Numerical simulation of fast ion loss detector measurements for fishbones on JET

Since the last IAEA Conference JET has been in operation for one year with a programmatic focus on the qualification of ITER operating scenarios, the consolidation of ITER design choices and preparation for plasma operation with the ITER-like wall presently being installed in JET. Good progress has been achieved, including stationary ELMy H-mode operation at 4.5 MA. The high confinement hybrid scenario has been extended to high triangularity, lower ρ * and to pulse lengths comparable to the resistive time. The steady-state scenario has also been extended to lower ρ * and ν * and optimized to simultaneously achieve, under stationary conditions, ITER-like values of all other relevant normalized parameters. A dedicated helium campaign has allowed key aspects of plasma control and H-mode operation for the ITER non-activated phase to be evaluated. Effective sawtooth control by fast ions has been demonstrated with 3 He minority ICRH, a scenario with negligible minority current drive. Edge localized mode (ELM) control studies using external n = 1 and n = 2 perturbation fields have found a resonance effect in ELM frequency for specific q 95 values. Complete ELM suppression has, however, not been observed, even with an edge Chirikov parameter larger than 1. Pellet ELM pacing has been demonstrated and the minimum pellet size needed to trigger an ELM has been estimated. For both natural and mitigated ELMs a broadening of the divertor ELM-wetted area with increasing ELM size has been found. In disruption studies with massive gas injection up to 50% of the thermal energy could be radiated before, and 20% during, the thermal quench. Halo currents could be reduced by 60% and, using argon/deuterium and neon/deuterium gas mixtures, runaway electron generation could be avoided. Most objectives of the ITER-like ICRH antenna have been demonstrated; matching with closely packed straps, ELM resilience, scattering matrix arc detection and operation at high power density (6.2 MW m −2) and antenna strap voltages (42 kV). Coupling measurements are in very good agreement with TOPICA modelling.

Section: Fast Particle/burning Plasma Physicsmentioning

confidence: 70%

Section: Fast Particle/burning Plasma Physicsmentioning

confidence: 99%

Overview of JET results

Paméla

Ongena²,

Contributors³

2011

“…Previous efforts [24][25][26] have utilized forward and backward time integration techniques to observe overlapping phase-space regions of interaction [27]. This report describes a more thorough methodology in which forward modeled particles are fully tracked to the detector geometry after biasing against the distribution of particles reverse integrated from the detector.…”

Section: Introductionmentioning

confidence: 99%

Simulating energetic particle losses in JET plasmas with a reverse integration biasing scheme

Bonofiglo¹,

Podestà²,

White³

et al. 2022

An integrated energetic particle transport model has been constructed in JET plasmas constrained by experimental fast ion loss measurements. The model incorporates a synthetic fast ion loss detector identical to JET's thin-foil Faraday cup fast ion loss detector array. The loss model combines analyses from the TRANSP and ORBIT-kick codes with enhanced features for producing the synthetic diagnostic. Extensions to the ORBIT code framework allow a full-orbit representation within the vacuum region that can map particles directly to an installed detector geometry. Since synthetic fast ion loss detectors are plagued by weak loss statistics, a novel reverse integration biasing scheme has been implemented to boost computational efficiency. The model is validated against experimental loss measurements induced by long-lived kink modes and is found to be in good agreement. This confirms the development of a fully integrated transport/loss model which can be quantitatively verified against experiment allowing for future validation and predictive studies. The model is particularly useful for more complicated plasma scenarios that involve multiple fast ion species such as JET's 2021 DT-campaign.

“…This is a well diagnosed discharge that has been previously documented for the study of fishbonerelated fast ion losses with a scintillator probe detector [24,25]. The main discharge characteristics and experimental findings are repeated below for convenience, for further details the reader is referred to [24].…”

Section: Experimental Observations and Simulation Setupmentioning

confidence: 87%

“…Here, the radial eigenfunctions are computed by the linear MHD code MISHKA-1 [32], which solves the ideal incompressible MHD equations. To reproduce a typical fishbone cycle, the obtained eigenfunctions are scaled with a time dependent amplitude and frequency that match the experimentally observed values, using the same procedure as in [24,25]. The amplitude is specified through a third order polynomial as follows.…”

Section: Experimental Observations and Simulation Setupmentioning

confidence: 99%

Study of fast-ion transport induced by fishbones on JET

Thun

Salmi²,

Perona

et al. 2012

Self Cite

Abstract. The impact of fishbone oscillations onto a confined fast ion population is simulated for a JET plasma and benchmarked against experiment quantitatively with the help of neutron rate measurements. The transient drops in volume integrated neutron emission are found to be mainly caused by the spatial redistribution of the (neutral beam injected) fast ion population confined in the plasma rather than by fast ion loss. The simulations yield a quadratic dependence of the neutron drop on the fishbone amplitude.It is found that the simulations are able to correctly reproduce the magnitude of the experimentally observed drop in volume integrated neutron emission to within a factor 2. Furthermore, frequency chirping is found to be important. Omitting the fishbone frequency chirp in the simulations reduces the magnitude of the neutron rate drop (and hence fast ion redistribution) to about half its original value.