New developments in the STOR-1M Tokamak

STOR-1M is a small tokamak with the following parameters: R=22 cm, a=3.5 cm, B/sub T/=1 T, I/sub p/<8kA (q(a)>3.5). it can be operated in three ways: (1) as a normal, Ohmically-heated tokamak; 2) with supplementary turbulent heating; and, 3) as an ac tokamak. Turbulent heating is attained by superimposing a short (15μs), intense (10 kA) current pulse on the existing OH current, and so far q(a) = 2.0 has been obtained with no major disruption. Initial results on ac operation have been presented previously. Recent improvements have included the addition of a fast hydrogen gas injection system to increase the electron density (to about 7x10/sup 13/ cm/sup -3/), and a feedback system for horizontal plasma position control. The feedback system has been used in normal tokamak discharges, but is most useful in turbulent heating discharges where the fast current pulse induces oscillations in position. For the controller, plasma position information is obtained using magnetic probes which measure the equilibrium field. The analog circuit used is able to follow rapid plasma displacement. The feedback signal conditioning circuits are of the conventional proportional-integral-derivative type. The control signals are digitized and applied to output drivers which switch the output power transistors. Three new diagnostics have been developed: a charge-exchange neutral energy analyzer, a soft X-ray detector for electron temperature, and a ruby laser Thomson scattering apparatus for electron temperature and density