Recent progress in modeling ICRF-edge plasma interactions with application to ASDEX Upgrade

Zhang, W.; Bilato, R.; Bobkov, V.; Cathey, A.; Siena, A. Di; Hoelzl, M.; Messiaen, A.; Myra, J. R.; López, G. Suárez; Tierens, W.; Usoltceva, M.; Wright, J. C.

doi:10.1088/1741-4326/ac38c8

Cited by 15 publications

(4 citation statements)

References 156 publications

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“…Future devices will therefore need to rely more on numerical simulation, backed by scarce measurements, to operate their heating systems. So far, modelling tools have been scarcely validated quantitatively against experiments in realistic geometry [4,5,6]. One can therefore attempt some extrapolation of the present results to future long pulse metallic DT machines, but also outline some remaining uncertainty in this prospect.…”

Section: Outlook For Future Long Pulse Metallic Dt Machinesmentioning

confidence: 96%

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The geometry of the ICRF-induced wave–SOL interaction. A multi-machine experimental review in view of the ITER operation

Colas¹,

Urbanczyk²,

Goniche³

et al. 2021

Nucl. Fusion

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As part of ITPA-Integrated Operational Scenario activities, this contribution reviews recent experimental characterizations of radio-frequency (RF)-induced scrape-off layer (SOL) modifications of various tokamaks worldwide and of the LArge Plasma Device at UCLA. The phenomenology, as observed using a large variety of measurement techniques, is consistent with expectations from RF sheath rectification. Emphasis is then put on the complex three-dimensional (3D) spatial patterns of the RF–SOL interaction, in relation to the magnetic topology and the spatial distribution of RF currents over the metallic structures surrounding the RF wave launchers. Dependence on the local plasma parameters in the antenna vicinity is also briefly addressed. The final part discusses implications for future devices.

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Section: Outlook For Future Long Pulse Metallic Dt Machinesmentioning

confidence: 96%

“…Reference [3] proposes a recent tutorial on RF sheath modelling in magnetic fusion plasmas. References [4][5][6] reviewed some comparisons of experiments with modelling in realistic geometry.…”

Section: Introductionmentioning

confidence: 99%

The geometry of the ICRF-induced wave–SOL interaction. A multi-machine experimental review in view of the ITER operation

Colas¹,

Urbanczyk²,

Goniche³

et al. 2021

Nucl. Fusion

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“…It follows that in some cases, increasing the distance between an ICRF antenna and the plasma to reduce their interactions based on linear intuition, can unexpectedly cause an increase of impurity production from local sources, reacting to sharp increase of RF sheath potentials. These phenomena can be modeled in different ways as summarized in [53]. This behavior was also experimentally observed in WEST during a scan of the radial position of an ICRF antenna, where the floating potential measured by a reciprocating probe did not directly decrease as the antenna was retracted but first passed by a maximum for intermediate position (cf.…”

Section: Poor Coupling Efficiency and Near-field Effectsmentioning

confidence: 73%

Main Challenges of Heating Plasma with Waves at the Ion Cyclotron Resonance Frequency (ICRF)

Urbanczyk¹

2022

Advances in Fusion Energy Research - From Theory to Models, Algorithms, and Applications

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Of all the techniques used for heating plasmas in fusion devices, waves in the Ion Cyclotron Resonance Frequency (ICRF ∼ MHz) continue to be exceptionally advantageous and unique insofar as it enables to deposit of power directly on ions in the core, significantly enhancing fast ion population together with fusion reaction products. However, because of the multiple inherent challenges—such as matching robustness, antenna design, wave coupling efficiency, wave propagation, wave absorption, and plasma surface interactions due to radiofrequency (RF) sheath excitation—ICRF is often one of the most complex heating systems to implement successfully. This chapter provides a brief introduction of these challenges and their respective underlying physics, together with examples of both simulations and experimental results from various tokamaks around the world. Finally, ICRF advantages and applications on present and future devices and perspectives of technological solutions are discussed and summarized.

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“…In analysing the extent to which these RF sheaths will produce high-Z plasma contamination and erode the vacuum chamber first wall, numerical modelling is often employed. The community-accepted approach for studying the effects of both near-and-far field RF sheaths on plasma-material interaction (PMI) is to model ion dynamics using a fluid or kinetic Debye-scale code [19]. Both of these models are capable of capturing the angle of incidence of ions crossing the sheath.…”

Section: Introductionmentioning

confidence: 99%

Resonance in radio frequency sheath admittance and enhanced impurity emission near the ion cyclotron frequency

2023

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Ion cyclotron resonance heating (ICRH) is of considerable interest among all auxiliary heating techniques, because it transfers power directly to ions, targets the high density core, and involves the cheapest radio-frequency (RF) components. During ICRH operation, RF sheaths form on the ICRH antenna itself, nearby hardware, and far-field surfaces. These sheaths are associated with large hot-spot formation and impurity emissions. This work presents high-resolution numerical modelling of RF sheaths in nuclear fusion scenarios using hPIC2, a Debye-scale particle-in-cell code. The modelling reveals a new RF sheath phenomenon which occurs when the radio frequency is resonant with a species ion cyclotron frequency or harmonic in an oblique magnetic field. This resonance of the RF sheath causes modifications of the energy-angle distributions of the ions impacting on the walls, with consequent increase in wall impurity emission. Due to the 1/R scaling of the magnetic field in a tokamak, such cases are possible on divertor or vacuum chamber surfaces, depending on the geometry of the tokamak and the RF heating scenario. A simple physics interpretation using a driven damped harmonic oscillator is proposed, where the ion sheath transit time plays the role of damping the RF sheath admittance. Critically, the resonance leads to increased ion heat flux at the wall as well as increased physical sputtering, despite a lack of increase in RF rectified sheath potential.

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Recent progress in modeling ICRF-edge plasma interactions with application to ASDEX Upgrade

Cited by 15 publications

References 156 publications

The geometry of the ICRF-induced wave–SOL interaction. A multi-machine experimental review in view of the ITER operation

The geometry of the ICRF-induced wave–SOL interaction. A multi-machine experimental review in view of the ITER operation

Main Challenges of Heating Plasma with Waves at the Ion Cyclotron Resonance Frequency (ICRF)

Resonance in radio frequency sheath admittance and enhanced impurity emission near the ion cyclotron frequency

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