| 1. |
- Abel, I, et al.
(författare)
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Overview of the JET results with the ITER-like wall
- 2013
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 53:10, s. 104002-
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Tidskriftsartikel (refereegranskat)abstract
- Following the completion in May 2011 of the shutdown for the installation of the beryllium wall and the tungsten divertor, the first set of JET campaigns have addressed the investigation of the retention properties and the development of operational scenarios with the new plasma-facing materials. The large reduction in the carbon content (more than a factor ten) led to a much lower Z(eff) (1.2-1.4) during L- and H-mode plasmas, and radiation during the burn-through phase of the plasma initiation with the consequence that breakdown failures are almost absent. Gas balance experiments have shown that the fuel retention rate with the new wall is substantially reduced with respect to the C wall. The re-establishment of the baseline H-mode and hybrid scenarios compatible with the new wall has required an optimization of the control of metallic impurity sources and heat loads. Stable type-I ELMy H-mode regimes with H-98,H-y2 close to 1 and beta(N) similar to 1.6 have been achieved using gas injection. ELM frequency is a key factor for the control of the metallic impurity accumulation. Pedestal temperatures tend to be lower with the new wall, leading to reduced confinement, but nitrogen seeding restores high pedestal temperatures and confinement. Compared with the carbon wall, major disruptions with the new wall show a lower radiated power and a slower current quench. The higher heat loads on Be wall plasma-facing components due to lower radiation made the routine use of massive gas injection for disruption mitigation essential.
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| 2. |
- Romanelli, F, et al.
(författare)
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Overview of the JET results
- 2011
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 51:9
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Tidskriftsartikel (refereegranskat)abstract
- Since the last IAEA Conference JET has been in operation for one year with a programmatic focus on the qualification of ITER operating scenarios, the consolidation of ITER design choices and preparation for plasma operation with the ITER-like wall presently being installed in JET. Good progress has been achieved, including stationary ELMy H-mode operation at 4.5 MA. The high confinement hybrid scenario has been extended to high triangularity, lower ρ*and to pulse lengths comparable to the resistive time. The steady-state scenario has also been extended to lower ρ*and ν*and optimized to simultaneously achieve, under stationary conditions, ITER-like values of all other relevant normalized parameters. A dedicated helium campaign has allowed key aspects of plasma control and H-mode operation for the ITER non-activated phase to be evaluated. Effective sawtooth control by fast ions has been demonstrated with3He minority ICRH, a scenario with negligible minority current drive. Edge localized mode (ELM) control studies using external n = 1 and n = 2 perturbation fields have found a resonance effect in ELM frequency for specific q95values. Complete ELM suppression has, however, not been observed, even with an edge Chirikov parameter larger than 1. Pellet ELM pacing has been demonstrated and the minimum pellet size needed to trigger an ELM has been estimated. For both natural and mitigated ELMs a broadening of the divertor ELM-wetted area with increasing ELM size has been found. In disruption studies with massive gas injection up to 50% of the thermal energy could be radiated before, and 20% during, the thermal quench. Halo currents could be reduced by 60% and, using argon/deuterium and neon/deuterium gas mixtures, runaway electron generation could be avoided. Most objectives of the ITER-like ICRH antenna have been demonstrated; matching with closely packed straps, ELM resilience, scattering matrix arc detection and operation at high power density (6.2 MW m-2) and antenna strap voltages (42 kV). Coupling measurements are in very good agreement with TOPICA modelling. © 2011 IAEA, Vienna.
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| 3. |
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Overview of the JET results
- 2015
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 55:10
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Tidskriftsartikel (refereegranskat)
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| 4. |
- Pucella, G., et al.
(författare)
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Overview of the FTU results
- 2022
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 62:4
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Forskningsöversikt (refereegranskat)abstract
- Since the 2018 IAEA FEC Conference, FTU operations have been devoted to several experiments covering a large range of topics, from the investigation of the behaviour of a liquid tin limiter to the runaway electrons mitigation and control and to the stabilization of tearing modes by electron cyclotron heating and by pellet injection. Other experiments have involved the spectroscopy of heavy metal ions, the electron density peaking in helium doped plasmas, the electron cyclotron assisted start-up and the electron temperature measurements in high temperature plasmas. The effectiveness of the laser induced breakdown spectroscopy system has been demonstrated and the new capabilities of the runaway electron imaging spectrometry system for in-flight runaways studies have been explored. Finally, a high resolution saddle coil array for MHD analysis and UV and SXR diamond detectors have been successfully tested on different plasma scenarios.
