| 1. |
- Meyer, H.F., et al.
(författare)
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Overview of physics studies on ASDEX Upgrade
- 2019
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 59:11
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Forskningsöversikt (refereegranskat)abstract
- The ASDEX Upgrade (AUG) programme, jointly run with the EUROfusion MST1 task force, continues to significantly enhance the physics base of ITER and DEMO. Here, the full tungsten wall is a key asset for extrapolating to future devices. The high overall heating power, flexible heating mix and comprehensive diagnostic set allows studies ranging from mimicking the scrape-off-layer and divertor conditions of ITER and DEMO at high density to fully non-inductive operation (q 95 = 5.5, ) at low density. Higher installed electron cyclotron resonance heating power 6 MW, new diagnostics and improved analysis techniques have further enhanced the capabilities of AUG. Stable high-density H-modes with MW m-1 with fully detached strike-points have been demonstrated. The ballooning instability close to the separatrix has been identified as a potential cause leading to the H-mode density limit and is also found to play an important role for the access to small edge-localized modes (ELMs). Density limit disruptions have been successfully avoided using a path-oriented approach to disruption handling and progress has been made in understanding the dissipation and avoidance of runaway electron beams. ELM suppression with resonant magnetic perturbations is now routinely achieved reaching transiently . This gives new insight into the field penetration physics, in particular with respect to plasma flows. Modelling agrees well with plasma response measurements and a helically localised ballooning structure observed prior to the ELM is evidence for the changed edge stability due to the magnetic perturbations. The impact of 3D perturbations on heat load patterns and fast-ion losses have been further elaborated. Progress has also been made in understanding the ELM cycle itself. Here, new fast measurements of and E r allow for inter ELM transport analysis confirming that E r is dominated by the diamagnetic term even for fast timescales. New analysis techniques allow detailed comparison of the ELM crash and are in good agreement with nonlinear MHD modelling. The observation of accelerated ions during the ELM crash can be seen as evidence for the reconnection during the ELM. As type-I ELMs (even mitigated) are likely not a viable operational regime in DEMO studies of 'natural' no ELM regimes have been extended. Stable I-modes up to have been characterised using -feedback. Core physics has been advanced by more detailed characterisation of the turbulence with new measurements such as the eddy tilt angle - measured for the first time - or the cross-phase angle of and fluctuations. These new data put strong constraints on gyro-kinetic turbulence modelling. In addition, carefully executed studies in different main species (H, D and He) and with different heating mixes highlight the importance of the collisional energy exchange for interpreting energy confinement. A new regime with a hollow profile now gives access to regimes mimicking aspects of burning plasma conditions and lead to nonlinear interactions of energetic particle modes despite the sub-Alfvénic beam energy. This will help to validate the fast-ion codes for predicting ITER and DEMO.
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| 2. |
- Lang, P. T., et al.
(författare)
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ELM control at the L -> H transition by means of pellet pacing in the ASDEX Upgrade and JET all-metal-wall tokamaks
- 2015
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Ingår i: Plasma Physics and Controlled Fusion. - : Institute of Physics Publishing (IOPP). - 0741-3335 .- 1361-6587. ; 57:4
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Tidskriftsartikel (refereegranskat)abstract
- In ITER, pellets are used for ELM pacing and fueling. More importantly, ELM control and in particular control of the first ELM needs to be demonstrated in the non-nuclear phase of ITER during operation in H or He. Whilst D pellets have been established as an ELM control technique in the stationary phase with D target plasmas in devices with C as plasma-facing component, the behavior of other isotopes in non-stationary phases are not so well known. Here, we report on new pellet triggering experiments in ASDEX Upgrade and JET that mimic specific ITER operating scenarios. Both machines are equipped with an all-metal wall; recent investigations have shown that pellet triggering and pacing become more intricate when an all-metal wall surface is employed. In both machines, ELM triggering has been shown to occur after injection of D pellets into D plasmas during extended ELM-free phases, often following the L -> H transition. In both devices the pellets are found to induce ELMs under conditions far from the stability boundary for type-I ELMs. Near the L -> H transition, induced ELMs in some cases are more likely to have type-III rather than type-I characteristics. Furthermore, in ASDEX Upgrade this study was conducted during L -> H transitions in the current ramp-up phase as envisaged for ITER. In addition, the pellet's ELM trigger potential has been proven in ASDEX Upgrade with a correct isotopic compilation for the non-nuclear phase in ITER, viz. H pellets into either He or H plasmas. Results from this study are encouraging since they have demonstrated the pellets' potential to provoke ELMs even under conditions that are quite far from the stability boundaries attributed to the occurrence of spontaneous ELMs. However, with the recent change from carbon to an all-metal plasma-facing component, examples have been found in both machines where pellets failed to establish ELM control under conditions where this would be expected and needed. Consequently, a major task of future investigations in this field will be to shed more light on the underlying physics of the pellet ELM triggering process to allow sound predictions for ITER.
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