STUDY OF THE IDEAL MHD STABILITY LIMIT FOR JET
Ideal MHD stability limits the beta that can be achieved. The stability of free boundary modes imposes a limit on beta as well as that of internal ballooning modes. Optimisation of the ballooning mode stability alone leads to flat q profiles, unlike those that are observed. Optimisation of the n = 1 free boundary mode stability leads to a q profile with q-o near one, namely with the maximum shear compatible with the internal kink stability requirement. This optimum corresponds to the naturally occurring q profile. For this optimum profile all modes seem to become unstable at about the same value of beta. The results are within 10%, in agreement with the scaling law up to the highest current studied of 12 MA. No claim is made that another optimisation with different source functions could not lead to higher beta with the same type of q profiles. But it should also be noted that in a stationary purely ohmic regime there is a constraint between the pressure and current profile, which could result in a lower beta limit than that found here. The implications of these results on the alpha heating power one could expect are investigated.
Bibliographic Reference: WRITE TO CONFEDERATION SUISSE, CEN DE RECHERCHES EN PHYSIQUE DES PLASMAS, ECOLE POLYTECHNIQUE FEDERALE DE LAUSANNE, 21 AVE DES BAINS, CH-1007 LAUSANNE (SWITZERLAND), MENTIONING REPORT LRP 263/85,
Record Number: 1989124079600 / Last updated on: 1987-01-01
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