Breakdown of a Coaxial Diode Transverse to a Uniform Magnetic Field

The breakdown of a coaxial diode transverse to a uniform magnetic field is an obstacle for the use of these devices for the microsecond range of pulse durations. A model of the breakdown was developed [1,2] that takes into account the evolution of cathode plasma from isolated emission sites into a closed plasma layer around the cathode in which a centrifugal instability subsequently develops. In the paper experimental results of checking of the model are reported. Investigated were dependencies of the diode commutation time tcom⊥ on the voltage U, beam current I, cathode radius rc and a plasma behavior in the electrode systems with some sections of a negative radius of curvature of an electric-field equipotential line. It was shown that the model [1,2] agrees with the experimental data if a condition neffd ≠ f(d) (where neff is the effective plasma concentration, d is the gap spacing) is satisfied. A possibility of lengthening of a pulse duration in coaxial diodes is discussed. An experimental set-up is presented that allows the time tcom⊥ to be increased by an order of magnitude.