Disruption current observations in HBT-EP with expanded tile sensor array

Using the newly installed toroidally complete set of four High Field Side Scrape-Off Layer (HFS SOL) tile arrays on the HBT-EP experiment, this poster presents direct observations of currents flowing around a tokamak during a disrupting plasma, building on previous HBT studies of disruption currents using jumpers between insulated sections [1]. During disruptions, currents several percent of plasma current flow in helical filaments around the inwardly crashing plasma column in the same direction as the plasma current. These filaments produce a periodic signal of increasing frequency on the tile arrays [2]. The remaining two tile arrays were installed with better poloidal resolution, providing data on currents flowing along the HFS at four locations separated by roughly 90˚ and each covering the same poloidal angle of about 80˚ around the HFS midplane. Using the fine poloidal resolution of the sensors, the spatial structure and rotation of the current filaments is detailed with comparison to the magnetic and fast camera data. Finally, the temporal structure of the currents is presented, with information on the frequency evolution of the signal as the disruption progresses. Changes to disruption currents due to the operation of the upcoming Runaway Electron Mitigation Coil (REMC), as well as the operation of control coils are discussed. Plans for biasing the tiles for use as actuators are discussed.

[1] J.P. Levesque et al 2017 Nucl. Fusion 57 086035

[2] A.R. Saperstein et al 2022 Nucl. Fusion 62 026044