ST Formation via Driven Relaxation of a Screw Pinch: Overview and Design Considerations of a Proposed Concept Exploration Experiment

An ST with a plasma center column (PCC) could potentially overcome all the disadvantages of a material column. Along with CHI, a PCC could: (1)~form an ST via driven relaxation of a screw pinch (SP), (2)~carry inboard TF coil current, (3)~assist ST sustainment in combination with rf/NBI, and (4)~eliminate neutron shielding and column replacement. Achieving these goals will require considerable research. We propose to study the physics of (1). Our concept is to form a symmetry-axis SP between two electrodes, each coaxial with annular CHI electrodes. By programming SP/CHI electrode currents/voltages, the SP will undergo driven relaxation resulting in an ST-PCC equilibrium. After discussing the project motivation/impact, goals, physics basis/assessment (see poster by X.~Tang), and plans for ST-PCC equilibria/stability numerical modeling, we will focus on design considerations/challenges of key hardware systems: (1)~SP source consisting of electrodes and axial field coils; (2)~CHI electrodes and bias field coils; (3)~power supplies; (4)~interface between outboard TF windings and SP electrodes; (5)~flux-conserving boundary with electrical breaks for SP/CHI electrodes and shape-optimized for equilibrium/stability; and (6)~diagnostics for characterizing ST-PCC formation.