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.