Achievement of Record<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi mathvariant="italic">β</mml:mi></mml:math>in the START Spherical Tokamak

Values of ${\ensuremath{\beta}}_{T}\ensuremath{\ge}30%$ have been achieved and sustained for several confinement times on the START spherical tokamak using additional heating provided by neutral beam injection. These values are more than twice the highest value previously obtained in a tokamak, and correspond to normalized $\ensuremath{\beta}$ values of ${\ensuremath{\beta}}_{N}\ensuremath{\ge}4$. In these shots values of ${I}_{p}&gt;{I}_{\mathrm{rod}}$ (where ${I}_{\mathrm{rod}}$ is the current flowing in the central toroidal field rod) have been obtained, which are considered to be necessary for spherical tokamak power plant. The results are compared with ideal-MHD stability theory.