Autoresonance in Mirror Machines

When the frequency of a chirped driving force passes through the linear frequency of an anharmonic oscillator, a continuous phase locking is established between the system and the driving force that controls the system’s state without the need for feedback. The driving amplitude can be small but should exceed a threshold value. The key point is that the system adjusts its energy state to preserve the resonance, provided the chirping is sufficiently slow. This effect is known as autoresonance (AR) and has been widely studied in various physical systems, including diocotron modes in a pure electron plasma, stimulated Raman scattering, cyclotrons, Malberg-Penning traps for antihydrogen trapping, ion-acoustic waves, and BGK modes. However, it has never been investigated in magnetic mirrors.



In the talk, I will show how to apply AR in magnetic mirrors, focusing on an application for the quick removal of a large fraction of fusion ash (e.g., α particles in D-T reactors) from a mirror-based fusion reactor. The idea is to autoresonantly increase the longitudinal energy of the α particles until they escape through the loss cone. As a result, most of the α particles near the machine’s center are removed from the mirror. The theoretical understanding is based on an analogy to the driven pendulum via the guiding center approximation, and agrees with the numerically solved, full 3D dynamics. Monte Carlo simulations quantify the method’s efficiency, which is essential for the reactor's continuous operation.