Visualization of Internal Magnetic Structure During Pellet Refueling of MAST Tokamak Plasmas

Fast visible imaging of Mega-Ampere Spherical Tokamak plasmas during injection of refueling pellets of frozen deuterium can sometimes vividly reveal their internal magnetic structure. Concentrated deposition of particles around the flux surface with unit value of field-line helicity results in locally increased bremsstrahlung emission which illuminates this whole surface or, occasionally, a single flux tube within it. Analysis of such images could be exploited to check equilibrium reconstruction models.