Analysis of Runaway-Electron-Driven Whistler Waves on MST

Abstract

This thesis presents a detailed linear and quasilinear analysis of runaway-electron-driven whistler waves using experimental data from shot 1220511040 on the Madison Symmetric Torus (MST). A key novel aspect of this work is the investigation of the previously overlooked normal Doppler resonance (n=+1), which offers a new perspective on wave-particle interactions. The analysis concludes that while both anomalous and normal Doppler resonances can be excited by runaway electrons, they correspond to distinct wave propagation characteristics: the anomalous Doppler branch implies forward-propagating waves, whereas the normal Doppler branch implies backward-propagating waves. Theoretically, the normal Doppler branch is subject to damping and requires an additional source of free energy for net growth. This work proposes that the spatial gradient of the runaway electron density can provide this necessary free energy, enabling the instability and potentially explaining key experimental observations.