Tritium removal from JET-ILW after T and D–T experimental campaigns

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The work describes the pedestal structure, transport and stability in an effective mass (A eff) scan from pure deuterium to pure tritium plasmas using a type I ELMy H-mode dataset in which key parameters that affect the pedestal behaviour (normalized pressure, ratio of the separatrix density to the pedestal density, pedestal ion Larmor radius, pedestal collisionality and rotation) are kept as constant as possible. Experimental results show a significant increase of the density at the pedestal top with increasing A eff, a modest reduction in the temperature and an increase in the pressure. The variations in the pedestal heights are mainly due to a change in the pedestal gradients while only small differences are observed in the pedestal width. A clear increase in the pedestal density and pressure gradients are observed from deuterium to tritium. The experimental results suggest a reduction of the pedestal inter-edge localized mode (inter-ELM) transport from deuterium to tritium. The reduction is likely in the pedestal inter-ELM particle transport, as suggested by the clear increase of the pedestal density gradients. The experimental results suggest also a possible reduction of the pedestal inter-ELM heat transport, however, the large experimental uncertainties do not allow conclusive claims on the heat diffusivity. The clear experimental reduction of η e (the ratio between density and temperature gradient lengths) in the middle/top of the pedestal with increasing A eff suggests that there may be a link between increasing A eff and the reduction of electron scale turbulent transport. From the modelling point of view, an initial characterization of the behaviour of pedestal microinstabilities shows that the tritium plasma is characterized by growth rates lower than the deuterium plasmas. The pedestal stability of peeling-ballooning modes is assessed with both ideal and resistive magnetohydrodynamics (MHD). No significant effect of the isotope mass on the pedestal stability is observed using ideal MHD. Instead, resistive MHD shows a clear increase of the stability with increasing isotope mass. The resistive MHD results are in reasonable agreement with the experimental results of the normalized pedestal pressure gradient. The experimental and modelling results suggest that the main candidates to explain the change in the pedestal are a reduction in the inter-ELM transport and an improvement of the pedestal stability from deuterium to tritium.

Section: Diagnosticsmentioning

confidence: 99%

Effect of the isotope mass on pedestal structure, transport and stability in D, D/T and T plasmas at similar β _N and gas rate in JET-ILW type I ELMy H-modes

Frassinetti,

Perez von Thun,

Chapman-Oplopoiou

et al. 2023

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“…ICWC was part of the tritium recovery strategy after JET D-T operations [12], with a total of ∼915 s ICWC dischargetime. JET ICWC plasma discharges are described in [28].…”

Section: Icwc Operationsmentioning

confidence: 99%

“…18 s long D2 gas ICWC discharges with 250-300 kW of coupled RF power at 29 MHz were generated, with on-axis resonance layer for the 2nd harmonic ion cyclotron resonance frequency for D+ ions (note however that ion-resonance absorption is not the main process involved in ICWC, see [29]). A 'barrel-shape' poloidal field of typically 15 mT on-axis was applied to maximise the wetted areas by ICWC plasmas [12]. Figure 11 shows RF voltages applied on the transmission line feedings the antennas at the start of a typical ICWC discharge.…”

Section: Icwc Operationsmentioning

confidence: 99%

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ICRH operations during the JET tritium and DTE2 campaigns

Jacquet,

Dumortier,

Lerche

et al. 2024

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The JET-ILW pure Tritium and Deuterium-Tritium (DTE2) experimental campaigns took place in 2021-2022. Tritium (T) and Deuterium-Tritium (D-T) operations present challenges not encountered in present day tokamaks [1]. This contribution focuses on Ion Cyclotron Resonance Heating (ICRH) operations in tritium and deuterium-tritium plasmas, starting with a summary of the program of improvements to the ICRH system which spanned a few years prior to these experiments. Procedures were implemented to address specific constraints from tritium and deuterium-tritium operations (tritium safety and reduced access to the RF generator area) and increase the system reliability and power availability during plasma pulses. Operation of the upgraded Real Time RF power control system that maximises the launched power while taking into account limitations from the system or antenna coupling is described. We also report on the result from dedicated pulses performed to assess the potential harmful impact of the 2nd harmonic tritium resonance in the plasma, close to the inner wall, when using the standard central hydrogen minority ICRH scheme. During DTE2, the ITER-Like Antenna (ILA) was not used because water leaked from an in-vessel capacitor into the vessel on day-2 of the experimental campaign. The lessons learnt from this incident are highlighted. Finally, the ICRH plant adjustments required to safely perform Ion Cyclotron Wall Cleaning discharges are described.

“…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

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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.