Convective and Diffusive Energetic Particle Losses Induced by Shear Alfvén Waves in the ASDEX Upgrade Tokamak

Abstract

We present here the first phase-space characterization of convective and diffusive energetic particle losses induced by shear Alfvén waves in a magnetically confined fusion plasma. While single toroidal Alfvén eigenmodes (TAE) and Alfvén cascades (AC) eject resonant fast ions in a convective process, an overlapping of AC and TAE spatial structures leads to a large fast-ion diffusion and loss. Diffusive fast-ion losses have been observed with a single TAE above a certain threshold in the fluctuation amplitude.

‘Beam-emission spectroscopy’ diagnostics also measure edge fast-ion light

“…For example, for PDX fishbones, when an edge neutral-particle analyzer was tuned to measure high-energy ions in resonance with the mode, the signal consisted almost entirely of coherent oscillatons [21] but, at lower energies, the incoherent portion of the signal was largest [25], with a time evolution resembling the f-FIDA signal reported here. More recent examples of a mixture of coherent and incoherent losses are reported in [26,27]. In the present case, the bump in signal is about 15% of the beam emission, consistent with a rough estimate based on equation (5).…”

High-resolution gamma ray spectroscopy measurements of the fast ion energy distribution in JET 4He plasmas

“…On the diagnostics side, most of the current knowledge derives from measurements of fast ions on middlesized machines, where instabilities are driven by particles with energies in the 100 keV range, either due to neutral beam injection (NBI) or generated by radio frequency (RF) heating. Recent progress in the detection of lost ions allowed phase space characterization of the losses [2,3], while a charge exchange recombination spectroscopy technique based on fast ion D α emission (FIDA) [4] showed flattening of the fast ion profile correlated with the onset of energetic particle instabilities [5,6]. As the energy of the ions is increased towards the MeV range, such as that of α particles in a burning plasma, many diagnostics currently used for these studies on middle-sized machines show limitations and new methods need to be sought.…”

Beam ion losses due to energetic particle geodesic acoustic modes

“…Based on the design used on ASDEX Upgrade [9,10], the light pattern resulting from ions striking a fast time response (decay time ∼500 ns) scintillator is imaged by a CCD camera, allowing measurements of the pitch angle and gyroradius of the beam ions reaching the detector. Light from the scintillator is also measured by a fibre-coupled photomultiplier to allow identification of AE and other high frequency instabilities.…”