Results from current drive experiments on the Helicity Injected Torus

Abstract

The Helicity Injected Torus [T. R. Jarboe, Fusion Technol. 15, 7 (1989)] is a low aspect ratio tokamak that is formed and sustained by coaxial helicity injection with no transformer. Toroidal plasma currents of over 200 kA have been achieved with electron temperatures in the 100 eV range and electron density between 1019 and 1020 m−3. The major radius is 0.3 m and the minor radius is 0.2 m. New results from equilibrium and stability analysis of the external magnetic diagnostics and new results from the Transient Internal Probe (TIP), an internal magnetic field diagnostic, are presented. A mechanism for the transfer of current drive on the open to the closed flux regions is presented.

The National Spherical Torus Experiment (NSTX) Research Program and Progress Towards High Beta, Long Pulse Operating Scenarios

“…Despite the large values of cyclotron harmonic involved (9)(10)(11)(12)(13)(14), significant wave damping is expected at large values of the ion beta. Acceleration of neutral beam injected 80 keV ions to 140 keV has been observed.…”

“…• The application of coaxial helicity injection [11,12] (CHI) has yielded a toroidal current of up to 400 kA, with observations of n=1 MHD activity that may be a prerequisite for closed flux surface formation.…”

“…Single and double null configurations can be generated, and elongations up to 2.5 and triangularities up to 0.8 have been achieved. Finally, the inner and outer halves of the vacuum vessel are electrically isolated from each other and can be biased for studies aimed at starting and sustaining the plasma non-inductively using coaxial helicity injection (CHI) [11].…”

“…-Strategies for initiating current non-inductively on NSTX by the process of coaxial helicity injection (CHI [11,12]) are being developed. CHI is implemented on NSTX by driving current along field lines that connect the inner and outer lower divertor plates.…”

Initial Results from Coaxial Helicity Injection Experiments in NSTX

“…These devices also employed passive wall stabilization for equilibrium control and confirmed that CHI could be used in the presence of an external toroidal. Later HIT was rebuilt as the HIT-II experiment, which extended CHI to a true ST device by employing 28 poloidal field coils for equilibrium control instead of from image currents induced on copper walls [14]. HIT-II produced substantial plasma currents (200 kA) using transformer action or using CHI [15].…”