l=1,2 high-beta stellarator

Abstract

The final scyllac experiments are described. These experiments utilized a feedback-stabilized, l=1,2 high-beta stellarator configuration and like the previous feedback-stabilization experiments were carried out in a toroidal sector, rather than a complete torus. The energy confinement time, obtained from excluded flux measurements, agrees with a two-dimensional calculation of particle end loss from a straight theta pinch. Because simple end loss was dominant, the energy confinement time was independent of whether equilibrium adjustment or feedback stabilization fields were applied. The dynamical characteristics of the toroidal equilibrium were improved by elimination of the l=0 field used previously, as expected from theory. A modal rather than local feedback control algorithm was used. Although feedback clearly decreased the m=1 motion of the plasma, the experimental test of modal feedback, which is expected from theory to be superior to local feedback, is considered inconclusive because of the limitations imposed by the sector configuration.

Ideal magnetohydrodynamic theory of magnetic fusion systems

“…However, as was stated previously, there is overwhelming empirical evidence that ideal MHD provides a rather accurate description of a wide variety of macroscopic plasma behavior. For examples of this, see, (1) Small gyroradius 1/2 y =2.28& 10 a n Furth (1975), Bartsch et al (1978), Bateman (1978), and Bodin and Newton (1980). There is good reason for this apparent good fortune, and the explanation is given in the next section with the introduction of the "perpendicular MHD" model.…”

Theta-pinch research at Los Alamos

“…In the context of Scyllac experiments, feedback stabilization is accomplished by optically detecting the transverse motion of the plasma column and then applying appropriate auxiliary fields in order to restore the plasma to the centre of the vacuum vessel. This method was successfully demonstrated in a series of sector experiments between 1975 and 1977 [36,37]. One important refinement in the final experimental configuration was the use of 2 = 2 fields in combination with 2 = 1, instead of the 2 = 0 used in early experiments.…”

A numerical study of high-beta stellarator equilibria

“…A partial list of the relevant experiments includes the early tests of the stellarator force in a straight geometry on Scylla-IV-3 [22], the 5-metre and 8-metre Scyllac toroidal sectors [12], the confinement experiments on the Scyllac full-torus [23], and Isar Tl-A [24] and Tl-B [25], the feedback stabilization experiments on a toroidal sector [26,27] and the final sector experiments on Scyllac with adjustable equilibrium fields [1,28].…”

“…[ 1 ], with similarly good agreement. They are summarized in Table V however, that the comparison in Refs [1,28] includes a correction for the instability force which takes into account the observed displacement of the plasma from the equilibrium position. Similar comparisons are made for the 2= 1,2 sector in Ref.…”