Full conversion from ohmic to runaway electron driven current via massive gas injection in the TCV tokamak

Decker, J.; Papp, G.; Coda, S.; Duval, B. P.; Sheikh, U.; Blanchard, P.; Choi, D.; Galperti, C.; Calacci, L.; Carnevale, D.; Ficker, O.; Gobbin, M.; Labit, B.; Macúšová, E.; Mlynář, J.; Plyusnin, Victor F.; Sauter, O.

doi:10.1088/1741-4326/ac544e

Cited by 7 publications

(4 citation statements)

References 58 publications

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“…The formation of a nominal RE beam on AUG and TCV is achieved via the injection of impurities into the plasma, as detailed in [9,10]. Low density plasmas are used on both machines, with addition ECRH heating being applied on AUG to generate the seed population.…”

Section: Benign Termination Scenariomentioning

confidence: 99%

Benign termination of runaway electron beams on ASDEX Upgrade and TCV

Sheikh,

Decker,

Hoppe

et al. 2024

Plasma Phys. Control. Fusion

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This paper discusses the development of a benign termination scenario for runaway electron (RE) beams on ASDEX Upgrade and TCV. A systematic study revealed that a low electron density (ne) companion plasma was required to achieve a large MHD instability, which expelled the conﬁned REs over a large wetted area and allowed for the conversion of magnetic energy to radiation. Control of the companion plasma ne was achieved via neutral pressure regulation and was agnostic to material injection method. The neutral pressure required for recombination was found to be dependent on impurity species, quantity and RE current. On TCV, ne increased at neutral pressures above 1 Pa, indicating that higher collisionality between the REs and neutrals may lead to an upper pressure limit. The conversion of magnetic energy to radiated energy was measured on both machines and a decrease in eﬃciency was observed at high neutral pressure on TCV. The benign termination technique was able to prevent any signiﬁcant increase in maximum heat ﬂux on AUG from 200 to 600 kA of RE current, highlighting the ability of this approach to handle fully formed RE beams.

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Section: Benign Termination Scenariomentioning

confidence: 99%

Benign termination of runaway electron beams on ASDEX Upgrade and TCV

Sheikh,

Decker,

Hoppe

et al. 2024

Plasma Phys. Control. Fusion

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“…In the time-asymptotic simulations, no radial transport of electrons has been added, and so, the confinement time of runaway electrons in these simulations corresponds to an overestimated, ideal confinement time. Moreover, recent studies performed in TCV conclude that ECRH/CD tend to degrade the confinement of runaway electrons, leading to their expulsion from the plasma [62]. Therefore, additional LUKE simulations have been performed, removing part of the runaway electron domain in velocity space, corresponding to momentum p ⩾ p crit , with p crit = m e c(E ∥ /E crit − 1) −1/2 [61].…”

Section: Comsol-luke Simulations Of Experimental Casesmentioning

confidence: 99%

Impact of microwave beam scattering by density fluctuations on the electron–cyclotron power deposition profile in tokamaks

Cazabonne,

Coda,

Decker

et al. 2024

Nucl. Fusion

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Electron-Cyclotron waves are a tool commonly used in tokamaks, in particular to drive current. Their ability to drive current in a very localized manner renders them an optimal tool for MHD mode mitigation. However, such applications require high accuracy and good control of the power deposition location to efficiently target the magnetic islands. It has been indirectly observed that the suprathermal electron distribution, resulting from the wave absorption, is broader than what is expected from experimentally-constrained forward drift-kinetic modeling. The present paper explores the possibility that beam scattering through the turbulent edge of the plasma may explain this observed discrepancy. In particular, full-wave studies exhibit three beam broadening regimes, from superdiffusive to diffusive, with an intermediate regime characterized by a Lorentzian beam profile with a slightly increased full-width at half maximum with respect to the quiet plasma case. In the Tokamak à Configuration Variable, dedicated plasma scenarios have been developed to test this hypothesis. A realistic worst-case fluctuation scenario falls into this intermediate beam broadening regime. By comparing the experimental hard X-ray emission from suprathermal electron Bremmstrahlung with the emission calculated by coupling a full-wave model to a Fokker-Planck solver, it is shown that that, in the tested cases, the beam broadening is not sufficient to explain the aforementioned discrepancy between simulation and experiment and that another mechanism must play the main role in broadening the suprathermal electron distribution.

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“…For ITER, this would mean that the confinement of EPs in the core could be maintained for a significant time after the TQ. Core confinement of a RE beam for up to 1 s has been observed at the TCV tokamak [83,84], where the RE scenario explicitly relies on the survival of a pre-disruption suprathermal electron seed. We have to note that it is not yet settled whether core confinement is expected in ITER, as some simulations suggest core stochastization leading to runaway loss [85,86].…”

Section: Alpha-driven Tae Mode Evolution In Mitigated Iter Plasma Dis...mentioning

confidence: 99%

The impact of fusion-born alpha particles on runaway electron dynamics in ITER disruptions

et al. 2023

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In the event of a tokamak disruption in a D-T plasma, fusion-born alpha particles take several milliseconds longer to thermalise than the background. As the damping rates drop drastically following the several orders of magnitudes drop of temperature, Toroidal Alfvén Eigenmodes (TAEs) can be driven by alpha particles in the collapsing plasma before the onset of the current quench. We employ kinetic simulations of the alpha particle distribution and show that the TAEs can reach sufficiently strong saturation amplitudes to cause significant core runaway electron (RE) transport in unmitigated ITER disruptions. As the eigenmodes do not extend to the plasma edge, this effect leads to an increase of the RE plateau current. Mitigation via massive material injection however changes the Alfvén frequency and can lead to mode suppression. A combination of the TAE-caused core RE transport with other perturbation sources could lead to a drop of runaway current in unmitigated disruptions.

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Full conversion from ohmic to runaway electron driven current via massive gas injection in the TCV tokamak

Cited by 7 publications

References 58 publications

Benign termination of runaway electron beams on ASDEX Upgrade and TCV

Benign termination of runaway electron beams on ASDEX Upgrade and TCV

Impact of microwave beam scattering by density fluctuations on the electron–cyclotron power deposition profile in tokamaks

The impact of fusion-born alpha particles on runaway electron dynamics in ITER disruptions

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