Energization of Proton via Beam-Driven Ion Bernstein Waves in p11B Plasmas

TL;DR

This paper demonstrates a nonlinear mechanism using Particle-In-Cell simulations that efficiently energizes background protons in p11B plasmas through ion Bernstein waves, potentially enhancing fusion reactions.

Contribution

It reveals a nonlinear wave cascade process that preferentially transfers energy to background protons in p11B plasmas, advancing understanding of ion energization in fusion.

Findings

Energy transfer to protons is dominant in nonlinear stage.

Ion Bernstein waves facilitate proton energization.

Non-Maxwellian energetic proton populations are generated.

Abstract

Energizing background ions plays a pivotal role in all forms of thermal nuclear fusion, as it can increase the fusion reaction rate without affecting the overall mechanical equilibrium. This is particularly critical for p11B fusion due to its exceptionally high operating temperature and substantial energy losses from bremsstrahlung radiation. Here, we report a nonlinear mechanism that efficiently transfers the energy of injected heating beams to background protons in p11B mixed plasmas, via fully kinetic Particle-In-Cell (PIC) simulations. When a proton neutral beam is injected into p11B plasmas, it triggers the excitation of ion Bernstein waves (IBWs) at harmonics of the proton cyclotron frequency. In the initial linear stage, the energy channels to background electrons and protons might be comparable, consistent with theoretical model for the energy transfer. However, in the latter nonlinear stage, the dominant channel transfers to background protons, generating a non-Maxwellian population of energetic protons. This transition is driven by a nonlinear spectral cascade of IBWs toward lower frequencies and longer wavelengths, which strengthens wave proton coupling while suppressing wave electron coupling.