 1st absorption
when it come closer to the Doppler shifted resonance and reflected back outside due to thecutoff. The total single pass absorption reaches to 80-90 %. In high density case, it reflectedback outside before coming to the 1st absorption area. The ray is strongly damped as 2nd
harmonic resonance in the absorption area of the bulk electrons. The resonance area for theenergetic electrons strongly shifts to the high field side (HFS) due to the relativistic effect andexpands to both of the HFS and LHS sides due to the Doppler shift effect. The energetic
electrons in various energy range are in the up-shifted resonance in wide velocity space there.
The ray does not access to the down-shifted resonance area of the energetic electrons. Threetype configurations with the up-shifted resonance, not the down-shifted resonance haveproposed to conduct the high efficiency ECCD experiment in QUEST.
Shin Kubo:

Study of excited EBW detection by sub-Tera-Hz scattering in the QUESTThe QUEST is a spherical tokamak device which has been working on the topic of steady-state
operation. One of the main issues is the non-inductive current drive, including the steady state
current drive. Among several non-inductive current drive methods, electron Bernstein wave
(EBW) heating/current drive is the most attractive method. Since the EBW can be excitedthrough mode conversion process, it is important to clarify and optimize the injection condition
by checking the excited EBW near the core region. Expected wavenumber in the perpendicular
to the magnetic field ranges 104-105m-1. The direct and detailed measurement of the density
fluctuation associated with the EBW gives clear evidence of the excited EBW inside the core,
since it is an electro-static wave. Such density fluctuation can be measured by the sub-Tera-Hz
wave scattering. Original idea was to apply 400 GHz gyrotrons developed for the collective

Thomson scattering (CTS) experiments. Loan term expires soon and HCN laser system in turnwill be prepared as a scattering source. Scattering optics will be designed using a quasi-opticalmethod developed.
Makoto Hasegawa

Long-time operation with high temperature wall (<400 C) on QUESTIn order to investigate the controllability of particle balance during long-term discharge in ahigh-temperature environment, long-term discharge was performed with the high-temperaturewall (hot wall) of QUEST kept at the set temperature of 400 °C. The QUEST hot wall has asheath heater embedded in it and is in contact with the cooling water pipe, so it can be actively
heated and cooled. Although the temperature was lower than 400 °C in some places due to aheater failure, it was confirmed that the experiment could be carried out safely by raising thetemperature of the hot wall to the set temperature of 400 ℃. And, it was confirmed that when
the cooling water was started to flow during the long-term discharge at 400 °C, the Ha emission
decreased and the particle supply was restarted accordingly. Thus, the temperature control of
the high temperature wall is effective even in this temperature range (400 ℃) and has a great
influence on the particle balance. In the future, temperature control will be performed more
appropriately, and data will be acquired statistically for analysis.
Qilin Yue

Preliminary results of Hydrogen Recycling with Fast Ejecting System ofTargeted sAmple (FESTA) on QUESTIn order to realize fusion power generation, the recycling of fuel particles, hydrogen and its
isotopes, is important in the plasma facing wall (PFW) to maintain steady operation, which has
a significant effect on particle balance. The hydrogen recycling on Q-shu University
experiment with Steady-state Spherical Tokamak (QUEST) has been only measured globallyand is limited after plasma discharge from PFWs. Therefore, a device named Fast Ejecting
System of Targeted Sample (FESTA) was developed to investigate hydrogen recycling locallyfrom a specimen by exposing it to high-temperature and density plasma in QUEST [1].
In this research, a stainless-steel type 316L specimen was exposed to QUEST plasma forthree times continuously under the same plasma discharge conditions. Using backgroundmodel [1], the released hydrogen flux from the plasma-exposed specimen increased overplasma exposures, indicating that hydrogen recycling became more dominant during plasma
discharges. Furthermore, it has been observed that the outgassing characteristics changed overplasma discharges, which is unknown for now and should be further investigated.
[1] Q. Yue, et al Plasma Fusion Res. 15 (2020) 240201
Kengo Kuroda:

Improved results of CHI discharge on remodeled system in QUEST

T-CHI current start-up by using newly designed simple electrode has been examined in
QUEST:• Improved result of HFS CHI discharge was obtained in 2021 Feb experiment• T-CHI system was remodeled on a large-scale in 2021 for higher performance of thecurrent drive.
We obtained progressive results (1~4) on the initial experiment on the remodeled system:
1. 100% of occurrence of breakdown is achieved with lower breakdown conditions
2. Absorber arc is prevented on higher level injector flux configuration
3. Achievement of more than 100kA of current drive
4. Flux evolved largely, but relatively high vertical field was required.

国際化推進共同研究概要
No. 5
21NU-4
タ イ ト ル： Joint study of calorimetric measurement of heat load and power
balance estimation and measurement and simulation of energetic
electrons loss in steady state operation (SSO) plasmas on QUEST
and EAST
研 究 代 表 者： LIU Haiqing

所内世話人： 花田 和明
研究概要： コロナの影響で来日はかなわなかったが、遠隔で双方の研究の内容の議論を行い、以下の結果を得た。


長時間運転で必ず問題になる局所的熱負荷による「ホット・スポット」
について議論を行った。特に今年度は EＡＳＴ装置でのホット・スポ
ットの原因が、炭素ダイバータの除熱性能とプラズマ加熱用波動の周辺部での衝突減衰によるものであることを見出した。



EAST 装置では炭素ダイバータをタングステン化して除熱性能を向上させて 1000 秒を超えるプラズマ維持に成功した。



関連する成果に関する論文を執筆中であり、そのほか以下の 3 編が掲載決定済みである。

[1] K. Hanada, ……, H.Q.Liu, et al., "Overview of recent progress on
steady state operation of all-metal plasma facing wall device QUEST",
Nuclear Materials and Energy 27(2021) 101013.
[2] Y. Q.Chu, H.Q.Liu, ……, K. Hanada, et al., “Study of themechanism of ITB formation and sustainment with optimized q profilesin ELMy H mode discharges on the EAST”, Plasma Phys. Control.
Fusion 63(2021) 105003.
[3] Y. Q.Chu, H.Q.Liu, ……, K. Hanada, et al., "MHD effect of internaltransport barrier on EAST tokamak", Plasma Science and Technology(2022) to be published.

Introduction
Steady state operation (SSO) of magnetic fusion devices is one of the goals for fusion research. The
longest steady-state H-mode plasma (#73999 discharge in EAST) with the USN divertor configuration
during the 2017 campaign was lasted 101.3 s at a plasma current of 0.4 MA. The hot spot appeared
from about 55 s to the end of the shot on the lower graphite divertor maybe one of the important reasonsfor the degradation of plasma quality and early termination. Hot spots as an interaction between plasmaand plasma facing components (PFCs) frequently prevent from maintaining high performance plasmas
through unwanted impurity emission. Moreover, the hot spots have a potential to make a meltdown of
PFCs which cause serious damages to the machine. After the appearance of the hot spot, the heat load
distribution on the first wall was significantly changed. The heat load decrement on the upper divertor
is 22.6 MJ from 55 s to 105 s, and this part of power was delivered from the upper divertor to the lower
divertor and to the guard limiters of the LHW injection systems. In order to achieve higher parameters
and longer duration plasma, it is necessary to find the reason for the appearance of the hot spot. The
power handling capability of tungsten divertor is about 10 MW m−2, it is a safer divertor material thangraphite for the excessive local heat load. So, a new lower tungsten divertor has been developed andinstalled in the EAST in early 2021, and the cooling system of the lower divertor has also been
upgraded.
In this year, the collaboration research focused on analyzing and finding the cause of hot spot formation,and comparing the heat load capacity of tungsten and graphite divertors through calorimetry.
Recent results in 2021
A relativistic guiding center orbit code (RGCO) has been finished and applied to investigate the prompt
loss of electrons accelerated by injected RF electric field. ECW (Electron cyclotron Wave) is the main
source of energetic electrons on QUEST. LHW (Lower Hybrid Wave) is an efficient way to heating
and drive the plasma current, and is the main source of energetic electrons on EAST. The RGCO canbe easily applied to both EAST and QUEST tokamaks, because the equilibrium magnetic fields for thesimulation are provided by the EFIT code. The orbit simulation can take into account the realistic wallgeometry outside the last closed flux surface (LCFS). The toroidal geometry (toroidal position of two
LHW antennas) is included in the code. So, it can be used to study the LHW power loss in the scrapeoff layer (SOL) and deposited in hot spots on the divertor. The result shows that the electron with pitch
angle from 130°to 180° in the dRmid zone in front of the LHW antenna can move along magnetic fieldlines then attack the lower divertor to form the hot spot, implying that the LHW power couples acrossthe entire width of the dRmid zone rather than mostly at the antenna face. The dRmid is the distance
between the LCFS and secondary last flux surface as shown in figure 1. And the simulation result isshown in figure 2. For shot 73999, it is the change of the plasma configuration (the magnitude ofdRmid gradually increases with time, confirmed by the EFIT equilibrium reconstruction) that leads tothe formation of hot spots on the lower divertor, thus causing the change of the heat load distribution

on the PFCs. The energetic electrons tracing code combined with the EFIT equilibrium code is a good
simulation framework for the research both on QUEST and EAST. Electron orbit mapping provided
by the code combination can be used to explain the experiment observations.
In early 2021, the material of lower divertor has been developed from graphite to tungsten, aiming at
achieving higher power handling capability and achieving longer H-mode operations. Combined withthe experience of long-pulse operation accumulated in previous rounds of experiments, EAST
achieved a long-pulse high-parameter plasma operation with 1056.66 s, the plasma configuration iswell controlled throughout this discharge. Discharge parameters are stable during the whole current
flat plateau. And the time evolution of heat load exhausted by the cooling water can be seen in figure
3. It can be seen in figure 3 that the heat load exhausted by the lower divertor is larger than that of theupper divertor, which is in line with the previous experimental conclusion of EAST. From 393 s to585 s, the exhausted heat load drops due to the drop in temperature of the cooling water, this is due tothe cooling water flow through the entire cooling circuit and get cooled.

Figure 1. The schematic diagram of the plasma configuration.

Figure 2. The electron orbit simulation, the start point in the SOL along the R coordinate.

Figure 3. The time evolution of heat load exhausted by the cooling water.

Discussions
This year, the collaboration research focused on the mechanism of the hot spot formation, comparing
the heat load capacity of tungsten and graphite divertors through calorimetry. In 2021, the material oflower divertor has been developed from graphite to tungsten, aiming at achieving higher power
handling capability and achieving longer H-mode operations. Combined with the experience of longpulse operation accumulated in previous rounds of experiments, EAST achieved a long-pulse highparameter operation with 1056.66 s, the plasma configuration is well controlled. Recent progress on
SSO of all-metal plasma facing wall device QUEST was also well studied in this year’s research. The
results in EAST and QUEST will provide crucial support for ITER and CFETR. Energetic electrons
are the main source of heat load which are generated by injected RF electric field. ECW (Electron
cyclotron Wave) is the main source of energetic electrons on QUEST. LHW (Lower Hybrid Wave) isan efficient way to heating and drive the plasma current, and is the main source of energetic electrons
on EAST. A significant fraction of LHW power applied to EAST can be lost to the scrape-off layer(SOL) and deposited in hot spots on the divertor rather than in the core plasma. This topic has been
researched on many devices such as JET and Tore-Supra. The result show that the LHW power flows
to these hot spots along magnetic field lines passing through the SOL in front of the antenna, implyingthat the LHW power couples across the entire width of the SOL rather than mostly at the antenna face.
The energetic electrons tracing code combined with the EFIT equilibrium code is a good simulation
framework for the research both on QUEST and EAST. Electron orbit mapping provided by the code
combination can be used to explain the experiment observations. This is a very interesting issue forthe coming year’s joint research.
In this year’s joint research, I have many fruitful discussions with Prof.Hanada’s doctor student, Mr.
Yunfei Wang, on his doctoral research issues. Three Co-Publications are achieved in 2021-2022.

Acknowledgement and comments:

Work supported by the international joint research at the Joint Usage of Research Centers for Applied
Mechanics for 2021. I would like to thank our host, Professor K. Hanada, who helps a lot during ourremotely research and very appreciate the fruitful discussions and comments. Also RIAM and QUEST
staffs are thanked for her kindly helps for this year’s joint research. We hope that the international joint
research at the Joint Usage of Research Centers for Applied Mechanics could continue to enhance
China-Japan cooperation on fusion plasma research in the future.
Co-Publications in 2021-2022:[1] K. Hanada, ……, H.Q.Liu, et al., "Overview of recent progress on steady state operation of allmetal plasma facing wall device QUEST", Nuclear Materials and Energy 27(2021) 101013.
[2] Y. Q.Chu, H.Q.Liu, ……, K. Hanada, et al., “Study of the mechanism of ITB formation andsustainment with optimized q profiles in ELMy H mode discharges on the EAST”, Plasma Phys.
Control. Fusion 63(2021) 105003.
[3] Y. Q.Chu, H.Q.Liu, ……, K. Hanada, et al., "MHD effect of internal transport barrier on EAST
tokamak", Plasma Science and Technology (2022) to be published.

