24aD24P
TOKASTAR-2における磁気面計測方法の検討
Examination of the Method to Measure Magnetic
Flux Surface on TOKASTAR-2
下岡 祐介 1，有本 英樹 1，藤田 隆明 1，岡本 敦 1、先砥 達也 1，
伊藤 宏真 1，村岡 賢治 1、杉岡諒一 1、安田幸平 2、横山亮磨 2
SHIMOOKA Yusuke1, ARIMOTO Hideki1, FUJITA Takaaki1,
OKAMOTO Atsushi1, SAKITO Tatsuya1, etal.
1

名古屋大学大学院工学研究科エネルギー理工学専攻、2
名古屋大学工学部物理工学科
1
Department of Engineering and Science, Nagoya University,
2
Physical Science and Engineering, Nagoya University
TOKASTAR-2 is a plasma confinement device
which has two coil systems, one for tokamak and theother for stellarator. The object of TOKASTAR-2 is to
study the influence of plasma current to helical plasma
and the influence of helical magnetic field application
to the tokamak plasma [1].
The stellarator coil system was designed to makeclosed magnetic flux surfaces without any plasma
current. However, due to the influence of manufacturalaccuracy, installational accuracy of coils and error
magnetic field, the location and shape of the helicalmagnetic flux surface can be deviated from theanalytical one. Then, the object of this study is tomeasure the magnetic flux surfaces experimentally.
There are mainly two methods to measure magnetic
flux surface, one using a fluorescent screen [2] and theother using a probe [3] for detecting electrons emitted
by an electron gun. These two methods use theproperty that injected electrons travel along the fieldlines. In the method using a fluorescent screen, amagnetic flux surface can be traced faster than theother one and a mechanical driving system is notneeded. An electron gun, which can be applied toeither of the two methods, was designed and fabricated.
Electrons are emitted from tungsten filament and thisgun has the mechanism to adjust radial position andangle of electron injection.
Figure 1 shows the orbit of electrons with different
energies in the typical magnetic configuration
condition. From the experiment with the fabricatedelectron gun in a test chamber, we estimated that theelectron energy needed to be larger than about 80 eV todetect the fluorescence of P15 and P24 (ZnO:Zn). As
shown in Fig. 1, the orbit of the electron with 80 eV
differs largely from the magnetic flux surface. Fromthese results, we concluded that significant
improvement of the electron gun is needed to apply themethod using a fluorescent screen to TOKASTAR-2.

Fig. 1. Orbits ofelectrons in the
typical magnetic
configuration
condition

The lowest electron energy needed for the method
using a probe was also examined.

Fig. 2. Time evolutionof (top) the acceleration
voltage of the electron
beam and (bottom) thevoltage of the resistanceconnected to the probe.

Figure 2 shows time evolution of the voltage ofresistance (1M) connected to a probe. The electron
beam was detected when acceleration voltage was 30V
and the pulse width was 200 μs. At the present, we try
to optimize the conditions of the value of resistanceand pulse width. The lowest electron energy that theprobe can detect is expected to be improved by changematerials of filament from tungsten to the other one,for instance thoria tungsten. After that, we will put
device in TOKASTAR-2.

[1] K. Yamazaki et al., J. Plasma Fusion Res. SERIES 8 1044 (2009).
[2] R.J. Colchin et al., Review of Scientific Instruments 60 2680 (1989).
[3] R.M. Sinclair et al., Review of Scientific Instruments 41 1552 (1970).