Experimental studies of field-reversed-configuration (FRC) confinement in FRX-C

A primary purpose of the large bore (0.5 m dia.) FRX-C field-reversed theta pinch experiment is to study the scaling of plasma particle containment time, tau/sub N/, with major radius, R, of the field-reversed configuration (FRC). At 20 mtorr fill pressure the FRX-C plasma parameters, anti n approx. 4 x 10/sup 15/ c/sup -3/, T/sub e/ approx. 100 eV, T/sub i/ approx. 150 eV, are comparable to those obtained in the smaller bore (0.25 m dia.) FRX-B device. Under these conditions, the present measurement of particle confinement time in FRX-C is tau/sub N/ approx. 140 ..mu..s, consistent with the scaling tau/sub N/ ..cap alpha.. R/sup 2/, when compared with the earlier FRX-B results. This favorable scaling has been observed with R/rho/sub i/ approx. 30 (rho/sub i/ = ion gyro radius), twice as large as in FRX-B, despite theoretical indications that various MHD instabilities would appear as R/rho/sub i/ was increased. The characteristics of hotter, neutron generating FRC plasma produced at lower fill pressure (5 mtorr), where anti n approx. 2 x 10/sup 15/ cm/sup -3/, T/sub e/ approx. 170 eV, T/sub i/ approx. 600 eV, are also presented. In this plasma regime an accurate determination of tau/sub N/ is difficultmore » because of the short stable period observed.« less