22F10Interaction between radial magnetic perturbation fields and fast electrons inLATE plasmas
LATEプラズマにおける径方向摂動磁場と高速電子の相互作用
Fumitake Watanabe, Masaki Uchida, Hitoshi Tanaka, Ryota Hayashi, Hikaru Mizogami,Toshiyuki Kanemitsu, Yuto Noguchi, Shota Omi, Kengoh Kuroda, Jun Katsuma,
Tadahiko Fukunaga and Takashi Maekawa
渡辺文武, 打田正樹，田中仁，林良太，溝上晃，金光俊幸，野口悠人，逢見翔太，黒田賢剛，勝間淳，福永忠彦，前川孝
Graduate School of Energy Science, Kyoto University
Oiwake-cho, Kitashirakawa, Sakyo-ku, Kyoto 606-8502, Japan
京都大学 〒606-8502 京都市左京区北白川追分町
Effects of externally applied radial magnetic perturbations (MPs) on fast and bulk electrons have been
investigated on the Low Aspect ratio Torus Experiment (LATE) device. When a small MP (δbr(R=25cm)/B0 ~3.6×10-4) is applied to plasma discharges with Bv ≥ 55Gauss, reduction of the perpendicular pressure due tothe high energy components and increment of the parallel one is estimated by magnetic analysis. In fact,
the plasma current is increased during the application of MP. At the same time, the confinement
improvement of the bulk plasma is also observed. However, the confinement improvement is not always
observed depending on several mode patterns of MPs. In this presentation, we will show effects on MP

fields produced by several MP coils in LATE plasmas.
In toroidally confined fusion plasmas, transportof particle and energy caused by externally appliedmagnetic perturbation field (MP) fields and/or
therefore stochastic fields is very important forcontrolling the plasma performance and MHD
instabilities. For example, losses of runaway
electrons (can reach high energies of several tens ofmegaelectronvolts) in ergodized plasmas withresonant magnetic perturbations (RMPs) areinvestigated in JFT-2M [1] and TEXTOR [2]. Lossof high energy electrons is smaller than that ofthermal electrons, because the large shift of the drift
surface of high energy electrons from the magnetic
surface causes a significant reduction in transportwith RMPs.
In the Low Aspect ratio Torus Experiment(LATE) device, MP coils have been installed fortransport and control studies of bulk and fastelectrons produced by electron cyclotron heating
and current drive (Fig. 1). The MP coils areconstituted by ten sets. Each one is wound around a
horizontal port section outside the vacuum vessel
generating a radial MP field.
Figure 2 shows a plasma discharge waveformwith the MP field produced by MP coils on the 4R
and 10R port sections. An significant modification
is observed with increases in Ip and neL as follows:
Ip = 6.97kA → 7.73kA and neL(R = 0.27m) =0.74×1017m-2 → 1.15×1017m-2 (Figs. 2(b) and 2(c)).
Moreover, according to a visible spectroscopy
measurement, the bulk electron temperature also

Fig.1. MP coils in the LATE device

increases, because the impurity line radiation of OV(excitation energy = 72eV) and CV (304eV) having
high excitation energies is significantly enhanced
compared with that without the MP phase.
Figures 3(a)-3(c) show the radial profiles ofplasma pressures mainly due to the high energy
components which is estimated by the magnetic
analysis method using data from seventeen flux
loops [3]. Here, P|| and P⊥ indicate the pressures ofparallel and perpendicular components to thetoroidal magnetic field, respectively. The P|| profileon plasma core region increases in the applied MP

Fig.2. Time traces of the ECH/ECCD plasma withthe MP field (IMP = 50AT), where Bt = 480G,
Bv(R=25cm) = 80G and Pinj = 29kW. (a) MP coil current(the total current is given in terms of the current in
one coil winding times the number of turns). (b)plasma current. (c) and (d) line-averaged electron
density at R = 27cm and R < 17cm, respectively. (e)Hard X-ray emission measured by a NaI scintillator
having a line of sight at the center post.

phase, although the P⊥ profile outside the lastclosed flux surface (LCFS) on the low filed side isclearly reduced. In addition, as shown in Fig. 2(e),reduction of the hard X-ray (HX) emission
measured by a NaI scintillator which mainly resultsfrom fast electrons hitting the center postcomponent is observed. Moreover, HX energy
spectra measured by the vertical pulse height
analysis system indicate reduction of the photon
count in the high energy range. These results
suggest that the applied MP field leads to theenhanced loss of the trapped electrons rather thanthe passing electrons. Furthermore, expanding of
the LCFS is estimated by the calculation. As aconsequence, the MP field have a positive effects
on ECH/ECCD plasmas under the high Bv
configuration, i.e. increase in Ip and improvementof the bulk plasma performance.
However, the confinement improvement is notalways observed depending on several mode
patterns of MPs. In this presentation, we will show
effects on MPs produced by several MP coils
shown in Fig.1. In addition to that, observation

Fig.3. Radial pressure profiles estimated by amagnetic analysis method with and without theapplied MP field on the horizontal cross-section. (a)parallel pressure, (b) perpendicular pressure and (c)sum of the pressures for the discharge as in Fig.2 (t =1.86s and 2.33s).

results by using additional AXUV detector arrayand magnetic probe array recently installed in theLATE device will be also presented.
References[1] H. Kawashima et al., J. Plasma Fusion Res. 70(1994) 868.
[2] K.H. Finken et al., Nucl. Fusion 47 (2007) 91.
[3] M. Uchida et al., Phys. Rev. Lett. 104 (2010) 065001.