Proton ring formation studies on the Cornell field-reversed ion ring experiment FIREX

Summary form only given. The goal of FIREX is to produce a field-reversed ring of greater than 500 keV protons. The ring is formed by axial cusp injection into a solenoid of an annular beam from a magnetically-insulated ion diode driven by a 1 MV, 800 kA, 150 ns pulser. The first phase of experiments using a passive flashover proton source is now complete. At 90% charge of the FIREX pulse power, the diode produces 12 mC of protons over 120 ns, while the voltage decreases from 850 to 550 kV. These protons are injected through the cusp into a 6 kG solenoid to form a ring. Diagnosis of ring formation with arrays of magnetically-insulated Faraday cups show that 6 mC are in the ring at 100 cm axial location in the solenoid, in agreement with simulations using the quasineutral FIRE code (1). However, the radial distribution of the ring protons differs significantly from the simulations, and is dependent on the pressure of the neutral hydrogen gas fill that is used in the solenoid to provide beam-formed plasma for charge neutralization of the ring.