Electromechanical Analysis of a Prototype 20 Tesla, Single Turn Toroidal Field Coil for Ignitex

The fusion ignition experiment (IGNITEX) device is a single turn coil tokamak designed to produce and control an ignited plasma using ohmic heating alone. The proposed high strength toroidal field (TF) magnet operates at a magnetic field onaxis of 20 T, using homopolar generators (HPGs). In this paper, the electromechanical analysis of a scaled down prototype (0.06 scale in linear dimensions) of the IGNITEX TF' magnet is presented. The objective of the Ignition Technology Demonstration (ITD) program is to design, build, and test the operation of a single turn, 20 T, TF coil, powered by an existing HPG power supply system. Unlike conventional TF coils that use multiple turns of the conductor, the single turn coil eliminates the need for tum-to-turn insulation; therefore, better utilizing the available area for stress and thermal management. Precooling of' the coil to liquid-nitrogen temperature permits the magnet to operate in a wider temperature regime without exceeding material properties. Scaling relationships presented in this paper show that temperatures and stresses of a scaled-down coil and their relative distribution will approximate predicted levels of the full-scale IGNITEX device. A finite element program (TEXCOR) which solves a set of coupled electrical circuit, magnetic diffusion, and thermal diffusion equations with temperature dependent properties was developed. TEXCOR provides temperatures and magnetic body force densities for stress analysis of the magnet structure. The effect of flatness tolerance stackups in the TF coil assembly is discussed and methods to characterize and minimize the negative effect of nonideal conditions are given. Generator fault scenarios are also addressed. The analysis results presented in this paper show the feasibility of a single turn, 20 T, TF magnet powered by HPGs. This work is sponsored by the Texas Advanced Technology Program and the Texas Atomic Energy Research Foundation.