Properties of dc helicity injected tokamak plasmas

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Abstract
Several dc helicity injection experiments using an electron beam technique have been conducted on the Current Drive Experiment (CDX) [Phys. Rev. Lett. 5 9, 2165 (1987)] and the Continuous Current Tokamak (CCT) [Phys. Rev. Lett. 6 3, 2365 (1989)]. The data strongly suggest that tokamak plasmas are being formed and maintained by this method. The largest currents driven to date are 1 kA in CDX (qa =5) and 6 kA in CCT (qa =3.5). An initial comparison of discharge properties with helicity theory indicates rough agreement. Current drive energy efficiencies are 9% and 23% of Ohmic efficiency in two cases analyzed. Strong radial electric fields are observed in these plasmas that cause poloidal rotation and, possibly, improved confinement.