Fast particle-driven ion cyclotron emission (ICE) in tokamak plasmas and the case for an ICE diagnostic in ITER

Abstract

Fast particle-driven waves in the ion cyclotron frequency range (ion cyclotron emission or ICE) have provided a valuable diagnostic of confined and escaping fast ions in many tokamaks. This is a passive, non-invasive diagnostic that would be compatible with the high radiation environment of deuterium-tritium plasmas in ITER, and could provide important information on fusion -particles and beam ions in that device. In JET, ICE from confined fusion products scaled linearly with fusion reaction rate over six orders of magnitude and provided evidence that -particle confinement was close to classical. In TFTR, ICE was observed from super-Alfvénic -particles in the plasma edge. The intensity of beam-driven ICE in DIII-D is more strongly correlated with drops in neutron rate during fishbone excitation than signals from more direct beam ion loss diagnostics. In ASDEX Upgrade ICE is produced by both super-Alfvénic DD fusion products and sub-Alfvénic deuterium beam ions. The magnetoacoustic cyclotron instability (MCI), driven by the resonant interaction of population-inverted energetic ions with fast Alfvén waves, provides a credible explanation for ICE. One-dimensional particle-in-cell (PIC) and hybrid simulations have been used to explore the nonlinear stage of the MCI, thereby providing a more exact comparison with measured ICE spectra and opening the prospect of exploiting ICE more fully as a fast ion diagnostic. For realistic values of fast ion concentration, nonlinearly saturated ICE spectra in these simulations closely resemble measured spectra. The PIC/hybrid approach should soon make it possible to simulate the nonlinear physics of ICE in full toroidal geometry. Emission has been observed at a wide range of poloidal angles, so there is flexibility in the location of ICE detectors. Such a detector could be implemented in ITER by installing a small toroidallyorientated loop near the plasma edge or by adding a detection capability to the ICRH antennae.

Observations of core ion cyclotron emission on ASDEX Upgrade tokamak

“…The possibility that this emission could be excited by fusion products at the location of their birth, in the plasma core, raises the intriguing possibility of using an ICE diagnostic as a passive non-perturbing method to study fusion born alpha particles in D-T burning fusion reactors such as ITER and DEMO. Note that a similar case has been made previously by McClements et al 1 , our paper strengthens their case with core ICE observations. ICE is a frequently observed phenomenon in toroidal magnetized plasma devices such as tokamaks and stellarators [2][3][4][5][6][7][8] .…”

Energetic particle-driven compressional Alfvén eigenmodes and prospects for ion cyclotron emission studies in fusion plasmas

“…A similar approach to CAE instabilities was developed in [53], where the slow instability limit was implied although no applications to ICE in experiments were made. Other papers dealing with ICE instabilities were limited to the strong instability as discussed below [10,26] (see also recent publications on those interactions in strong instability limit [13,14] and in earlier papers [12,15]). More recent formulations of CAE growth rates in applications to STs analyze the growth rate expressions accounting for EP drift frequency contributions which carefully address not only the cyclotron but EP drift frequencies [54,55].…”

“…The interactions between oscillations and the fast ions included realistic drift ion motion [12]. The homogeneous ICE theory was recently reviewed in [13,14]. Nevertheless, the limit of the homogeneous plasma allowed to make the case for ICE applications to tokamaks as a diagnostic originally proposed in [6,15] (see also recent review [16]).…”

Core plasma ion cyclotron emission driven by fusion-born ions

“…The source of fast tritium is, again, D-D fusion reactions. This result is important as it strengthens the case of an ICE-based passive non-intrusive diagnostic to monitor the presence of fusionborn alpha particles in D-T magnetized fusion plasmas in JET, ITER, CFETR, or DEMO [2].…”