The Formation of a Tokamak-like Plasma in Initial Experiments Using an Outboard Plasma Gun Current Source
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Solenoid-free tokamak startup via point-source DC helicity injection is demonstrated on the Pegasus Toroidal Experiment using a high current density, low impurity plasma gun mounted near the outboard midplane. A threshold in the vacuum vertical magnetic field strength that allows the injected current filament to relax into a tokamak-like topology is observed. A simple 2-D model of the vacuum magnetic field suggests this threshold is the maximum field strength that allows a toroidally connected field null to form. Discharges with I p ≈ 17 kA are produced using less than 2 kA of injected current and no inductive drive. The tokamak-like discharges exhibit current decay times about five times longer than the injected current decay, expansion of the plasma into the vacuum region and a significant increase in the line-integrated density.
KeywordsDC helicity injection Solenoid-free startup Plasma guns
The authors thank E. Hinson, J. Cole, A. Robinson, and A. Wiersma for their assistance with Pegasus operations and G. Winz, B. Lewicki, B. Kujak-Ford for the design and construction of the outboard plasma gun system. This work supported by US DOE Grant DE-FG02-96ER54375.
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