Inductive Field-Reversed Configuration Accelerator for Tokamak Fueling

Abstract

Compact toroids can be used for fueling other fusion devices by accelerating them to high enough velocities to penetrate strong magnetic fields. In the simplest analysis, the kinetic energy density of a flux-excluding object 1/2ρv2 must exceed the magnetic field energy density B2/2μ0 of the field to be pushed aside. Field reversed configurations (FRCs) are a type of compact toroid that are particularly efficient for this application due to their high density and thus lower required energy per unit mass. FRCs are also formed and accelerated inductively, thus minimizing possible impurity contamination. The Tokamak Refueling by Accelerated Plasmoids (TRAP) experiment was built to develop the inductive acceleration method and test the ability of high-velocity FRCs to penetrate transverse magnetic fields. Simple models have been developed for both the acceleration and penetration processes to determine fueler parameters required for a given tokamak field. Experimental results are given for the acceleration process. Half-milligram FRCs with number densities of 1022 m-3 were accelerated to velocities of 200 km/s, sufficient to fuel tokamaks with Tesla magnetic fields. The technology is easily extendable to much higher FRC densities and velocities, sufficient to fuel the largest, highest-field tokamaks.