The Formation of a Tokamak-like Plasma in Initial Experiments Using an Outboard Plasma Gun Current Source

• Published in: Journal of fusion energy Vol. 28; no. 2; pp. 140 - 143
• Main Authors: Battaglia, D. J., Bongard, M. W., Fonck, R. J., Redd, A. J., Sontag, A. C.
• Format: Journal Article
• Language: English
• Published: Boston Springer US 01.06.2009; Springer Nature B.V
• Subjects: Current sources; Decay; Discharge; Electrodes; Electrons; Energy Systems; Experiments; Field strength; Helicity; Magnetic fields; Nuclear Energy; Nuclear Fusion; Original Paper; Pegasus; Physics; Physics and Astronomy; Plasma; Plasma guns; Plasma Physics; Solenoids; Sustainable Development; Tokamak devices; Topology; Two dimensional models; Plasma guns; DC helicity injection; Solenoid-free startup
• ISSN: 0164-0313; 1572-9591
• DOI: 10.1007/s10894-008-9165-y

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.