Alfvén eigenmode stability in a JET afterglow deuterium plasma and projections to deuterium–tritium plasmas

Abstract

Performance of fusion devices strongly relies on good confinement of energetic particles. Therefore, investigation of energetic particle transport by magneto-hydrodynamic instabilities is one of the key aspects in development of plasma scenarios. Alfvénic instabilities in particular can lead to significant losses of alpha particles essential for plasma self-heating. A so-called afterglow scheme has been developed to study destabilization of Alfvén Eigenmodes (AEs) by alpha particles and associated energetic particle transport on the JET tokamak. In this work, the linear stability of AEs is discussed for the partial afterglow phase in a JET deuterium plasma discharge and for the full afterglow phase in a projected deuterium-tritium plasma. Thanks to recent upgrades in the tokamak transport code TRANSP, one can account for contributions of different energetic particle species to mode stability. Analysis of deuterium plasmas shows that AE growth rates are extremely sensitive to energy and distribution of fast ions. An increase in fast ion energy can lead to more unstable AEs. In the afterglow phase of projected deuterium- tritium plasmas, energetic particles mostly drive the AEs. However, drive by alpha particles is comparable to the one by beam ions and their contribution to the net growth rate might be hard to separate. According to the discussed projections, destabilization of AEs might be ineffective because the background plasma damping significantly exceeds the energetic particle drive. In this case development of an alternative plasma scenario that allows to overcome such damping would be required in future experiments.

Fast ion transport by sawtooth instability in the presence of ICRF–NBI synergy in JET plasmas

“…Computed neutron rate is two times higher than measured one because most of the neutrons are still produced by the beam-target fusion reaction, however it reproduces main trends observed in the experiment. Uncertainties entering the particle balance equation and their contribution to the simulation results are discussed in more detail in [29].…”

NBI optimization on SMART and implications for scenario development

“…Based on the results on NBI optimization from section 4, simulations are first limited to predicting expected values of electron and ion temperature for a prescribed plasma rotation in the current flat-top phase. To reduce uncertainties in the predictive runs, electron density and plasma rotation are prescribed, as their predictions are presently unreliable when multiple transport channels are simultaneously activated in TRANSP predictions [41]. Density and rotation values are based on available results from other compact (or spherical) tokamaks with parameters similar to SMART, such as LTX [42,43] and Globus-M [44].…”