(TC) Report
Date: June 12, 2024
Time: 10:22 - 16:45
Shot#: 193036 – 193153 (118 shots)

June 13, 2024 (T. Tokuzawa)

Prior wall conditioning: None
Divertor pump: ON
Gas puff: H2, Ne Pellet: NO, IPD: NO
NBI#(1, 2, 3, 4, 5)=gas(H, H, H, H, H)=P( 3.1, 2.8, 2.9, 3.5, 2.6)MWECH(77GHz)=ant(5.5-Uout (or 1.5U), 2-OUR)=P(337, 380)kW
ECH(154GHz)=ant(2-OLL, 2-OUL , 2-OLR)=P(389, 580, 606)kW
ECH(56GHz)=ant(1.5U)=P( - )kW
ICH(3.5U, 3.5L, 4.5U, 4.5L)=P( -, -, -, - )MWNone
TopicsRemarks:
1. Study on the effect of magnetic shear on mode structure and associated turbulent transport (Y. Kishimoto (KyotoU.), K. Tanaka) ) [#193036 - #193079]
2. Effect of the electric field on impurity transport (T. Ido (Kyushu U.), A .Shimizu) [#193080 - #193105]
3. Real-time plasma control using turbulence level signal (H. Sakai (Kyushu U.), K. Tanaka) [#193106 - #193130]
4. Real-time plasma control under low-turbulence conditions focusing on turbulent transition (T. Kinoshita (Kyushu1U.), K. Tanaka) [#193131 - #193153]

Research Proposal for 25th Experiment Campaign(2024) on LHD

Study on the effect of magnetic shear on mode structure and associatedet al. NF
turbulent transport （モード構造と乱流輸送における磁気シアの効果 ） Points : Ishizawa,
57, 066010 (2017)

Proponent : Y. Kishimoto(Kyoto U.)
NIFS contact person: K. Tanaka

Member : H. Himura, A. Sanpei, T. Inoue (KIT), Y. Otani (QST),
K. Imadera, A. Ishizawa, R. Matsui, D. Yu, W. Wang, J.Q. Li （SWIP）
Shirai et al., NF39, 1713 (1999)

Motivation• Magnetic structure, ι and/or 𝑞𝑞, and 𝑠𝑠,̂ are through to be a
key control parameter in both tokamak and helical system.
• Weak and/or zero shear plasmas, where ballooning
symmetry is broken, are interested, leading to ITBs, e.g.
optimum shear (JET), where the magnetic field is no longer
the primary factor to regulate the mode structure.
Work by T. Fukuda et al. using LHD (22nd IAEA , 2008 ）• Transport was studied by changing ι profile by NBCD(~100kA) in LHD, but showing L-mode characteristics.

Normal qWeak/flat q

Strongly
Reversed q

Zero shear linearly unstable→ nonlinearly stable (ZF generation rate)
Profile stiffness for changing sConclusion : … the pronounced effect of magnetic shear in tokamaks
was not obvious for plasmas with the turbulent structure pertaining
to helical plasmas. (….) kinetic profiles respond little. (NIFS-901)• A case considered that such a stiffness results in theoperation under the critical threshold, P< Pc , for profile change• PIC signals showed a reduction of turbulence inflat ι regime, so further studies be necessary, e.g. whetherthe phenomena results in linear stability or nonlinear effect
Revisit of experiment by T. Fukuda et al. (2008)• We revisit the results using similar discharge as Fukuda et al.,and study the relation between 𝑠𝑠̂ and fluctuation spectrum by
PCI and other advanced diagnoses.
• We will also add additional ECH to find the response between
the finite shear case and week shear case.

2

Spatial structures of density, electric potential and density fluctuations in the core region during
perpendicular NBI (T. Ido, A. Shimizu, M. Nishiura)
Shot #: 193080 - 193105
Experimental conditions: (Rax, Polarity, Bt, γ, Bq) = (3.75m, +1.375 T, 1.254,100%), ne ~ 0.5 x 1019 (m-3)

Previous Campaign

NBI#5

Balanced tangential NBI + modulated perpendicular NBI
Electric potential

Background and motivation:•The initial motivation of the experiment is to verify a theoretical study on theHIBP
influence of energetic trapped particles on the electric fields. （Ref. H.Yamaguchi,
IAEA-CN TH/P6-29 (2018)).

