R. Kumazawa

T. Yamamoto

National Institute for Fusion Science (NIFS-Repository)

§ 1 7. Comparison of Transfer Efficiency of High Energy Ion at Inward-Shifted and Standard Magnetic Axis Kumazawa, R., Yamamoto, T. (Nagoya Univ.) In the minority ICRF heating the most of the RF power is absorbed by minority ions!). The bulk plasma is heated by high energy ions via a slowing oown process due to electrons in the following power balance equation about the tail and bulk plasmas; d~ail _ p W,ail Tt-Th A - r tail ' E d~ulk = W,ail _ Wbulk dt rJ2 r E The heating power source for the bulk plasma is a tenn of Wta),t/2. A transfer efficiency lltms is oofined as what fraction of absorbed power is transferred to the bulk plasma using a following equation; p = W,ail p = W,ail abs r tail' tms r / 2 ' E s P r mil 1 1 1 11 - -E.:!lL - _E_ -- - --+ --tms - P - r /2' r tail - r / 2 r loss' abs sEE lltms is expressed using a ratio of 'tEtail/'t/2. When the energy loss time 'tE10SS is much longer than the electron slowing oown time, the transfer efficiency becomes 100%. It is also expressed as the ratio of Ttai1 to Teff: r tail ~ail = _E_~ff' rJ2 T 'I 11 = ---1!!L tms ~ff' In the Monte Carlo simulation lltms is scaled as shown in the following equation2): P l' tad T 1Jtms = tms = _E_ = -1EJl. = _________ _ ~bs rs /2 I:fJ 1 + C~bsT:2(nH / nJ-1 n;2 . Here C is a numerical factor to evaluate lltms; C oopends on the magnetic configuration and the magnetic strength. It is ootermined using the ratio of Ttail to Teff for 2 cases as OOscribed in the previous section and plotted in Fig. 1, where the abscissa is P absTe 2(nJneylne-2. C is ootermined to be Cexp::::{).032 at Rax=3.75m and 0.005 at Rax=3.6m, respectively. C is also evaluated in the Monte Carlo simulation to be CMc=O.043 at Rax=3.75m and 0.004 at Rax=3.6Om as shown in Fig.I. These experimental values fairly agree with the Monte Carlo simulation results. The reduction of the transfer efficiency is caused by a OOcrease in the energy loss time of high energy ions 'tE10SS. It is expressed using the transfer efficiency T]tms in the following equation; 130 tail /2 loss _ l' E1's _ 11tms /2 l' E - tail - r s • rJ2 - rE I-11tms It is plotted in Fig.2, whose abscissa is neP abs-ITe-O'\nJnerl. The energy loss time ranges in 0.I-O.2s in the plasma discharge at Rax=3.75m; however it is expected 10 times longer at Rax=3 .6m than that because C was 1110. >-0.8 C,) c: Q) '(3 0.6 :E Q) Co 0.4 -en c: ctS .= 0.2 . ~ , '. ~ ... · ----- · -------- - -----f- - ------------~~·-.. ~~·- ;.;~ • : CMc=ofo43 .... o------------------------------~ o 50 100 150 200 P absTe2(nJne)·1 ne·2 Fig.l Dependence of transfer efficiency in the cases of Rax=3.6m and =3.75m with the calculation results from the Monte Carlo simulation. 0.30 r---.....--...,...-...,..---r-~,......---. 0.20 - - ------------ -- - - -------~------ - ---------- - -- -- ----~------- -en ~ 0 .Q ~ 0.10 o 0.00s--~-~----~----~ o 0.02 0.04 0.06 nee 1 019m- 3) PabS' 1 (MW)Te( ke V)- 0.5n'/ne Fig.2 Depenoonce of energy loss time of high energy ions on neP abs·1Te·O,5(nJnerl. References 1) K.Saito et. aI., NucI. Fusion 41 (2001) 1021. 2) S .Murakami et. aI., Nucl. Fusion 39 (1999) 1165. 

Comparison of Transfer Efficiency of High Energy Ion at Inward-Shifted and Standard Magnetic Axis

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