Initial Coil Configurationss for the Columbia REconfigurable eXperiment (C-REX): A Hybrid Tokamak-Stellarator
Jacob Halpern, Columbia University
We outline early design results for C-REX, a hybrid tokamak-stellarator experiment with planar toroidal field coils (TFs) and high temperature superconducting magnetic dipole coils. This device is intended to have the same size and aspect ratio as the High Beta Tokamak - Extended Pulse (HBT-EP) device at Columbia University. C-REX will operate with magnetic fields on the order of ~0.5-1T and can be used for multiple experimental studies, including runaway electrons, 3D physics (quasi-axisymmetry (QA) vs. axisymmetry, divertor, and island physics), and beta limits. Magnetic shaping will be provided by a combination of shifts/tilts of the TFs and varying the current in the dipoles, allowing for both axisymmetric and non-axisymmetric equilibria. Our initial efforts focus on demonstrating the ability for the same coil configuration with realistic engineering constraints to create both axisymmetric and QA plasmas. We discuss the necessary magnitudes of TF shifts/tilts, dipole quantity and size, and equilibrium properties best suited for this experiment. As magnetic dipoles are a recently proposed alternative to modular coils for stellarators, we also aim to answer open questions in the field such as the effects of dipole current regularization and multiple dipole sizes/shapes.