Several aspects of the secondary emission avalanche along an insulator surface (which is believed to play a role in insulator flashover) are addressed theoretically. The saturation condition for the two extremes of supply-limited and space-charge-limited current are obtained in analytic form, and comparison with the computer simulation of Anderson is made. Also, the effect of a strong magnetic field parallel to the insulator surface and perpendicular to the electric field is analyzed, taking account of the distribution of emission angles. It is found that the critical magnetic field for inhibition of flashover is reduced by a factor of about 2 when the distribution of angles is included in the calculation.

An analysis of space-charge-limited counterstreaming flow of ions and electrons in a high-voltage planar diode in the presence of a strong transverse magnetic field is presented. A two-component one-dimensional cold-fluid model is used which includes most self-consistent effects. A substantial enhancement of ion current by a factor of 3–6 is found at fields slightly larger than the critical magnetic insulation field.

Magnetic insulation obtained by employing the magnetic field of the line current in coaxial vacuum-transmission lines is studied in experiments on two different relativistic electron-beam accelerators, spanning the voltage range 0.4–10 MV. Effective magnetic insulation at fields up to 1.3 MV/cm is demonstrated. The self-limiting impedance is measured and compared to a number of theories for magnetic insulation and it is found that none of the ’’standard’’ theories successfully describes the data. However, computer simulations using a self-consistent two-dimensional particle code give good agreement with the experimental data, as does a proposed modification of the parapotential flow model.

Electrical breakdown across a vacuum/plastic interface in the presence of applied or self-generated magnetic fields, B?3.5 T, was investigated. The E×B drift of charged particles near the interface in these experiments was away from the insulator surface. The self-magnetic field effects on a plastic vacuum insulator flashover were examined with inductive loads, particle beam loads, and imploding plasma loads. Average breakdown electric fields of up to 38 MV/m were observed. Power densities of 100 TW/m2 were passed through acrylic-vacuum interfaces. The flashover electric fields were improved over the B = 0 fields from previous experiments by factors of 7.1, 5.0, and 1.8 for the −45°, 0°, and +45° insulators, respectively.

A two-dimensional electromagnetic particle code has been used to investigate the effect on magnetic insulation of a beam of electrons injected longitudinally into the coaxial vacuum gap. It is found that a parapotential beam, though force balanced at the input, does not propagate more than a short distance before being totally disrupted, apparently by beam instability. Even a very hollow beam is lost to the anode by a diffusion process which may explain the anomalous current leakage observed in some experiments.