High-<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>β</mml:mi></mml:math>, Gas-Stabilized, Mirror-Confined Plasma

A neutral-beam-sustained plasma in the $2XIIB$ mirror machine is stabilized by hydrogen gas ionized at one mirror. Peak plasma energy densities that exceed the energy density of the vacuum field ($\stackrel{^}{\ensuremath{\beta}}\ensuremath{\equiv}\frac{8{\stackrel{^}{n}}_{\mathrm{D}}{\overline{E}}_{\mathrm{D}}}{B_{\mathrm{vac}}^{2}}\ensuremath{\gtrsim}1$) are achieved with deuterons of average energy ${\overline{E}}_{\mathrm{D}}\ensuremath{\approx}9$ keV, peak density ${\stackrel{^}{n}}_{\mathrm{D}}\ensuremath{\approx}1.5\ifmmode\times\else\texttimes\fi{}{10}^{14}$ ${\mathrm{cm}}^{\ensuremath{-}3}$, in a magnetic field ${B}_{\mathrm{vac}}=0.56$ T. These high $\ensuremath{\beta}'\mathrm{s}$ are sustained for the duration of gas and neutral-beam injection, with no evidence of a $\ensuremath{\beta}$ limit.