A.V. Krasilnikov

M. "Sasao

M. Isobe

S." Iiduka

National Institute for Fusion Science (NIFS-Repository)

§31. Measurement of High Energy Neutral Particles from ICRF-/NBI-Plasmas by Natural Diamond Detectors Sasao, M., Isobe, M., Krasilnikov, A.V. (Troitsk Inst. for Inn. & Fusion Res.), liduka, S. (Dept. Nue!. Eng., Nagoya Univ.) During the 3rd campaign ofLHD experiment, high energy neutral particle spectra have measured by two specially developed natural diamond detectors(NDD's)[ 1]. Parallel particles are supplied by 90 - 110 kV neutral beam injectors, and detected as fast neutral atoms by NDD viewing the helical plasma tangentially. Perpendicular particles are generated by ICRF, and detected by a NDD viewing the plasma center chord perpendicularly. Fig. 1 shows the experimental arrangement of the perpendicular measurement. The viewing angle and the viewing volume are limited by 2 apertures, one is fixed (3 mm-diam.), the other is changeable, and the detector size, so that the counting rate is high enough for the statistics and low enough below the pile-up limitation. A pulse of fixed height is continuously supplied to the preamplifier in order to monitor the gain drift and the pile-up. Energy calibration of the system has been done by using an alpha source (Am-241) installed in the vacuum chamber. The energy resolution at 5.4 MeV was 8.7 % (FWHM). During the campaign, the perpendicular system worked properly for most of shots, but the tangential system often suffered from the pile-up problem. The tail temperature (T eff) during ICRF was derived assuming the ICRF accelerates protons perpendicularly. Then the particle flux to the detector per second in the energy interval dE can be expressed as where the particle distribution of ( m )( m )//2 m(v/ + v/)/2 m(v/ )/2) f(vx' vy• vz) = - - exp( )exp( 27ff1. 2;a; Tl. ~' is considered (I:Jf = Tl..)' We assumed that the charge exchange process between a high energy proton and an HO or an Heo atom dominates for the production of neutral particles. Fig. 2 shows an example of the time evolution of the tail temperature(T eff) during ICRF which is imposed on a NBI heated plasma (shot 12962). In most of discharge of this scenario, a clear increase of T eff is observed. After the ICRF termination, the T eff is gradually decreasing. In this case, the e-folding decay time of T eff , i.e. the relaxation time, is about 200 msec. II II Diag. Hall(II) II II Router II II II j 4.5L II == ==~ II AMP D I I Pulser D Figure 1 Schematic View of Experimental Arrangement of the perpendicular measurement. 0.00 0,$0 2.50 ~,O 55 :z: .&00 :e 3.00 "0 .::. a.oo '\ ~. 1,00 40 5' ~ 20 !t:: ~Q) 0 12962 ~~ :; : ~ 0 0.5 1.~ time s) 2 2.5 Figure 2. Time evolution of Teff during ICRF which is imposed on a NBI heated plasma. (12962: Bo=2.75T, Rax=3.6m) . References [ 1] A. V. Krasilnikov, et al. J. of Plasma and Fusion Research, Vol. 75 (1999) PP. 967-976 35 3 

Measurement of High Energy Neutral Particles from ICRF-/NBI-Plasmas by Natural Diamond Detectors

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