Observation of electron holes and lower-hybrid turbulence during magnetic reconnection experiments on VTF*

We report a detailed study of electrostatic turbulence observed during magnetic reconnection experiments on the Versatile Toroidal Facility (VTF) [1], including identification of modes, exploration of instability mechanisms, and studies of correlation with the reconnection events and electron energization. Electrostatic fluctuations are observed by arrays of small, high-bandwidth, impedance-matched Langmuir probes. Broadband fluctuations are found, including lower-hybrid (LH) waves and higher-frequency Trivelpiece-Gould (TG) waves. Strong nonlinear turbulence, consisting of large-amplitude, positive-potential spikes identified as electron phase-space holes, is also observed [2]. We believe that the LH modes are driven unstable by steep electron temperature gradients, while TG and electron holes arise from bump-on-tail instability of high energy electrons. In both cases, it is believed that the modes arise as a consequence of electron energization by the reconnection events.\\{} [1] J. Egedal, \textit{et al.}, \textit{PRL} \textbf{98}, 015003 (2007). \\{} [2] W. Fox, \textit{et al.}, \textit{PRL} \textbf{101}, 255003 (2008).