First laboratory detection of anomalous resistivity and electron heating by lower hybrid drift waves inside reconnecting current sheets with a guide field*

Magnetic reconnection plays an important role in explosive phenomena in magnetized plasmas such as solar flares and geomagnetic storms. Various waves and instabilities can be generated in the reconnecting current sheets due to abundantly available free energy and affect the reconnection dynamics. One frequently observed wave is lower hybrid drift waves (LHDW) which can be either quasi-electrostatic (ES-LHDW) or electromagnetic (EM-LHDW), depending on the plasma and field conditions. From the linear theory [1], we find that the characteristics of LHDW are determined by electron beta and the relative perpendicular drift velocity between electrons and ions normalized to the local sound speed. In the low electron beta regime with a guide field, strong ES-LHDW is observed inside the electron diffusion region in the Magnetic Reconnection Experiment (MRX). By using a specially developed probe [2], fluctuations in density and the out-of-plane component of the electric field are measured to correlate to generate a significant (~20% of the reconnection electric field) anomalous resistivity [4]. The observed small phase difference between the two fluctuations is consistent with our linear models [1,3], which suggests the important role played by the Lorentz force in generating the anomalous resistivity. We have performed quasilinear analysis and showed that ES-LHDW can generate anomalous electron heating exceeding the classical Ohmic heating in laboratory plasma [4]. We also found a positive correlation between the electron temperature and the amplitude of LHDW, and the correlation grows stronger with larger guide fields. Our work demonstrates the importance of wave-particle interaction during collisionless reconnection.

[1] J. Yoo et al., Geophys. Res. Lett. 47 (2020). DOI:10.1029/2020GL087192

[2] Y. Hu, J. Yoo, H. Ji, A. Goodman, and X. Wu, Rev. Sci. Instrum. 92, 033534 (2021).

[3] J. Yoo et al., Phys. Plasmas 29, 022109 (2022).

[4] J. Yoo et al., Phys. Rev. Lett. 132, 145101 (2024).