The Small Tight Aspect Ratio Tokamak Experiment

Low-aspect-ratio tokamaks offer both the economic advantage of smaller size and a number of physics advantages which are not available at conventional aspect ratio. The Small Tight Aspect Ratio Tokamak (START) [Fusion Technology 1990, edited by B. E. Keen, M. Huguet, and R. Hemsworth (North-Holland, Amsterdam, 1991), Vol. 1, p. 353] was conceived as a first substantial test of tokamak plasma behavior at low aspect ratio. It has achieved plasma currents up to 200 kA, peak densities of approximately 2 X 10(20) m-3 and central electron temperatures of approximately 500 eV at an aspect ratio of 1.3-1.5. Central beta values of approximately 13% have been measured and the volume-averaged beta [beta] can approach the Troyon limit. Plasmas are naturally elongated (kappa less than or similar to 2.0) and are vertically stable without feedback control. Major disruptions have not been observed at low aspect ratios (A less-than-or-equal-to 2.0).