Exploration of kinetic plasma physics through in situ phase-space measurements in laboratory plasmas

The PHAse Space MApping (PHASMA) experiment was constructed to measure electron and ion velocity distribution functions in space relevant plasmas. PHASMA includes a unique set of optical diagnostics for the measurement of three-dimensional velocity distribution functions, magnetic fields, turbulence, and the three-dimensional structure of merging flux ropes. Here, we describe the key features of PHASMA and show that in rf plasmas, the ion heating appears to depend strongly on the helicity of the waves launched into the plasma. We also show that during electron-only reconnection, three-dimensional measurements of the electron velocity distribution are consistent with electron heating by the parallel electric field and exclude other possible acceleration mechanisms. At the same time, the ions gain more energy than is available from the Poynting flux in the region around the X-point and given the larger physical excursions of the ions, it is likely that their energy gain comes from a much larger volume around the X-point.