Argon ion temperature evolution in magnetic reconnection

Laser induced fluorescence (LIF) measurements were conducted during magnetic reconnection of two argon plasma flux ropes in the PHAse Space MApping (PHASMA) experiment. The flux ropes are generated using two plasma guns. A pulsed laser was used to induce LIF near the separatrix at several wavelengths for an ensemble of reproducible gun shots. Signal over several shots at one wavelength is then averaged together to determine the magnitude of the ion velocity distribution function (IVDF) at a single wavelength. The process is repeated for 20 wavelengths to build up a discrete IVDF at a particular time during reconnection. A fit to the measured IVDF provides a measure of the ion temperature and the bulk ion flow. This process is repeated for several times throughout the reconnection event to determine ion temperature evolution in time. The ion temperature magnitude and evolution is discussed in the context of electron temperature measurements from the PHASMA Thomson scattering system, Langmuir triple probe, and retarding field energy analyzer measurements. We also discuss different methods for processing the LIF time series measurements to obtain the IVDF magnitude.