Improved Confinement in the SSPX Spheromak
Abstract
Energy confinement in the SSPX spheromak has increased significantly. Improvements are due to higher formation current followed by a longer flat-top current with additional tuning of vacuum bias flux to produce a radial profile of current density/magnetic field that is slightly peaked at the magnetic axis. The discharge evolves through an optimum profile indicated by a minimum in magnetic field fluctuations during which time, the q=safety factor profile is also slightly peaked and lies between the two lowest order resonant surfaces with 1/2 < q < 2/3 (q = n/m = toroidal/poloidal mode). Electron temperature Te has increased over previous results from 120 eV to > 200 eV, electron thermal diffusivity in the core is reduced by a factor of four to < 10 m^2/sec. Ohmic power density Poh in the core is about the same, but edge dissipation, which dominates, is reduced. Higher Te and lower Poh doubles the electron energy confinement time within the separatrix to > 200 μs.
- Publication:
-
APS Division of Plasma Physics Meeting Abstracts
- Pub Date:
- October 2003
- Bibcode:
- 2003APS..DPPGP1078M