Ion beam stabilization of rotational instability in a field-reversed configuration with rigid rotation

Abstract

The rotational instability of a field-reversed configuration (FRC) can be suppressed by applying a multipole magnetic field. The multipole field, however, breaks the axisymmetry and may compromise configuration. An alternative method using injected ‘‘beam’’ ions would preserve the symmetry. This method is studied here within the framework of a multifluid model for which a variational principle has been developed and solved using the Rayleigh–Ritz technique. This approach leads to an analytic solution for a rigid-rotor equilibrium and allows the straightforward derivation of marginal stability conditions. This was not possible with a previous hybrid simulation which, though more complete, was cumbersome to apply. It is found that if the ratio of the rotational frequency of beam ions to that of the background ions exceeds a critical value, the radial displacement of the plasma and beam ions are opposite, and the rotational instability can be suppressed. The effect of compressibility of beam ions on the stability is also examined. The stability analysis is applied to present or near-term experimental devices and a future reactor. The beam energy and current need only be a small fraction of those of the background plasma in order to stabilize the rotational instability. These results are in qualitative agreement with previous results from a hybrid particle simulation.

Neutral beam injection heating on field-reversed configuration plasma decompressed through axial translation

“…Especially, the NBI can be an ultimate candidate for additional heating and sustainment of a high-beta FRC plasma [2,33], because it provides steady power input to FRC plasmas with wide ranges of temperature and density. The NBI is also expected to stabilize various global modes in a FRC plasma [34,35]. The world's first NBI experiments on an FRC plasma has been performed in the FIX device [30].…”