(Signature)

Haiqing Liu(Name in print) Haiqing Liu

国際化推進共同研究概要
No. 6
21NU-5
タイトル:

Soft

x-ray

spectraininboardpoloidal

field

null

(IPN)

configuration and relevant physical research on QUEST
研 究 代 表 者： JIE Yinxian

所内世話人： 花田 和明
研究概要： コロナの影響で来日はかなわなかったが、遠隔で双方の研究の内容の議論を行い、以下の結果を得た。


IPN 配位での粒子の損失機構として粒子軌道計算に基づいた検討を行った。本研究によって EAST、QUEST 双方の磁場配位で計算可能な相対論的効果を含んだ粒子軌道計算を完成させた。



関連する成果に関する論文を執筆中であり、そのほか以下の２編が掲載決定済みである。

[1] Y. Q.Chu, …, Y.X. Jie,…, K. Hanada, et al., Plasma Phys. Control.
Fusion 63(2021) 105003.
[2] Y. Q.Chu, …, Y.X. Jie,…, K. Hanada, et al., Plasma Science andTechnology (2022) to be published.

Research subject: Soft x-ray spectra in inboard poloidal field null (IPN) configuration
and relevant physical research on QUESTDue to COVID-19 pandemic，this year we worked remotely. Soft x-ray spectra system is a very
important diagnotic on tokamaks. It is one of the most widely used in measuring the palsma electron
tempreture and MHD phenomenons. The whole system needs modification to get more detail date to
get the position of IPN and relevant physical research on QUEST.
First, I discussed the mission with Mr. Canbin HUANG. The mission of QUEST is to develop thescientific basis for achieving a steady state condition at sufficiently high beta (~20%), with highconfinement and low collisionality. Operating Tokamak at a high poloidal beta value is usuallyattactive and this makes the spherical tokamak an interesting choice for future reactors.The maximum
achievable βp, however, is limited by a so called equilibrium limit, where an inboard poloidal
magnetic field null (IPN) appears at the high field side of the vacuum vessel.Inboard poloidal fieldnull (IPN) configuration in a high Bp discharging was reported first time on TFTR in 1991. In thosedischarge the evolution of the poloidal field measured at the midplane on the inboard side of the TFTR
vacuum vessel was studied.As Ip was ramped down, and Bp increased, the midplane poloidal field
decreased and eventually become negative, indicating that the separatrix had crossed the coil position
and moved into the vacuum vessel. The separatrixlimited discharge was sustained until the end of thebeam heating phase.

In QUEST, such an IPN configuration is easily achieved under a high magnetic

mirror ratio and high Bz/Bt values (≈10%) via electron cyclotron (EC) heating and current drive. A
soft x-ray spectra system was set up on QUEST and got some primary date.The whole system needs
modification to get more detail date to get the position of IPN on QUEST.
Investigation of loss mechanism of the energetic electron in QUEST provides finally a good
assistance of confinement of alpha particle in the international thermo-nuclear fusion reactor (ITER)
and designing fusion devices such as Japan DEMO and CFETR (China Fusion Engineering Test
Reactor) in China.

Co-Publications in 2021-2022:[1] Y. Q.Chu, …, Y.X. Jie,…, K. Hanada, et al., Plasma Phys. Control. Fusion 63(2021) 105003.
[3] Y. Q.Chu, …, Y.X. Jie,…, K. Hanada, et al., Plasma Science and Technology (2022) to be published.

(Signature)(Name in print)

Y. JieYinxian Jie

国際化推進共同研究概要
No. 7
21NU-6
タ イ ト ル： Joint study of long pulse high beta discharges and related egde
turbulence transport in steady state operation (SSO) plasmas on
QUEST and EAST
研 究 代 表 者： GAO Xiang

所内世話人： 花田 和明
研究概要： コロナの影響で来日はかなわなかったが、遠隔で双方の研究の内容の議論を行い、以下の結果を得た。
EAST でのプラズマ加熱の高効率化に向けてプラズマと波動の結合について議論をしてきた。



EAST では波動加熱の高効率化に向けて低域混成波用のアンテナを FAM
から PAM に変更した。しかしプラズマ蓄積エネルギーの増加は観測されなかったため、この問題の検討を開始した。現在検討を進めている最中である。



関連した研究で、以下の１編が掲載決定済みである。

[1] K. Hanada, ……, X. Gao, et al., "Overview of recent progress on
steady state operation of all-metal plasma facing wall device QUEST",
Nuclear Materials and Energy 27(2021) 101013.

Introduction
This year, given the situation of COVID-19, the joint research was done remotely.
Steady state operation (SSO) of tokamak plasma is one of the basic requirements for future fusion
reactors. Long pulse high beta operation is one of important missions for ITER. Joint study long pulse
high beta discharges in SSO plasma research field on QUEST and EAST is strongly supporting ITER
experiment from both experience and theory. In this year, the collaboration research focused on the
power balance in SSO high performance discharge and coupling of injected energy and plasma during
discharge, which is benefit for the SSO high beta discharges of EAST and QUEST.

New results in 2021
The Experimental Advanced Superconducting Tokamak (EAST) research program concentrates on
demonstrating steady-state high-performance H-mode operations with ITER-like tungsten divertor.
Calorimetry was applied to actively water-cool the plasma facing components (PFCs) by increasing
the water temperature for power balance investigation. A new lower tungsten divertor has beendeveloped and installed in the EAST superconducting tokamak in early 2021 to replace the previous
graphite divertor with power handling capability increasing from <2 MW m−2 to ∼10 MW m−2, aiming

at achieving long-pulse H-mode operations in a full metal wall environment with the steady-state

divertor heat flux of ∼10 MW m−2. In 2021 EAST winter campaign, the record longest steady-state
long-paused high-parameters plasma #106915 was sustained for up to 1056.66 s with net injectedenergy exceeding ~1.42 GJ in the DSN configuration. It can be seen in figure 1 that the dischargeparameters are stable. The loop voltage is well controlled to be nearly 0 V, which means that almost
all of the plasma current is noninductive. The strike point is almost unchanged, which means that theplasma configuration is well controlled. H/H+D rises slowly because of the live application of lithium
to the PFCs. The first wall maintains a strong pumping capacity, and the particle recirculation iscontrollable. Figure 1 (b) shows that except for ICRF-N limiter, the temperature of other PFCs are
relatively stable.
Heat load analysis of this discharge using calorimetric measurement in figure 2 indicates that the watertemperature increment of the upper divertor became almost constant for the first time at about 250 s,
for the second time at about 864 s. During this time, the temperature of cooling water decreases because
after about 400 s, the cooling water goes through a complete cycle and is effectively cooled by theexternal cooling tower.

Figure 1. Parameters of shot 106915. (a): Time evolution of Poloidal Beta, Loop Voltage, injected energy, lineaveraged electron density, Da and js, (b): time evolution of temperature about main PFCs.

Figure 2. The time evolution of cooling water temperature increment in the upper divertor, lower divertor and otherpart of the PFCs.

In a LHW modulation experiment (EAST USN shot 74864) during 2017 EAST Campaign, the hot spot
appeared in the lower graphite divertor. Some important parameters of shot 74864 can be seen in figure
3. The auxiliary heating power are consisted of ~0.65 MW LHW1, ~0.65 MW LHW2. The duty ratioof LHW1 and LHW2 are 50% and each heating period is about 1 s. The line-averaged electron density
is well controlled as a constant. The stored energy at 5 s is ~0.54×105 J, it can be clearly observed thatthe injection of LHW has a significant effect on increasing plasma stored energy. Figure 4 (a) is thephoto taken by IR camera in port G, the LHW 2 antenna and two graphite limiters are on the left sideof the figure. Figure 4 (b) is the average temperature evolution over time of the four zones marked infigure 4 (a). The temperature in zone 1 is strong related to the injection of LHW 1, but is weak related
to the injection of LHW 2. This indicates the heat deposition at zone 1 was caused by LHW 1 injection.
The temperature in zone 3 and 4 changed with the injection of LHW 1 and 2 simultaneously, because
the heat load of upper divertor in USN configuration is from core plasma ultimately. After the
GENRAY/ CQL3D simulation, it can be concluded that the non-resonant collision absorption (one of
the mechanisms of LHW power deposit, which mainly occurs in the SOL zone) causes the hot spot
appearance during the LHW1 injection. For LHW1, more energy is deposited in the SOL, so lessenergy is deposited in the plasma core, which is not conducive to the improvement of the main plasma
parameters.

Figure 3. Parameters of shot 74864. (a): plasma current, (b): auxiliary heating power of LHW 1 and LHW 2, (c)line-averaged electron density measured by the 6th chord of the POINT system, (d): stored energy.

Figure 4. (a): IR camera photo of EAST chamber and location marks from zone 1 to zone 4 in discharge 74864. (b):The evolution of average temperature over time for the four zones.

Discussions
The major motivation of this project is to realize SSO plasma, based on QUEST and EAST device. In
2021 EAST winter campaign, the LHW1 antenna was changed from FAM to PAM, aiming at
achieving better coupling between LHW power and plasma. But in some shots, the increase in the
LHW1 power did not appear as an increase in plasma stored energy, indicating that this part of energy
is not constrained by the main plasma. We will focus on the studying of the wave-plasma physics, suchas coupling between LHW power and plasma, for achieving high-parameter SSO of the tokamak.
In 2022, this subtheme will continue pursue in long pulse high beta discharges and related pedestal
structure and edge turbulence transport in SSO plasma on QUEST and EAST. Comparison andcombination study based on the calorimetry and other diagnostics will continue be done on bothdevices. The combined study will be helpful for understanding the underlying physics and obtaining
H mode plasma on QUEST. It is benefit for the long pulse high beta discharges of EAST and QUEST.

Acknowledgement and comments:
Work supported by the international joint research at the Joint Usage of Research Centers for Applied
Mechanics for 2021. I would like to thank our host, Professor K. Hanada, who helps a lot during ourremotely research and very appreciate the fruitful discussions and comments. Also RIAM and QUEST
staffs are thanked for her kindly helps for this year’s joint research. We hope that the international joint
research at the Joint Usage of Research Centers for Applied Mechanics could continue to enhance
China-Japan cooperation on fusion plasma research in the future.
Co-Publications in 2021-2022:[1] K. Hanada, ……, X. Gao, et al., "Overview of recent progress on steady state operation of all-metal
plasma facing wall device QUEST", Nuclear Materials and Energy 27(2021) 101013.

(Signature)

Xiang Gao

(Name in print) Xiang Gao

国際化推進共同研究概要
No. 8
21NU-7
タ イ ト ル： Improved EFIT code of the plasma equilibrium reconstruction for
physical study on QUEST
研 究 代 表 者： QIAN Jinping

所内世話人： 花田 和明
研究概要： コロナの影響で来日はかなわなかったが、遠隔で双方の研究の内容の議論を行い、以下の結果を得た。


過渡的な電磁応答で発生する金属容器の渦電流は、プラズマの平衡磁場配位の計算に大きな影響があることが知られている。今年度はフ―リエ展開を用いた渦電流の計算コードを開発してプラズマ平衡計算
EFIT に適用した。検討の結果、5、６次のモード展開が適当であることが判った。



この渦電流の効果は、プラズマ電流やプラズマ形状にはほとんど影響がなかったが、蓄積エネルギーには大きな影響が見られた。EAST では
ディアマグで計測した蓄積エネルギーと平衡計算で得た蓄積エネル
ギーに差があったが、渦電流を考慮した結果、この差が非常に小さくなる結果を得た。



この渦電流の影響は QUEST ではより顕著になると予測されるため、双方にとって重要な結果を得たこととなる。



関連した研究で、以下の１編が掲載決定済みである。

[1] K. Hanada, ……, X. Gao, et al., "Overview of recent progress on
steady state operation of all-metal plasma facing wall device QUEST",
Nuclear Materials and Energy 27(2021) 101013.

（様式 11・拠点）

RESEARCH REPORT

Date Feb.

Visiting scientist: (name)(position)

Jinping Qian
Professor(university / institute) Institute of Plasma Physics,
Chinese Academy of Sciences
Host scientist: (name)(position)(university / institute)

Research period: (from)K.

HanadaProfessor
Kyushu(to)

University

13 2022

（様式 11・拠点）

Research subject: Develop and improve EFIT code of the plasma equilibrium
reconstruction for SSO operation and advanced physical study on QUESTDue to COVID-19 pandemic，this year we worked remotely. We improved theequilibrium reconstruction with eddy current calculation. The method of using Fourier
expansion model to represent eddy current distribution for the improvement of equilibrium
reconstruction is explored. It is shown that vacuum vessel current can be generally
determined with the Fourier expansion model through the equilibrium reconstruction.
Comparison of the eddy current distributions reconstructed with Fourier expansion model
against the presets are presented. The reconstructed results are found to reasonably agreewith the presets. The experimental equilibrium reconstruction is improved with thereconstructed eddy current.
To test Fourier expansion model in reconstructing eddy current, benchmarking and testare performed to calculate the eddy current with the simulated magnetic data. The magnetic
data are simulated from the equilibrium analysis with an EAST double-null divertor
equilibrium. From the equilibrium analysis, the 35 flux loops and 38 magnetic probes are
simulated. The equilibrium is computed on a 65 × 65 (R, Z) grid using the EFIT code. In
order to test Fourier expansion model’s capability, the different eddy current distributions
are assumed. Then these extra signals are computed through Green function and merged
correspondingly to the 35 flux loops and 38 magnetic probes. Finally, the simulated
magnetic data is used as the inputs to test the equilibrium reconstruction and eddy current
distribution.
Here, the five kinds of eddy current distribution are reconstructed and compared withthe presets. And every preset eddy current distribution is reconstructed by EFIT using
different order Fourier expansion models. As shown in figure1, the reconstructed eddy
current distributions agree well with the preset ones.
One important element in the reconstruction of the preset eddy current distributions is
the choice of an appropriate Fourier expansion model. The unknown parameters [a0, an, bn]
are determined by LSM (least square method), which means that higher order Fourier
expansion model would improve fitting accuracy with sufficient external magnetic data inideal conditions. However, the finite magnetic measurements suggesting the limited
unknown parameters can be used in LSM fitting. To check the sensitivity against the
number of fitting parameters for the Fourier expansion model, we vary the Fourier
expansion order from 1 to 15. Reconstructed eddy current distribution’s RMSEs (root meansquare error) are shown in figure 2. According to the data analysis, 5-order and 6-order
Fourier expansion model are appropriate model with sufficiently high accuracy for different
eddy current distributions, as shown in figure 2. Note that smaller RMSE represent ahigher-precision reconstruction.

