Transport and fluctuations in high temperature spheromak plasmas
- Lawrence Livermore National Laboratory, Mail Stop L-637, 7000 East Avenue, Livermore, California 94550 (United States)
Higher electron temperature (T{sub e}>350 eV) and reduced electron thermal diffusivity ({chi}{sub e}<10 m{sup 2}/s) is achieved in the Sustained Spheromak Physics Experiment (SSPX) by increasing the discharge current=I{sub gun} and gun bias flux={psi}{sub gun} in a prescribed manner. The internal current and q=safety factor profile derived from equilibrium reconstruction as well as the measured magnetic fluctuation amplitude can be controlled by programming the ratio {lambda}{sub gun}={mu}{sub 0}I{sub gun}/{psi}{sub gun}. Varying {lambda}{sub gun} above and below the minimum energy eigenvalue={lambda}{sub FC} of the flux conserver ({nabla}xB-vector={lambda}{sub FC}B-vector) varies the q profile and produces the m/n=poloidal/toroidal magnetic fluctuation mode spectrum expected from mode-rational surfaces with q=m/n. The highest T{sub e} is measured when the gun is driven with {lambda}{sub gun} slightly less than {lambda}{sub FC}, producing low fluctuation amplitudes (<1%) and 1/2<q<2/3. Transport analysis shows a reduction in {chi}{sub e} as T{sub e} increases, differing from Bohm or open field line transport models where {chi}{sub e} increases with T{sub e}. Detailed resistive magnetohydrodynamic simulations with the NIMROD code support the analysis of 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.
- OSTI ID:
- 20783130
- Journal Information:
- Physics of Plasmas, Vol. 13, Issue 5; Other Information: DOI: 10.1063/1.2192469; (c) 2006 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 1070-664X
- Country of Publication:
- United States
- Language:
- English
Similar Records
Energy confinement and magnetic field generation in the SSPX spheromak
Modeling the Effects of (lambda)-gun on SSPX Operation: Mode Spectra, Internal Magnetic Field Structure, and Energy Confinement