Y. Torii

National Institute for Fusion Science (NIFS-Repository)

§25. Evaluation of Energy Confinement Time and Heating Efficiency in ICRF Heated Plasma Torii, Y. (Nagoya Univ.) The energy confinement time of the LHD plasma has been observed to be 1.,5 t imes larger than the Interna-tional Stellarator Scaling (ISS95) 1). In the third cycle, ICRF modulation experiment was carried out to evaluate the energy confinement time, TE , in the diffrent method. In this experiment, the radiated HF power from an-tenna, Pant, was modulated in the following way, Pant = POant + IP lant I sin wt where w, P Oant and Plant are modulation angular fre-quency, an average and a modulated RF power from an-tenna, respectively. Then the modulated plasma stored energy H Tp is vVp = l¥po + IH'pll sin(wt + 5) where 5, }l!po and lVpl are the phase difference in the wave forms between the Plant and the lVpl , all average and a modulated plasma stored energy, respectively. The absorbed power by the plasma, Pabs , is calculated to be 17 Pant by introducing the heating efficiency '7. The TE is a function of the modulated frequency and J etc. The heating efficiency 17 is calculated with lFpl , Plant 1 wand 5 etc. We considered three models to analyze TE asssuming different dependence of the energy confinement time on the various parameters such as t.he R F heating power and the plasma temperature, T; i.e. (a)TE = const. 2 ), (b )TE = APabs Ct and (C)TE = BT(3. Assuming lVp1 '-~< l¥po and P labs « POabsl we substitute three types of TE: Plant = IPlant I sinwt and H'pl = 11Vpl : sin(u.,t + J) to the following equation, dH ' pl lVp1 - dt = 1]Plant - --. TE using of Fourier transformation and linear approxima-tion, TE is calculated as shown on Table I, which shows calculation results of TES and 1]S . Hereafter~ TE and '1 calculated by modulation method are written with su·· perscript M:i.e. TEM and 1]1\1. To evaluate 0:, j3 in the case of model (b) and (c), we use the ISS95 scaling law 1 ) , T 1SS9 5 - 0 0 ~{ 9a2.21Ro.65p - 0.59"-'-().51B 0 .8 3( (2) 0.4 E - . ne t L. j. 7r 2/3 Then we assume 0: =- 0 .. 59 and ;3 := ·- 1.44 . From experimental result. (Fig .l), we calculated TEl\[ and 17 M , and compared them wi th TE P and 17 P calucu-lated with usual met.hod, (dvVp / dt)t"n - O - (dlVp / dt)t..ff +O - ------ ---(at steady st.ate, dvVp / dt 0) Table II shows TEM I TE P sand 11''''1 /It s of each three models. It is fouIld that TEM s of any model (a) -( c) didn't have an agreement with TE P but that 17Ms of model (a) and (c) shows good agreement with rt . To have a good agreement with TE P , changing ;3, TE A·r of model (c) can be fixed. In this experiment, if we assume f3 = - 0.7.5, TEM has a good agreement with TE P , In ISS9.5 t.he dependence of P on TE corresponds to TE ex: p - 0.45. In t.his shoL it turned out t.o be an effective method of TE to ca.1culate it from the phase difference between Tl'p and P on power modulation experiment. And we also calculate 1'1 for another method. The model (c) shows a good agreement. wi t.h act ual TE and '7 . SO TE should be explained as a function of t.emperature. Table I: Three models of TE"\'! s and 17 M s I III tan .i: I '------I I T'l l I i, U I I ! ~ . pI ! I  (a) II_~~ ____ ~ W\t 1+tan2J1J:\:J __ 1 ~r-t-~ tallJ I 1 R. 11Vpl il (b) I I --w 1 +---- ! I w _t-a + 1 t.an 2 J IP lant I i I !. tauJ I ;' 1 11Vpl i i I (c) i (1 -,3) - I w\/1+-2-.--, i L I w ~ , tan () IPlant l I S'100 2 ;u ~~50~~1~~ $: ant ~ o 0 --o 1 2 3 4 5 6 t(s) Fig.1: Time evolutions of lVp and Pant. Modulation fre-quency is 4Hz . (B = 2.7ST, RF frequeucy = :38.47MHz) Table II: Three models of TE J'! / TEFS aud 1/1, [ / 1]P S in the case of 0: := -- 0 . .59 and t3 = -- 1.44 Reference 1) U.Stroth, d al., Nucl . Fusion 36, 1063(1 996) 2) T.SllOji : <:'1 al., In st.itute of Plasma Physics Reserch Report. Nagoya, IPP.I-79,5(1986) 29 

Evaluation of Energy Confinement Time and Heating Efficiency in ICRF Heated Plasma

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