（様式 11・拠点）

Figure 1 Preset and reconstructed of five kinds of vessel current. Black line is the preset and red line, blue line,
green line and purple line represets the reconstructed ones with 3-order, 7-order, 11-order and 15-order
Fourier expansion model respectively.

（様式 11・拠点）

Figure 2 RMSE (root mean square error) of the five kinds of eddy current distribution’s recontrction withdifferent order Fourier expansion model.

Furthermore, we test the eddy current distribution reconstruction algorithms using
experimental EAST data. An EAST high loop voltage single-null divertor discharge(discharge 91929) is used. The reconstruction of discharge 91929 at 7500 ms is shown infigure 3. The reconstructed magnetic surfaces, the evolution of χ2 and the maximum relative
error of ψ during the iterations reconstructed with consideration of eddy current arecompared with those without eddy current in figure 3(a), 3(b) and 3(c) respectively. As
shown in figure 3(c), the two reconstructed magnetic surfaces are basically same. Both χ2and the relative ψ error decrease rapidly as the iterations proceed. The global plasma
parameters are compared in table 1. As excepted, most global parameters are close whileplasma stored energy Wp(KJ) increases from 60kJ to 80kJ.
The time history of plasma stored energy using the diamagnetic measurement (redcurves) compared with the reconstruction with (blue) and without (green) consideration ofeddy current are shown in figure 4. It is obvious that the reconstructed plasma stored energy
with the consideration of eddy current is consistent with the diamagnetic measurement,
while the other shows a trend of decrease during the discharge.

（様式 11・拠点）

Figure 3 Comparison of magnetic surfaces, the evolution varying with iterations of χ2 and the error
reconstructed with consideration of the eddy current (red solid line and blue line for magnetic surface, χ2 anderror respectively) and those (black dashed line and red line for magnetic surface, χ2 and error respectively)
leaving out the eddy current for an EAST high loop voltage discharge 91929 at 7500 ms.
Table 1 Comparison of several parameters for two EAST reconstructions with and without consideration of
vacuum vessel eddy current for discharge 91929 at 7500 ms.

Case
Ip(MA)
Ω(m3)
a(m)
k
δU
RM(m)
ZM(m)
Wp(kJ)

With eddy
current
0.46
10.60
0.45
1.6
0.59
1.87
0.05
60

Without eddy
current
0.46
10.57
0.43
1.7
0.62
1.88
0.04
81

（様式 11・拠点）

Figure 4 Evoluiton of plasma stored energy by diamagnetic measurement (red line ) with the reconstructed
one taking account of eddy current (blue line) and the one (green line) reconstructed with regardless of eddy
current.

In addition, the total eddy current is computed and compared with the measured one
using Rogowskii coil outside and inside the vessel during the whole discharge in figure 8.
As shown in figure 5, they agree well with each other during the whole discharge, and thecomparison shows that the reconstructed eddy current is reasonable.

Figure 5 Comparison of measured eddy current (red line) and reconstructed (blue line).

Co-Publications in 2021-2022:[1] K. Hanada, ……, J. Qian, "Overview of recent progress on steady state operation of
all-metal plasma facing wall device QUEST", Nuclear Materials and Energy 27(2021)
101013.

(Signature)(Name in print)

J. Qian
Jinping Qian

国際化推進共同研究概要
No. 9
21NU-8タ イ ト ル： Local plasma parameter measurements using a multi-color tomographysystem研 究 代 表 者： CAVEDON Marco

所内世話人： 文 贊鎬

研究概要：
この国際共同研究は RIAM で行われているトモグラフィーを用いた乱流計測をさらに発展させ、プラズマの発光強度ではなく、より基本的な物理量である電子密度・温度の二次元揺動計測手法を確立することを目的とした。複数のヘリウムの輝線を二次元計測することで、それらの強度の比率から電子温度・密度を推定することができる。この手法では原子のモデル計算によって輝線の強度を電子温度・密度の関数として正確に予測することが不可欠である。
マックスプランク・プラズマ物理学研究所の ASDEX-Upgrade トカマクの実験データを用いてヘリウムの原子モデルの検証を行なった。また複数の輝線の強度を適切に組み合わせることで信号の電子密度・温度依存性を調整し、電子温度または密度のみの揺動スペクトルを抜き出す解析手法を開発した。この手法により EDA H-mode における電子温度・密度それぞれの揺動スペクトルを 90kHz まで計測することに成功した。

Local plasma parameter measurements using a multi-color tomographysystemUniversità di Milano-Bicocca Marco Cavedon

Introduction:
The aim of this research is to establish a method to measure local electron density andtemperature on a turbulence time scale by using line ratios. Two-dimensional fluctuating
structures have been characterized by inverting the intensities of emission lines at PANTA.
Emission line intensities depend on electron density, electron temperature and neutrals, each ofwhich plays a different role in turbulence and resulting transport. Therefore, extracting
fluctuations of individual quantities helps further understand the physics of magnetized plasmas.
The same technique is also applicable to the tomography system at PLATO currently underdevelopment.
Since PANTA allows for the direct comparison between the line-ratio techniques and probe
measurements, this research can also provide the basis for the further development of Helium
beam emission spectroscopy and gas puff imaging, which have been installed on many large
devices including ASDEX-Upgrade, NSTX-U, JET and W7-X. At the moment, PANTA is the only
device where the reliable validation of the line-ratio technique for the electron temperature anddensity measurements against Langmuir probes can be conducted. This is why the joint research
between Riam and Max Planck institute for plasma physics (IPP) has been initiated.
Results:
Unfortunately, a visit to Riam was
not possible due to the outbreak of
Covid-19. Thus, main efforts weremade at IPP by using the thermal
helium beam spectroscopy system
at ASDEX-Upgrade tokamak(AUG)[1]. Figure 1 shows thecomparison between theexperimentally observed He I line
ratios and the collisional radiativemodeling at the electron density of
9.2e+18 m-3 and the electron temperature of 75.2 eV (calculated by Dr. Ralph Dux at IPP). The
experimental result is well reproduced. A similar comparison was also made for the He I emission
coefficients provided by Open ADAS[2], which has been often used in preceding works. It was
found that Open ADAS often fails to match the relative intensities of all four lines being observedat AUG.
In addition to the atomic models, achieving high time resolution is another major challenge inresolving the two-dimensional turbulence structure. To this end, a new line-ratio analysis
technique has been developed[3]. In this technique, a quantity that is only sensitive to either
electron density or electron temperature can be constructed by applying arithmetic operations
to observed line intensities. Unlike conventional approaches, which utilize only three lines todetermine the electron temperature and density, the proposed technique is able to make use of
all available line intensities and, thus, improves the signal to noise ratio. The noise contribution

can further be removed by correlating two measurements that probe the same location but arerecorded by using independent light-detection systems. By using this technique, the electron
density and temperature fluctuation spectra for an EDA H-mode discharge were successfully
resolved up to 90 kHz as shown in Fig 2.
The funding of this joint research, which was originally for travel expense, was used forpurchasing some parts of the spectroscopy diagnostic system being developed for PANTA and
PLATO. This system will be able to provide wide range spectra (200-1050 nm), and further
comparison between the atomic models and measurements can be made for Helium and othergases.

Reference[1] M. Griener, E. Wolfrum, M. Cavedon, R. Dux, V. Rohde, M. Sochor, J. M. Muñoz Burgos, O.
Schmitz, and U. Stroth, Rev. Sci. Instrum. 89, 10D102 (2018).
[2] Summers H P 2004 The ADAS User Manual version 2. 6th edn.
[3] T. Nishizawa, M. Griener, R. Dux, G. Grenfell, D. Wendler, S. Kado, P. Manz, and M.
Cavedon, Review of Scientific Instru- ments 92, 103501 (2021).

国際化推進共同研究概要
No. 1021NU-9タ イ ト ル： High power mm wave transmission line technology for advanced fusion
devices
研 究 代 表 者： LECHTE Carsten Hanno

所内世話人： 出射 浩
研究概要：
国際熱核融合実験炉（ ITER ）実験では、プラズマパラメータ分布の詳細な細部制御により、燃焼プラズマを閉じ込めることが重要である。電子サイクロトロン加熱・電流駆動では、局所的にプラズマ電流を駆動することで不安定性（磁気島）を抑制することが期待されている。磁気島は kHz〜10 kHz 程度の周期でプラズマ断面を回転する。磁気島の回転に併せて局所
電子サイクロトロン加熱・電流駆動することで高効率な抑制が可能となる。現在、kHz〜10
kHz で入射位置を変えるスイッチ素子が開発中である。九州大学での低電力試験後、量子科学技術研究開発機構（QST）で高電力試験を行ったが、スイッチボックス内でアーキングが発生した。アーキング抑制に向け、スイッチボックス内のミラーを精査し、ミラー面での損傷を確認した。ドイツでのミラー面の再加工に向けた検討・準備、アーキング観測のためのカメラシ
ステムの検討・導入を進めた。

Report of collaboration between RIAM and IGVP in FY2021:
The MQIV FADIS diplexer for ITER with automatic tuning at
QST
Mr. Dr. Carsten Lechte
Introduction: The MQIV diplexer developed at IGVP is a fast switch, power combiner, and mode
filter for 170 GHz using a Fabry-Perot resonator in a compact box design that is vacuum capableand can be directly interfaced with the 63.5 mm ITER ECRH waveguides which are available at
QST. Our technical partners at TNO in the Netherlands have designed and built a fast mechanicaltuning control unit for the device that is also vacuum-compatible. It uses feedback to fix the output
power to either the resonant or the non-resonant output port, compensating for changes in the
gyrotron frequency and mechanical expansion of the resonator. The activities of this year haveconcentrated on improving the high-power compatibility and the calibration of the powermonitoring sensors at the input and the two outputs of the diplexer.

DN

DR
IN

Fig 1: Diplexer integration into the gyrotron test stand at QST. DN and DR are the dummy loads at
the non-resonant and the resonant channel, respectively, and IN is the input waveguide.
The following problems were identified during testing in 2020: Arcing was happening continuouslyon the coupling gratings and probably also on the resonator mirrors. In full power operation, such
events would necessitate the termination of the pulse, which would make the device unusable. In
addition, the stray radiation caused by the arcs was degrading the control test results.
Since no travel to Japan was possible in 2021, the work was either of theoretical nature (design
and analysis), or parts have to be sent to IGVP for remanufacturing.
Arc mitigation: It was found in 2020 after electropolishing of the problematic mirror surfaces, thatthe material defects in the surfaces were not just irregularities in shape, but there could also becavities which outgas material that is then causing the arc. After careful analysis of the video
footage from some arcing events, it was decided to return the mirrors to IGVP, where a galvanicallydeposited “known-good” copper layer will be put down, and the 4 surfaces of the main resonator,
which see the greatest incident power, will be remachined. The mirrors are on the way to IGVP.
Arc detection: The resonator box has 2 viewports and an additional 4 feedthroughs for coolinglines, which are not currently used for cooling and are fitted with plexiglas windows. All 6 openings
can be fitted with cameras to observe a large percentage of the mirror surface area. With
stereoscopic vision, we can discriminate between arcs on surfaces and in the volume.
Improvement of power monitor signal: The polarisation of the power monitoring horn antennas
has been fixed.
Stray radiation mitigation: Mounting hardware for holding the absorbing ceramic tiles near thematching mirrors has been devised.

国際化推進共同研究概要
No. 11
21RE-1
タ イ ト ル： Highly robust and reliable DC breaker based on SiC for the low
carbon society
研 究 代 表 者： KAMINSKI Nando

所内世話人： 齋藤 渉
研究概要：
SiC Cascode 素子を評価する過電流遮断テストボードの作製を行った。TO-247-3pin パ
ッケージを接続する仕様で、過電圧保護用に最適化された RC スナバ、バリスタを追加することで、被測定素子に余分なストレスが印加されない状況が実現された。オフセッ
ト電圧を変化させることで、過電流遮断のトリガレベルを 0～200A の範囲で調整可能なことを確認した。

Highly robust and reliable DC breaker based on SiC for the low
carbon society
Nando Kaminski,
The University of Bremen

In 2021, RIAM was provided with an Over Current Breaker (OCB) test board, containing the
OCB-FET itself, the JFET in cascode configuration to increase the voltage rating and theovervoltage protection consisting of a varistor and an RC-snubber. RIAM was also provided
with the control box generating the required off-set voltages to turn the normally-off MOSFETs
into normally-on devices, to control the turn-off threshold and to reset the OCB after it triggered.
Both parts together fulfil the task of a controllable overcurrent breaker.
During 2021 this OCB test board has been improved. The latest version is shown in figure 1.
The board is equipped with a socket to accommodate a single TO-247-3pin SiC-JFET, whichis connected in cascode configuration to increase the voltage rating (centre top). The
overvoltage protection consists of an optimised RC-snubber in parallel to a varistor (bottom
right). On the left, the LV-OCB with some gate protection is shown. The operation of this board
is comparable to previous generations, but achieves less stress on the devices.

