Experimental Evidence of Ion Acceleration at Internal Reconnection Events in the MAST-U Spherical Tokamak

Spherical tokamaks often have internal reconnection events (IRE) and ion acceleration was observed in ohmic plasmas previously[1]. These events correspond with a sudden relaxation of the safety factor at the IRE. In this work, a solid state neutral particle analyzer (SSNPA) [2] diagnostic oriented to measure mainly trapped and co-passing beam ions in Mega Amp Spherical Tokamak Upgrade (MAST-U) shows significant signal rise following internal reconnection events (IRE). Initial analysis suggests that fast-ions are accelerated in ~200 micro seconds to > 60 keV energies. Weight function analysis for the SSNPA also indicates that these higher energy fast ions are redistributed from orbits with very low pitch to orbits with slightly negative pitch. Additional analysis from other fast ion diagnostics[3,4] is also presented, further narrowing the region of fast-ion phase space accelerated by the IREs.