Simulation of the AE activity in JET D-T discharges using a Landau closure model*

The plasma in future nuclear fusion reactors will be heated by neutral beam injectors (NBI) and high frequency electromagnetic waves as well as fusion born alpha particles. Energetic particles (EPs), with energies up to two orders of magnitude larger than the thermal plasma, can trigger Alfven Eigenmodes (AE) and induce harmful EP losses, reducing the plasma heating efficiency and the economical viability of the reactor. The present study is dedicated to analyze the AE activity in JET D-T discharges, the closest experiment to reactor-like operation. There, AEs are driven by the combined effect of tangential NBIs and ion cyclotron resonance heating (ICRH) driven EP. Linear and nonlinear simulations are performed with the gyro-fluid FAR3d code to reproduce the AE activity observed in the discharge #99896, including the effect of multiple EP populations. The linear simulations reproduce the AE activity in the frequency range of 150-180 kHz, identifying unstable n=2 to 4 TAEs with frequencies between 152 to 164 kHz at the inner plasma region, triggered by highly energy passing Deuterium populations injected by the tangential NBIs, further accelerated by the effect of the ICRH up to ~1 MeV. In addition, low frequency modes below 40 kHz are identified as fish-bones, triggered by energetic trapped Hydrogen induced by the ICRH. On the other hand, the alpha density is too small to destabilize AEs in the experiment. Nonetheless, increasing artificially the alpha density by one order of magnitude, an n=1 BAE with a frequency around 60 – 80 kHz can be destabilized in the inner plasma region. Nonlinear simulations including single or multiple EP species are performed to study the AEs saturation phase. Important nonlinear couplings are identified between different EP populations along with the generation of zonal structures that may affect the performance of future fusion reactors.