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HSX is a quasi-helically symmetric (QHS) stellarator currently under construction at the Torsatron-Stellarator Laboratory of the University of Wisconsin - Madison. This device is unique in its magnetic design in that the magnetic field spectrum possesses only a single dominant (helical) component. This design avoids the large direct orbit losses and the low-collisionality neoclassical losses associated with conventional stellarators. The restoration of symmetry to the confining magnetic field makes the neoclassical confinement in this device analogous to an axisymmetric q = 1/3 tokamak.The magnet coil design has been attained through the application of the HELIAS1 approach developed at IPP Garching. The 48 modular twisted coils produce a magnetic field with R0 = 1.2 m, = .15 m, 0 = 1.04, a = 1.11, V” ~ -.6% (well), and B < 1.4 T. Plasma production and heating will be accomplished with the application of up to 200 kW of 28 GHz Electron Cyclotron Resonant Heating (ECRH).The HSX device has been designed with a clear set of primary physics goals; demonstrate the feasibility of construction of a QHS device, examine single particle confinement of injected ions with regard to magnetic field symmetry breaking, compare density and temperature profiles in this helically symmetric system to those for axisymmetric tokamaks and conventional stellarators, examine electric fields and plasma rotation with edge biasing in relation to L-H transitions in symmetric versus non-symmetric stellarator systems, investigate QHS effects on 1/v regime electron confinement, and examine how greatly-reduced neoclassical electron thermal conductivity compares to the experimental χe profile.The HSX magnet coil fabrication has just commenced, and ancillary components are either under fabrication or have been designed and are ready for fabrication. A support structure has been designed to allow independent, accurate coil alignment coupled with good coil support for the magnetic and thermal loads. The vacuum vessel is helical in shape, following the magnetic separatrix with 3 cm clearance, and is to be explosively fabricated from stainless steel. Magnetic flexibility has been incorporated into the design through the inclusion of a set of independently powered auxiliary coils. These coils permit rotational transform control, the addition of magnetic mirror and symmetry breaking magnetic field perturbations, and variation of the magnetic well depth.Initial assembly and coil alignment will occur as the components are fabricated, with completed final assembly planned for August 1996. First plasma production is planned for the end of 1996.
Anderson et al. (Sat,) studied this question.