R. Kumazawa

National Institute for Fusion Science (NIFS-Repository)

§21 . Parameter Range of ICRF Heated Plasma Kumazawa, R. Various experiments using ICRF heating were succeechl in the actltional heating and the plasma sustenance at the 3rd experimental campaign. In this section, parameter ranges of ICRF heated plasma are described. 1) Plasma density vs. ICRF heated power A scaling of the ~nsity limit on Helical system was rerived from experimental rnta obtained at medium size revices. That is given as a function of the heating power, the magnetic field strength and the size of ~vice, i.e. P, B, a, and R [l]. A relation between the average line electron rensity and the heating RF power, PICH was examined regarding ICRF heated plasmas. The maximum average electron rensity so far achieved was 1.9xl019m-3 at ICRF heating power of 1.3 MW. The ~nsity limit on the LHD derivedfrom the scaling [1] is nee (m-3) = 2.7xI019 P(MW) The highest ~nsity can be dxluced 3.5xlOI9m-3 at 1.3MW of ICRF heating power. All the operated ~nsity is lower than the limit predicted by the scaling. The fraction of the radiated power to the heating RF power, P raiPICH was no more than 40 % even in ne=8.7xl0 1Rm-3 at PICH =OAIMW, in which the ~nsity was 80 % of the ~nsity limit. In the highest rensity discharge, i.e. 1. 9xI 019m-3 the ICRF heating power was gradually reduced from 1.3MW to OAMW before turn-off of RF power. During this period the ~nsity was about the same. Then the fraction of PraiPRF increased with the recrease in the RF power and it could be consequently estimated that the limit ~nsity (Prad/PR~.9) was ncc=1.9xI019m-3 at PICH =OAOMW, which is about 1.8 times larger than that of the above-mentioned scaling. Another discharge with the high ~nsity of 5.0xl019m-3 could be achieved at NBI heated plasma with lAMW, which did not exhibit the ~nsity limit yet [2]. The higher rensity will be achieved in the 4th experimental campaign, consi~ring the same heating quality of the ICRF heating as that of the NBI heating. 2) High temperature plasma A relation between the plasma stored energy, Wp and the average electron ~nsity was examined at the heating power of 1.2~1.4MW in ICRF and ECH heated plasmas, extracting cbta from the wi~ range of the electron ~nsity, i.e. from 4.0xI0 18m-3 to 1. 9x] 01 9m-3. The relation fits to the scaling of the ~nsity of 15595, in which Wp is proportional to neO.S1. The electron temperature at the magnetic axis Te(O) increases with the recrease in the average electron ~nsity. The maximum electron temperature of Te(0)=3.8keV was obtained at ne=4.5xI01Rm-3. The electron temperature scales with ne-0 .41, which is the same scaling of 15595. . LHD "' , - 10MW -'.-_._-_ .... . __ . __ ._---_. _. --_. __ ..... _-• 3MW ICH • ... plasma . w 101 102 103 time(s) Fig.l Achieved range in diagram of fusion triple product vs. operation time. 3) Fusion triple product at long pulse operation One of the main objectives of the LHD project is the long pulse operation. The long pulse operation for 68 seconds was achieved in the plasma of 1 IOkJ, ne = 1.0 x I019m-3 and Teo~Tjo=2.0keV with the ICRF heating power of 0.85 MW. This is rescribed in the other section titled as "Long pulse plasma sustenance by ICRF heating". The energy confinement time 'tE was 0.16 seconds and the fusion triple product was ne(O) 'tETj(O) =3.2xl0 18m-3keVsec (see Table 1). This was plotted in the diagram of fusion tIi pIe product vs. operation time of Fig.1. Here other long pulse discharges were also plotted; 15, 30 45 seconds operation at the same fusion tri pIe product as that of the 68 seconds discharge. The higher fusion triple product, i.e. ne(O) 'tETj(O) = 6.5xl01Rm-3keVsec (see Table 1) was also plotted, which was obtained at the highest plasma stored energy of 200kJ with 5 seconds. The final goal of the LHD steady state operation is at the high fusion triple product, i.e. ne(O) 'tETj(O)= 1.5xl019m-3 keVsec at 3MW and 6.0xI0 19m-3keVsec at IOMW as also shown in Fig.1. As the triple fusion product increases with the plasma ~nsity, these goals will be achieved at higher plasma ~nsity, i.e. ne=4.5xI0 19 ~ I.7xl02°m-3. Table 1 nc(xlO I9m-3 ) l:,,(sec) Tj(O)(keV) ncl:ETj(O) pulse (xIO IRm3 keVsec) length(sec) 1.0 0.16 2.0 3.2 1.9 0.2 1.7 6.5 References III 5.5udo et. AI., Nuclear Fusion 30, 11(1990). 121 Y.Takeiri, private communication. 68 5 25 

Parameter Range of ICRF Heated Plasma

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