Overview of Recent Results from SSPX
Author: R. D. Wood
Requested Type: Poster Only
Submitted: 2006-12-18 18:28:31
Co-authors: D.N. Hill, H.S. McLean, E.B. Hooper, T.A. Casper, B.I. Cohen, L.L. LoDestro, J.M. Moller, L.D. Pearlstein, C.A. Romero-Talamás
Lawrence Livermore National Laboratory
7000 East Ave.
Livermore, CA 94550
The SSPX is a 1m diameter magnetized coaxial gun-driven experiment designed to explore the physics of confinement and magnetic field generation. Here we provide an overview of the advances in understanding SSPX field generation and confinement and in modeling spheromak physics with improved comparisons to experimental data. Recent results from the SSPX spheromak experiment demonstrate the potential for obtaining good energy confinement (Te > 350eV and radial electron thermal diffusivity comparable to tokamak L-mode values) in a self-organized toroidal plasma. Improved confinement results are obtained by increasing both gun flux and current to increase the magnetic field while keeping a relatively flat current profile to minimize magnetic fluctuations. A newly installed solid-state programmable modular capacitor bank is expected to produce plasmas with higher magnetic fields and longer pulses which should lead to even higher electron temperatures (Te > 500eV).
At temperatures above 300eV, it becomes possible to use modest (1.8MW) amounts of neutral beam injection (NBI) auxiliary heating to significantly change the power balance in the core plasma, making it an effective tool for improving transport analysis. Initial modeling results show that a substantial fraction of the injected beam, of order 70%, is confined as fast ions, which is sufficient to raise the electron temperature and total plasma pressure in the core by a factor of two.
Magnetic field build up experiments using the modular capacitor bank have produced discharges (long formation) with the highest edge poloidal fields measured on SSPX and discharges (multi-pulse) that continue to build magnetic field in a stepwise manner. The ratio of Bp/Igun for the multi-pulse discharges (~0.9T/MA) exceeds the value of Bp/Igun=0.65T/MA obtained with a standard discharge (fast formation followed by sustainment discharge). The higher ratio with the new injected current waveforms may reflect the longer total formation pulse duration (building to higher field due to longer current pulse) than previous discharges, as suggested by simulations. In the near future, another 15 modules of the modular bank will be ready for operations. Future experiments will include adding more pulses to the multi-pulse waveform, longer formation pulse, long pulse sustainment and mega-ampere injected current discharges.
* Work performed under the auspices of the US DOE by University of California Lawrence Livermore National Laboratory under contract W–7405–ENG–48.