The physics basis for WHAM and breakeven in a Compact High Field Mirror

Cary Forest

University of Wisconsin-Madison

Wednesday, May 18, 2022


NW17-218 Hybrid

PSFC Seminars

Abstract:  In this talk I will give an overview of the design for the Wisconsin HTS Axisymmetric Mirror. The experiment has been funded by ARPA-E and is a partnership between the UW Madison, MIT and Commonwealth Fusion Systems has been formed to build and operate a compact, high-field simple mirror WHAM. Success will demonstrate a pathway to a cost-effective VNS for blanket testing and other applications requiring a large flux of 14 MeV neutrons, and also show how compact end plugs can now be built for axisymmetric tandem mirrors. It builds on recent physics breakthroughs in stability and confinement, critical technological advances in superconductivity, and the availability of high power reactor relevant heating systems. Two mirror coils are being constructed using REBCO high temperature superconducting material by CFS (17 T mirrors). Hot and high density target plasmas will be created using high frequency ECH; fast
sloshing ions will be created and energized by a novel RF heating scenario in which neutral beam injection is used to fuel ions which are then accelerated in situ to high energy by high harmonic fast waves. Quasi-stationary plasmas (plasma duration >> ion slowing down and characteristic confinement times) will be created with electron temperatures of 1 keV, average ion energies of 20 keV and a densities that that approach the plasma pressure limit.  The key physics challenges for the mirror are, as they have always been, operating with MHD and kinetic stability—our strategies for overcoming these instabilities will be discuss. The end product will be a realistic conceptual design of a low cost ($100M) break-even class axisymmetric simple mirror we call WHAM++ that will also be able to demonstrate the endplug conditions needed for energy production in tandem mirror we concept we call Hammir.  Both of these devices will employ direct energy conversion of lost power to further improve efficiency.  Finally, several lucrative off-ramps for this research have been identified that would lead to fusion neutron sources useful for academic and industrial purposes that may help accelerate progress towards fusion energy by stimulating additional investment.