30D34PGAMMA10 エンド部エンド部へのターゲットプレートへのターゲットプレート挿入
ターゲットプレート挿入による挿入によるコアプラズマでのコアプラズマでの高電位形成での高電位形成
High Potential Formation in Core Plasma
due to Target Plate Insertion in End Region of GAMMA10
水口正紀、坂本瑞樹、古舘鎌一、吉川正志、大木健輔、定村康太郎、
武田寿人、市村和也、中嶋洋輔、今井剛
M. Mizuguchi, M. Sakamoto, K. Furutachi, M. Yoshikawa, K. Oki, et. al.
筑波大学プラズマ研究センター
Plasma Research Center, University of Tsukubavery negative value due to the plug-ECH. When thecore plasma potential did not increase due to applying
the plug-ECH with insertion of the target plate, thetarget plate potential was a very negative value (about-1500 V). Figure 2 shows z (magnetic lines direction)
axial profiles of the time-averaged potential. It is foundthat the potential in the high potential period washigher than that of the low potential period in thewhole plasma region. The increment of the potential
was larger in the west region than in the east region.

Potential[V]800(a) core plasma potential
600
lowpotential
period400

highpotential
periodplug-ECH (120 kW)

200

Potential[V]05000(b) target plate potential-500-1000-1500-2000
150

155

1000

east plug

160165170

175

Time[ms]
Fig. 1. Time evolutions of (a) core plasma potential, (b)target plate potential.

Potential[V]It is known that potential and electric field areimportant for the core plasma confinement. One of theimportant issues of divertor study is core-edge
coupling. In a mirror device, the relation between
central plasma and end plasma seems to be similar tothat between upstream of SOL and divertor region. We
have studied relation between floating potential oftarget plate in the end region and the central plasma
potential in the tandem mirror device GAMMA10.
GAMMA10 is a tandem mirror device withminimum-B anchor and mainly separated into four
sections, from the central to the end. A tungsten target
plate was inserted at 70 cm downstream from the west
end coil. The radius of the target plate is 5 cm and theprojected radius at the central cell (Rcc) is about 4.4
cm. The plasma was initiated by a plasma gun at theeast end and sustained using ion cyclotron heating.
Electron cyclotron heating at plug regions (plug-ECH)
produces positive potential (i.e. plug potential) for theaxial confinement.
The plasma potential was measured by using a gold
neutral beam probe which was installed at the central
cell of GAMMA10. The plug potential was evaluatedfrom ion energy distribution of end loss analyzers
which were installed at the east and west end regions.
The west and east end loss analyzers measured at Rcc= 5.3 cm and Rcc = 4.4 cm, respectively.
When the target plate was inserted to the west end
region, the core plasma potential significantly
increased up to ~500 V at the low plug-ECH power(120 kW). This potential value corresponds to that ofhigh power plug-ECH (250~380 kW) without theinsertion of the target plate. And it was also observedthat the high core plasma potential was formed withinsertion of the target plate in the middle of theplug-ECH period as shown in Fig. 1. When the coreplasma potential increased due to applying theplug-ECH with insertion of the target plate, the target
plate potential was in the range of a potential value
without the plug-ECH (-50 ~ -200 V) although thetarget potential was expected to become a very
negative value (about -1500V) from analogy of
behavior of the end plate potential, which was always awest plugcore

0-1000east end platetarget-2000-15-10-50Z[m]51015Fig. 2. Z axial profiles of the time-averaged potential at
low potential period (circle) and high potential period(triangle) respectively. The low potential period andthe high potential period are shown in Fig. 1(a).