Progress in the SSPX Spheromak





Citation of Original Publication

McLean, H S, Woodruff, S, Hill, D N, Bulmer, R H, Cohen, B I, Hooper, E B, Moller, J, Ryutov, D D, Stallard, B W, Wood, R D, Holcomb, C T, Jarboe, T R, and Romero-Talamas, C. 2003. "Progress in the SSPX Spheromak". United States.


This is a work of the United States Government. In accordance with 17 U.S.C. 105, no copyright protection is available for such works under U.S. Law.
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The spheromak [1], with its simply connected geometry, holds promise as a less expensive fusion reactor. It has reasonably good plasma beta and can be formed and sustained in steady state with a magnetized coaxial plasma gun. The Sustained Spheromak Physics Experiment [2] (SSPX) shown in Fig. 1 was constructed to investigate the key issues of magnetic field generation and energy confinement. In addition to the coaxial gun, nine magnetic field coils are utilized to shape the vacuum magnetic flux. This flexibility allows operation in many different regimes producing very different plasma characteristics. Pulse length is extended and magnetic field strength is increased. Improved surface conditioning produces plasmas with low impurity content, and higher electron temperature, Te. Electron heat transport within the separatrix is reduced by a factor of 4. The results strongly suggest the existence of closed flux surfaces even though the plasma is connected to the coaxial source. The CORSICA Grad-Shafranov 2-d equilibrium code [2] with data from edge magnetic probes along with Te and electron density ne from Thomson scattering is used to calculate internal profiles: normalized current λ= µ₀J/B, safety factor = q, ohmic heating, thermal energy density, and thermal diffusivity =χe. Ohmic heating is calculated by assuming spatially constant Spitzer resistivity with Zeff = 2.3 estimated by VUV spectroscopy.