A Particle-in-Cell Simulation for the Traveling Wave Direct Energy Converter (TWDEC) for Fusion Propulsion

A Particle-in-cell (PIC) simulation model has been developed to study the physics of the Traveling Wave Direct Energy Converter (TWDEC) applied to the conversion of charged fusion products into electricity. In this model the availability of a beam of collimated fusion products is assumed and the simulation is focused on the conversion of the beam kinetic energy into alternating current (AC) electric power. The model is electrostatic, as the electrodynamics of the relatively slow variations of the ion motion can be treated in the quasistatic approximation. A two-dimensional, axisymmetric (radial-axial coordinates) geometry is considered. An ion beam is injected from one end and travels along the axis through ring-shaped electrodes with externally applied time-varying voltages, thus modulating the beam by forming a sinusoidal pattern in the beam density. Further downstream, the modulated beam passes through another set of ring electrodes, now electrically floating. The modulated beam induces an alternating potential difference between adjacent electrodes. Power can be drawn from the electrodes by connecting a resistive load and as energy is dissipated in the load, a corresponding drop in beam energy is measured. The model focuses on the key TWDEC process by simulating the time-dependent transfer of energy from the ion beam to a resistive load connected to the electrodes.