A. Ejiri

Group" CHS

K. Kawahata

K. Matsuoka

R. "Pavlichenko

"Pavlichenko,  R.

Ejiri, A.

Matsuoka,  K.

Kawahata,  K.

CHS, Group"

NIFS-Repository (National Institute for Fusion Science)

§27. Electron Density Measurements with Pulsed Radar Reflectometer Pavlichenko, R. (Grad. Univ. Advan. Studies), Ejiri A. (Univ. of Tokyo), Matsuoka, K., Kawahata, K., CHS Group Microwave reflectometry becomes a popular di-agnostic for density measurements in magnetically confined plasma. Recently, the pulsed radar re-flectometry, as the novel approach to such kind of measurements, was introduced [1, 2].We have con-structed a pulsed radar reflectometer for the Com-pact Helical System (CHS) [3]. This was the first attempt to use pulsed radar system for the helical systems. Preliminary free space time measurements have been done to calibrate the timing electronics. In-stead of the plasma cut-off layer, a metallic mirror is used and moved by 0.5-0.9m in front of antenna. A spatial resolution of 3 x 10-3m has been reached, that comes from the accuracy of TAC output read-ing. As a wave polarity, ordinary and extraordinary modes are launched. We probed the plasma with microwave pulses of 1.9nsec. The plasmas were ini-tiated by IBW (Ion Bernstein Wave) or ECH and heated by NBI and ECH. These measurements were done for discharges with the magnetic field from 0.85T to 1. 76T and maximum electron density up to 6 x 1020m-3 . Figure 1 shows the typical traces for the time delay of the reflected microwave pulses. The time behavior of the time delay agrees with the calcula-tion of this scenario by assuming the parabolic den-sity profile. For time to position inversion instead of assuming the whole profile, we assume a linear pro-file between the plasma edge and the cut off. Then the estimated position of the cut off layer coincides well with Thomson scattering measurements (Fig-ure 2). The spatial accuracy of the determination of the position of the reflected layer (spatial accuracy of the density profile reconstruction) during plasma measurements becomes about 5 - 8 x 10-3m. 6 ' 'lost pulses' 4 ECH 'noise' -6 reflection from CHS inner wall ~ . shot #71205 time, [ms] Figure 1: Time of flight evolution during CHS plasma discharge for the shot #71205 Plasma density profile # 71205 q; q; B1=1.54T Q) ~ q; t R.,.=92.1cm (J) <I> ·s <I> ,.,~ q, e -0 e ~ ;£- + SSGHz 'iii q; c ~ Q) <ll * 51GHz '0 <1) ~ 1 (J)® Radar <1) c. Thomson 0 0 00 70 80 90 100 110 120 130 major plasma radius, em Figure 2: Comparison of density profiles from the Thomson scattering system and from pulsed radar for the same discharge (shot #71205) References [1] Hugengoltz, C.A.J and Heijnen, S.H. : Rev. Sci. Instrum. 62(199]) 1.100. [2] Pavlichenko, R. et al. : Ann. Rep. NIFS(1995-1996)241. [3] R.Pavlichenko, et al. J.Plasma Fusion Res. Series l(J 998)378 219 

Electron Density Measurements with Pulsed Radar Reflectometer

Electron Density Measurements with Pulsed Radar Reflectometer

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