Figure 1: Latest version of the OCB board for accommodating TO247-3pin as the cascoded
SiC switch increasing the voltage rating.
Another variant has been designed to accommodate TO-247-4pin SiC-MOSFETs (up to
3 pcs.). The design is shown in figure 2. This version can be used for the 1700V SiC MOSFETs
developed within the national project SiC DCBreaker by Infineon Technologies AG. The
switching waveforms do not differ significantly, because the transients are determined mostly
by the interaction between the overvoltage protection and the outside circuitry, not significantly
by the OCB or the cascaded switch.

SiC-MOSFET

Figure 2: Latest version of the OCB board for accommodating TO247-4pin as the cascoded
SiC switch, here a signal experimental 1700V SiC-MOSFET.
The trigger level of the OCB-switch was determined by an automated test bench. Figure 3
shows the trigger level depending on the off-set voltages. In contrast to initial results, the trigger
level forms a smooth contour. In other words, the trigger level can be easily controlled bymeans of the off-set voltages.

Figure 3: Trigger level of a fully populated OCB test board under various gate-voltage off-sets.
The trigger level can be easily controlled.

国際化推進共同研究概要
No. 12
21RE-2タ イ ト ル： Flexible energy harvesting system
研 究 代 表 者： JEON Insu

所内世話人： 東藤 貢
研究概要：
本研究では、天然高分子であるセルロース等の高分子材料と合成高分子を用いて新規ゲル材料の開発を試みた。開発したゲル材料の物理的特性を調べたところ、500MPa に達する弾性率、55MPa の高強度、および 2200s/m の電気伝導性を示した。さらに、−50 oC から 35 oCの温度環境下で 14 日間も優れた物理的特性を維持できることが分かった。開発したゲル材
料は次世代のエネルギー用材料としての使用が期待される。

Flexible energy harvesting system
Chonam National University, Prof. Insu Jeon

Summary
Next-generation applications, such as flexible electronic devices, sensors, actuators, and soft robotics, requireanisotropic functional soft materials with controlled, directional electrical and heat conductivities, mechanicalproperties, and responsiveness, as well as shape-morphing capability, complex designability, and wide operationaltemperature ranges. However, a combination of these functions in any single class of materials has been very rarely
seen to date. In this study, a novel class of multi-anisotropic gels is developed to realize all these functions through a
new fabrication route. The gels are synthesized by integrating cellulose with poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) in tripropylene glycol. The prepared gels exhibit high electrical and thermal
conductivities of ≈200 S m−1 and ≈1.49 W m−1 K−1, respectively, with exceptional Young’s modulus (≈500 MPa) andtensile strength (≈55 MPa), which are much better than the previously reported mechanical properties of PEDOTbased gels (modulus/strength ≤ 10 MPa). Moreover, the gels exhibit self-welding ability and maintain their properties
for 14 d over a wide temperature range (from −50 to 35 °C), covering almost the entire atmospheric temperature
range on Earth surface. It is believed that the developed gels are promising candidates for application in many nextgeneration flexible devices, some of which are experimentally demonstrated in this study

MethodFirst, isotropic water-equilibrated (cellulose/PEDOT:PSS)(x/y) hydrogels were prepared (the detailed procedure is
described in the Supporting Information). The hydrogels were subsequently immersed in TriPG for ≈2 d for solvent
exchange, during which TriPG was replaced multiple times to ensure complete exchange of solvent molecules in thegel network. Finally, the gels were stabilized in air at ≈25 °C for 1 d to obtain the desired isotropic(cellulose/PEDOT:PSS)

TriPG

gels,

which

were

then

characterized.

To

preparetheanisotropic(cellulose/PEDOT:PSS) (x/y)@a/b TriPG gels, the corresponding isotropic hydrogels were dried at a processtemperature (a) of ≈25 or 90 °C under clamping at a prestretching strain (b) of 0% or 40% along the length of the gel(x-axis) for 2 d. Thereafter, the gels that dried while clamped were sequentially immersed in water for 1 d and TriPG
for ≈2 d. Finally, the gels were allowed to stabilize by maintaining them under ambient conditions (humidity = 30–
70%, temperature ≈ 25 °C) for 1 d, unclamped, and characterized in detail after placing them in an air atmospherefor ≈2 h. The data for each type of gel were collected from three measurements and presented as mean values, withthe error bars representing the mean absolute deviation (n = 3). To compare the properties of the anisotropic gels, theDA was calculated from the absolute ratio of their mean properties between the parallel and perpendicular directions.

Results

The gels in this study were fabricated via a facile drying and reswelling process, as shown in Figure 1. Owing to thesynergistic effect of the components, the gels exhibit multi-anisotropic functions, including anisotropic mechanical,
electrical, and thermal properties, along with applicability in a wide temperature range (from −50 to 35 °C), as wellas easy weldability and efficient fabrication of complex and flexible structures.

Figure 1. (a) Chemical structures of cellulose, PEDOT:PSS, and TriPG. (b) Schematic diagram of the synthesis of
the anisotropic (Cellulose/PEDOT:PSS) TriPG gels. The as-prepared (Cellulose/PEDOT:PSS) hydrogel was clamped
under a predetermined pre-stretching strain of 0% or 40% along the length direction (x-axis) and was allowed to dry
under this confined condition at a temperature of ~25 °C or 90 °C. The dried gel was reswelled sequentially in waterand TriPG, stabilized in air, and finally unclamped to obtain the desired anisotropic (Cellulose/PEDOT:PSS) TriPG
gel, wherein the solvent molecules (TriPG) within gel network were stabilized mostly by intra- and intermolecularhydrogen bonding (H bond) with cellulose polymers.

To determine the optimal composition for the TriPG gels, we prepared a series of (Cellulose/PEDOT:PSS)(x/y)
hydrogels and (Cellulose/PEDOT:PSS)(x/y) TriPG gels using the steps illustrated in Figure S1 and analyzed theirproperties using tensile tests and electrical and thermal conductivity measurements. As the PEDOT:PSS
concentration increased from 0 to 1 wt% at a set cellulose concentration of 1.5 wt%, the Young’s modulus, tensile
strength, and work of extension of the TriPG gels increased gradually, whereas those of the corresponding hydrogels
decreased. However, as the cellulose concentration increased from 0.5 to 1.5 wt% at a set PEDOT:PSS concentrationof 1 wt%, the mechanical properties of both the TriPG gels and corresponding hydrogels increased gradually. Thesechanges in the mechanical properties of the gels were in agreement with the changes in their final solvent contents.
Our compositional study indicated that TriPG can serve as a good solvent for integrating both cellulose and
PEDOT:PSS into gel materials despite their highly contrasting chemical structures. While the mechanical propertiesof the TriPG gels increased proportionally to the concentrations of cellulose and PEDOT:PSS, the mechanicalproperties of the hydrogels did not exhibit the same trend. The swelling ratio of the TriPG gels (~80 wt% TriPG
content) was lower than that of the corresponding hydrogels (~90 wt% water content); thus, the mechanical propertiesof the former were superior to those of the latter. Moreover, the highest recorded electrical conductivity of the TriPG
gels was higher than that of the hydrogels. Furthermore, cellulose is electrically non-conductive, whereas
PEDOT:PSS is highly conductive; consequently, the electrical conductivity of the TriPG gels and correspondinghydrogels strongly depends on the final PEDOT:PSS concentration and PEDOT:PSS-to-cellulose concentration ratio.
The final density of PEDOT:PSS in the TriPG gels should be higher than that in the hydrogels because the solvent
content of the gels decreased during solvent exchange, which increased the electrical conductivity of the TriPG gels.
Increasing the PEDOT:PSS concentration at a set cellulose concentration or decreasing the cellulose concentration
at a set PEDOT:PSS concentration led to an increase in the gel electrical conductivity because the PEDOT:PSS-tocellulose ratio increased. Among the TriPG gels, the (Cellulose/PEDOT:PSS)(1.5/1) TriPG gel presented the best
mechanical properties (Young’s modulus of 47.62 ± 5.52 MPa, tensile strength of 7.13 ± 0.59 MPa, and work ofextension of 5.55 ± 1.17 MJ m−3), and the (Cellulose/PEDOT:PSS)(0.5/1) TriPG gel presented the best electricalconductivity (10.111 ± 1.182 S m−1). The (Cellulose/PEDOT:PSS)(1/1) TriPG gel that had excellent mechanicalproperties (Young’s modulus of 33.28 ± 6.36 MPa, tensile strength of 4.57 ± 0.36 MPa, and work of extension of
3.47 ± 0.52 MJ m−3) and a reasonably high electrical conductivity (5.708 ± 0.887 S m−1) was selected for further
studies.

When cellulose hydrogels are anisotropically dried under confined conditions, well-aligned hierarchical fibrous
cellulose structures form along the constraint direction, which afford hydrogels with anisotropic properties after
reswelling.[20] Moreover, drying induces the crystallization of the PEDOT:PSS colloidal domains. This leads to anincrease in the length of the PEDOT:PSS chains, which serve as electrical pathways, and thus significantly increases
the electrical conductivity of PEDOT:PSS-based gels.[45,48] The gels developed in this study comprised both cellulose
and PEDOT:PSS. Therefore, we analyzed the effect of the drying treatment on the gel properties. First, we preparedisotropic pre-dried (Cellulose/PEDOT:PSS)(1/1) TriPG gels by drying the corresponding hydrogels at ~25 °C in theabsence of constraints and under biaxial clamping (lengthwise and widthwise) at a strain of 0%, followed bysequential reswelling in water and TriPG and stabilization in air at ~25 °C. The gel without constraints shrank in all
directions (length, width, and thickness), whereas only the thickness of the biaxially clamped gel decreased
significantly. We determined that the final solvent contents of both pre-dried TriPG gels decreased significantly, andthe gels presented isotropic mechanical properties along their lengths and widths. Moreover, the properties of the predried TriPG gels were superior to those of the isotropic TriPG gel prepared without drying the corresponding hydrogel.
In particular, the solvent content of the pre-dried TriPG gel after biaxial clamping was ~56 wt%, and the Young’s
modulus, tensile strength, work of extension, and electrical conductivity were ~4, ~4, ~2, and ~10 times higher,
respectively, than those of the corresponding isotropic gel obtained without drying. These results implied that drying
the gels induced cellulose aggregation and PEDOT:PSS crystallization, which led to a dramatic decrease in solvent
content and a notable improvement to the gel mechanical and electrical properties.

Based on these results, we expected that applying unidirectional constraints to the hydrogels during drying would

induce directional orientation and aggregation of the polymers, which could yield corresponding TriPG gels withmulti-anisotropic properties. We prepared unidirectional pre-dried TriPG gels by drying the corresponding hydrogelsat ~25 °C and clamping them at pre-stretching strains of 0% and 40% along the length direction (Figures 1); these
are termed anisotropic (Cellulose/PEDOT:PSS)(1/1)@25/b TriPG gels (where 25 is the process temperature (°C) andb is the pre-stretching strain). As the hydrogels were constrained at two ends, their width and thickness decreased
significantly during drying, whereas their lengths did not change. This caused aggregation and alignment of the linear
rigid polymers (cellulose and PEDOT:PSS) along the length direction in accordance with the principle of “drying in
confined condition method,” reported previously.[20] The solvent content of the final anisotropic TriPG gels was ~60
wt%. The gel properties were analyzed along the directions parallel and perpendicular to the clamping direction,
which showed that the gels presented excellent properties, with high degrees of mechanical and electrical anisotropy(Figures 2a and c). Increasing the clamping pre-stretching strain from 0% to 40% during drying led to remarkableincreases in the stiffness/strength and electrical conductivity and a decrease in the work of extension in the direction
parallel to the clamping direction, whereas opposite trends were observed in the direction perpendicular to theclamping direction (Figures 2a, 2c). Moreover, increasing the pre-stretching strain significantly increased theanisotropy. The average Young’s modulus, tensile strength, and electrical conductivity in the direction parallel toclamping for the (Cellulose/PEDOT:PSS)(1/1)@25/0 gel were 2.45, 1.85, and 2.49 times higher, respectively, thanthose in the direction perpendicular to clamping, whereas those of the (Cellulose/PEDOT:PSS)(1/1)@25/40 gel were
up to 6.09, 3.59, and 4.84 times higher, respectively.

Figure 2. Representative tensile stress–strain curves in the directions parallel and perpendicular to clamping of the(a) anisotropic (Cellulose/PEDOT:PSS)(1/1)@25/b TriPG gels prepared by drying the corresponding hydrogels at

~25 °C under clamping at pre-stretching strains (b) of 0% and 40% and (b) anisotropic (Cellulose/PEDOT:PSS)(1/1)@a/40 TriPG gels obtained by drying the corresponding hydrogels at temperatures (a) of ~25 and 90 °C underclamping at a pre-stretching strain of 40%. (c) and (d) Electrical conductivity in the directions parallel andperpendicular to clamping of the gels in (a) and (b), respectively. (e) In-plane thermal conductivity of the anisotropic(Cellulose/PEDOT:PSS)(1/1)@25/40 gel parallel and perpendicular to the clamping direction. DA values are shown
above the plots in (c), (d), and (e).

Conclusion
We successfully developed a novel class of anisotropic gels by integrating cellulose and PEDOT:PSS, which are biofriendly, high-value polymers, in TriPG, a green organic solvent. Despite the significant differences in the structuresand properties of the two polymers, the novel fabrication method proposed in this study enabled the creation of a
hybrid gel with excellent mechanical, thermal, and electrical properties, multiple types of strong anisotropy, selfwelding capability, and extremely high stability over a wide temperature range. Furthermore, we demonstrated thesuitability of the prepared gels for fabricating complex flexible electrical circuits, flexible connectors, and solvent
sensors. Through the extensive study of changing the composition of cellulose, PEDOT:PSS, and TriPG, as well asother parameters like pre-stretching strain and process temperature, (Cellulose/PEDOT:PSS)(1/1)@90/40 TriPG gel
was determined to be the optimal anisotropic gel. Considering these remarkable properties and facile synthesis, thedeveloped gels are expected to have a high potential for numerous applications in next-generation flexible devices.

