Dynamics in plasmas with high wave intensity

Electron Cyclotron Resonance Heating (ECRH) is widely utilized in fusion research to heat plasma and drive currents within magnetic confinement devices. However, at sufficiently high injected microwave power levels, the interaction between injected electromagnetic waves and plasma may trigger nonlinear phenomena, notably Parametric Decay Instabilities (PDI). Understanding these instabilities is crucial, as they significantly affect power absorption efficiency and plasma heating distribution. In this project, the occurrence and spatial behavior of PDI in the NORTH tokamak are experimentally investigated. Using a combination of a fast-movable probe inserted into the plasma and an external antenna, signals associated with PDI are measured and analyzed. Spatial scans are performed at several radial positions within the tokamak, allowing detailed mapping and characterization of the instability across the plasma radius. This approach provides insights into how PDI evolves spatially under conditions of varying wave intensities and plasma parameters. Experimental results reveal an intriguing spatial structure of PDI within the NORTH tokamak, clearly distinguishing three characteristic regions: primary, secondary, and transitional. Each region displays unique spectral features and wave interactions, elucidating the complex nonlinear processes governing energy transfer from injected microwaves to lower-frequency ion waves. These findings enhance our understanding of wave-plasma interactions and contribute valuable knowledge toward optimizing ECRH schemes for future fusion reactors.