S. "Ohi

Y." Tomita

National Institute for Fusion Science (NIFS-Repository)

§28. Study on Heating and Sustaining of FRC Plasma by Ion Ring Injection Ohi, S., (Osaka Univ. Engi.) Tomita, Y. A field reversed configuration (FRC) has intrinsic features, i.e. pure poloidal magnetic field confinement, open field configuration outside the separatrix of plasma, and extremely so high plasma beta as more than 0.9. These features are the high potential of PRes for the fusion burning plasma, especially in D-3He fuel cycle reactors. Due to the features, on the other hand, conven-tional methods are not available technically for the sustain-ment of the configuration (heating of plasmas and supply of reversed magnetic flux) and for further heating of plasmas up to the temperature range of the fusion burning in FRCs. An axial injection method of pulsed intense ion beams (or ion rings) were proposed for the configuration sustain-ment and the further heating in this study and its actuali-zation has been investigated It is planned to experiment-ally test the actualization on FfHX (FRC Transport and Heating Experiment, Osaka Univ.) device. As showed in Fig. I., the d~vise consists of 3 parts (pulse ion beam diode, beam drift tube, and fonnation area of target plasma). Details of the diode are seen in Ref. 1. Expected parameters of the ion diode are as follows; beam energy: 5OkV, beam current: 2kA, output power: l00MW, output energy: lkJ. The main purpose of FfHX is to investigate transport mechanisms in FRC plasmas. In our study on the transport, a following scaling of plasma confinement was obtained!); h=(l+1.2Xlo'( ~~' T)=(1+1.2Xlo'e-27) where h is a kind of confinement anomaly-parameter and a ratio of the confinement time inferred from I-D classical MHD transport calculation to experimental confinement times (decay times), and where e=tslrs' Is is plasma length and rs is radius. In a case where plasma is so extremely prolate as plasma aspect ratio of e=15-20, therefore, confinement times obtained in experiments are I-D classical and are (0.3 JU/1411o), where 110 is Spitzer's resistivity 2). This scaling indicates that the confinement in FRCs is basically classical and degrades as E becomes smaller due to 2-D transport effect. In order to experimentally verify the dependence of the confinement time on E and electron temperature Te, the experimental devise FfHX was constructed. Preliminary results of plasma fonnation in the devise are reported here. A pinch coil is 22cm in diameter and l.5m in length. Diameter of parts of 12cm long at both coil ends is 20cm to make larger field of a mirror ratio of Lion the axis. Total energy of the main bank is 24kJ at charging voltage of SOkV. The pinch field rises to 5.1kO in 1.61ls at 45kV charging. Bias field is 3300. Filling gas of deuterium is 17 mTorr and is ionized by z-discharge current. A plasma radius rs is inferred from 0<1> and external field at chA (near coil mid-plane) in Fig.2. A value of xs I , 10 - - - -i- coil vail ----i-------t--------i-----+-iii -1-------------1-----------i---------] 6 - ! _ : ~. ! i -.--.----.-.-~.----.---j----1 i l -t------~------------- 1---- --.. z ! i o Z8 .., 60 80 180 NaiD. start t (fIS) Fig.2. Separatrix radius at a position of chAo (=rslrw) is almost constant in time and is 0 . .50- 0.55, where rw is the coil radius. Life time of plasmas is 70-80/lS. In Fig.3 are showed diamagnetic flux signals (0<1» at chA, 9 64l (arb_) ch..4 ch..9 ch.l0 ~'-.H--T'=--.,.000331 I -~-----+----t--I 60 BO 100 t (ta) Fig.3. Diamagnetic flux signals at near mirror field. (49cm from the mid-plane), 10 (58cm from the mid-plane). These signals show that plasmas expand up to the position of the mirror coil and continue to push the mirror field during all the plasma life time (no axial shrink). So far, the plasma confinement is, so-called, the mirror field confine-ment caused by faster decay of external field pressure than plasma pressure. References 1) S.OHI, Fusion Tech. Trans, 27, April,349, 1995. 2) S. HAMADA, Nucl. Fusion,26, 729, 1986. magnetically Insulated geometrically focused pulsed ion-beam g=r!~ .... ion beam drift magnetic field FRe plasma formation and confinement ar~a _----160cm 888888888 8 z ........ .. If Fig. I. Full schematics of FfHX (FRC Trdllsport Experiment) devise, Osaka University. 302 

Study on Heating and Sustaining of FRC Plasma by Ion Ring Injection

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