Evaluation of multipactor thresholds for coaxial lines subject to surface conditioning for the WEST ion cyclotron antenna

Sleiman, Eva Al Hajj; Hillairet, J.; Belhaj, Mohamed; Dadouch, S.

doi:10.1016/j.fusengdes.2022.113325

Cited by 6 publications

(15 citation statements)

References 26 publications

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“…Space-charge effects in coaxial multipactor have also been studied analytically by Sorolla et al [95]. It is notable that in recent times we observe an increasing reliance on software tools such as CST [71,72,96,97] and Spark-3D [69] for multipactor simulation in complex geometries, such as the cylindrical and elliptical coaxial lines, rf cavities, tapered waveguides, etc.…”

Section: Multipactor In Coaxial Lines and Complex Geometriesmentioning

confidence: 99%

“…Computational studies of multipactor are summarised in the review articles of Kishek [3] and Iqbal [62]. Also noteworthy is that in recent years, along with numerical and analytical studies, much emphasis has been put on computer aided simulations of multipactor discharge using software such as MSAT (Multipactor Simulation and Analysis Tool) [63,64], MEST (Multipactor Electron Simulation Tool) [65,66], FEST-3D (Finite-volume Explicit STructured 3-Dimensional) [67,68], Spark3D [69], and CST (Computer Simulation Technology) [70][71][72][73].…”

Section: Introductionmentioning

confidence: 99%

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Recent advances in multipactor physics and mitigation

et al. 2023

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Recent progress made in the prediction, characterisation, and mitigation of multipactor discharge is reviewed for single‐ and two‐surface geometries. First, an overview of basic concepts including secondary electron emission, electron kinetics under the force law, multipactor susceptibility, and saturation mechanisms is provided, followed by a discussion on multipactor mitigation strategies. These strategies are categorised into two broad areas – mitigation by engineered devices and engineered radio frequency (rf) fields. Each approach is useful in different applications. Recent advances in multipactor physics and engineering during the past decade, such as novel multipactor prediction methods, understanding space charge effects, schemes for controlling multipacting particle trajectories, frequency domain analysis, high frequency effects, and impact on rf signal quality are presented. In addition to vacuum electron multipaction, multipactor‐induced ionization breakdown is also reviewed, and the recent advances are summarised.

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Section: Multipactor In Coaxial Lines and Complex Geometriesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Recent advances in multipactor physics and mitigation

et al. 2023

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“…We rely on the X-ray photoelectron spectroscopy (XPS) [22,23] data analysis, obtained for a WEST ICRH antenna representative material sample of silver-coated stainless steel, to monitor the chemical surface modifications [10], and relate it to the multipactor simulation results to estimate the molecular desorbed rate R.…”

Section: Pump-impinging Molecular Flux Evaluation ϕmentioning

confidence: 99%

Multipactor predictions for ion cyclotron resonance heating antennas of the tokamak WEST ^*

Al Hajj Sleiman,

Hillairet,

Belhaj

et al. 2023

Nucl. Fusion

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During the plasma experimental campaigns performed on the tokamak WEST, a performance-limiting observation has been made on the Ion Cyclotron Resonance Heating (ICRH) system composed of three identical antennas. When only one antenna is powered while the remaining two are off, an increase in the internal pressure is measured within the non-powered antennas. The internal pressure of the non-powered antennas exceeds a safety pressure interlock whose threshold is 4.5 × 10 − 3 Pa, and consequently, the application of the RF power is prohibited to avoid plasma creation within these antennas. In this paper, the multipactor phenomenon caused by the inter-antennas’ coupling is shown to be responsible for the pressure increase observed in the non-powered antennas. Additionally, an analytic estimation of the pressure rise caused by the multipactor is compared to that observed experimentally.

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“…Before operating the RF heating system on vacuum or plasma, the ICRH antennas are subject to in-situ conditioning treatments: baking (during the general tokamak baking) and RF conditioning. RF conditioning is an antenna-surface conditioning technique based on short RF power pulses (ms), used to clean and remove impurities deposited on the surfaces [19]. In some conditions that we would like to identify, these RF power pulses trigger multipactor inside the different components of the antenna.…”

Section: A Teey Characteristics Within West Relevant Operational Cond...mentioning

confidence: 99%

“…In some conditions that we would like to identify, these RF power pulses trigger multipactor inside the different components of the antenna. Multipactor discharges -among other possible phenomena -are known to be responsible for the elimination of hydrocarbon elements, and adsorbed hydroxides from the surfaces of the antennas' components [19]. As a result of baking and RF conditioning, the emission properties of the antenna's surfaces are modified.…”

Section: A Teey Characteristics Within West Relevant Operational Cond...mentioning

confidence: 99%

Multipactor-Triggering Powers’ Modelling of a WEST ICRH Antenna During RF Conditioning

Sleiman

Hillairet

Belhaj³

2023

IEEE Trans. Plasma Sci.

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During RF conditioning of the ion cyclotron resonance heating (ICRH) system on WEST, under vacuum, pressure rises are measured inside the antennas. A proposed hypothesis for the cause of this phenomenon is multipactor, an electron multiplication process taking place in RF devices under vacuum. Modelling multipactor conditions in a resonant antenna, i.e., under high standing wave ratio, requires particular precautions. This paper proposes a methodology to determine the multipactor conditions in such a context. Using the proposed approach, the operational conditions, expressed as the generator's RF powers, of the appearance of multipactor inside a WEST ICRH antenna during its RF conditioning under vacuum, are deduced. Calculations are performed for two different surface states: when the surface is baked but non-conditioned, and when it is baked and fully conditioned. For the non-conditioned surface state, it is shown that when only one side of the under-conditioning ICRH antenna is powered, the off-mode side is prone to multipactor when its capacitors are tuned. Detuning the capacitors on the offmode side suppresses almost the multipactor on the non-powered side for the frequency range of interest. Moreover, it is shown that the fully conditioned antenna surface state can suppress the appearance of multipactor in some regions of the antenna.

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Evaluation of multipactor thresholds for coaxial lines subject to surface conditioning for the WEST ion cyclotron antenna

Cited by 6 publications

References 26 publications

Recent advances in multipactor physics and mitigation

Recent advances in multipactor physics and mitigation

Multipactor predictions for ion cyclotron resonance heating antennas of the tokamak WEST ^*

Multipactor-Triggering Powers’ Modelling of a WEST ICRH Antenna During RF Conditioning

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Evaluation of multipactor thresholds for coaxial lines subject to surface conditioning for the WEST ion cyclotron antenna

Cited by 6 publications

References 26 publications

Recent advances in multipactor physics and mitigation

Recent advances in multipactor physics and mitigation

Multipactor predictions for ion cyclotron resonance heating antennas of the tokamak WEST *

Multipactor-Triggering Powers’ Modelling of a WEST ICRH Antenna During RF Conditioning

Contact Info

Product

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Multipactor predictions for ion cyclotron resonance heating antennas of the tokamak WEST ^*