Spheromak injection into a tokamak
Recent results from the Caltech spheromak injection experiment [to appear in Phys. Rev. Lett.] are reported. First, current drive by spheromak injection into the ENCORE tokamak as a result of the process of magnetic helicity injection is observed. An initial 30% increase in plasma current is observed followed by a drop by a factor of 3 because of sudden plasma cooling. Second, spheromak injection results in an increase of tokamak central density by a factor of 6. The high-current/high-density discharge is terminated by a sharp peaking of the density profile followed by an interchange instability. In a second experiment, the spheromak is injected into the magnetized toroidal vacuum vessel (with no tokamak plasma) fitted with magnetic probe arrays. An m=1 (nonaxisymmetric) magnetic structure forms in the vessel after the spheromak undergoes a double tilt; once in the cylindrical entrance between gun and tokamak, then again in the tokamak vessel. In the absence of net toroidal flux, the structure develops a helical pitch (the sense of pitch depends on the helicity sign). Experiments with a number of refractory metal electrode coatings have shown that tungsten and chrome coatings provide some improvement in spheromak parameters. Design details of a larger, higher-current spheromak gun with a new accelerator section are also discussed.
© 1990 American Institute of Physics. Received 13 November 1989; accepted 21 February 1990. We would like to acknowledge the assistance of Frank Cosso and Dave Cutrer. It is a pleasure to acknowledge the suggestions of and useful discussions with J.H. Hammer and C.W. Hartman of Lawrence Livermore National Laboratory and C.W. Barnes, J.C. Fernández, T.R. Jarboe, and I. Henins of the Los Alamos National Laboratory. This work was supported under U.S. Department of Energy Grant No. DE-FG03-86ER53232. Paper 117, Bulletin of the American Physical Society 34, 1913 (1989). [M.R.B. was an] invited speaker [at the American Physical Society Meeting]. [M.R.B. was an] United States Department of Energy, Fusion Energy Postdoctoral Research Fellow.
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