|icc_2006_mclean_ucrl_216536f.pdf||2006-02-21 10:28:10||Harry McLean|
Energy transport in high temperature spheromak plasmas
Author: Harry S. McLean
Submitted: 2005-12-16 16:53:49
Co-authors: B.I.Cohen, D.N.Hill, E.B.Hooper, J.M.Moller, C.Romero-Talamas, R.D.Wood
Lawrence Livermore National Laboratory
7000 East Avenue
Livermore, CA 94550
Higher electron temperature (Te > 350eV) with reduced electron thermal diffusivity (< 10 m^2/s) is achieved in the Sustained Spheromak Physics Experiment (SSPX) by increasing the discharge current and gun bias flux in a prescribed manner. Magnetic fluctuations are maintained at small amplitude (< 1%) by programming the ratio of gun current to gun flux in the formation gun. Scanning this ratio above and below the "Taylor-state" eigenvalue of the flux conserver after formation of the spheromak varies the q = safety factor profile and produces the m/n = poloidal/toroidal magnetic fluctuation mode spectrum expected from mode-rational surfaces with q=m/n. Highest Te is measured when 1/2 < q < 2/3 and the ratio of current to flux is 0.9 times the flux conserver eigenvalue. Transport analysis shows a reduction in thermal diffusivity as Te increases, differing from Bohm or open field line transport models where diffusivity increases with Te. Detailed resistive MHD simulations with the NIMROD code support the analysis of SSPX energy confinement in terms of the causal link with the q-profile, magnetic fluctuations associated with low-order mode-rational surfaces, and the quality of magnetic surfaces.
Please place with other SSPX posters.