NBI#4•In the previous campaigns, the peculiar spatial structures of 𝜙𝜙 and density profiles
were observed in the central region during the perpendicular NBI #4, but notduring the perpendicular NBI #5.

Results:• The intensity of the HIBP was so unstable that we could not analyze the 𝜙𝜙 anddensity profiles.

• Density fluctuations were observed near the core region only in the caseof NBI#4. We will analyze the spatial structures of the fluctuations.

Power (a.u.)•The purpose of this experiment is to clarify their poloidal structures and toinvestigate the influence of the structures of the electric field on the turbulence
and impurity transport.

#193092

101010NBI #4NBI #5w/o perp. NBI-5-6-7110Frequency (kHz)100

Real-time plasma control using turbulence level signal

H. Sakai (Kyushu Univ.), K. Tanaka

Shot No: #193106-193130
Experimental conditions: (Rax, Polarity, Bt, γ, Bq) = (3.6 m, CW, 2.75 T, 1.2538, 100 %)Gas-puff: H2
ramp-upApproach
Turbulence is suppressed when turbulence mode changes
between ITG and RI in LHD. Based on this physics, we tried tocontrol the plasma in low turbulence using gas-fueling. Realtime turbulence level (TL) signal was used for FB control astarget value. Heating power was fixed to use NB#1,2 andECH#4,5,7.

w/ control
gas fuelinggas fuelingResult Turbulence curve was appeared at ne~2.5-3.0x in the shot
for ramp-up (this is good reproduction).
 If TL became larger than the target, gas fueling was turnedoff. The gas was turned on when it detects that it is far
from the target value. Target value was evaluated by “thedetected lowest value×1.1” Low TL plasma wassuccessfully maintained.

tatgetNext objective (6/14)
 The heating pattern will be varied over time within a single
discharge to confirm if the TL is always minimal at that time.

𝑛𝑛𝑒𝑒 [× 1019 /𝑚𝑚3 ]𝑛𝑛𝑒𝑒 [× 1019 /𝑚𝑚3 ]Real-time plasma control under low-turbulence conditions focusing on turbulent transition
T. Kinoshita(Kyushu Univ.), Y. Morishita(Kyoto Univ.),
Shot No: #193131~193153 (23shots)
N. Kenmochi, H. Funaba, K. Tanaka, H. Sakai (Kyushu Univ.)
Gas-puff: H
Experimental conditions: (Rax, Polarity, Bt, γ, Bq) = (3.6 m, CW, 2.75 T, 1.2538, 100 %)Motivation
A turbulence and its driven anomalous transport are minimized when the dominate turbulence mode changes in LHD. The
condition of turbulence transition is expressed by ne=4.20Te-5.28 (TT condition). The aim of this study is to control theplasma to satisfy TT conditions and to realize low-turbulence plasma.
Results• Two different approaches were used to satisfy the TT condition.
One is Te control under constant ne. The other is ne control
under constant heating conditions.
• The right figure shows an example of the former Te control
approach. Here, ne was changed stepwise by feedback control.
• At t=4-5s, since target Te (Te_tgt) is much higher than current Te(Fig(c)), the heating power are reduced (Fig(a)). As thetemperature decreases, the turbulence level also decreases.
However, due to the high NBI heating, the temperature could
not be lowered any further at t=5-5.6s. At t=5.6-6.6s, Te_tgt
increased slightly and turbulence decreased significantly as it
became closer to Te. At t=6.6-7.6s, Te_tgt and Te are almost thesame, which means that the TT condition is satisfied. As theresult the turbulence is minimized. At t=7.6~, the density
increases further and Te_tgt>Te, so the heating power increases.

(c)
(a)

(b)

(d)

Plan The NBI base heating power is reduced to allow
room for temperature control by ECRH.