Ideal MHD stability of high β_p plasmas and β_p collapse in JT-60U

摘要

Analyses of ideal MHD stabilities of high β_p plasmas show that the occurrence of β_p collapse in JT-60U is consistent with the violation of the low n kink mode stability boundary. It is demonstrated theoretically that the pressure profile, internal inductance, li, qs/q0 and β_p influence the ideal stability limit, g, imposed by the low n kink mode and the infinite n ballooning mode; here, g = βt/(I/aBt). Peaking of the pressure profile decreases the stability limit g to low values (2-1.5) in both high li (～1.2) and low li (～0.8) plasmas, though the maximum g value does not strongly depend on β_p and qs/q0. In a high li plasma with peaked pressure, the stability limit is determined by internal low n kink modes, especially by the infernal mode in the low q0 region, while, in the low li plasma, it is determined by the infinite n ballooning mode. Broadening of the pressure profile combined with the high li (～1.2) significantly increases the stability limit g (～5) and makes the displacement more global, though the g value decreases with β_p for fixed values of qs/q0. Experimentally, by the broadening of the pressure profile with high li (>1.2), high g (～4) plasmas are obtained and no β_p collapse is observed, which is consistent with non-violation of the ideal MHD stability boundary.