K. Ida

M." Osakabe

S. "Okamura

National Institute for Fusion Science (NIFS-Repository)

§5. Observation of Resonant Loss Cone in FNA Spectrum Okamura, S., Ida, K., Osakabe, M. Fast neutral particle measurement in CHS (FNA) usually gives clear Maxwellian spectrum for the low density NBI plasmas. It is because the injected beam from NBI.#l passes through the plasma in front of FNA measurement which supplies sufficient neutral density in the plasma for the charge exchange process. The ion temper-ature derived from FNA spectrum is very close to the TVCXS for most of discharges in CHS. During the experiments for getting high ion temperature, FNA ion temperature gave signifi-cantly low value of Ti compared with TVCXS measurement. It may happen for FNA measure-ments when the spectrum range used for getting slope is low energy part in which the contribution of boundary plasma is large. But the spectrum range used for getting Ti was around several times Ti for this measurement. In addition, if the spec-trum range close to Ti was taken which is the energy range used for the doppler shift analysis of TVCXS, the result was very close to the TVCXS measurement. The shape of spectrum was convex· which is very rare for usual FN A spectrum. The time variation of ion temperature is shown in Fig. 1 for two different ranges of spectrum used to obtain the slope. Figure 2 shows the full spectrum for the per-pendicular particles. The tail component appears which is supplied by the pitch angle scattering of slowed down beam particles. The slope fitting is made for the bulk component in the range of 0.5 keV < E < 2 keV indicated by small triangles. Figure 3 shows the spectrum in the low energy range. The fitting is made for 0.2 ke V < E < 1 ke V which clearly shows the loss of particles in the energy range above 1 ke V. This energy range corresponds to the resonant loss cone of trapped ions caused by the positive electric field. A preliminary measurement of ener-gy distribution of parallel particles does not show such convex shape of spectrum. 222 600 ~ 500 E :J u 400 Q) a. (/) 0 300 Q) a. <75 200 100 Rax = 92.1 em Bt = 1.76 T -o-- 0.5 keV < E < 2 keV ------ 0.2 keV < E < 1 keV Time(ms) Fig. 1 Time variation of spectrum slope Ch. 1-16 13 T1me :140.0 ms - 150 . 0 ms 4490 v N0a1.92E 07 8.6 ~ 3~0~----~----~~~------~------J Energy(keV) Ch . 10 65535 Fig. 2 Full spectrum of perpendicular particles 1997 . 3.H Ch. 1-16 T1me :100.0 ms - 110.0 ~s ~~. 0:---"--__ ---:-'0 ~. 6__ __ll__Ll._2 ____ ___J_l._8 _____ 2.1_. 4 ____ __J3. 0 Energy(keV) Ch. IO 65535 Fig. 3 Low energy spectrum 

Observation of Resonant Loss Cone in FNA Spectrum

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