23P106-P
Measurement of Electron Heating by Magnetic Reconnection in the UTST
DeviceUTST装置における磁気リコネクション時の電子加熱現象の検証
Naoto Suzuki, Shuji Kamio, Qinghong Cao, Hirotomo Itagaki, Takenori G Watanabe, Koichiro
Takemura, Kotaro Yamasaki, Koji Ishiguchi, Ryota Imazawa, Takuma Yamada, Michiaki Inomoto,Yasushi Ono, Yuichi Takase
鈴木直人, 神尾修治, 曹慶紅, 板垣宏知, 渡辺岳典, 竹村剛一郎, 山崎広太郎, 石口孝治,今澤良太, 山田琢磨, 井 通暁, 小野 靖, 高瀬雄一
Graduate School of Frontier Science, The University of Tokyo,
5-1-5,Kashiwanoha,Kashiwa,Chiba 277-8561,Japan東京大学大学院新領域創成科学研究科〒277-8561

千葉県柏市柏の葉 5-1-5Formation of high-beta spherical tokamaks (STs) are investigated in the UTST device which have all of themagnetic coils located outside the vacuum vessel. When two STs are merged together to form a single ST,
poloidal magnetic energy of the initial STs is converted to plasma thermal energy through magnetic
reconnection. A Thomson scattering measurement system has been developed to conduct quantitativeevaluation of the reconnection heating and high-beta equilibrium of the STs formed by plasma merging
method.

1. Introduction
Ballooning mode is one of the most serious
instabilities which limit the beta value of tokamak
plasmas. The second stability region of theballooning mode is attractive since it allows largepressure gradient to provide a high-beta equilibrium,
however, transition from first to second stability
region through narrow window requires difficult
profile controls of pressure and plasma current. The
plasma merging method has demonstrated theformation of high-beta ST by high-power heating
provided by magnetic reconnection [1,2]. The
purpose of this research is to investigate theelectron heating mechanism in the magnetic
reconnection event by using newly developed
Thomson scattering measurement system.

sign, two STs are formed at the upper and lowersides.
④Since the directions of the PF coil current and
two STs become contrary, two STs are pushed
toward the mid-plane and merged to form a single
high-beta ST.

Fig.1 Schematic view of the UTST device.

2. Experimental Setup
The UTST device (see fig.1) forms a high-beta
ST by double null merging (DNM) method shownin fig.2 [3].
①The currents of the equilibrium field (EF) andtoroidal field (TF) coils make static spiral magnetic
field inside the device. Hydrogen gas puffed in thedevice is ionized by the two washer guns located at
the bottom and middle of the device.
②The current of the poloidal field (PF) coilmakes two null points on which there are only
toroidal magnetic and electric fields. Toroidal
electric discharge is initiated on these points.
③When the current of the PF coil changes its

Fig.2 Plasma merging by the DNM method.

3. Two-dimensional Thomson Scattering
Measurement SystemThomson scattering (TS) measurement is one of
the most reliable diagnostics to measure theelectron temperature of fusion plasma. The
scattered light is collected by collection lenses withdiameter of 150 mm and introduced to filter
polychromators to analyze the spectrum. The widthof the spectrum depends on the electron
temperature. Since the power of the TS light is verysmall, we have to verify the possibility of theelectron temperature measurement beforehand. We
estimated the output voltage of the detectors E [V]in the polychromator from the power of the YAG
laser P [W], the electron density ne [m-3], the lengthof the scattering volume L [m], differential
scattering cross section [m2], the solid angle ofthe collection optics Ω [srd], transmissivity of thelenses and windows including the interference filter
T, and the sensitivity of the detector K [V/W].

(1)
The estimated voltages from the threepolychromator are shown in Fig.4. Opticalcomponents including the YAG laser and thecollecting lenses are located on a single stand,which is able to slide along the radial direction, so
this system can measure two-dimensional electron
temperature profile. The initial results by using theTS system will be presented in the poster.

Fig.4 Estimated output voltages of detectors for threemeasurement positions.

Acknowledgments
This work was supported by JSPS KAKENHI(22246119 and 22686085) and the Global COE
Program “Secure-Life Electronics”, MEXT, Japan.
References[1] Y. Ono and M, Inomoto, Phys, Plasma 7,(2000) 1863.
[2] T. Kimura, S. Miyazaki, Y. Ueda, Y. Ono, J.
Plasma Fusion Res., 80, (2004) 249.
[3] Y. Ono, M. Inomoto, Y. Takase, IEEJ Trans,130, (2010) 334.

Fig.3 Thomson scattering measurement points
superimposed on the experimental results of 2D
magnetic measurement