FRX-L: A High-density Field Reversed Configuration

We present the progress on the high-density Field Reversed Configuration (FRC) experiment (FRX-L) presently being studied at LANL. FRX-L is a magnetized-target injector for MTF experiments; the experimental setup not only allows us to diagnose the plasma during formation and in situ but also to translate it into a hollow aluminum liner (flux conserver) where compression would take place. Subsequent heating of the FRC plasma by compressing it inside this imploding flux conserver should allow access to fusion conditions. The actual compression of the plasma to fusion conditions will be performed at the Shiva-Star facility at AFRL. Diagnosing the FRC plasma during formation, translation, and compression is challenging due to the short timescales, high energy densities, high magnetic fields, and restricted access. Our goal is an FRC with density n 10^17 cm^-3, T_i=T_e 100-300 eV, external B 5 T, and a lifetime of 10-20μs. We will present results to date on the formation of the high-density FRC, including the Pre-Ionization (PI) phase. From our previous experience, the PI process is crucial for good FRC formation, and not well understood. The hydrogen gas fill is ionized by the ringing theta coil discharge (θ-PI) technique, which applies a rapidly oscillating axial magnetic field superimposed upon the slower-timescale magnetic bias field, of comparable magnitude. The PI process occurs just prior to applying a much (10 X) higher reverse field that causes the frozen-in field lines to radially contract and form the closed field lines for the FRC.