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Samuel Irvine & Bernard Reman

Location: PS128

Samuel Irvine: 'Nonlinear self-consistent kinetic simulations of the anomalous Doppler instability'

The anomalous Doppler instability is a key relaxation mechanism for suprathermal electron populations in magnetic confinement plasmas. The underlying physics of this instability involves a shift from parallel to perpendicular electron motion, accompanied by the excitation of waves at frequency and wavenumber satisfying the anomalous Doppler resonance condition. The relevance of this effect in magnetic confinement plasmas is becoming increasingly apparent as diagnostics with improved time resolution are deployed. We use first principle particle in cell simulations to demonstrate the significance of this effect on fast kinetic timescales showing the existence of both a wave-wave anomalous Doppler effect as well as a secondary instability due to the resultant positive slope in the parallel electron distribution function.

Bernard Reman: 'Modelling ICE (ion cyclotron emission) via hybrid simulation of the MCI (Magneto acoustic Cyclotron Instability)'

Abstract: Suprathermal ion cyclotron emission (ICE) is detected from all large toroidal magnetic confinement fusion (MCF) plasmas, both tokamak and stellarator. Its frequency spectrum has narrow peaks at sequential cyclotron harmonics of the energetic ions at the outer midplane edge of the plasma. ICE was the first collective radiative instability driven by confined fusion-born ions observed in deuterium-tritium (D-T) plasmas in JET and TFTR, and the magnetoacoustic cyclotron instability (MCI) is the most likely emission mechanism. For a recent review, see R O Dendy and K G McClements, Plasma Phys. Control. Fusion 57 044002 (2015). ICE is proposed as a diagnostic for confined energetic ions in ITER; see K G McClements, R d’Inca et al., Nucl. Fusion 55 043013 (2015). Second generation ICE measurements are now being taken from the LHD stellarator and from the conventional aspect ratio KSTAR tokamak, and are imminent for the QUEST spherical tokamak. These measurements are taken at sampling rates far higher than for first generation ICE, in combination with multiple other advanced diagnostics. This enables fresh insights into the physics of confined energetic ions in MCF plasmas, and also into the interaction between these ions and MHD activity. Exploitation of second generation ICE measurements requires a corresponding advanced modelling capability for the emission mechanism, the MCI. Here we report MCI studies using a 1D3V hybrid code (L Carbajal et al., Phys. Plasmas 21 012106 (2014)) which simulates the selfconsistent full gyro-orbit kinetics of energetic and thermal ions, the electric and magnetic fields, and a massless neutralising electron fluid. We focus on the sub-Alfvénic regime of the MCI, for plasma conditions appropriate to ICE measurements associated with neutral beam injected ions in LHD. For the first time, we are able to follow the sub-Alfvénic MCI into the nonlinear saturated regime, thereby strengthening the link to measured LHD ICE spectra.'

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