Speaker
Description
Future nuclear fusion reactors will be heated by neutral beam injectors (NBI) and high frequency electromagnetic waves as well as fusion born alpha particles. Consequently, a reactor relevant plasma hosts multiple energetic particle (EP) populations that will interact non-linearly between them and the thermal plasma, affecting the system stability and leading to potential harmful effects on the device performance. The present study is dedicated to the analysis of the effect of multiple EP species on the thermal plasma stability and alpha particle transport in reactor relevant configurations. In addition, the effect of NBI EP on the stability of LHD thermal plasma is explored. Linear and nonlinear simulations are performed with the gyro-fluid FAR3d code based on the JET D-T discharge #99896 and the LHD discharge 116190. The analysis indicates EPs have a stabilizing effect on thermal plasma instabilities in the linear and saturation phase. This is explained by the EP stabilizing effect on thermal plasma instabilities due to the non-reactive part of the resonance term in the dispersion relation, leading to an extraction of the plasma wave energy. For reactor relevant plasma, considering alpha particle and NBI EP populations, the simulations show important changes on the internal kink and AE stability compared to single EP species, indicating the important role of the nonlinear interaction between different EP populations. Particularly, multiple EP species show significant alpha particle losses in configurations with improved internal kink stability following single EP species. This result may indicate present day experiments with negligible alpha particle populations cannot fully explore the stability of reactor relevant plasma. Another consequence of the present study applies to the alpha power build-up in burning plasma, notably during the ramp-up phase. The interaction between a rather low alpha particle population with current driven modes near the q=1 surface and in the presence of other EP population could lead to enhanced losses and lower heating power of the alpha particles, reducing the device performance in the flat-top phase. In addition, the decrease of the interchange mode growth rate with respect to the EP density in the LHD case may help to understand why inward shifted configurations heated by NBI show lower MHD activity compared to Mercier criteria predictions.
| Presentation type | Oral |
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