Comparison of ion cyclotron wall conditioning discharges in hydrogen and helium in JET

Kovtun, Y.; Wauters, T.; Matveev, D.; Bisson, R.; Jepu, I.; Brezinsek, S.; Coffey, I.; Delabie, E.; Boboc, A.; Dittmar, T.; Hakola, A.; Jacquet, P.; Kirov, K.; Lerche, E.; Likonen, J.; Litherland-Smith, E.; Loarer, T.; Lomas, P.; Lowry, C.; Pawelec, E.; Perez von Thun, C.; Meigs, A.; Maslov, M.; Monakhov, I.; Noble, C.; Silburn, S.; Sun, H.; Taylor, D.; Tsitrone, E.; Widdowson, A.; Sheikh, H.; Douai, D.

doi:10.1016/j.nme.2023.101521

Cited by 2 publications

(1 citation statement)

References 34 publications

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“…Wall conditioning was performed during the first three days of C43 by carrying out back-and-forth transitions from helium to hydrogen and hydrogen to helium (He → H and H → He, respectively) [15]. During these changeover phases, approximately 16 s long ion cyclotron wall conditioning (ICWC) pulses [16,17] were carried out with the coupled RF power being in the range of 0.16 MW for H-ICWC (He → H) and 0.24 MW for He-ICWC (H → He) [17]. After each step, a series of pre-designed, ICRH-heated plasma pulses in the limiter and divertor configurations (either in H or He) was carried out to study the evolution of the plasma purity.…”

Section: Wall Conditioning Investigationsmentioning

confidence: 99%

Helium plasma operations on ASDEX Upgrade and JET in support of the non-nuclear phases of ITER

Hakola,

Balden,

Baruzzo

et al. 2024

Nucl. Fusion

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For its initial operational phase, ITER has until recently considered using non-nuclear hydrogen (H) or helium (He) plasmas to keep nuclear activation at low levels. To this end, the Tokamak Exploitation Task Force of the EUROfusion Consortium carried out dedicated experimental campaigns in He on the ASDEX Upgrade (AUG) and JET tokamaks in 2022, with particular emphasis put on the ELMy H-mode operation and plasma-wall interaction processes as well as comparison to H or deuterium (D) plasmas. Both in pure He and mixed He+H plasmas, H-mode operation could be reached but more effort was needed to obtain a stable plasma scenario than in H or D. Even if the power threshold for the LH transition was lower in He, entering the type-I ELMy regime appeared to require equally much or even more heating power than in H. Suppression of ELMs by resonant magnetic perturbations was studied on AUG but was only possible in plasmas with a He content below 19%; the reason for this unexpected behaviour remains still unclear and various theoretical approaches are being pursued to properly understand the physics behind ELM suppression. The erosion rates of tungsten (W) plasma-facing components (PFCs) were an order of magnitude larger than what has been reported in hydrogenic plasmas, which can be attributed to the prominent role of He2+ ions in the plasma. For the first time, the formation of nanoscale structures (W fuzz) was unambiguously demonstrated in H-mode He plasmas on AUG. However, no direct evidence of fuzz creation on JET was obtained despite the main conditions for its occurrence being met. The reason could be a delicate balance between W erosion by ELMs, competition between the growth and annealing of the fuzz, and coverage of the surface with co-deposits.

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Section: Wall Conditioning Investigationsmentioning

confidence: 99%

Helium plasma operations on ASDEX Upgrade and JET in support of the non-nuclear phases of ITER

Hakola,

Balden,

Baruzzo

et al. 2024

Nucl. Fusion

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ICRF production of plasma with hydrogen minority in Uragan-2M stellarator by two-strap antenna

Kovtun,

Moiseenko,

Lozin

et al. 2024

Physics of Plasmas

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The experiments on medium-size stellarator Uragan-2M (U-2M) in Kharkiv, Ukraine, are carried on in support of the Wendelstein 7-X (W7-X) experimental program. The scenario ion cyclotron frequency range (ICRF) plasma production at the hydrogen minority regime had been experimentally tested on U-2M and was qualified at the Large Helical Device (LHD). The paper presents the results of further research on the ICRF plasma production. The ICRF discharge studies were carried out in a H2 + He mixture with a controlled hydrogen concentration ranging from few percents to 75%. The two-strap like antenna mimicks the W7-X antenna operated in monopole phasing. The applied RF power was in the range of ∼100 kW. Relatively dense plasma of up to Ne ∼ 1019 m−3 was produced near the first harmonic of the hydrogen cyclotron frequency. The maximum temperature of the electrons and ions was not more than a few tens of electron volt. The characteristic features of RF plasma production and the propagation of electromagnetic waves in the experimental conditions are discussed. The experiments on U-2M and LHD indicate that the minority scenario of ICRF plasma production appears to be scalable and could be used in large stellarator machines. This is, in particular, important for the future experiments ICRF production of target plasma in W-7X in conditions where electron cyclotron resonance heating start-up is not possible.

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Comparison of ion cyclotron wall conditioning discharges in hydrogen and helium in JET

Cited by 2 publications

References 34 publications

Helium plasma operations on ASDEX Upgrade and JET in support of the non-nuclear phases of ITER

Helium plasma operations on ASDEX Upgrade and JET in support of the non-nuclear phases of ITER

ICRF production of plasma with hydrogen minority in Uragan-2M stellarator by two-strap antenna

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