Relaxation of pressure anisotropy due to Alfvén-ion-cyclotron fluctuations observed in ion-cyclotron-range-of-frequency–heated mirror plasmas

Abstract

Alfv\'en-ion-cyclotron modes are generated over a wide range of anisotropy parameter ${\mathrm{\ensuremath{\beta}}}_{\mathrm{\ensuremath{\perp}}}$(${\mathit{T}}_{\mathrm{\ensuremath{\perp}}}$/${\mathit{T}}_{\mathrm{\ensuremath{\parallel}}}$${)}^{2}$ in ICRF-heated central cell plasmas of the GAMMA 10 tandem mirror. The fluctuations are observed at a small driving force in the convectively unstable region predicted theoretically in an infinite plasma. Before reaching the \ensuremath{\beta} limit of ${\mathrm{\ensuremath{\beta}}}_{\mathrm{\ensuremath{\perp}}}$=3.52\ifmmode\times\else\texttimes\fi{}(${\mathit{T}}_{\mathrm{\ensuremath{\parallel}}}$/${\mathit{T}}_{\mathrm{\ensuremath{\perp}}}$${)}^{2}$, above which the absolute instability is predicted, relaxation of pressure anisotropy is observed for the first time by use of an array of diamagnetic loops together with a Faraday cup and secondary-electron emission detectors.