国際化推進共同研究概要
No. 1321RE-3タ イ ト ル： Numerical Wave Tank for Floating Offshore Wind Turbine Structures
研 究 代 表 者： WAN Decheng

所内世話人： 胡 長洪
研究概要：
本国際化推進共同研究について、共同研究・研究集会とも予定通り実施した。共同研究について、浮体式洋上風車の波浪中性能や、風車間干渉などの問題に対して数値シミュ
レーション関する検討が行われ、関連の研究成果は 8 編の国際学会論文に纏められ採択された。R4 年 1 月 21 日にオンライン国際研究集会「The 3rd International Symposiumon Novel Computational and Experimental Methods for Complicated Fluid-StructureInteractions」が開催され、外国から 30 名、日本から 26 名の参加者があり、流体・構造連成解析問題に関する数値解析方法及び水槽実験方法の高精度化・高効率化に関して有意義な国際研究集会となった。

Report for 2021 RIAM International Joint Research Project[21RE-3]

Numerical Wave Tank for Floating Offshore Wind Turbine
Structures
Decheng Wan
School of Naval Architecture, Ocean and Civil Engineering, Shanghai Jiao Tong University, China

1. Purpose
Offshore Wind Turbine (OWT) is considered as one of the most promising renewable energy sources fromocean. The OWT is exposed to severe ocean environment such as typhoon (hurricane) and extreme waves, andhas to be designed to withstand those ocean environments. During the design, the evaluation of theenvironmental loading on the OWT has been relying on the empirical simulation tools and the physical wave
tank model test. Recently, there has been breakthrough in the physics-based simulation of offshore platforms,
which is called as the Numerical Wave Tank (NWT). The NWT is considered to replace partly the physicaltank model test in the near future for OWT design. This joint research project focuses on some importantresearch topics in NWT development, and provides an opportunity for researchers, especially younger
researchers, including but not limited to SJTU and RIAM, to exchange their knowhow on their researches.

2. Research Plan
The major research topics of this joint research project is new CFD solver development, large scale parallel
simulation technique, fluid-structure interaction simulation, fully-nonlinear wave model for ocean waves, andadvanced wind modeling, etc. CFD codes which are developed in SJTU and RIAM will be compared to theexperiments. In the end of 2021, as the main event of this international joint research project, the 3rdInternational RIAM Symposium on Novel Computational and Experimental Methods for Complicated FluidStructure Interactions will be carried out. Researchers involved in this joint research project will present anddiscuss their research progresses.
The members involved in this collaborative research are shown in the following table.
Researcher’s Name

Name of University
or Institute

Present Status or Grade(graduate students)

Decheng Wan

SJTU

Professor

Representative person (CFD )Jianhua Wang

SJTU

Assistant Professor

Co-researcher (CFD)

Cheng Liu

SJTU

Associate Professor

Co-researcher (CFD)

Weiwen Zhao

SJTU

Assistant Professor

Co-researcher (CFD)

Liushuai Cao

SJTU

Assistant Professor

Co-researcher (CFD)

Xiaosong Zhang

SJTU

PhD student

Co-researcher (CFD)

Zhiqiang Liu

SJTU

PhD student

Co-researcher (CFD)

Chongyi Huang

SJTU

PhD student

Co-researcher (CFD)

Seiya Watanabe

RIAM

Assistant professor

Co-researcher (CFD)

Researcher role

Mohamed M. Kamra

RIAM

Research Fellow

Co-researcher (CFD)

Hongzhong Zhu

RIAM

Research Fellow

Co-researcher (Experiment)

Changhong Hu

RIAM

Professor

RIAM Attendant

3. Summary of Collaboration Research
In 2021, due to the international travel restriction, research discussions have been made online. Main topics
that have been studied include (1) numerical simulation of asymmetrical wake flows of a yawed wind turbine;(2) numerical analysis of aero-hydrodynamic responses of floating offshore wind turbine considering blade
deformation; (3) numerical investigations of wake flows of counter-rotating wind turbines in shear inflows;and (4) forces prediction of a hydrofoil by combined machine learning and CFD approach. The research results
have been presented at the 2021 ISOPE conference and the 3rd International Symposium on Novel
Computational and Experimental Methods for Complicated Fluid-Structure Interactions.
International conference papers related to this joint research project in 2021 are listed as follows.
1) Dezhi Wei; Decheng Wan; Changhong Hu: Numerical Simulations of Asymmetrical Wake Flows of a
Yawed Wind Turbine, Proc. the 31st International Ocean and Polar Engineering Conference, Rhodes,
Greece, June 2021. Paper Number: ISOPE-I-21-1193
2) Chunhui Ma; Decheng Wan; Changhong Hu: Numerical Study of Passive Control of Flow-Induced
Oscillation of Cylinder with Symmetric Strips, Proc. the 31st International Ocean and Polar Engineering
Conference, Rhodes, Greece, June 2021. Paper Number: ISOPE-I-21-3226
3) Yang Huang; Decheng Wan; Changhong Hu: Numerical Analysis of Aero-Hydrodynamic Responses of
Floating Offshore Wind Turbine Considering Blade Deformation, Proc. the 31st International Ocean andPolar Engineering Conference, Rhodes, Greece, June 2021. Paper Number: ISOPE-I-21-1197
4) Heming Bai; Yang Huang; Decheng Wan; Changhong Hu: Numerical Investigations of Wake Flows ofCounter-Rotating Wind Turbines in Shear Inflows, Proc. the 31st International Ocean and Polar
Engineering Conference, Rhodes, Greece, June 2021. Paper Number: ISOPE-I-21-1198
5) Minsheng Zhao; Decheng Wan; Changhong Hu: Numerical Simulation of Propeller Cavitation Flows in
Non-Uniform Flow Fields, Proc. the 31st International Ocean and Polar Engineering Conference,
Rhodes, Greece, June 2021. Paper Number: ISOPE-I-21-4147
6) Hao Hu; Di Deng; Decheng Wan; Changhong Hu: Numerical Analysis of Vortex-Induced Vibrations ofa Slender Flexible Riser under Platform Motions, Proc. the 31st International Ocean and Polar
Engineering Conference, Rhodes, Greece, June 2021. Paper Number: ISOPE-I-21-3220
7) Songtao Chen; Weiwen Zhao; Decheng Wan; Changhong Hu: Numerical Investigation of VortexInduced Motions of a Circular Cylinder with Free Surface, Proc. the 31st International Ocean and Polar
Engineering Conference, Rhodes, Greece, June 2021. Paper Number: ISOPE-I-21-3219
8) Hongjie Cao; Decheng Wan; Changhong Hu: Forces Prediction of a Hydrofoil by Combined Machine
Learning and CFD Approach, Proc. the 31st International Ocean and Polar Engineering Conference,
Rhodes, Greece, June 2021. Paper Number: ISOPE-I-21-3176

As a main event of this international joint research project, ‘The3rd International Symposium on Novel
Computational and Experimental Methods for Complicated Fluid-Structure Interactions’ has been held on
January 21, 2022. Due to the global pandemic situation of COVID-19, the symposium was held online. On
the symposium, overseas and domestic scholars were invited to present their recent researches on their recent
research results on development of computational and experimental methods for complicated fluid-structureinteractions. The program of the symposium is as follows.

The 3rd International Symposium on Novel Computational and Experimental Methods
for Complicated Fluid-Structure Interactions
Date: January 21, 2022
Place: Zoom Meeting Room (From 9:00 Japan time)
Organized by Research Institute for Applied Mechanics, Kyushu University

TIME TABLE
9:50 -10:00

Opening Address by Changhong Hu

Session 1

High Performance Numerical Method

10:00 - 10:30

Yingyi Liu (RIAM, Kyushu University)

10:30 - 11:00

Computational Accuracy and efficiency for Diffraction Transfer Matrix using Hybrid
Source-dipole Formulations
Zhiteng Gao, Ye Li (Shanghai Jiao Tong University, China)

11:00 - 11:30

Validation and Improvement of Actuator Line Model in the Large-Eddy Simulation ofWind-Turbine Wakes
Lei Tan (RIAM, Kyushu University)

11:30 - 12:00

Motion and Load Characteristics of a Barge-Type Vertical-Axis Floating Wind Turbinewith Moonpools
Tomoaki Hirakawa (Akita University)
Improved BEM Simulation for Wave-Body Interactions by Elastic Mesh Techniques

12:00 - 13:00

Lunch breakSession 2

Tidal Current and Wave Energy

13:00 - 13:40

Daisaku Sakaguchi, Reiko Yamada, Yusaku Kyozuka (Nagasaki University)
Invited Lecture

13:40 - 14:10

Design Optimization of Tidal Current Turbines by Meta-model Assisted Genetic
Algorithms
Mohamed Kamra, Rui Yamamoto, Changhong Hu (RIAM, Kyushu University)
Application of Machine Learning to Wake Prediction of Tidal Current Turbine

14:10 - 14:40

Patxi Garcia Novo (Nagasaki University)

14:40 - 15:10

Tidal Stream Energy as a Potential Continuous Power Producer: A Case Study for WestJapan
Peiwen Cong (Dalian University of Technology, China)
Numerical Evaluation of the Hydrodynamic Performance of Multi-Degree-of-Freedom
Floating Oscillating Water Column (OWC) Devices

15:10 - 15:20

Break

Session 3

Offshore Wind Energy

15:30 - 16:00

Dezhi Wei, Decheng Wan (Shanghai Jiao Tong University, China)

16:00 - 16:30

Analytical Modeling of Multiple Yawed Turbine Wakes: Considering the Effects ofTransverse Wake Velocity
Xiaobo Zheng, Ye Li (Shanghai Jiao Tong University, China)

17:00 - 17:30

Aerodynamic Response of a Pitching Foil to Vortex Shedding - Some Inspiration for the
Vertical-Axis Wind Turbine
Ali Alkhabbaz, Ho-Seong Yang, Watchara Tongphong, Young-Ho Lee (Korea Maritime &Ocean University, Korea)
Aerodynamic Performance Analysis of Floating Wind Turbine Experiencing Platform Surge
MotionNitin Thulkar (Chartered Engineer IET, UK)

17:30 - 18:10

A Unified Seakeeping and Maneuvering Analysis of Multiple Linked Towing System with
Triangular Bodies
Zhiqiang Hu (Newcastle University, UK)

16:30-17:00

Invited Lecture
Application of SADA Method on Dynamic Performances Analysis of FOWT : Case of Studywith Full-Scale Hywind Data
18:10 - 18:20

Closing Address by Decheng Wan

国際化推進共同研究概要
No. 1421RE-4
タ イ ト ル： Software-in-the-Loop combined Artificial Intelligence method for
Dynamic Response Analysis of FOWTs
研 究 代 表 者： HU Zhiqiang

所内世話人： 胡 長洪
研究概要：
浮体式洋上風力発電システム用のセミサブ型浮体の運動特性解析に Software-in-theLoop 法と AI 技術を応用する国際化推進共同研究について今年度は予定通り実施した。
特に、SADA 手法に対して検討を行い、有望な成果が得られた。R3 年１月に応研で開催さ れ た オ ン ラ イ ン 国 際 研 究 集 会 「 The 3rd International Symposium on Novel
Computational

andExperimental

MethodsforComplicated

Fluid-StructureInteractions」に参加し、「Application of SADA Method on Dynamic Performances
Analysis of FOWT : Case of Study with Full-Scale Hywind Data」のタイトルで共同利用成果の発表を行い、参加者との研究交流を行った。

Report for 2021 RIAM International Joint Research Project[21RE-4]
Software-in-the-Loop combined Artificial Intelligence method for
Dynamic Response Analysis of FOWTs
Zhiqiang Hu
Marine, Offshore and Subsea Technology, School of Engineering, Newcastle University, UK

During year of 2021, although we couldn’t attend the RIAM symposium at Kyushu University
in person due to pandemic, but international collaborations were conducted steadily. Zhiqiang
Hu attended the RIAM symposium online in Jan 2021, and gave a presentation on the topic of
SADA, a new innovative AI-based methodology for dynamic performance analysis of floating
offshore wind turbines. After the symposium, Zhiqiang Hu led his research team and continued
investigation on AI+FOWTs, especially the engineering application of SADA on FOWTs.
During the year of 2021, the collaborative research outcomes are listed as below.
1) The 3rd International Symposium on Novel Computational and Experimental Methods forComplicated Fluid-Structure Interactions is planned to be held online at RIAM Kyushu
University in Jan 2022. Zhiqiang Hu has agreed to attend and will give a presentation on
the topic of ‘Application of SADA method on Dynamic Performances Analysis of FOWT:
Case of Study with Full-Scale Hywind Data’.
2) During year 2021, the collaborative research is carried out to conduct engineering
applications of the Artificial Intelligence knowledge-based method, SADA, on the fullscale measurement data of FOWT. This investigation also received the kind support from
ORE Catapult UK, as they provided the valuable full-scale measurement data from Hywind
FOWT in Scotland. The SADA method was applied to perform numerical optimization anddynamic responses prediction of the FOWTs, based on the full-scale data from one FOWT
in Hywind Farm. The numerical model imbedded in SADA was trained to be intelligent forthe objective Hywind FOWT under different sea states, and then it can be used to do moreprediction and analysis.
3) Based on the research in year 2021, a collaborative conference paper entitled ‘Dynamic
Performance Prediction of Hywind Floating Wind Turbine based on SADA Method andFull-Scale Measurement Data’ has been accepted to be published on MARTECH
Conference 2022. Prof Changhong Hu is the co-author of this paper. At this moment, thepaper is under the revision status. If it can be accepted, it will be presented in May 2022.
1. RIAM international symposium
The 3rd International Symposium on Novel Computational and Experimental Methods forComplicated Fluid-Structure Interactions was held online on 21st Jan 2022. Zhiqiang Hu
attended this symposium and gave a presentation on the topic of ‘Application of SADA method
on Dynamic Performances Analysis of FOWT: Case of Study with Full-Scale Hywind Data’.

