Investigation on evolution of cathode plasma expansion velocity of a magnetically insulated coaxial diode

The cathode plasma expansion velocity evolutions of a magnetically insulated coaxial diode (MICD) are investigated in theory and particle-in-cell (PIC) simulation. The temporal evolution trends of the axial and radial velocities all reveal “V”-shape profiles, but the trends of radial velocities are not obvious. The axial velocity is different from that of planar diodes as “U”-shape profiles because the guiding magnetic field breaks down the dynamic equilibrium between the diode and thermal electron current densities for MICDs. Moreover, the increasing plasma thermal electron current density decides the augment of the axial plasma expansion velocity with the constant voltage. The enhanced magnetic field can not change this increasing trend but is conducive to slow it down.