Space Charge Limited Currents Calculations in Coaxial Cylindrical Diodes Using Particle-in-Cell Simulations

ABSTRACT

Three dimensional particle-in-cell (PIC) simulations are conducted to measure the space charge limited (SCL) currents in coaxial cylindrical diodes. New cut-cell emission and absorption boundary algorithms implemented in the electromagnetic PIC code, VORPAL are utilized for this study. Comparisons of VORPAL SCL current results are made with i) theoretical SCL current results for the one dimensional planar diode, ii) analytical solutions of SCL current results for the one dimensional and two dimensional cylindrical diode cases, and iii) an experimental cylindrical diode operated as a virtual cathode oscillator. VORPAL SCL current results show agreement within a few percent with the analytical two dimensional cylindrical diode results for the non-relativistic operating voltages of 1-100 kV and within error bars with the experimental cylindrical diode results for the diode operating voltage of 340 kV.