PBGUNS Output: Relativistic Electron Beam

Trajectories and Equipotentials for Phermex electron gun.

The program produces plots of the trajectories, equipotentials, the exit plane (or intermediate) current density distributions, emittance plots at desired planes, and current density distributions from the cathode. A relativistic electron beam is shown; this gun was developed at LANL for the Phermex pulsed X-ray generator. It operates at 600 kV and 500 A. The results are displayed at the minimum resolution recommended for this problem (a 181 by 81 matrix, with an 8 to 1 fine mesh over the cathode, with 209 trajectories). The current and all other parameters are in excellent agreement with experiments. Results include the self-induced fields generated by the beam.

The Emittance plots are generated at 24.3 and 35.0 on the z-axis and the plot at the waist is shown below. The errors in the trajectories appear in the emittance plots where they cause small fluctuations in the plots. These are caused by errors primarily at the emission surface and can be reduced by increasing the fine mesh ratio. The errors are generally less than a milli-radian on the 5 mrad scale.

Emittance plot at Phermex gun beam waist.

Emittance plot near exit plane of Phermex gun.

Shown below are the fine matrix equipotentials and the exit plane current density distribution for the Phermex gun. The thermal gap can be seen quite clearly on the fine matrix. The simulation requires at least three fine matrix points in the thermal gap. The overlay of the average current density and the last cycle indicate good convergence for the simulation.

Equipotentials on the field emitter fine matrix.

Exit plane current density distribution for Phermex gun.