Thermal equilibration from the long-range collisions in $e^{\mathrm{-\thinspace }}$/ $H^{\mathrm{-}}$ magnetized NNP.

We measure the particle slowing-down rate in a strongly magnetized ($r_{ce} ,r_{cH} \ll \lambda_{D} )$ weakly coupled ${e^{-}} \mathord{\left/ {\vphantom {{e^{-}} {H^{-}}}} \right. \kern-\nulldelimiterspace} {H^{-}}$nonneutral plasma. The plasma consists of near-room-temperature electrons ($T_{e} \approx 0.03-0.1eV)$ with an admixture (up to 20{\%}) of negative hydrogen ion, $H^{-}$. Here, $n_{e} \sim 10^{7}/cm^{3},\;n_{H^{-}} \sim 10^{6}/cm^{3}$. It was suggested recently [1] that for repulsive Coulomb interactions in the strongly magnetized regime, the slowing-down rate can be greatly enhanced by collisions with impact parameter $\rho $ in the range $r_{cH} <\rho <\lambda_{D} $. We measure the thermal equilibration rate $\nu^{H/e}$ between the cold electrons and the bounce-dynamically heated negative ions, and have found the typical rate $\nu^{H/e}\approx 1/\sec $ which is a factor of 5 smaller than the enhanced rate of [1] estimated for the given above plasma parameters. Possible reasons for the observed discrepancy will be analyzed, including hidden effects like a radial mass-separation, non-uniform $T_{e} (r)$ \begin{figure}[htbp] \centerline{\includegraphics[width=0.38in,height=0.19in]{020720191.eps}} \label{fig1} \end{figure} profile, etc. This enhanced particle slowing-down rate contributes also to the collisional damping of plasma waves, and affects the cyclotron cooling rate for electrons. [1] D.H.E. Dubin, Phys. Plasmas 21, 052108 (2014).