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Sustained Spheromak Physics Experiment

The Sustained Spheromak Physics Experiment, SSPX, will study spheromak physics with particular attention to energy confinement and magnetic fluctuations in a spheromak sustained by electrostatic helicity injection. In order to operate in a low collisionality mode, requiring T e > 100 eV, vacuum techniques developed for tokamaks will be applied, and a divertor will be used for the first time in a spberomak. The discharge will operate for pulse lengths of several milliseconds, long compared to the time to establish a steady-state equilibrium but short compared to the L/R time of the flux conserver. The spheromak and helicity injector ("gun") are closely coupled, as shown by an ideal MHD model with force-free injector and edge plasmas. The current from the gun passes along the symmetry axis of the spheromak, and the resulting toroidal magnetic field causes the safety factor, q , to diverge on the separatrix. The q -profile depends on the ratio of the injector current to spheromak current and on the. magnetic flux coupling the injector to the spheromak. New diagnostics include magnetic field measurements by a reflectometer operating in combined 0- and X-modes and by a transient internal probe (TIP).