Suppression ofωciInstability in a Mirror-Confined Plasma by Injection of an Electron Beam

A hot ion plasma (${\overline{E}}_{i\perp }\simeq 400$ eV, $n\simeq {10}^{13}$ ${\mathrm{cm}}^{-3\mathrm{}}$) is trapped in a minimum-$B$ mirror system. A strong instability at ${\omega }_{\mathrm{ci}}$ is observed for neutral densities <${10}^{11}$ ${\mathrm{cm}}^{-3\mathrm{}}$. We have observed the suppression of this instability when an electron beam (≥42 kW) is injected into the plasma. We believe the suppression is due to a population of hot electrons produced and trapped in the mirror by the beam-plasma interaction.