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| 5. |
- De Angeli, M., et al.
(författare)
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Pre-plasma remobilization of ferromagnetic dust in FTU and possible interference with tokamak operations
- 2019
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Ingår i: Nuclear Fusion. - : IOP PUBLISHING LTD. - 0029-5515 .- 1741-4326. ; 59:10
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Tidskriftsartikel (refereegranskat)abstract
- Experimental evidence of the pre-plasma remobilization of ferromagnetic dust in FTU is presented. Thomson scattering data and IR camera observations document the occurrence of intrinsic dust remobilization prior to discharge start-up and allow for a rough calculation of the average mobilized dust density. Exposures of calibrated extrinsic non-magnetic and ferromagnetic dust to sole magnetic field discharges reveal that the magnetic moment force is the main mobilizing force, as confirmed by theoretical estimates. Pre-plasma remobilization probabilities are computed for varying dust sizes. The impact of prematurely remobilized dust on the breakdown and burn-through start-up phases is investigated together with the discharge termination induced once the plasma plateau is established.
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| 6. |
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| 7. |
- De Angeli, M., et al.
(författare)
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Evidence for high-velocity solid dust generation induced by runaway electron impact in FTU
- 2023
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 63:1
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Tidskriftsartikel (refereegranskat)abstract
- Post-mortem and in situ evidence is presented in favor of the generation of high-velocity solid dust during the explosion-like interaction of runaway electrons with metallic plasma-facing components in FTU. The freshly-produced solid dust is the source of secondary de-localized wall damage through high-velocity impacts that lead to the formation of craters, which have been reproduced in dedicated light gas gun impact tests. This novel mechanism, of potential importance for ITER and DEMO, is further supported by surface analysis, multiple theoretical arguments and dust dynamics modeling.
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| 8. |
- Hirai, T., et al.
(författare)
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R&D on full tungsten divertor and beryllium wall for JET ITER-like wall project
- 2007
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Ingår i: Fusion engineering and design. - : Elsevier BV. - 0920-3796 .- 1873-7196. ; 82:15-24, s. 1839-1845
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Tidskriftsartikel (refereegranskat)abstract
- The ITER reference materials have been tested separately in tokamaks, plasma simulators, ion beams and high heat flux test beds. In order to perform a fully integrated material test JET has launched the ITER-like Wall Project with the aim of installing a full metal wall during the next major shutdown. As a result of R&D projects in 2005-2006, bulk tungsten tiles are foreseen at the outer horizontal target and tungsten coating at the other divertor tiles. In some regions of the main chamber, beryllium coated Inconel tiles and bulk beryllium tiles are utilised which include marker tiles as erosion diagnostics. This paper gives an overview of the R&D carried out in the frame of the ITER-like Wall Project on the development of an inertially cooled bulk tungsten tile design and the characterization of tungsten and beryllium coating technologies.
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| 9. |
- Maier, H., et al.
(författare)
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Tungsten and beryllium armour development for the JET ITER-like wall project
- 2007
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 47:3, s. 222-227
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Tidskriftsartikel (refereegranskat)abstract
- For the ITER-like wall project at JET the present main chamber CFC tiles will be exchanged with Be tiles and in parallel a fully tungsten-clad divertor will be prepared. Therefore three R&D programmes were initiated: Be coatings on Inconel as well as Be erosion markers were developed for the first wall of the main chamber. High heat flux screening and cyclic loading tests carried out on the Be coatings on Inconel showed excellent performance, above the required power and energy density. For the divertor a conceptual design for a bulk W horizontal target plate was investigated, with the emphasis on minimizing electromagnetic forces. The design consisted of stacks of W lamellae of 6 mm width that were insulated in the toroidal direction. High heat flux tests of a test module were performed with an electron beam at an absorbed power density Up to 9 MW m(-2) for more than 150 pulses and finally with increasing power loads leading to surface temperatures in excess of 3000 degrees C. No macroscopic failure occurred during the test while SEM showed the development of micro-cracks on the loaded surface. For all other divertor parts R&D was performed to provide the technology to coat the 2-directional CFC material used at JET with thin tungsten coatings. The W-coated CFC tiles were subjected to heat loads with power densities ranging up to 23.5 MW m(-2) and exposed to cyclic heat loading for 200 pulses at 10.5 MW m(-2). All coatings developed cracks perpendicular to the CFC fibres due to the stronger contraction of the coating upon cool-down after the heat pulses.
