Fluctuations and Electron Heating in MRX Guide-Field Reconnection Experiments

Abstract

The effects of a strong guide field on electron heating and electromagnetic fluctuations during magnetic reconnection are studied in a laboratory plasma. Using extensive radial scans in the magnetic reconnection layer under different guide field strengths, profiles of electron temperature, electron density and fluctuation amplitudes are obtained and analyzed. Electron temperature peaks sharply at the x-point as the guide field increases, indicating that guide fields may play a role in enhancing electron energy gain. Fluctuation peaks, in comparison, are relatively broad, with notable peaks only in the highest guide field case. For this case, there is positive correlation between electron temperature and fluctuation amplitude at the x-point, indicating the possibility of the role of fluctuations on electron heating. Additionally, a strong guide field appears to cause an asymmetric electron density negatively correlated with electron temperature. It is speculated that the presence of a guide field may contribute to increased electron energy gain by providing better confinement of electrons in the diffusion region, where they can be accelerated by E||. It is also possible, given the low density at the x-point, that there may be a population of highly energized runaway electrons being measured by the Langmuir probe. To investigate this, it would be necessary to make less ambiguous measurements of electron energy with energy analyzers. Furthermore, it would be necessary to do a quantitative study on the effect of the guide field on electron transit time, as well as the possible role of fluctuations in electron heating at the x-point.