Using Diode Simulatons to Verify of Plasma Physics Codes

The planar diode, a device where an electron current traverses an AK gap driven by an external electric potential has been studied for many years 1 , 2 , 3 , 4 . Diode physics couple conservation laws with electromagnetics (EM). The relative simplicity of these plasma/EM coupled devices and the fact that in some cases analytic solutions are available make diodes a good candidate for rigorous plasma code verification. Jaffe 1 provided the cold diode solution with a finite velocity beam of electrons emitted at the cathode suitable for particle-in-cell (PIC) code comparisons. Rokhlenko and Lebowitz 2 presented a fluid model of the cold diode which led Hamlin et al. 3 to develop a warm diode model that includes effects of pressure through an adiabatic equation of state for comparison with multi-fluid (MF) plasma codes and a relativistic solution for comparison to special relativistic hydrodynamic (SRMF) codes. Akimov and Schamel 4 added a simple collision term to a fluid model and showed that it captures the Mott-Gurney 5 space-charge-limited law. We have constructed cold, warm, relativistic and collisional diode simulations for verifying four plasma physics codes: PIC, MF, SRMF and hybrid, all currently under development. We discuss diode simulation set-up for and solution strategies for each plasma model, limitations of the analytic models and present rigorous verification of: PIC of a cold diode 1 , MF of a warm diode 3 , SRMF of a warm relativistic diode 3 , and PIC, MF and hybrid codes of a collisional diode 4 .