J." Nuhrenberg

M. Okamoto

N. Nakajima

S. "Murakami

National Institute for Fusion Science (NIFS-Repository)

§ 13. Energy Confinement Time for ICRF Heated Plasma in Heliotron/Torsatrons Murakami, S., Nakajima, N., Okamoto, M. Nuhrenberg, J. (Max-Pianck-lnstitut fur Plasma Physik, Germany) ICRF heating produces a high energy tail distri-bution and this modifies the total energy confine-ment of plasma when the tail distribution is large enough. Additionally the orbit loss of the high en-ergetic particle would reduce the energy confine-ment time in non-axisymmetric configurations. In this paper we have investigated the global energy confinement time for ICRF heated plasma in he-liotron/torsatrons including the effects of tail dis-tribution and losses of those particles. The power loss due to the orbit loss of tail ions is consistently included based on the results of Monte Carlo sim-ulations. Considering the tail ions and bulk plasma separately we can derived the formula of global confinement time as (1) where 1], if:ulk, and T8 are the heating efficiency, the energy confinement time for bulk plasma and the slowing down time. Based on the results of Monte Carlo simulation[ 1] we assume the heating efficiency of the ICRF minority heating as 17 = 1/(1+CP absTan-PB-Y). Then the global energy con-finement time is derived as TE = 1][Fn6BE(1]P abs)-a +~nt<36-5)B~'(7]P abs)~(l-ol], (2) where we assume -t;;ulk = Fn6BEP-a. The results are applied to the ICRF minority heating in the plasma of LHD. We here assume the density, temperature, and magnetic field strength dependencies on the heating efficiency as a ~ 3, {3 ~ 3, and r ~ 1 with the same faction of minority 142 ion density. The constant C has been obtained as C = 0.082 for LHD with 3% of minority fraction. Fig. 1 shows the heating efficiency with changing the density. We can see the strong density depen-dency. Fig. 2 shows the energy confinement time as a function of RF input power in the LHD. The obtained slowing down time for the LHD plasma is shorter than the energy confinement time and the reduction of energy confinement time from the value of simple LHD scaling due to the power loss is found (Fig. 1). Since the heating efficiency is sensitive to the density (Fig. 2), the stronger den-sity dependency on the energy confinement time is observed. O.R .i O.tl ~ I 0.4 0.2 0 0 ICRF lk:otins in'"" UIO <n>=0.2 ·· --<n>=0.4 --<n>:(lf\ · · - --<n>~-R ···· ·· <n>=I.O ···· .. . 6 R 10 12 14 RF iftro~ ro-< IMWI Fig. 1: Heating efficiencies of ICRF minority heating in the LHD with changing the density. o.n 0.2 ! -~ fl. I~ j 8 0.1 r (IJI~ 0 --... () ICRF Ikotin' in'"" tHO <n>:0.6 tau E --lou_E(h<oii) · ----lou .J2 loto_IJIO tl R 10 12 14 RF i"l"~ J'OW<'r IMWI Fig. 2: Energy confinement time as a function of RF input power in the LHD: {n) = 0.6 x 1020m-3 References 1) Murakami, S., et al., Nuclear Fusion 34 (1994) 795. 

Energy Confinement Time for ICRF Heated Plasma in Heliotron/Torsatrons

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