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| 10. |
- Castaldo, C., et al.
(författare)
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Diagnostics of fast dust particles in tokamak edge plasmas
- 2007
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 47:7, s. L5-L9
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Tidskriftsartikel (refereegranskat)abstract
- The use of electrostatic probes as a diagnostic tool of the dust particles in the tokamak edge plasmas is investigated. Probe measurements of electrostatic fluctuations in the scrape-off layer of the Frascati Tokamak Upgrade revealed that some features of the signals can be explained only by a local non-propagating phenomenon. These signal features are shown to be both in qualitative and quantitative agreement with ionization, and consequent extra charge collected by the probes, due to the impact of micrometre-sized dust at a velocity of the order of 10 km s(- 1). Electron microscope analysis of the probe surface yielded direct support for such an interpretation.
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| 11. |
- De Angeli, M., et al.
(författare)
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Note : Simultaneous electrical and optical detection of expanding dense partially ionized vapour clouds
- 2011
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Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 0034-6748 .- 1089-7623. ; 82:10, s. 106101-
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Tidskriftsartikel (refereegranskat)abstract
- The scheme and construction of an electro-optical probe able to collect charge and detect optical emission from expanding dense partially ionized vapour clouds are reported. The instrument can be applied to phenomena such as dust impact ionization and solid target laser ablation. First, results of measurements of expanding plasma cloud formed upon ablating W target are presented. Use of the instrument in different experimental facilities, including tokamak, is discussed.
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| 12. |
- Giovannozzi, E., et al.
(författare)
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Dust in FTU with the Thomson scattering diagnostic
- 2008
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Ingår i: AIP CONF PROC. - : AIP. ; , s. 213-214
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Konferensbidrag (refereegranskat)abstract
- The Thomson scattering diagnostic has been used to measure the dust present in plasma discharges on FTU tokamak after disruption. The vaporization of the dust particles due to die high power of the laser used by the Thomson scattering diagnostic imply that only a rough estimate of the particle size could be derived from the elastic scattering of the laser light. A simple model for dust particle evaporation has been used to infer the size of the dust particle from the scattered light data.
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| 13. |
- Philipps, V., et al.
(författare)
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Development of laser-based techniques for in situ characterization of the first wall in ITER and future fusion devices
- 2013
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 53:9, s. 093002-
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Tidskriftsartikel (refereegranskat)abstract
- Analysis and understanding of wall erosion, material transport and fuel retention are among the most important tasks for ITER and future devices, since these questions determine largely the lifetime and availability of the fusion reactor. These data are also of extreme value to improve the understanding and validate the models of the in vessel build-up of the T inventory in ITER and future D-T devices. So far, research in these areas is largely supported by post-mortem analysis of wall tiles. However, access to samples will be very much restricted in the next-generation devices (such as ITER, JT-60SA, W7-X, etc) with actively cooled plasma-facing components (PFC) and increasing duty cycle. This has motivated the development of methods to measure the deposition of material and retention of plasma fuel on the walls of fusion devices in situ, without removal of PFC samples. For this purpose, laser-based methods are the most promising candidates. Their feasibility has been assessed in a cooperative undertaking in various European associations under EFDA coordination. Different laser techniques have been explored both under laboratory and tokamak conditions with the emphasis to develop a conceptual design for a laser-based wall diagnostic which is integrated into an ITER port plug, aiming to characterize in situ relevant parts of the inner wall, the upper region of the inner divertor, part of the dome and the upper X-point region.
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| 14. |
- Ratynskaia, Svetlana V., et al.
(författare)
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In situ dust detection in fusion devices
- 2008
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Ingår i: Plasma Physics and Controlled Fusion. - : IOP Publishing. - 0741-3335 .- 1361-6587. ; 50:12, s. 124046-
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Tidskriftsartikel (refereegranskat)abstract
- Diagnostics for monitoring dust in tokamaks during plasma discharges, both established and currently being developed, are discussed with a focus on the range of dust parameters they can detect. Visible imaging can currently be used for dust particles bigger than a few mu m and velocities below 1 km s(-1). The dust impact ionization phenomenon can be used for the detection of particles with velocities above a few km s(-1). Laser light scattering gives an insight into the amount of sub-micron dust. Aerogels, light porous materials, allow capturing of dust particles without destroying them and determining their velocity. Other methods include the microbalance technique and electrostatic dust detectors. A recent suggestion to use the effects of dust on collective scattering for diagnostic purposes is also discussed.
