Fast 3D Optical Tomography for Observing Reconnection Dynamics in PHASMA

A newly developed 192-voxel optical tomographic array has been used to monitor dynamics arising from flux ropes in the PHASe MApping experiment (PHASMA). Purpose built transimpedance amplifiers and collection optics allow for per-voxel spatial resolution of 6mm and time resolution exceeding 200MHz. Tomographic reconstructions using emission light time series are able to resolve the ~1MHz fluctuations coincident with reconnection onset, believed to be lower hybrid drift waves, and are in close agreement with simultaneous measurements of the floating potential and magnetic field. Unlike probe based methodologies, the tomographic system is able to resolve features deep within the diffusion region without obstructing the flux ropes, shedding additional light on the role of wave-particle interaction to mediate energy transfer during electron-only reconnection. These measurements highlight the capabilities of optical tomography to complement or even replace probe-based measurements with a completely nonperturbative option.