The physics basis for a Q≈1 high-field, compact, axisymmetric mirror*

A public-private team has been formed to pursue the axisymmetric mirror path to fusion: ARPA-E has funded the construction of an high temperature superconducting prototype called the Wisconsin HTS Axisymmetric Mirror (WHAM), that involves the UW Madison, a new startup company Realta Fusion, MIT and CFS. The 3 step development path begins with a small mirror, WHAM1.0, to establish MHD stable plasmas relying on vortex and FLR stabilization by fast ions of a high mirror ratio simple mirror, a reactor scale simple mirror WHAM++ that uses 100+ keV neutral beam injection to validate the confinement, macro and microstability in a simple mirror, and finally a tandem mirror that uses two WHAM++ configurations with ≈1MeV, RF heated ions for the end plugs of a HTS Axisymmetric Magnetic Mirror Reactor (Hammir). This talk will review the physics basis for WHAM++ and address the TRLs for magnets, heating sytems, MHD techniques, and microstability for mirror distribution functions. I will rely on bounce averaged drift kinetic/Fokker-Plank solutions for mirror confined fast ions that show Q>1 is acheivable in a simple mirror with mirror ratio > 10. Direct energy recovery greatly improves prospects even for electrical breakeven. MHD stability will come from FLR stabilization for m>1, and plasma shaping, divertors, vortex and feedback stabilization at high β for m=1. Microinstabilty will rely upon sloshing ions and high mirror ratio. A direct energy convertor appropriate for the axisymmetric exhaust of the mirror should be capable of recovering more than 50% of the lost energy thereby increasing the the gain even further. Breakeven is possible even for small energy input (several MWs). Applications of WHAM++ include use as a blanket test facility, a minor actinide burner and as a source of efficient process heat. Power production for an industrial scale will be with Hammir. *This work has been supported by ARPA-E, the Wisconsin Alumni Research Foundation and CFS.