Alfvén resonance heating in Uragan-2M torsatron

Abstract

Uragan-2M is a medium-size torsatron with reduced helical ripples. This machine has the major plasma radius R = 1.7 m, the average minor plasma radius rp ≤ 0.24 m and the toroidal magnetic field B0 ≤ 2.4 T. The Alfven resonance heating in a high k‖ regime is advantageous for small size machines since it can be realized at smaller plasma densities than the minority and second harmonic heating. The Alfven resonance heating is examined numerically in the approximation of radially non-uniform plasma cylinder with identical ends. The numerical model for wave excitation and propagation accounts for the longitudinal electron thermal motion and the finite ion gyroradius which allow the model to treat correctly the propagation and damping of the kinetic Alfven wave in hot plasma. A compact antenna consisting of four loop elements is chosen to provide operation in a high k‖ regime. The major drawback of such an approach is the presence of plasma peripher y heating owing to unavoidable excitation of low k‖ Alfven resonances. Calculations show that, with the proper choice of heating regime, the periphery heating has an acceptable level and the major part of the power is deposited inside plasma column.