A noninductive current drive concept, based on internal pressure-driven currents in a low-aspect-ratio toroidal geometry, has been demonstrated on the Current Drive Experiment Upgrade (CDX-U) [Forest et al., Phys. Rev. Lett. 68, 3559 (1992)] and further tested on DIII-D [in Plasma Physics and Controlled Nuclear Fusion Research, 1986, Proceedings of the 11th International Conference, Kyoto (International Atomic Energy Agency, Vienna, 1987), Vol. 1, p. 159]. For both experiments, electron cyclotron power provided the necessary heating to breakdown and maintain a plasma with high-βp and low collisionality (εβp∼1, ν*≤1). A poloidal vacuum field similar to a simple magnetic mirror is superimposed on a much stronger toroidal field to provide the initial confinement for a hot, trapped electron species. With application of electron cyclotron heating (ECH), toroidal currents spontaneously flow within the plasma and increase with applied ECH power. The direction of the generated current is independent of the toroidal field direction and depends only on the direction of the poloidal field, scaling inversely with magnitude of the later. On both CDX-U and DIII-D, these currents were large enough that stationary closed flux surfaces were observed to form with no additional Ohmic heating. The existence of such equilibria provides further evidence for the existence of some type of bootstrap current. Equilibrium reconstructions show the resulting plasma exhibits properties similar to more conventional tokamaks, including a peaked current density profile which implies some form of current on axis or nonclassical current transport.

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The luminous region of the plasma cloud surrounding deuterium pellets injected into a tokamak is studied spectroscopically. At the time of peak luminosity the electron density is 2.4x 10 17 cm -3 to within 30% and the temperature is at most 2.0 eV. The intensity ratio of the Balmer-alpha and -beta light from the pellets, the total number of emitted photons, and the apparent size of the radiating region are consistent with local thermodynamic equilibrium at this temperature and density.PACS numbers: 52.40. Hf, 52.70.Kz In the past decade experiments have been performed in which pellets of solid hydrogen or deuterium with dimensions of 0.070-4.0 mm and velocities of 90-1300 m/s were injected into tokamak plasmas.