Space-charge limited currents in coaxial diodes with electron backscatter

The effect of backscattered electrons on space-charge limited currents of c ylindrical (coaxial) diodes with anode center conductors is studied. The sc attered electrons are parametrized by a fractional current density alpha an d fractional energy beta of the incident electrons. For bipolar flow, curre nt enhancement factors of 2.5 are calculated for alpha, beta similar or equ al to0.5. Comparison of the model equations to one-dimensional particle-in- cell simulations with fully integrated Monte Carlo scattering algorithms de monstrates very good agreement for a range of energies and anode materials. In the absence of backscattering, the bipolar diode impedance decreases fo r increasing ratio of cathode to anode radius r(c)/r(a) for ratios greater than about 20. (C) 2001 American Institute of Physics.