Point-Source Helicity Injection Current Drive System for the Pegasus Toroidal Experiment
Recent Pegasus experiments are developing solenoid-free startup techniques using point-source magnetic helicity injection. These plasma sources, called “plasma guns”, ionize a stream of gas in a discharge channel, and bias this channel with respect to an external electrode, driving current along the plasma stream, which relaxes into a tokamak-like equilibrium. The relaxed discharges formed by these injectors exhibit high current amplification, which is the ratio of total toroidal current to the gun-driven current. The development and present design of these injectors are described, and time traces from a typical discharge are presented.
KeywordsMagnetic confinement Tokamak Helicity injection
The authors thank Jon Cole, Alex Robinson, and Amy Wiersma for their assistance with Pegasus operations. We also thank G. Fiksel (U. Wisconsin) for many helpful discussions on plasma gun design. This work is supported by the US Department of Energy, Office of Fusion Energy Sciences, under grant DE-FG02–96ER54375.
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