The stability of axisymmetric tandem mirror plasmas with respect to interchange, rotational, and ballooning modes is investigated in the paraxial approximation. The stabilizing effects of finite orbits, rigid energetic fast-drifting electrons, nearby conducting walls, and line-tying by a cold plasma halo are incorporated. Numerical calculations are performed to construct equilibria with finite plasma pressure and to determine linear stability by integrating a two-dimensional, initial-value equation. These numerical calculations support and extend analytical results. Analytical and numerical stability criteria are obtained.

Data on field-reversal experiments in the neutral-beam-injected 2XIIB mirror machine are reported. The best result is an estimated field-reversal parameter ζ = ΔB/Bvac = 0.9 ± 0.2 with vacuum field strength Bvac = 4.35 kG. Experiments at higher field strength Bvac = 6.7 kG achieved ζ = 0.6 ± 0.1. Ion energy confinement ⟨nτEi⟩ for the Bvac = 6.7 kG experiment is less than that predicted by classical Spitzer electron drag. Ion-cyclotron oscillations increasing with injected neutral-beam current suggest that ion-cyclotron losses are present and that ΔB/Bvac could be increased by improving stabilization of the ion-cyclotron oscillations.

The combination of finite-ion-Larmor-radius effects and surface stabilization by contact with a lateral wall or with a line-tied cold-plasma blanket can stabilize interchange modes at low plasma beta (beta=plasma pressure/magnetic pressure) in axisymmetric mirror devices. This is illustrated analytically in a simple one-dimensional radial model and numerically with a two-dimensional stability code for anisotropic mirror plasmas and parameters appropriate to the TRW symmetric tandem mirror experiment [Phys. Fluids 28, 1503 (1985)].

The effect of non-axisymmetric perturbations on the magnetic surfaces of a levitron is investigated. A Hamiltonian theory is developed for predicting the formation of both primary and secondary magnetic islands for the main resonances. Numerical calculations are made for a range of levitron parameters and compared with results of the Hamiltonian theory. Good agreement is obtained both for island width and for local rotational transform of the islands. A simple criterion for island destruction and the consequent stochasticity of the field lines agrees well with numerical results. A ring tilt of 0.5 degree is found to destroy the magnetic surfaces in the neighbourhood of the main resonances (i = π, 2π).

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