K.Y. Watanabe

T. Morisaki

Watanabe,  K.Y.

Morisaki,  T.

NIFS-Repository (National Institute for Fusion Science)

§43. Study of Plasma Boundary in LHD Experiment Watanabe, K.Y., Morisaki, T. It is important to construct the consistent MHD configuration with measured data when we study something in balk plasma. To determine the MHD equilibrium configuration, the plasma boundary, plasma pressure and its profile, toroidal current and its profile are necessary when well-defined magnetic surfaces exist. In this paper, we study the plasma boundary in LHD experiment. Here, we focus 1.5T H2 Rax=3.75m operations. Fig. 1 (1) shows the normalized electron pressure profiles in torus outside at toroidal angle with horizontally elongated cross-section. Te and ne are estimated ~y Thomson and FIR measurements. There are data with 3 different beta value, 0.3%, 0.5% and 0.9%, thus central beta values are different by 3 times in data. Fig.1 (2) shows the connection length of magnetic field line to wall in vacuum at same toroidal angle in (1). Arrow 'a' corresponds to the outermost magnetic surface estimated from the existence of well defined nested magnetic surface, where the non-trivial electron pressure exists. However, the value is less than 0.7 0.6 Q) t- Q) 0.5 C "0 ~ 1U E o c 0.4 0.3 0.2 0.1 4~0 4~0 4~0 4roO 4000 4mO 4000 4000 5000 R (mm) 103 10 1 ~~wu~uw~ww~wu~~~~~~~ 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 5 R (m) Fig.1 (1) Electron pressure profile in various beta discharges. (2) Connection length of magnetic field line at horizontally elongated cross-section. 111 O' of central value and the electron pressure in outer region is small and it affects the MHD equilibrium configuration little. There are some theoretical predictions for behavior in finite beta. LHD experiment suggests that the radiai iocations, where electron pressure is almost zero, don't change independently of beta. Next we show the limiter experiment using ICRF antenna. ICRF antenna touches plasma in torus outside at toroidal angle with vertically elongated cross-section. Fig.2 (1) shows the connection length of magnetic field line at toroidal angle with vertically elongated cross-section. In Fig.2 (1), magnetic surfaces indicated by arrow '4190', '4180' and '4160' correspond to '4190', '4180' and '4160' in Fig.1 (2). The outer region than '4180' corresponds to stochastic layers. Fig.2 (2) shows the measured electron pressure, Pe' profiles with various limiter locations. The Pe-O location in '4160' limiter location experiment is quite different from that in '4180' limiter location. It shows that the electron pressure remains when the limiter isn't inserted deeply enough to the well-defined closed magnetic surfaces. And when the limiter is inserted deeply, the Pe-O locations estimated by FIR and Thomson measurements in torus inside and outside are consistent with MHD equilibrium calculations. -.. C"') '4 50' 104~~~TT.r~~~TT~~~~~~~ 1-- LC30 (m) I 1 uu~~~~ww~~~~wwwu~~~wu 4.16 4.17 4.18 4.19 4.2 4.21 4.22 4.23 R (m) -neTeC4220'\ E 1000 <n -neTe(4200) -neTe('4190') ..... CI) i -neTe('41801 -11-naTe(,4160') {!!. 500 CI) C O~~~~~~~~~~~ 4~0 4~0 4~0 4roo 4000 4mO 4000 4000 5000 R (mm) Fig.2 (1) Connection length of magnetic field line at vertically elongated cross-section. (2) Electron pressure profile in various limiter locations. 47 

Study of Plasma Boundary in LHD Experiment

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