Process for Energy Transfer to the Electron Population at Large Distances in Gamma Ray Bubbles

Resonant interaction of unmagnetized ions with lower hybrid modes that are excited by the positive slope in the distribution of magnetized electrons serves as a mechanism for transferring the longitudinal energy of electrons to the perpendicular energy of ions. This mechanism, considered originally for the explanation of the enhanced rf emission at $\omega\cong\omega_{pi}$ (ion plasma frequency) and the associated enhanced ion heating observed in Alcator [1], was also proposed by one of us (B. C.) to successfully explain the formation of ``ion conics'' in the suprauroral region [2]. The inverse process of electron energization due to resonant interaction with lower hybrid modes that are excited by an energetic ion population (e.g. a streaming ion population) could be relevant to the formation of the outer edge region of gamma ray bubbles [3]. We proposed a similar process in 1976, considering lower hybrid modes injected in a confined plasma column as the driver of an electron current [4]. \\[4pt] [1] B. Coppi, F. Pegoraro, R. Pozzoli, and G. Rewoldt, Nucl. Fusion, 16, 309 (1976).\\[0pt] [2] T. Chang and B. Coppi, Geophys. Res. Lett., 8, 1253 (1981).\\[0pt] [3] The Fermi-LAT Collaboration, Science, 328, 725 (2010).\\[0pt] [4] B. Basu and B. Coppi, RLE Report PRR-76/4, MIT, Cambridge, MA, 1976.