Ion-Bernstein-Wave Heating and Improved Confinement in the Alcator C Tokamak

Abstract

Plasma heating by directly launched ion Bernstein waves is investigated in the Alcator C tokamak at densities ${\overline{n}}_{e}\ensuremath{\gtrsim}1\ifmmode\times\else\texttimes\fi{}{10}^{20}$ ${\mathrm{m}}^{\ensuremath{-}3}$. For injected rf powers ${P}_{\mathrm{rf}}\ensuremath{\lesssim}180$ kW, bulk-ion-temperature increases of $\ensuremath{\Delta}{T}_{i}\ensuremath{\lesssim}380$ eV, as well as improvements in global particle and central impurity confinement times by a factor of 2-3, are observed. In certain regimes, the energy-confinement time improves relative to the initial Ohmic value. At higher densities (${\overline{n}}_{e}\ensuremath{\gtrsim}2\ifmmode\times\else\texttimes\fi{}{10}^{20}$ ${\mathrm{m}}^{\ensuremath{-}3}$), the heating ceases to be efficient.