Current Drive and Alpha-Channeling-Driven Rotation *

The electric field associated with a planar electrostatic wave has no average momentum, and thus as the wave damps, the momentum of the plasma has to be conserved. How, then, can waves be used to extract charge and drive currents, both of which rely on transferring momentum to the plasma? We show how wave-mediated momentum exchange between nonresonant and resonant particles can drive net currents in spite of the constraint [1]. This momentum-exchange current drive can provide a possible magnetogenesis mechanism in astrophysical settings [2]. Applying our results to the wave-mediated diffusion of hot alpha particles in a magnetized plasma, we show that, for some waves, the hot ion charge is not extracted, but is instead cancelled by a return current in the nonresonant particles [3]. This cancellation current is analogous to the zeroth-order cancellation of cross-field currents in classical transport [4], and analogies with collisional rotation relaxation [5] will be discussed. Finally, we show how spatial wave structure can enable charge extraction. This charge extraction in turn permits ExB rotation to be driven by alpha channeling, providing a possible path to hot-ion-mode fusion. 

[1] I. E. Ochs and N. J. Fisch, Momentum-Exchange Current Drive by Electrostatic Waves in an Unmagnetized Collisionless Plasma, Phys. Plasmas, 27, 062109 (2020). [2] I. E. Ochs and N. J. Fisch, Magnetogenesis by Wave-driven Momentum Exchange, ApJ 905, 13 (2020). [3] I. E. Ochs and N. J. Fisch, Nonresonant Diffusion in Alpha Channeling, PRL 127, 025003 (2021). [4] I. E. Ochs and N. J. Fisch, Favorable Collisional Demixing of Ash and Fuel in Magnetized Inertial Fusion, PRL 121, 235002 (2018). [5] E. J. Kolmes et al., Radial Current and Rotation Profile Tailoring in Highly Ionized Linear Plasma Devices, Phys. Plasma 26, 082309 (2019).