IDEAL MHD STABILITY OF HIGH BETA(P) PLASMAS AND BETA(P) COLLAPSE IN JT-60U

Analyses of ideal MHD stabilities of high beta(p) plasmas show that th e occurrence of beta(p) collapse in JT-60U is consistent with the viol ation of the low n kink mode stability boundary. It is demonstrated th eoretically that the pressure profile, internal inductance, l(i), q(s) /q(0) and epsilon beta(p) influence the ideal stability limit, g, impo sed by the low n kink mode and the infinite n ballooning mode; here, g = beta(t)/(I/alpha B-t). Peaking of the pressure profile decreases th e stability limit g to low values (2-1.5) in both high l(i) (similar t o 1.2) and low ei (similar to 0.8) plasmas, though the maximum g value does not strongly depend on epsilon beta(p) and q(s)/q(0). In a high l(i) plasma with peaked pressure, the stability limit is determined by internal low n kink modes, especially by the infernal mode in the low q(0) region, while, in the low l(i) plasma, it is determined by the i nfinite n ballooning mode. Broadening of the pressure profile combined with the high l(i) (similar to 1.2) significantly increases the stabi lity limit g (similar to 5) and makes the displacement more global, th ough the g value decreases with epsilon beta(p) for fixed values of q( s)/q(0). Experimentally, by the broadening of the pressure profile wit h high l(i) (> 1.2), high g (similar to 4) plasmas are obtained and no beta(p) collapse is observed, which is consistent with non-violation of the ideal MHD stability boundary.