High-Density Discharges in the Alcator Tokamak

Peak plasma densities in excess of ${10}^{15}$ ${\mathrm{cm}}^{\ensuremath{-}3}$ have been obtained in the Alcator tokamak with $60<~{B}_{T}<85$ kG. The highest average density so far achieved is ${\overline{n}}_{e}=6\ifmmode\times\else\texttimes\fi{}{10}^{14}$ ${\mathrm{cm}}^{\ensuremath{-}3}$; the corresponding ${n}_{0}{\ensuremath{\tau}}_{E}=2\ifmmode\times\else\texttimes\fi{}{10}^{13}$ ${\mathrm{cm}}^{\ensuremath{-}3}$ s. These ultrahigh-density discharges exhibit (i) nearly complete energy equilibration between electrons and ions, (ii) severe attenuation of energetic-neutral-particle fluxes, (iii) a minor role of impurities, and (iv) energy-confinement properties consistent with neoclassical estimates.