This presentation introduced the latest collaborative research outcomes of Zhiqiang Hu andChanghong Hu’s research teams on FOWTs during year 2021. This presentation introduced thestructure of SADA methodology and its first successful engineering application on one FOWTat Hywind Scotland Farm. After the presentation, Zhiqiang Hu made fruitful discussions withothers who were interested in this new method. After the symposium, professor Changhong Hu
and Zhiqiang also made a detailed discussion and confirmed to continue the collaborative
research in the field of AI+FOWTs in the year 2022.
2. Collaborative research on AI technology for FOWTs
In the year of 2021, a collaborative research on the engineering application of AI-based
technology for dynamic responses analysis of FOWTs was conducted well. This study started
with introducing a case study for the dynamic performance analysis of Hywind FOWT by using
full-scale data through the application of SADA. The full-scale data used was collected by one
of Hywind FOWTs in Scotland. The analysis of dynamic performance of FOWT can be
optimized by using the trained SADA model in terms of platform motions, tower top, and blade
tip deformation. The analysis results show that SADA can predict the Hywind supporting
floater motions with high accuracy, although some design parameters are not accessible. Basedon the comparison and validation of platform motion predictions, it can be proved that SADA
is a reliable and cost-effective method for dynamic performance analysis of FOWTs. In
summary, the SADA method can bring an innovative vision for FOWTs’ full-scalemeasurement technology in engineering applications.
In addition, thanks for the support and collaboration in 2021, a collaborative conference paper
submitted to MARTECH Conference 2022. The paper is titled ‘Dynamic Performance
Prediction of Hywind Floating Wind Turbine based on SADA Method and Full-Scale
Measurement Data’. This paper has been accepted for publication and the first author will givea presentation on MARTECH2022 conference.
In year 2022, the collaborative research between Newcastle University and Kyushu University
will be conducted to a further step. The research will be extended to FOWT design field, and it
is expected that a new design method, named Interactive Integrated Design method will be
proposed, based on AI+FOWTs SADA method. In UK, there are quite a lot opportunities forthe development of FOWTs designs in the coming years, but design methods are not mature
enough to support design of large offshore wind turbine. Therefore, the collaborative researchon FOWT design has a promising future. The AI technology application in offshore renewableenergy is also the strong side of Professor Changhong Hu’s research team. It is expected there
will be fruitful research outcomes in year 2022.

国際化推進共同研究概要
No. 1521RE-5
タ イ ト ル ： Joint study on the next generation of high frequency with
controllability and reliability in power semiconductor device
technologies
研 究 代 表 者： EKKANATH MADATHIL Sankara Narayanan
所内世話人： 齋藤 渉
研究概要：
1.2kV 系のトレンチ IGBT とトレンチクラスターIGBT の比較を三次元 TCAD シミュレーションを用いて行った。オン電圧－ターンオフ特性の比較に加えて、ターンオン損失比較を行った。トレンチクラスターIGBT では、高い電流増幅率によるターンオン損失低減に加えて、PMOS 動作による負性容量の抑制が得られる。これらの効果から損失－
トレードオフも改善される。加えて、三次元スケーリング設計によるターンオン動作の解析も行った。シミュレーション結果からターンオン損失の劇的な減少を確認し、150℃動作において、k=3 のスケーリングにより電力損失を 40%低減できるという結果が得られた。

Joint study on the next generation of high frequency with controllability andreliability in power semiconductor device technologies
Sankara Narayanan Ekkanath Madathil
The University of Sheffield, United Kingdom

Abstract
In this paper, performances of 1.2-kV Trench IGBT(TIGBT) and Trench Clustered IGBT (TCIGBT) arecompared through 3-D TCAD simulations. Comparative
on-state and turn-off performances have been reported
previously. Herein we show much lower turn-on loss (Eon)of TCIGBT due to its higher current gain and the negativegate capacitance effect is effectively suppressed by the
self-clamping feature and PMOS actions in comparison to
the TIGBT. In addition, the impact of 3-D scaling rules onturn-on performance is analyzed in detail. Simulation results show significant reduction of Eon in both TIGBT and
TCIGBT. The k3-TCIGBT shows a 40% reduction of
power loss compared to the k3-TIGBT at 150°C.
1. Introduction
The trends in the development of silicon MOS-Bipolar
devices are devoted to increase in power density as well as
power efficiency. Remarkable efforts have been made to improve the turn-off energy loss (Eoff) versus on-state voltage
drop (Vce(sat)) trade-off. For example, the 3-D scaling concepts
on TIGBT [1, 2] and Trench Clustered IGBT (TCIGBT) [3],as shown in Fig. 1, have resulted in significant improvementof Eoff -Vce(sat) trade-off. Due to the enhanced thyristor effect,
the scaled TCIGBT shows even lower Vce(sat) than the scaled
TIGBT, as shown in Fig. 2. Moreover, Fig. 3 shows that the
PMOS actions enable the TCIGBTs to show lower Eoff than
the TIGBTs. Recently, the TCIGBTs have been experimentally evaluated to show Dynamic Avalanche (DA) free behavior and low power loss at high current density operations [46]. In addition to the on-state and turn-off behavior, the turnon performance is also important for TIGBTs and TCIGBTs
to achieve high switching frequency with low power loss. In
this paper, the turn-on behavior of TIGBT and TCIGBT are
studied via 3-D TCAD simulations [7]. Furthermore, the impacts of 3-D scaling rules on the turn-on performance of
TIGBT and TCIGBT are analyzed in detail.
2. Comparison of Turn-on Performance
The cross-sections of the TIGBT and TCIGBT are shownas the k1 structures in Fig. 1. The threshold voltages are kept
identical to compare the turn-on performance. A double pulse
inductive test circuit as shown in Fig. 4 is used to simulate theswitching behavior. Fig. 5 compares the turn-on waveforms
at rated current and identical gate resistance (Rg). It can beseen that TCIGBT shows much higher turn-on dI/dt anddV/dt than the TIGBT. This is because the thyristor structure

within TCIGBT exhibits a higher current gain than the BJT
structure within TIGBT, as expressed in Equations (3) and (4).
Therefore, TCIGBT shows much lower turn-on energy loss(Eon) than the TIGBT. In addition, in the TIGBT, the P-float
potential (VPF) rises up during turn-on. The voltage difference
across the gate oxide (VPF - Vge) can induce a reverse displacement current to charge the gate capacitance to a negativevalue, which has a significant impact on the dV/dt and dI/dt
controllability [8]. Fig. 6 shows the VPF and Vge of TIGBT and
TCIGBT during turn-on while Fig. 7 compares the potential
distribution and hole current flowlines when Ic = 100 A and
Vce = 600 V. It is shown that there is a significant potential
difference between VPF and Vge in the TIGBT, which is causedby the current flow within the P-float region. However, in the
TCIGBT, the P-base potential is clamped under a low value
due to the self-clamping feature and the hole current is evacuated through the PMOS directly. Hence, the potential difference across the gate oxide is marginal and the negative gate
capacitance effect is therefore successfully suppressed.
3. Impact of Scaling Rules on Turn-on PerformanceFig. 8 compares the switching waveforms and gate charge(Qg). As shown, the Qg is scaled in k3-TIGBT due to thescaled trench gate while the dV/dt and the dI/dt of k3-TIGBT
are increased compared to that of k1-TIGBT due to reduced
input capacitance, as shown in Fig. 9 and Fig. 10. Hence, thescaling rules result in significant reduction of Eon in both
TIGBT and TCIGBT, as shown in Fig. 11. Due to suppressionof negative gate capacitance, better turn-on dI/dt controllability with respect to the Eon of TCIGBT compared with TIGBT
is shown in Fig. 12. At dI/dt = 5 kA/µs, k3-TCIGBT shows a
70% reduction of Eon compared to that of k3-TIGBT. Fig. 13
compares the total power loss of TIGBTs and TCIGBTs. As
shown, scaling rules result in a 10% reduction of total power
loss in both TIGBTs and TCIGBTs. k3-TCIGBT shows a
40% reduction of Eon compared to k3-TIGBT at Tj = 425 K.
4. Conclusions
The behavior of TIGBT and TCIGBT with scaling design
are studied. The negative gate capacitance is suppressed in
the TCIGBT due to the self-clamping feature. The scaling
rules on TIGBT and TCIGBT reduce Eon significantly. The
k3-TCIGBT shows high power efficiency due to enhanced
thyristor effect and good switching controllability.

Fig. 1. Scaling concepts on (a) TIGBT [1] and (b) TCIGBT [3].

Fig. 2. Comparison of I-V performance.

Fig. 3. Comparison of Eoff.

Fig. 4. Test circuit configuration.

Fig. 5. Comparison of turn-on performance.

Fig. 6. Comparison of VPF and Vge during turn-on.

Fig. 7. Comparison of current flowlines andpotential distribution during turn-on.

Fig. 8. Comparison of turn-on waveforms.

Fig. 9. Comparison of turn-on dV/dt.

Fig. 10. Comparison of turn-on dI/dt.

Fig. 11. Comparison of turn-on energy loss.

Fig. 12. Comparison of dI/dt-Eon trade-off.

Fig. 13. Comparison of total power loss.

References: [1] K. Kakushima, et al., IEDM 2016, pp. 10.6.1-10.6.4. [2] T. Saraya, et al., IEDM 2018, pp. 8.4.1-8.4.4. [3] P. Luo, et al., IEEE Trans. Electron
Devices, vol. 65, pp. 1440-1446, 2018. [4] P. Luo, et al., IEDM 2019, pp. 12.3.1-12.3.4. [5] P. Luo, et al., IEEE Trans. on Electron Devices, vol. 67, pp. 36913697, 2020. [6] P. Luo, et al., IEEE Trans. on Power Electronics, vol. 36, pp. 3304-3311, 2021. [7] I. Synopsys, Sentaurus Device User Guide: Version R2020.09. [8] Y. Onozawa, et al., IEEE Trans. on Industry Applications, vol. 43, pp. 513-519, 2007.

国際化推進共同研究概要
No. 1621RE-6
タ イ ト ル： Predictions of the wave power absorption by a large Floating
Oscillating Water Column (OWC) wave energy converter based on aHigher-order Boundary Element (HOBEM) method
研 究 代 表 者： CONG Peiwen

所内世話人： 劉 盈溢
研究概要：

この研究では、複雑な形状の振動水柱（OWC）発電装置の流体力学的解析のため、数値方法が開発された。物理的には、デバイスが自由に移動した
り波に係留されたりする状況では、チャンバー内の気流の動きが、内部の流体表面の変化およびデバイスの流体力学的応答と密接に関連していた。
これらの結合効果を考慮に入れることにより、適切な境界積分方程式が補足的な理論的関係で定式化された。次に、境界値問題は、高次境界要素法（HOBEM）を使用して解決された。波と動的空力を取得した後、連成運動と流体力学的効率を積分によって評価した。特に、固定 OWC に限定された
従来の方法とは異なり、提案された方法は、結合された剛体運動で浮いているものに適用可能であることが証明されていた。したがって、波力吸収を最大化するために、最適なタービンパラメータが数学的に導き出された。
線形量に加えて、非線形の波漂流力は、遠場の寄与と内部流体表面上の振動空気圧を説明する、新しく導出された定式化によって評価された。上記の方法論と結果として得られたツールに基づいて、さまざまな浮動型デバ
イスの数値研究が実行された。

[1] Cong, P., Teng, B., Bai, W., Ning, D., Liu, Y. (2021). Wave power absorption by an oscillating watercolumn (OWC) device of annular cross-section in a combined wind-wave energy system. Applied
Ocean Research, 107, 102499.
[2] Liu, Y., Liang, H., Kashiwagi, M., Cong, P. (2021). Alternative approaches of evaluating Diffraction
Transfer Matrix and Radiation Characteristics using the hybrid source-dipole formulation. Applied
Ocean Research, 114, 102769.

国際化推進共同研究報告書
No.
21RE-6
タ イ ト ル：

Predictions of the wave power absorption by a large Floating Oscillating Water Column(OWC) wave energy converter based on a Higher-order Boundary Element (HOBEM)
method研究代表者：

CONG, PEIWEN

所内世話人：劉 盈溢

Introduction
The ocean is vast and powerful, enabling marine renewable energy to be potentially a significant energy
supply. Due to the high power density and longtime availability, considerable efforts and advances have been
made in exploiting the power of ocean waves worldwide, and a variety of wave energy converters have been
invented to harvest the wave energy. Among different classes of designs, the oscillating water column (OWC)
device has been widely regarded as one of the most promising options[1].
In addition to wave energy, wind energy is also a great source of renewable energy. Wind energy converters
have been used for the harvesting and exploitation of the available enormous wind energy resources. Offshore
wind turbine technology has been being developed rapidly in recent years, and it can be considered as theleading technology in the offshore renewable energy sector[2]. For both the offshore wind turbine and the wave
energy converter, there is a need for a reduction in the cost and the further development. Due to the natural
correlation, wave energy may also be of considerable amount where the offshore wind energy resource is rich.
Significant opportunities and benefits have been identified through an integration of the energy systems ofdifferent technologies into one single platform. Due to the various possible advantages as a result of the
combination of the wind and wave energy converters, several concepts of the combined system have been
proposed. Examples include the integration of a point-absorber-type wave energy converter with a semisubmersible type or a spar type wind turbine; integration of an OWC with a floating or bottom-mounted
offshore wind turbine, and semisubmersible flap concept.

