I. Katsumata

M . Ye

N. Ezumi

N. Ohno

S. Masuzaki

S. Takamura

Y. Uesugi

National Institute for Fusion Science (NIFS-Repository)

§43. Measurement of LHD Divertor Plasmas using Ion Sensitive Probe and Divertor Langmuir Probes Uesugi, Y., Ezumi, N., Ohno, N., Ye, M . .' Takamura, S. (Nagoya Univ.), Katsumata, 1., Masuzaki, S. (NIFS) Temperature measurement of divertor plasmas using divertor probes, such as Langmuir probes and Ion Sensitive Probes (ISP) 1) is one of the key issues for studying the di-vertor performance in the long pulse discharges with high power neutral beam and RF heating. Particle and energy transport between the ergodic region and divertor along the magnetic field line is another concern. So far Doppler broad-ening of impurity ion lines or asymmetric double probe2) have been used to measure the ion temperatw-e in the divertor plasmas. Here we employ ISP to measure the ion and elec-tron temperature of the divertor plasmas. The ISP has a simple structure compared with the asymmetric double probe. Before installing ISP to LHD, we have tested its performance characteristics for Ti measurement in a linear divertor simulator, NAGDIS-II. After applying some DC biasing voltage to the guard electrodes of ISP to reduce the noise current to the probe, we have obtained a clear I-V char-acteristic curve shown in Fig. 1. This curve gives Ti of about 2 eV, whose value agrees well with that measured with Dop-pler broadening of line radiation from Hell (468.6 nm), as shown in Fig. 2. Here, the ion temperature is changed by adding helium neutral gas into the plasma. A prototype of ISP for '\ ~0.1 •• •• Fig. 1 • ••• • • • -20 -15 -10 -5 o Vp[V] Voltage-current characteristic curve of ISP obtained in NAGDIS-II helium plasma. The magnetic field is 0.2 T, the electron density and temperature are 5x10 18m-3 10 ~~~!.~~~~~~~~========~ D. Ti (spec) .... .co .............. t <> Ti(ISP) • Te (ISP) LHD will be continuously developed, taking account of the structure of the magnetic filed in the divertor plasma. Since density and electrostatic fluctuations in the divertor plasma must be strongly related to the plasmas in the edge and ergodic layer due to fast electron transport along the magnetic field line, high frequency component of the ion saturation current obtained at the divertor probe (61#2) is analyzed preliminary. A contour plot of the fluctuation intensity of the ion saturation current in the frequency-time space is shown in Fig. 3. The fundamental frequency of the fluctuation is 2~2.5 kHz and gradually changes in time. And higher hannonic components are strongly observed as shown in the figure. The magnetic fluctuations observed by a mag-netic pickup coil have the same frequency spectra. The cor-relation between the magnetic fluctuations and those of the density and electrostatic potential in the divertor plasmas will be studied to investigate the particle transport from the edge region to the divertor plasma. o~(c~)----------------~ ............... N 2; 5000 >-o c (l) 6- 10000 (l) u: -----15000 -L-"--~--"---'----'---r-~ 0.75 1 .25 Time (sec) 1.75 Fig. 3 Fluctuation spectra of the ion saturation current in the divertor probe. References 1) Katsumata, 1., Contrib. Plasma Physics, 36 A: 1996)73. 2) Uehara, K.; Kawakami, T.; Amemiya, H.; Hothker, K.; CosIer, A.; Bieger, W. Nuclear Fusion. 38, (1998) 1665 . 47 

Measurement of LHD Divertor Plasmas using Ion Sensitive Probe and Divertor Langmuir Probes

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