Particle-in-Cell Simulation Studies of Electron and Ion Dynamics in Positive Polarity Rod-Pinch Diode

Flash X-ray (FXR) sources for dynamic radiography operate in different electron beam diode geometries depending on the applied voltage and impedance of the pulse power systems driving them. Rod-pinch (RP) diode is a suitable candidate for accelerating voltages up to few MeVs. It is desirable to have a small source size (0.5-3 mm) with a higher X-ray dose for a better figure of merit (FoM) “for short pulse” radiographic sources. A 3-D particle-in-cell (PIC) simulation study to optimize the RP source geometry for voltages in the range 0.8-3 MeV is presented here. Single disk and double disk cathodes were studied for the cathode to anode radius ratio of 10 and having a 1 mm anode radius. Comparison has been made with space charge-limited (SCL) model for cylindrical diode and critical current model for both single species electron only, as well as with both electron and ion PIC simulation. The electron current collected at the anode tip for single disk cathode and double disk cathodes has been compared for various accelerating voltages. Double-disk cathode with a 3 mm separation between the disks would provide better FoM as an X-ray source for operating voltages in the range 0.8-3 MV.