Alfonso G. Tarditi

Numerical and Experimental Investigation on the Traveling Wave Direct Energy Converter Concept

Computational models of the Traveling Wave Direct Energy Converter (TWDEC) have been developed with the goals of: demonstrating the physics of charged particle deceleration and energy conversion, supporting the development of an experimental TWDEC test article, and optimizing its performance. The first model is a 2D axisymmetric, electrostatic, particle-in-cell (PIC) simulation which includes the presence of electrodes and of an external circuit load impedance. The second model is based on an analytical approach, modeling the ion bunches as point charges, resulting in fast simulation at the expense of a reduced accuracy in the modeling of the beam dynamics. The PIC model is designed to investigate the physics of the TWDEC while the second model provides the ability to optimize electrode spacing for the maximum particle deceleration efficiency. In a concurrent experimental effort, a TWDEC test article is being developed to provide the first direct measurements of energy converted from a decelerating ion beam.

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

A Particle-in-cell 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; the simulation is focused on the conversion of the beam kinetic energy into alternating current (AC) electric power. The model is electrostatic, as the electro-dynamics of the relatively slow ions can be treated in the quasistatic approximation. A two-dimensional, axisymmetric (radial-axial coordinates) geometry is considered. Ion beam particles are injected on one end and travel 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 oating. The modulated beam induces a time alternating potential di erence between adjacent electrodes. Power can be drawn from the electrodes by connecting a resistive load. As energy is dissipated in the load, a corresponding drop in beam energy is measured. The simulation encapsulates the TWDEC process by reproducing the time-dependent transfer of energy and the particle deceleration due to the electric eld phase time variations.