The Parameter Space of Magnetized Target Fusion
(aka Magneto-Inertial Fusion)

Irvin R. Lindemuth

Magnetized target fusion (MTF), aka magneto-inertial fusion (MIF), is an approach to fusion that compresses a preformed, magnetized (but not necessarily magnetically confined) plasma with an imploding liner or pusher. MTF/MIF operates in density regime in between the eleven orders of magnitude (1011) in density that separate inertial confinement fusion (ICF) from magnetic confinement fusion MCF. MTF/MIF combines the compressional heating of ICF with the magnetically reduced thermal transport and magnetically enhanced alpha heating of MCF. Compared to MCF, the higher density, shorter confinement times, and compressional heating as the dominant heating mechanism potentially reduces the impact of magnetic-field-driven instabilities. Compared to ICF, the reduced density leads to orders-of-magnitude reduction in the difficult-to-achieve areal-density parameter and a significant reduction in required implosion velocity and radial convergence, potentially reducing the deleterious effects of implosion hydrodynamic instabilities. This seminar discusses fundamental analysis and simple time-dependent modeling to show where significant fusion gain might be achieved in the intermediate density regime. The fundamental analysis [Lindemuth & Siemon, Amer. J. Phys. 77, 407 (2009)] shows that the fusion design space is potentially a continuum between ICF and MCF. Additional analysis [I. R. Lindemuth, Phys. Plas. 22, 122712 (2015)] shows that practical considerations limit the space in which ignition might be obtained. Generic time-dependent modeling [Phys. Plas. 22, 122712] addresses the key physics requirements and parameters needed (target plasma initial density, temperature, and magnetic field; implosion system size, energy, and velocity) for multiple conceptual approaches to MTF/MIF, e.g., cylindrical with axial magnetic field, spherical and cylindrical with azimuthal magnetic field. The modeling shows energy gains greater than 30 can potentially be achieved for each type of target and that high gain may be obtained at extremely low convergence ratios, e.g., less than 15, for appropriate initial conditions. The seminar also provides a non-exhaustive review of past and present MTF/MIF efforts and notes the renewed interest in MTF/MIF within the US (e.g., ARPA-E's ALPHA program) and abroad.