Status of the PBFA-II light ion beam fusion program

A summary of recent progress and the present status of the PBFA-II (Particle Beam Fusion Accelerator II) light-ion beam fusion program is given. An analytic theory of applied-B ion diodes has been developed that correctly predicts the diode operating points at peak power, and there is agreement between simulations and experiment for the ion beam transport to the diode axis. The anode plasma has been identified as an area for study to improve the ion beam focusing and diode impedance behavior further. An extensive array of ion beam diagnostics has been developed and proven to operate well in the harsh X-ray environment of PBFA II. Work on interpreting data from these diagnostics has provided insights into the physics of beam generation and transport and has stimulated advances in both analytic and calculational modeling of the processes. Three plasma opening switch configurations have been identified and tested. Efficient ion beam generation has been demonstrated, and a focal spot diameter of <5.5 mm at 3/4 energy has been achieved. The peak proton power density achieved on PBFA II has risen from ~0.3 TW/cm² to ~3.8 (+0.7, -0.8) TW/cm², and the total proton energy on a 1.0-cm radius target has increased from 30 kJ to 140 kJ