ITER visible spectroscopy reference system first mirror plasma cleaning in radio-frequency gas discharge – circuit design and plasma effects

Ushakov, A.G.; Verlaan, Ad; Stephan, U.; Steinke, O.; Bock, Maarten De; Maniscalco, Matthew; Verhoeff, Peter

doi:10.1016/j.fusengdes.2020.111546

Cited by 13 publications

(6 citation statements)

References 8 publications

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“…In our system, ion energy distributions with two peaks were observed, which did not significantly change when the frequency varied from 40 to 50 MHz. In similar research [19], merging of ion energy peaks was more noticeable for broader frequency variations: from 45 MHz to 60 MHz. In table 1, the ion energy in the middle of the distribution is taken as a characteristic ion energy of the ion flux.…”

Section: Rfea Measurements Without the Notch Filtermentioning

confidence: 54%

“…In earlier experiments, feasibility of plasma cleaning was discussed for the Ultra-Wide Angle Visible Spectroscopy diagnostic system [2,17,18]. The electrical circuit of the plasma cleaning system was modeleld for the Visible Spectroscopy Reference System [5,19]. For the ETS system, parameters of critical components such as the notch filter element and the so-called 'pre-matching' vacuum L-C circuit were analytically considered for several operational frequencies [9], however were not yet studied experimentally.…”

Section: Cleaning Discharge Requirementsmentioning

confidence: 99%

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Radio-frequency plasma to clean ITER front-end diagnostic mirrors in geometry of Edge Thomson Scattering system

Ushakov¹,

Veldhoven²,

Rijnsent³

et al. 2022

Phys. Scr.

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The ITER Edge Thomson scattering (ETS) system provides electron temperature and density profile measurements in the ITER tokamak for plasma control. In collection optics, the front-end metallic first and second mirrors are expected to experience contamination with beryllium and tungsten degrading performance. Plasma cleaning based on a low-pressure radiofrequency discharge is expected to sputter contaminants. In the ETS, a water-cooled first mirror is combined with a powered electrode. Water cooling was realized as a notch filter for the driving frequency, and the electrode was grounded for a DC- voltage. A new breadboard reproducing the ETS mirror geometry was developed for experimental modelling. The notch filter uses equivalent cables. To understand the cleaning effect, ion energies and fluxes were measured in 40-50 MHz discharges in argon and helium at 1-10 Pa with and without the notch filter. Without a notch filter with minimum power losses, 2-4·1018 ions·m-2s-1 ion fluxes with energies of 100-140 eV were produced. With the notch filter, the peak ion energies were 30-50 eV. The power in the plasma was lower than 50 W with ion fluxes of – 1.5-1.9 1018 ions·m-2s-1. 53-m-long cable feeds equivalent to those of a real system were studied at 13-50 MHz and produced significant power loss: more than 95% at 40-50 MHz. A pre-matching element is essential to reduce power losses. A lower radiofrequency may be less sensitive to pre-matching and may be considered for mirrors without water cooling. A 40 MHz discharge is proposed for cleaning due to better stability, higher ion energies and possibly better uniformity. Powers in plasma in the range of hundreds of Watts may be needed to achieve ion fluxes suitable for cleaning. This requires more powerful components and shall be addressed in later experiments. The results are important for plasma cleaning in ETS and in other diagnostics where water-cooled first mirrors are used.

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Section: Rfea Measurements Without the Notch Filtermentioning

confidence: 54%

Section: Cleaning Discharge Requirementsmentioning

confidence: 99%

Radio-frequency plasma to clean ITER front-end diagnostic mirrors in geometry of Edge Thomson Scattering system

Ushakov¹,

Veldhoven²,

Rijnsent³

et al. 2022

Phys. Scr.

Self Cite

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“…It is one of the first systems to issue a warning when the conditions of the nuclear fusion plasma are out of operational bounds and damage to the machine is imminent. As many of ITER's subsystems, the VSRS implements exotic technologies and materials, and its design involves highly specialized scientific analyses (Kajita et al, 2019;Ushakov et al, 2020). Our goal is to improve the organizational communication by identifying critical interfaces that are managed by multiple parties.…”

Section: Demonstrationmentioning

confidence: 99%

Challenges Of Big-science: A Matrix-based Interface Model To Manage Technical Integration Risks In Multi-organizational Engineering Projects

Beernaert¹,

Etman²,

Bock³

et al. 2022

DS 121: Proceedings of the 24th International DSM Conference (DSM 2022), Eindhoven, the Netherlands, October, 11 - 13, 2022

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Tomorrow's big science systems are in development today. Success depends on global collaboration in which multiple international parties produce unique assemblies. Inter-organizational barriers, interests and technical conflicts often complicate the design and realization process. It is especially difficult to manage a system's interfaces over such boundaries. We propose a model-based approach to support integrators in such situations. Combining a system architecture model, Integration Readiness Levels (IRLs) and a network of actors, we can derive a newly introduced Collaborative Interface Risk Index (CIRI) that highlights risky interfaces, the organizational patterns that are required for successful integration and a progress indicator that tracks how many interfaces have been defined sufficiently. We demonstrate the method for one of ITER's diagnostic subsystems, which is being developed by six distributed organizations. The result is a Multi-Domain Matrix (MDM) that gives a complete overview on the complexity and risks of the collaborative engineering project.

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“…A ubiquitous problem for optical diagnostics is the decrease in performance of plasma-facing mirrors suffering from this environment (Litnovsky et al, 2019). Hopes are that an active cleaning system, which is currently in development (Ushakov et al, 2020), can effectively mitigate this problem. But given the low maturity of this technology, it is likely that new problems emerge during its development.…”

Section: Definitions and Relevant Literaturementioning

confidence: 99%

Tracing the Emergence of Design Problems and Their Impacts on the Complexity of Engineering Solutions

et al. 2021

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The design of ITER, a large-scale nuclear fusion reactor, is intertwined with profound research and development efforts. Tough problems call for novel solutions, but the low maturity of those solutions can lead to unexpected problems. If designers keep solving such emergent problems in iterative design cycles, the complexity of the resulting design is bound to increase. Instead, we want to show designers the sources of emergent design problems, so they may be dealt with more effectively. We propose to model the interplay between multiple problems and solutions in a problem network. Each problem and solution is then connected to a dynamically changing engineering model, a graph of physical components. By analysing the problem network and the engineering model, we can (1) derive which problem has emerged from which solution and (2) compute the contribution of each design effort to the complexity of the evolving engineering model. The method is demonstrated for a sequence of problems and solutions that characterized the early design stage of an optical subsystem of ITER.

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ITER visible spectroscopy reference system first mirror plasma cleaning in radio-frequency gas discharge – circuit design and plasma effects

Cited by 13 publications

References 8 publications

Radio-frequency plasma to clean ITER front-end diagnostic mirrors in geometry of Edge Thomson Scattering system

Radio-frequency plasma to clean ITER front-end diagnostic mirrors in geometry of Edge Thomson Scattering system

Challenges Of Big-science: A Matrix-based Interface Model To Manage Technical Integration Risks In Multi-organizational Engineering Projects

Tracing the Emergence of Design Problems and Their Impacts on the Complexity of Engineering Solutions

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