24C08
Present Status of Divertor Simulation Experiments Using an End-cell of a Large
Tandem Mirror Device
大型タンデムミラー装置端部を用いたダイバータ模擬実験計画の現状
Yousuke Nakashima, Hisato Takeda, Kazuya Ichimura, Katsuhiro Hosoi, Makoto Ichimura, Isao
Katanuma, Tsuyoshi Kariya, Junko Kohagura, Mizuki Sakamoto, Tomoharu Numakura, Mafumi
Hirata, Ryutaro Minami, Masayuki Yoshikawa, Ryuya Ikezoe, Takashi Ishii, Hideaki Ueda,
Tsuyoshi Imai
中嶋洋輔，武田寿人，市村和也，細井克洋，市村 真，片沼伊佐夫，假家 強，小波蔵純子，坂本瑞樹，沼倉友晴，平田真史，南 龍太郎，吉川正志，池添竜也，石井 貴，上田英明，
今井 剛
Plasma Research Center, University of Tsukuba
1-1-1, Tennoudai, Tsukuba, Ibaraki 305-8577, Japan筑波大学プラズマ研究センター 〒305-8577 つくば市天王台1-1-1This paper describes the recent results of divertor simulation experiments using the GAMMA 10 tandem
mirror device. In typical hot-ion-mode plasmas, measurements of heat and particle fluxes have been carriedout by using the diagnostics installed at the end-mirror exit. The parallel ion temperature Ti// obtained fromthe probe and calorific measurements increases with the RF power and agrees with the direct measurementof end-loss ion energy. The above results showed that the central-cell plasma could well control theperformance of the plasma flow from the end-mirror exit. Near-term research plan for detailed PWI study
and for further development of heat and particle fluxes is also described.

1. Introduction
In ITER discharges, heat load to the divertor
materials is estimated to be 5~20 MW/m2 in steadystate and more at the transition phase [1]. To solve
this problem, various so-called divertor simulators
have been developed and a number of experimental
approach have been made toward the realization ofdivertor.
In a large tandem mirror device GAMMA 10,
plasma production/heating systems with the same
scale of fusion devices have been equipped andhigh-temperature plasmas have been produced [2].
As a future research plan, making use of theadvantage of open magnetic field configuration, weare planning to start a study of divertor simulation
under the closely resemble to actual fusion plasma
circumstances and to directly contribute thesolution for realizing the divertor in ITER. For theabove purpose, development of a new axisymmetric divertor configuration and high heat-flux
experiment in the end-mirror region are started[3-4]. In this paper, present status of theinvestigation on the characteristics of plasma flowfrom the end-mirror exit of GAMMA 10 performed
to validate its applicability to the divertor
simulation studies is reported.
2. Experimental Setup
Figure 1 shows the schematic view of thevacuum vessel of the west end-cell of GAMMA 10and the plasma in the end-mirror region, together
with the location of the diagnostic equipment. Inorder to proceed the research plan of the divertor
simulation, several diagnostics have been preparedsuch as directional probes, calorimeters, and arraysof ion-energy analyzer as shown in Fig.1.
A high-speed camera and visible spectrometer
also have been installed together with target disks
consist of tungsten, carbon and stainless steel on arotational mount at the down stream of theend-mirror exit in order to observe plasma materialinteractions on the target materials.
In GAMMA 10, a seed plasma is initiallyFig. 1 Schematic view of the experimental setup.

injected from plasma gun at both ends and theplasma is build up with two ICRF waves (RF1 andRF2) together with gas puffing. Axially confining
potential is produced by ECH at both plug/barriercells using high power gyrotrons.
3. Experimental Results
In typical hot-ion-mode plasmas (ne0 ~2×1018 m-3,
Ti0 ~5 keV in the central-cell)[2], measurement ofheat and particle fluxes from the end-mirror exit has
been carried out. Heat flux is measured with thecalorimeter and is determined from the temperaturerise of the tip in a plasma discharge. Particle-flux
density is determined from ion saturation current
measured with directional probe.
Figure 2 shows ICRF power dependence on theparallel component of ion temperature, Ti// in theend-loss plasma flux measured with the directional
probe and the calorimeter. Ti// directly measured byusing end-loss ion energy analyzer (ELIEA)
installed in the end-cell, which is located 300 cm
away from the end-mirror exit, is also plotted in
Fig.2. Both data agree with each other and is in
proportion to the ICRF power.

Fig. 2 ICRF power dependence on parallel iontemperature.

In Fig. 3, the ion-current density measured with
ELIEA (Isat) is plotted as a function with theline-density of plasma electrons measured at thecentral-cell (NLcc). A good linearly is observed andzEXIT = 300 cm

8Isat ( x10 -4 A/cm2 )Isat642034567

NLCC ( x1013 cm-2 )Fig. 3 Density dependence on ion-current density
measured at the end-cell.

it is clearly found that the central-cell plasma
parameters can well control the parameters ofend-loss ion flux.
4. Near-term Research Plan
Based on the above shown results, the following
research plan has been considered in near future:(1) Installation of the divertor experimental-cell(D-cell) with V-shaped target in the end vacuum
chamber and generation of strong plasma-surface
interactions and realization of plasma detachment
using gas injection,(2) Installation of test material pieces in front of theD-cell and high the heat flux plasma irradiationand surface analyses,(3) Divertor pumping experiment using the large
capacity helium cryopumping system,(4) Building-up the heat flux by adding a new RF
system to the end-mirror cell.
The schematic drawing of the future researchplan is shown in Fig.5.

Fig. 4 Schematic drawing of the future researchplan in the GAMMA 10 end-cell.

5. Summary
In the GAMMA 10 west end-cell, high-powerplasma-flux generation experiments have beenperformed. Measured results of heat and particle
fluxes showed that the central-cell plasma could
effectively control the performance of the plasma
flow from the end-mirror exit.
References[1] E. Tsitrone, J. Nucl. Mater. 363-365 (2007) 12.
[2] T. Tamano, Phys. Plasmas 2 (1995) 2321.
[3] Y. Nakashima, et al., Fusion Eng. Design volume 85
issue 6 (2010) 956-962.
[4] Y. Nakashima, et al., Trans. Fusion Sci. Technol. 59
No.1T (2011) 61-66.