Retarding field energy analyzer measurements of ion temperature in a two flux rope experiment at the LArge Plasma Device *

The heating and acceleration of ions due to magnetic reconnection have been observed in space, such as in planetary magnetospheres and the solar corona, as well as in various plasma simulations and laboratory experiments. These observations help to understand the heating process and the physics of reconnection as the energized ions tend to acquire most of their energies from the release of stored energy in the magnetic fields. In a study of magnetized flux ropes on the LArge Plasma Device (LAPD), two 11 m long kink-unstable flux ropes were created within a 18 m long background plasma using separate lanthanum hexaboride (LaB₆) sources. A retarding field energy analyzer specifically constructed for the two flux rope experiment was used to determine the ion temperature at localized points within the plasma. The background ion temperature was estimated to be 4 eV. The results were also compared to broadened He II spectral lines. In addition, the time-dependent ion temperature oscillates between 4 and 8 eV and is well-correlated with the localized magnetic field, which oscillates at the rope kink frequency. The occurrence of bimodal distribution functions at the ion temperature peaks suggest that ions are being accelerated and they could be jetted along the background magnetic field.