Excitation of the lower-hybrid drift instability in the outflow of electron-only magnetic reconnection

We report experimental evidence for the lower-hybrid drift instability in the current sheet normal direction of electron-only magnetic reconnection. In our laser-driven capacitor-coil experiment, the system size ($\sim$3 ion skin depths) places it in the electron-only regime. Yet, Thomson scattering reveals out-of-plane electron drift oscillations at the local lower-hybrid frequency, with kinetic energy density reaching $\sim$18% of the local magnetic energy density. Linear theory with the measured parameters predicts more than ten e-folding times of growth, indicating that the instability reaches the nonlinear regime within the measurement window. Supported by particle-in-cell simulations, these results demonstrate the importance of ions in the dissipation and energy transfer in electron-only reconnection where their significance has not been previously recognized.