External micro-controller adjustment of the radial position of in-vessel walls in HBT-EP

Tokamak’s internal walls act as passively-stabilizing conductors that suppress plasma instabilities through induced eddy currents. HBT-EP’s in-vessel walls are divided toroidally into 10 sections and poloidally into 2 sections; for a total of 20 upper and lower wall segments. Each wall segment has an approximate 4 cm radial range of motion and each segment’s radial position can be changed with an external DC motor without breaking vacuum. Using an Arduino Feedback and Control System (AFCS), HBT-EP operators can configure the position of all wall segments within minutes between HBT-EP operational periods. The AFCS’s user-interface allows HBT-EP operators to view the real time positions of each wall segment and set their positions manually or into pre-defined configurations. We use the AFCS to study the effects of variable wall geometry boundary conditions on plasma modes and scrape-off layer currents.