Fig. 1 Overview of a combined concept consisting of a monopile wind turbine and an attached OWC device
In this study, a novel combined concept consisting of an oscillating water column (OWC) device and an
offshore wind turbine is proposed. As shown Fig. 1, the wind turbine is supported by a monopile foundation,and the OWC is coaxial with the foundation. The OWC is partly submerged with its bottom open to the sea.
An air duct, which houses an air turbine, is installed on the roof of the chamber. Within the chamber, theexterior shell of the OWC and the monopile foundation are connected by four vertical stiffening plates.
Correspondingly, the whole chamber is divided into four fan-shaped sub-chambers. The performance of the
proposed system is then investigated.
Methodology
Governing equations
It is assumed that the fluid is inviscid and incompressible with a constant density ρ, the fluid motion isirrotational, and the wave steepness is small. The linear potential flow theory can then be used, and there
exists a velocity potential Ф(x; t) satisfying the Laplace’s equation in the fluid domain. That is∇ 2 Φ ( x; t ) =0.

(1)

The combined system is exposed to the action of a plane incident wave of amplitude A, and frequency ω. The
wave heading is β with respect to the positive x-direction. A frequency-domain analysis is conducted, and alltime-dependent variables are assumed to be harmonic. The time factor can then be separated, and the velocity
potential will have the following form

Φ ( x; t ) =Re φ (1) ( x ) e − iωt  ,in which ‘Re’ is the real part of a complex variable; i=

(2)

−1 .

Besides Laplace’s equation, the velocity potential must satisfy appropriate boundary conditions. On theexterior free surface Se (r ≥ Re), there is only the atmospheric pressure P0. However, the inner free surface Si (a≤ r ≤ Ri) is subjected to an air pressure distribution of P0 + Pc(t), in which Pc(t) is the oscillating air pressure.
Due to the high sound speed in air and the low frequency of ocean waves, the oscillating air pressure can beconsidered spatially uniform throughout the whole chamber[3]. Referring to Sarmento and Falcão (1985)[4],after assuming isentropy and using a linear wave theory, the mass flux of the air through a linear turbine isrelated to the oscillating air pressure bydM a
V dP KD=ρ a Qc − 20 c = Pc ,
dt
c dt
N

(3)

in which Ma is the mass of the air in the chamber; Qc is the change rate of the total volume of air inside thechamber; V0 is the air volume in the chamber in calm water; ρ a is the air density; D is the diameter of theturbine rotor; N is the speed of the turbine rotation; c is the speed of the sound in air; K is an empiricalcoefficient depending on the design of the turbines. For simple harmonic motions with
Qc ( t ) = Re  qc e − iωt  ;(4a)

Pc ( t ) = Re  pc e − iωt  ,(4b)

qc = Λpc ,(5)

we can havein which qc and pc are the amplitudes of the volume flux and the oscillating air pressure, respectively. The
parameter Λ is expressed as
Λ= χ − iωµ ,

(6)

χ=

KD
;
N ρa

(7a)

µ=

V0
.
c2 ρa

(7b)

with

χ depends on the design of the air turbine, and can be adjusted by some ways, such as varying the rotational
speed N. μ represents the effect of compressibility of air in the chamber, and is analogous to a spring constant.
Boundary equations
In the hydrodynamic analysis, the effect of the oscillating air pressure should be considered properly. Then, on
the mean plane of the free surface (z = 0), the combined kinematic and dynamic boundary condition is givenby∂φ ω 2iω
−
φ =pc , on Si ;
∂z
g
ρg

(8a)

∂φ ω 2− φ=
0, on Se .
∂z g

(8b)

On the mean wet surface of the combined system Sb, the boundary condition is given by∂φ= 0, on Sb ,∂n

(9)in which n is the normal unit vector pointing outward from the fluid domain. In the same way, the boundary
condition on the impermeable sea bed (z = –h) is∂φ= 0, on z = − h.
∂z

(10)

To ensure the uniqueness of the solution, φ has to satisfy the Sommerfeld radiation condition at a substantial
distance from the structure. That is∂
lim r  (φ − φI ) − iκ 0 (φ − φI )  =
0,
r →∞
 ∂r


(11)

in which φI ( x ) represents the incident velocity potential, and it is given byφI ( x ) = −iAg cosh κ 0 ( z + h ) iκ 0 ( x cos β + y sin β )e,ωcosh κ 0 h(12)

in which κ 0 is the wavenumber. κ 0 and ω satisfy the relationship ω 2 = gκ 0 tanh κ 0 h , with g being thegravitational acceleration.

Power take-off model
The captured power Wc is the time-averaged rate of work done by the oscillating air pressure pushing the air
through the air turbine[5]. Wc can be evaluated according to 1 t +Tˆ
Wc = lim
Pc ( t ) Qc ( t ) dt  .
∫ˆˆT →∞ T
 t




(13)

For regular incident wave, Wc can be further expressed as
=
Wc

1
1
2
∗

Re  p=Re [ Λ ] pc .
c qc 
2
2(14)

Following Cruz (2008)[6], the wave energy extraction efficiency Ec (also known as the relative capture width)
for the present combined system is defined as
=
Ec

Wc
Wc
=
,
Win 2 ( Ri – a ) Pin(15)

in which Win is the wave power of the free incident wave passing through the width of 2(Ri – a) over a wave
period; Pin , representing the power flux density of the incident wave, is determined according toPin =1
ρ gA2C g .
2(16)

In Eq. (16), Cg is the group velocity of the incident wave.
Results
The distribution of the wave elevation in the vicinity of the combined system at ω = 1.38 rad/s is calculated
and shown in Fig. 2 with different turbine parameters. χ = +∞ corresponds to a condition that the inner freesurface open to the air, and the air turbine is removed (N = 0). Around ω = 1.38 rad/s, the total volume flux
maximises, and the captured wave power attains a local maximum. In addition, at this frequency, the radiationsusceptance vanishes, and the radiation conductance maximises. It suggests that this frequency corresponds tothe piston (or pumping) natural frequency of the water column in a moonpool. As a result, when the inner freesurface is open to the air, significantly amplified wave elevation is observed at this wave frequency (see Fig.
2(a)). In Fig. 2(a), the distribution of the wave elevation within the whole chamber is almost uniform, and thefluid within the chamber moves like a rigid body. With a decrease of the turbine parameter, more damping
effect is applied on the inner free surface, and the wave elevation gradually loses its uniform distribution. Its
magnitude varies more and more apparently along the circumferential direction, causing a breakdown of thepiston-like motion.
We then examine the effect of the wave heading on the wave elevation in the vicinity of the system. The
distribution of the wave elevation amplitude at ω = 1.38 rad/s is shown in Fig. 3 with β varying from 0 to π/4.
Under different wave headings, the wave elevation within each sub-chamber distributes almost uniformly. As
β increases, the wave elevation in the upstream and downstream sub-chambers gets enhanced, while in theremaining two sub-chambers, the wave elevation gets gradually less obvious. When β increases to π/4, thedistribution of the wave elevation is symmetry with respect to θ = π/4, and significantly amplified wave
elevation can be observed in the downstream sub-chamber.

Fig. 2 Distribution of the surface elevation amplitude in the vicinity of the combined system at ω = 1.38 rad/swith Re = 6 m, d = 3 m, e = 0.06 m, h = 20 m, A = 1 m, and β = 0 for (a) χ = +∞, (b) χ = 2χopt, (c) χ = χopt, and(d) χ = 0.5χopt

Fig. 3 Distribution of the surface elevation amplitude in the vicinity of the combined system at ω = 1.38 rad/swith Re = 6 m, d = 3 m, e = 0.06 m, h = 20 m, A = 1 m, and χ = χ opt for (a) β = 0, (b) β = π/12, (c) β = π/6, and(d) β = π/4.
References

[1] Falcão A F de O. Wave energy utilization: A review of the technologies. Renewable and Sustainable Energy Reviews, 2010, 14(3):899-918.
[2] Heath T V. A review of oscillating water columns. Philosophical Transactions of the Royal Society London, Series A:
Mathematical, Physical and Engineering Sciences, 2012, 370(1959): 235-245.
[3] Sarmento A J N A, Falcão A F O. Wave generation by an oscillating surface-pressure and its application in wave-energy extraction.
Journal of Fluid Mechanics, 1985, 150: 467-485.
[4 Sheng W A, Alcorn R, Lewis A. On thermodynamics in the primary power conversion of oscillating water column wave energy
converters. Journal of Renewable and Sustainable Energy, 2013, 5(2): 023105.
[5 Evans D V, Porter R. Efficient calculation of hydrodynamic properties of OWC-Type devices. Journal of Offshore Mechanics andArctic Engineering, 1997, 119(4): 210-218.
[6 Cruz J. Ocean Wave Energy. 2008, Springer, Berlin, Heidelberg, Germany.

国際化推進共同研究概要
No. 17
21RE-7
タ イ ト ル： Downwind Turbine Technologies, Model Development and Verification
研 究 代 表 者： HÖNING Leo

所内世話人： 吉田 茂雄
研究概要：
ダウンウィンドロータは将来の超大型風車および浮体式洋上風車の発電コスト（LCOE）
削減に有望な技術である．本研究では，洋上/陸上の風車を含めて，ダウンウィンド風車が有効な設計条件を調査する． 対象とする研究テーマには，動的応答，荷重，制御，および LCOE への影響などを含む．
ダウンウィンド風車の空力弾性解析の精度を向上させるために，4 つのタワーシャド
ウモデル，1 つのナセルブロッケージモデルが開発された．さらに，2MW のベースラインモデルを開発し，各サブタスクに提供された．さらに，フリーヨーアイドリングの評価方法が提案され，実機により検証された．超大型風車に対するダウンウィンド風車の利点は，システムエンジニアリングのアプローチを通じて示された．さらに，ダウンウ
ィンド風車の革新的な概念が研究され，超大型風車に対するダウンウィンド風車の利点が示された．

21RE-7 Downwind Turbine Technologies, Model Development and Verification
Applicant: Leo, Hoening, Fraunhofer Institute for Wind Energy Systems
RIAM Attendant: Shigeo Yoshida

1. OUTLINES
1.1 Member(IWES) Leo Hoening, Bernhard Stoevesandt(X1 Wind) Alex Raventos, Rocio Torres(NREL) Nick Johnson(BWC) Sandy Butterfield(UVA) Eric Loth
(AIST) Tetsuya Kogaki, Shigemitsu Aoki
(Hitachi) Soichiro Kiyoki, Shigehisa Funabashi, Nobuo Namura(WEIT) Masataka Owada, Yoshitaka Totsuka(UTokyo) Atsushi Yamaguchi(RCCM) Noriki Iwanaga(KU RIAM) Shigeo Yoshida
1.2 Outlines of the Task
WP1) Model Development& Verification
WP1-1) 2MW Baseline Turbine Model
WP1-2) Tower Shadow
WP1-3) Nacelle-Rotor Interaction
WP1-4) Stability & Control
WP1-5) Complex Terrain
WP2) Design and LCOE Assessment
WP2-1) Blade Optimization for DTs
WP2-2) Scalability Benefits for DTs
WP3 Recommended Practice
WP3-1) Standards Evaluation for DTs
WP3-2) RP for DTs

2. REPORTS
WP1-1) Baseline Model, UTokyo
Aeroelastic models of a 2MW baseline downwind turbine model were defined. The tower was designed to avoid
resonace in the opration conditions as shown in Fig 1. The Bladed and FAST models were delivered to themembers to proceed the verification study in each research subject.

Fig 1 Steady characteristics of aeroelastic models
WP1-2) CFD Result, IWES
- Model: Hitachi 2MW-80m downwind- Wind speed: 8.6 m/s (steady)- Pitch angle: 1.6 deg- CFD solver: OpenFOAM- 1/3 domain (steady), full WT (unsteady)- Number of cells: 16million per bladeFig 2 CFD model outline
WP1-2) Tower Shadow, KU
Some research results on tower shadow modeling of downwind turbines in Blade-Element and Momentum(BEM) method, which was not considered in the former methods were reported.
(1) Load Equivalent Model [1]The load equivalent model tower shadow model was introduced. The wind speed profile of the tower wake isdefined based on the load fluctuation calculated by the CFD. It showed good agreement with the measurement.
(2) Tower Variable Load [2]The variable load model of downwind turbine tower, which was not considered in the previous model, isformulated as below, using lifting-line theory.
CdT∆=

π DT 
2 

2U 0 

−U 0

du
dv
dw 
+ rΩ
−w

dxT
dxT
dxT 

It was verified by the CFD of rotor-tower-nacelle configurations at rated and cut-out operating conditions. It
shows fairly nice agreement with the CFD in particular out-board section and at low thrust conditions as shown in
Fig 6. However, there still be some more room for improvement in inboard sections.

Fig 3 Rotor thrust and torque of a downwind turbine
stiff model around the tower shadow at 13 m/s [1]Blade Element

Fig 4 Mainshaft bending a 2 MW prototype downwind
turbine at 13 m/s [1]Tower Section

Fig 5 Outlines of the model [2]Fig 6 Variable loads of the downwind turbine tower at
100% rotor radius: (T) 13 m/s, (B) 25 m/s [2](3) Tower Average Load [3]The average tower load model was also introduced based on the momentum theory, which consists with velocity
and pressure gradient terms.