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| 15. |
- De Angeli, M., et al.
(författare)
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Cross machine investigation of magnetic tokamak dust : Morphological and elemental analysis
- 2021
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Ingår i: Fusion engineering and design. - : Elsevier BV. - 0920-3796 .- 1873-7196. ; 166
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Tidskriftsartikel (refereegranskat)abstract
- The presence of magnetic dust can be an important issue for future fusion reactors where plasma breakdown is critical. Magnetic dust has been collected from contemporary fusion devices (FTU, Alcator C-Mod, COMPASS and DIII-D) that feature different plasma facing components. The results of morphological and elemental analysis are presented. Magnetic dust is based on steel or nickel alloys and its magnetism is generated by intense plasma material interactions. In spite of the strong similarities in terms of morphology and composition, X-ray diffraction analysis revealed differences in the structural evolution that leads to non-trivial magnetic responses.
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| 16. |
- De Angeli, M., et al.
(författare)
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Cross machine investigation of magnetic tokamak dust; structural and magnetic analysis
- 2021
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Ingår i: Nuclear Materials and Energy. - : Elsevier BV. - 2352-1791. ; 28
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Tidskriftsartikel (refereegranskat)abstract
- Magnetic dust collected from multiple fusion devices (FTU, Alcator C-Mod, COMPASS) that feature different plasma-facing components (PFCs) and toroidal magnetic fields has been analyzed by means of the X-ray diffraction technique aiming to investigate the nature and origin of dust magnetism. Analysis led to the conclusion that the main mechanism of ferromagnetic dust formation is the change of iron crystalline phase from austenitic to ferritic during the re-solidification of stainless steel droplets. Analysis also revealed differences in the collected dust structure and an unexpectedly high amount of stainless steel based dust in its native austenitic phase. Theoretical estimates showed that the magnetic moment force can also mobilize strongly paramagnetic adhered dust prior to the establishment of proper tokamak discharges. The post-mortem analysis of dust collected during pure magnetic discharges in FTU confirmed these estimates.
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| 17. |
- Giovannozzi, E., et al.
(författare)
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Dust measurement with Thomson scattering in FTU
- 2008
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Ingår i: AIP Conference Proceedings. - : AIP. - 0094-243X .- 1551-7616. ; 988, s. 148-151
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Tidskriftsartikel (refereegranskat)abstract
- The size distribution of dust particles present in FTU after disruptions has been evaluated in the range 0.05 mu m - 0.1 mu m using the Thomson scattering system. Rayleigh approximation has been used to estimate the dust size. The distribution, although the radii considered do not differ more than an order of magnitude, behave like a power law. The laser energy density far exceed that necessary to vaporize, at least partially, the particles. This can affect the previous estimate of the particle sizes, and suggests that the effective radii might be larger than the estimated values. A preliminary analysis on the broad band signal is presented.
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| 18. |
- Malaquias, A., et al.
(författare)
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Development of ITER relevant laser techniques for deposited layer characterisation and tritium inventory
- 2013
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Ingår i: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115 .- 1873-4820. ; 438:Suppl., s. S936-S939
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Tidskriftsartikel (refereegranskat)abstract
- Laser Induced Breakdown Spectroscopy (LIBS) is a potential candidate to monitor the layer composition and fuel retention during and after plasma shots on specific locations of the main chamber and divertor of ITER. This method is being investigated in a cooperative research programme on plasma devices such as TEXTOR, FTU, MAGNUM-PSI and in other various laboratorial experiments. In this paper LIBS results from targets of D-H-rich carbon films and mixed W-Al-C deposits on bulk tungsten substrates are reported (simulating ITER-like deposits with Al as proxy for Be). Two independent methods, one to determine the relative elemental composition and the other the absolute contents of the target based on the experimental LIBS signals are proposed. The results show that LIBS has the capability to provide the relative concentrations of the elements on the deposited layer when the experimental conditions on the targets surface are identical to the calibration samples.
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