AIP Digital Archive
The ELMO snaky torus concept [Furth and Boozer (private communication, 1983)] is investigated in a helically symmetric model with low beta and large aspect ratio (the curvature radius of the magnetic axis over the plasma radius). The equilibria are obtained by expansions in the inverse aspect ratio and plasma beta. Application of the energetic-particle- modified Mercier criterion [Zheng and Tsai, Phys. Fluids B 4, 1416 (1992)] to the analytical equilibria confirms that the interchange mode can be stabilized in helically symmetric systems in the low-beta regime by suitably introducing drift-nonreverse energetic particles. The results show that, for effective stabilization, it is better that the pressure profile of the energetic component depend on the radius quadratically, and peak at midplane in the poloidal angle, and the volume occupied by the energetic particles, the aspect ratio, and the ratio of the curvature to the torsion of the magnetic axis should be large when the energetic particles are drift nonreverse.
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