Plasma-Wave Interactions

Most tokamaks use microwaves for plasma heating. This heating takes place at a specific resonance location in the plasma centre at the electron cyclotron resonance layer. Since plasmas are highly non-linear media, high-amplitude waves may couple to other plasma waves before reaching the plasma centre.

Originally, such effects were not expected at the power levels used for heating magnetically confined plasmas. However, our research at TEXTOR, ASDEX Upgrade, and Wendelstein 7-X has demonstrated that microwave heating beams can produce a variety of plasma waves near half the frequency of the microwave heating frequency.

This effect is currently being investigated at ASDEX Upgrade and Wendelstein 7-X. Additionally, DTU is constructing the Plasma wAve Cavity Experiment (PACE) device in the PPFE labs in order to perform dedicated experiments to improve the understanding of this nonlinear dynamics.

Schematic of microwave decay and scattering
Numerical particle-in-cell simulations of non-linear generation of plasma waves