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Spheromaks with lifetimes of 1 ms are produced in the CTX experiment. This paper describes the diagnostics and measurements on plasmas which, for CTX-produced plasmas, are the hottest and longest-lived discharges using a solid copper flux conserver. These spheromaks are formed using a static hydrogen background gas filling the entire vacuum system before the discharge. The density rapidly decays in 150–300 μs from an initial value of (1–3) × 1014 cm−3 to a steady-state plateau with a value of (1–4) × 1013cm−3,determine d by the pressure of the gas fill. A multi-point Thomson scattering system measures the radial profiles of electron temperature and density. Peak temperatures of over 40 eV are observed, and the average temperature increases in time by Ohmic heating from 15 eV to over 30 eV. Equilibrium models for the magnetic field structure are used to calculate values of peak local beta (8–13%), volume-averaged beta (3–8%), and engineering beta (10–25%). The operation with a filling gas results in a reduction of the impurity radiation power as measured by spectroscopy. Improved vacuum practices, discharge cleaning and the use of the static gas fill have resulted in discharges in which the radiation power loss is not dominating the energy balance late in time. Particle loss and the associated ionization and heating of the neutral particles required to maintain the density plateau appear to be the major energy loss processes in the spheromak.

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In the FRX-C/T experiment [Proceedings of the 9th Symposium for Engineering Problems of Fusion Research (IEEE, New York, 1981), p. 1751], field-reversed configuration (FRC) plasmas have been formed in, and launched from, a field-reversed theta-pinch source and subsequently trapped in an adjacent confinement region. No destructive instabilities or enhanced losses of poloidal flux, particles, or thermal energy are observed for FRC total trajectories of up to 16 m. The observed translation dynamics agree with two-dimensional magnetohydrodynamic (MHD) simulations. When translated into reduced external magnetic fields, FRC’s are observed to accelerate, expand, and cool in partial agreement with adiabatic theory. The plasmas reflect from an external mirror and after each reflection, the axial kinetic energy is reduced by approximately 50%. Because of this reduction, FRC’s are readily trapped without the need of pulsed gate magnet coils.

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