Stabilization of beam heated plasmas by beam modulation

TL;DR

This paper demonstrates that modulating the intensity of a beam in plasma can suppress instabilities, leading to long-term stability without feedback, with potential applications in large plasma systems.

Contribution

The authors introduce a numerical optimization method to design beam intensity profiles that suppress plasma instabilities without feedback mechanisms.

Findings

Optimized beam profiles significantly reduce plasma instabilities.

Stability persists after the beam is turned off.

Robustness against perturbations in beam profiles.

Abstract

A constant intensity beam that propagates into a stationary plasma results in a bump-on-tail feature in velocity space. This results in an instability that transfers kinetic energy from the plasma to the electric field. We show that there are intensity profiles for the beam (found by numerical optimization) that can largely suppress this instability and drive the system into a state that, after the beam has been switched off, remains stable over long times. The modulated beam intensity requires no feedback, i.e. no knowledge of the physical system during time evolution is required, and the frequency of the modulation scales approximately inversely with system size, which is particularly favorable for large plasma systems. We also show that the results obtained are robust in the sense that perturbations, e.g. deviation from the optimized beam profiles, can be tolerated without losing the ability to suppress the instability.