| 1. |
- Chellaï, O., et al.
(author)
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Millimeter-wave beam scattering and induced broadening by plasma turbulence in the TCV tokamak
- 2021
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In: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 61:6
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Journal article (peer-reviewed)abstract
- The scattering of millimeter-wave beams from electron density fluctuations and the associated beam broadening are experimentally demonstrated. Using a dedicated setup, instantaneous deflection and (de-)focusing of the beam due to density blobs on the beam path are shown to agree with full-wave simulations. The detected time-averaged wave power transmitted through the turbulent plasma is reproduced by the radiative-transfer model implemented in the WKBeam code, which predicts a ∼50% turbulence-induced broadening of the beam cross-section. The role of core turbulence for the considered geometry is highlighted.
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| 2. |
- Coda, S., et al.
(author)
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Physics research on the TCV tokamak facility: From conventional to alternative scenarios and beyond
- 2019
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In: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 59:11
-
Journal article (peer-reviewed)abstract
- The research program of the TCV tokamak ranges from conventional to advanced-tokamak scenarios and alternative divertor configurations, to exploratory plasmas driven by theoretical insight, exploiting the device's unique shaping capabilities. Disruption avoidance by real-time locked mode prevention or unlocking with electron-cyclotron resonance heating (ECRH) was thoroughly documented, using magnetic and radiation triggers. Runaway generation with high-Z noble-gas injection and runaway dissipation by subsequent Ne or Ar injection were studied for model validation. The new 1 MW neutral beam injector has expanded the parameter range, now encompassing ELMy H-modes in an ITER-like shape and nearly non-inductive H-mode discharges sustained by electron cyclotron and neutral beam current drive. In the H-mode, the pedestal pressure increases modestly with nitrogen seeding while fueling moves the density pedestal outwards, but the plasma stored energy is largely uncorrelated to either seeding or fueling. High fueling at high triangularity is key to accessing the attractive small edge-localized mode (type-II) regime. Turbulence is reduced in the core at negative triangularity, consistent with increased confinement and in accord with global gyrokinetic simulations. The geodesic acoustic mode, possibly coupled with avalanche events, has been linked with particle flow to the wall in diverted plasmas. Detachment, scrape-off layer transport, and turbulence were studied in L- and H-modes in both standard and alternative configurations (snowflake, super-X, and beyond). The detachment process is caused by power 'starvation' reducing the ionization source, with volume recombination playing only a minor role. Partial detachment in the H-mode is obtained with impurity seeding and has shown little dependence on flux expansion in standard single-null geometry. In the attached L-mode phase, increasing the outer connection length reduces the in-out heat-flow asymmetry. A doublet plasma, featuring an internal X-point, was achieved successfully, and a transport barrier was observed in the mantle just outside the internal separatrix. In the near future variable-configuration baffles and possibly divertor pumping will be introduced to investigate the effect of divertor closure on exhaust and performance, and 3.5 MW ECRH and 1 MW neutral beam injection heating will be added.
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| 3. |
- Martin, P., et al.
(author)
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Overview of RFX-mod results
- 2009
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In: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 49:10, s. 104019-
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Journal article (peer-reviewed)abstract
- With the exploration of the MA plasma current regime in up to 0.5 s long discharges, RFX-mod has opened new and very promising perspectives for the reversed field pinch (RFP) magnetic configuration, and has made significant progress in understanding and improving confinement and in controlling plasma stability. A big leap with respect to previous knowledge and expectations on RFP physics and performance has been made by RFX-mod since the last 2006 IAEA Fusion Energy Conference. A new self-organized helical equilibrium has been experimentally achieved ( the Single Helical Axis-SHAx-state), which is the preferred state at high current. Strong core electron transport barriers characterize this regime, with electron temperature gradients comparable to those achieved in tokamaks, and by a factor of 4 improvement in confinement time with respect to the standard RFP. RFX-mod is also providing leading edge results on real-time feedback control of MHD instabilities, of general interest for the fusion community.
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| 4. |
- Yadykin, Dimitriy, 1977, et al.
(author)
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Scientific workflows for MHD stability chain analysis of tokamak plasmas
- 2015
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In: 42nd EPS Conference on Plasma Physics. ; 39E, s. P.178-
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Conference paper (other academic/artistic)abstract
- The onset of MHD activity in present tokamak plasmas plays a detrimental role inthe discharge performance and operational limits. A comprehensive characterisation of themodes observed and stability boundaries often call for the comparison of theexperimentally measured toroidal/poloidal mode spectra and propagating frequenciesagainst the predictions from linear MHD codes. In addition, predicting the MHD stabilityboundaries in operational plasma scenarios foreseen for ITER and under investigation forfuture devices such as DEMO plays an essential role in fusion research. Thus, thebenchmark of high-resolution MHD equilibrium and stability solvers is an important stepin the verification and validation of the involved numerical codes. Such benchmarks aregreatly facilitated when all codes share the same physics and machine data ontology andmethods for reading and writing the data, as in the European Integrated Modellingframework [1], presently maintained by the EUROfusion Code Development WorkPackage. Under its auspices, a scientific workflow, coded in Kepler [2] and dedicated tothe analysis of MHD activity in tokamak plasmas, has been developed, that can becoupled to equilibrium reconstruction codes or discharge simulator scientific workflows.The workflow presently includes HELENA [3], CHEASE [4] and CAXE [5] equilibriumcodes and ILSA [6], MARS [7], MARS-F [8] and KINX [5] linear MHD stability codes.This paper presents the benchmark of the codes integrated therein on custom-madecircular and elongated plasma equilibria as well as JET and AUG plasma equilibriaderived from experimental data. The study involved internal kink and global modesextending to the vacuum region. Radial and poloidal convergence analysis and growthrate dependence of global modes on the distance of the ideal conducting wall to theplasma boundary are addressed. Examples of interchangeability between some of theinvolved codes, an added value of the workflow user interface, are also included.
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