∆CdTV = ∆CdTV + ∆CdTP() π2 µ ddξµ=
−CdT 0 1 − µT 2 +

T

T

T

The model was validated by the wind tunnel test. It shows good agreement with the wind tunnel test data as
shown in Fig 7.

Fig 7 Rotor thrust to tower drag: (T) 13m/s, (B) 25 m/s[3]

Fig 8 Tower section drag to the rotor thrust and theclearance between the rotor and the tower: (T) 50 %R,(B) 80 %R [3](4) Dynamic Blade Load [4]The dynamic blade load model was reported. This model was developed based on the former study of Munduate[5]. Two points were modified from the reference; 1) application of Moriarty’s tower wake model [6] and 2) wakeentrance condition. Fig 9 shows the analysis and experiment results on a 1.0 m diameter model. Where, UG
indicates University Glasgow’s former model and KU does present model. The present model was successfully
shown the increase in load before the wake entrance was modeled better than the previous work.
The scale effects of the model were investigated. Fig 10 is the simulation results for the similar models. The top,
middle and bottom subplots are analysis results with x1 model (1 m rotor diameter), x3 (3 m), and x10 (10m),respectively. Here the tip speeds are set to be identical. As shown in these figures, the variation of the lift
coefficients are decreasing as the scale getting larger.

Fig 9 Blade section (75% rotor radius) lift coefficient torotor azimuth, UG model [4]Fig 10 Blade section lift coefficient to rotor azimuth:scale (T) x1, (M) x3, (B) x10, KU model [4]WP1-3) Nacelle Blockage Effect, NREL [7]1. Outlines
With respect to the three-dimensional effects in the blade-element and momentum (BEM) method, the tip/root
affect is one of the most essential considerations because of the edges at the blade tip and root. Although only
“loss” has been focused on the root effect, downwind rotors are expected to have stronger blockage effect, that is anaerodynamic interaction with the nacelle. The nacelle blockage effects on the rotor performance and loads weremodeled and verified numerically.
To evaluate the present method, CFD was conducted for typical nacelle shapes shown in Fig 11. Here, “EM”
indicates engineering model defined in this section.

Fig 11 CFD Cases [7]2. CFD Results
The wind speed distributions of typical configurations, 20 m x 30 m bullet and ellipsoid, calculated by CFD are
shown in Fig 12. The latter is the EM configuration of the former one. They show similar distributions in the
upwind and middle of the bodies.
CFD results for the three nacelle shapes with the three rotor planes are shown in Fig 13. The lines from left toright, are upwind, middle, and downwind respectively. Note: the rectangle EM is wider in the middle.

Fig 12 Normalized velocity by CFD around the 20 m x 30 m bullet (left) and ellipsoid (right) nacelles [7](a) Various nacelle shapes.
(b) Various nacelle heights of ellipsoid.
Fig 13 Normalized velocity profiles along rotor planes. Solid, darker lines: CFD results. Dashed, lighter lines: EM
results [7]The relationship between boundary layer height BLH from CFD, and Reynolds numbers ReL, ReH, and aspectratio of all the nacelles are shown in Fig 14. No correlation is found between BLH and Re, though an inverse
relationship is found between BLH and aspect ratio. No correlation is found between maximum speed up and Re,
though an inverse relationship is found between maximum speed up and aspect ratio as shown in Fig 15. No
correlation is found between Cp and Re, though an inverse relationship is found between Cp and aspect ratio asshown in Fig 16.

Fig 14 BLH from CFD vs. ReL, ReH, and aspect ratio for all nacelles [7]Fig 15 Maximum speed-up from CFD vs. ReL, ReH, and aspect ratio for all nacelles [7]Fig 16 Rotor CP in CFD flow field vs. ReL, ReH, and aspect ratio for all nacelles [7]3. Conclusions
Nacelle blockage effects on rotor loads and performance were found to be insignificant (<0.5%) for all except
low-aspect-ratio nacelles. For all cases studied, nacelle blockage was seen to increase rotor loads and performance.
The potential-flow engineering model developed here has negligible (sub-millisecond) computational cost.
The engineering model was validated against CFD, yielding like BEM results, with both models yielding Cp
within 0.7% for all runs. For cases with the most significant blockage effects (20 x 30-m ellipsoid and bullet), therelative error in Cp between the two models was within 1% and 11%, respectively.
Consider the wind speed distribution induced by the nacelle by CFD or experiment. In cases of the BEM with thewind speed distribution at the rotor plane is determined by simulations or experiments. In cases of the elliptic
nacelle, the following model introduced by the potential model is applicable.
WP1-4) Stability, Hitachi [8][9]The extreme loads of a 5.2 MW DT in parked condition in Typhpoon #21 in 2017 were simulated. Yaw angles
by the measurement and the analysis are shown in Fig 17. Blade root flapwise bending moment are shown in Fig 18.
The results are consistent with the measurement.

Blade Flapwise Bending Moment
Normalized by the Load of Active Yaw Control[-]

10minutes Averaged Yaw Misalignment[deg]

10
5
0
-5
-10
-15
-20
-25

Measurement(13-15hour)
Measurement(13.5-14.5hour)
Simulation(13.5-14.5hour)
35404510minutes Averaged Wind Speed[m/s]50

Fig 17 Yaw misalignment to wind speed [8][9]

1

0.8

0.6

0.4

0.2
Each Seed & Each Blade
Typical value0-0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5
Long-period Change Rate of Wind Direction [deg/s]

Fig 18 Blade root flapwise bending to wind directionchange rate [8][9]WP2-2) Scalability Benefits, Hitachi [10]1. Outlines
Fatigue calculation and tower shadow model were introduced in this research. Natural frequencies in flap-wiseand edgewise are the output of the optimization. Design variables are not optimized for pre-bent blades as present
cost is not considered. Less than 5m is recommended due to the manufacturing and transportation. The tower
shadow model is too pessimistic. Therefore, the advantage of downwind turbines is underestimation.
WISDEM, the system engineering code developed by NREL, was modified to consider the tower shadow effectof downwind turbines.
2. Conditions- Wind class: 1A- Downwind: prebent 0 m- Upwind-1: prebend max 6 m- Upwind-2: prebend max 20 m
3. Results
Downwind turbine shows lower LCoE than upwind turbines.
Here, the cost of the production and transportation of the prebent blades are still not considered in the cost modelof the prebent blades. Therefore, LCoE of the upwind turbines are estimated a little optimistic.

Fig 19 LCoE to rotor diameter [10]Fig 20 Design parameters to the rotor diameter [10]Fig 21 Optimal blade shapes [10]WP2-2) Largest Wind Turbine, UVA[11]Morphing blades, which adapt the alignment of the blade in acoordance with the thrust and the centrifugal forces,
are promising concept for super large wind turbines.
The studies in SUMR show promising results, such as 27% RNA mass reduction and 24% LCoE reduction, bu
the fatigue load reduction.

βo

CONR

Fig 22 Typical force to wind speed [11]SUMR

Fig 23 Concept of the SUMR blade [11]Fig 24 von Mises stress of CONR (top) and SUMR (bottom) [11]Fig 25 Average moment (left) and its DEL (right) to wind speed [11]Table 1 Dimensions of the CFD Model [11]
CONR
SUMR
3-Blades2-BladesRotor Mass
100%
73%
Power Output
100%
98%
LCoE
100%
76%

3. REFERNCES[1] Yoshida, S., Load Equivalent Tower Shadow Modeling for Downwind Turbines, European Wind Energy
Conference, 2007.
[2] Yoshida, S., Combined Blade-Element Momentum - Lifting Line Model for Variable Loads on Downwind
Turbine Towers, energies, 2018.
[3] Yoshida, S., et al., Effect of Rotor Thrust on the Average Tower Drag of Downwind Turbines, energies, 12, 2,
227-241, 2019.
[4] Yoshida, S., Dynamic Stall Model for Tower Shadow Effects on Downwind Turbines and Its Scale Effects ,energies, 1-19, Energies 2020, 13, 5237, 2020.
[5] Munduate, X., Coton, F.N., Galbraith, R.A.M., An Investigation of the Aerodynamic Responses of a Wind
Turbine Blade to Tower Shadow, J. Solar Energy Engineering, 126, 1034-1040, 2004.
[6] Moriarty, P.J. and Hansen, A.C., AeroDyn Theory Manual, NREL/EL-500-36881, National Renewable Energy
Laboratory, 2005.
[7] Anderson B., Branlard E., Vijayakumar, G., Johnson, N., Investigation of the nacelle blockage effect for adownwind turbine, J. Phys. Conf. Ser. 1618 062062, 2020.
[8] Kiyoki, S., et al., Evaluation of wind loads by a passive yaw control at the extreme wind speed condition and its
verification by measurement, GRE2018, 2018.
[9] Okuno, A., et al., alidation of Extreme Loads of Wind Turbine by Measurement Data and Simulation, JWEAWind Energy Utilization Symposium 2018.
[10] Namura, N., Shinozaki, Y., Design Optimization of 10MW Downwind Turbines with Flexible Blades andComparison with Upwind Turbines, J.Phys.: Conf. Ser. 1618 042021, 2020.
[11] Noyes, C., et al., Analytic analysis of load alignment for coning extreme‐scale rotors, Wind Energy,
2020:23:357-369, 2020.

国際化推進共同研究概要
No. 1821RE-8タ イ ト ル： Analysis of Multi-Rotor System Wind Turbines
研 究 代 表 者： ISMAIEL Amr Mohamed Metwally

所内世話人： 吉田 茂雄
研究概要：
マルチロータシステム（MRS）風車は，コストと品質が比較的成熟した風車が使用できることと，構造上・輸送上のメリットのため，将来の超大型風車のコンセプトとして有望視されている．MRS の荷重計算のための空力弾性ツールを開発している．このツール
は，シングルロータ風車に関して，既存の空力弾性ツール FAST で検証した後に，ロー
タ数 2～4 個の MRS について検討した．検討の結果，固有振動数が非常に重要であることを確認した．また、3 ロータと 4 ロータの MRS のタワー動的応答を比較することにより，4 ロータが，より技術的に実現可能であることが示された．

RIAM International Joint Research
General Information

Grant No. 18 21RE-8
Title: Analysis of Multi-Rotor System Wind Turbines
Name of the research representative: Assist. Prof. ISMAIEL, Amr Mohamed Metwally
Affiliation: Future University in Egypt (FUE)
Email: amr.mohamed@fue.edu.eg
Research subject field: Renewable Energy
Name of RIAM attendant: Prof. Shigeo YOSHIDA

Abstract:

Multi-Rotor System (MRS) wind turbines can be a good alternative to large-scale wind turbines
in terms of structural and logistic advantages. An in-house tool was developed in order to analyze
the support structure of MRS wind turbines. The tool was verified by comparing the results of asingle-rotor wind turbine to an equivalent analysis using the software tool FAST. Then, threedifferent configurations of MRS were studied: including two, three, and four rotors. The tower
dynamics were calculated for the main tower in each configuration, as well as the side-booms
supporting the two rotors in the twin-rotor configuration. The analyses have shown that the natural
frequencies are of big importance and are dominant over the loading regarding the tower dynamics.
It has also shown that by comparing the tower dynamics of three and four-rotor configurations, thefour-rotor configuration is more technically feasible. In the future, some of the assumptions whichwere used in developing the code will be removed, in order to get more realistic results and be able
to analyze the wind turbine over all ranges of wind speeds.

Research outcomes:

This research is an extension to a PhD thesis made by the research representative. In the PhD phase,aeroelastic analysis has been made for a twin-rotor configuration and compared to a single rotor
which has been verified numerically [1].
As an extension, analysis for the side booms holding the rotors on the T-shaped tower has been
conducted. Deflections of the side-boom tip in the fore-aft (Out of plane) and in the side-side (Inplane) has been calculated for different turbulent wind fields of classes A, B, and C. Figure 1 shows
the deflections for wind turbulence class A. Different diameters for the side booms were studied
to determine the relation between the boom size and its structural behavior.
It was found that in the in-plane deflections are dominated by the weight of the rotors, regardlessof the turbulence of the wind field, the deflection kept almost a constant value. While the out-ofplane deflections were dominated by the random behavior of the aerodynamic loads in the
turbulent wind field and induced high, unfavorable vibrations. It was also found that the bending
stiffness of the side-booms is directly proportional to its diameter and has a second-order relation
with the mean deflection value [2].

4

1.2

3.5

1

3
2.5
Deflection (m)Deflection (m)

0.8

0.6

0.4

2
1.5
1

0.2

0

0.5

0

100

200

300
Time (s)

400

500

600

0

0

100

200

300

400

500

600

Time (s)(a) Fore-aft direction(b) Side-side direction
Figure 1. Deflections of the side booms tip for turbulence class A

The results of this work have also emphasized that the tower natural frequencies are dominant overthe loads in regards of the tower dynamic responses, and hence the importance of the natural
frequencies.

Future Approach
In order to have a better judgment on the feasibility of the three-rotor compared to four-rotor windturbines, more analyses should be conducted. Pitch control should be added and then compare
different wind loads in the high-power region. Power output and cost of energy should also betaken into consideration for comparison.
Wind tunnel experiments and parametric analysis on the rotor spacing will be a great contribution
to the field. Machine learning approach can be adopted to find an optimum rotor spacing for better
performance.

References[1] A. Ismaiel and S. Yoshida, "Aeroelastic Analysis of a Co-Planar Twin Rotor Wind Turbine,"
Energies, vol. 12, p. 1881, 2019.
[2] A. Ismaiel and S. Yoshida, "Aeroelastic Analysis for Side-Booms of a Coplanar Twin-Rotor Wind
Turbine," International Journal of Aerospace Engineering, vol. 13, no. 4, pp. 135-140, 2020.