| 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. |
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| 3. |
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| 4. |
- Bergsåker, Henric, et al.
(författare)
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Nuclear reaction analysis with ion microbeam of cross sections of surface layers deposited in tokamak divertor
- 2007
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Ingår i: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115 .- 1873-4820. ; 362:2-3, s. 215-221
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Tidskriftsartikel (refereegranskat)abstract
- Ion micro beam analysis has been applied to the investigation of plasma deposited layers covering the divertor tiles in the JET tokamak. Since the layers are about 100 μm thick they are too thick to be completely investigated by ordinary ion beam analysis. Cross sections of the layers were prepared by cutting and polishing. Elemental depth profiles were determined from the two dimensional images that could be derived by nuclear reaction analysis and resonant backscattering spectrometry, using ion beams focused to a few μm spot size. A combination of analysis methods are shown, which allow measurements of the concentration profiles of carbon, beryllium, deuterium, oxygen and stainless steel components at levels of a few percent, with an accuracy better than 10%.
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| 5. |
- Emmoth, Birger, et al.
(författare)
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Fuel removal from bumper limiter tiles by using a pulsed excimer laser
- 2005
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Ingår i: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115 .- 1873-4820. ; 337-39:1-3, s. 639-643
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Tidskriftsartikel (refereegranskat)abstract
- Samples of a limiter tile from the TEXTOR tokamak were investigated by scanning electron microscopy and nuclear reaction analysis both before and after laser heating. SEM images showed spheres and thin flakes covering the surface which are the areas modified by plasma particles striking under grazing angles. Due to roughness of the surface there are shadowed regions between the 'flakes'. Laser pulses did not lead to expected common ablation of the surface. Features that looked like 'melting' of thin surface layers were rather observed. The initial deuterium content in the surface layer of tiles was of the order of 10(18) D atoms per cm(2). After the laser light impact the content decreased with 60-70%; by reducing the deposited power by a factor four, the deuterium content was decreased by 40-50%. We make the interpretation that we approach a threshold of the laser detritiation method in fusion devices.
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| 6. |
- Emmoth, Birger, et al.
(författare)
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In-situ measurements of carbon and deuterium deposition using the fast reciprocating probe in TEXTOR
- 2009
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Ingår i: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115 .- 1873-4820. ; 390-91, s. 179-182
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Tidskriftsartikel (refereegranskat)abstract
- Silicon samples were exposed in the scrape-off layer of the TEXTOR plasma using a fast reciprocating probe, with the aim of studying carbon deposition and deuterium retention during Dynamic Ergodic Divertor (DED) operation. Separate samples were exposed for 300 ms at the flat-top phase of neutral beam heated discharges. The exposure conditions were varied on a shot-to-shot basis by external magnetic perturbations generated by the DED in the m/n = 3/1, DC regime, base configuration. Nuclear Reaction Analysis (NRA) was used to characterise collector sample surfaces after their exposure. Enhanced concentrations of both carbon and deuterium (C 3-10 x 10(16) at./cm(2), D 8-60 x 10(15) at./cm(2)) were found. The D/C ratio was less than unity which indicates that most of the carbon and deuterium were co-deposited. Carbon e-folding lengths of about 2 cm were found on both toroidal sides of the probe independent of DED perturbations.
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| 7. |
- Emmoth, Birger, 1945-
(författare)
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Ionic impacts on solids and sputtering phenomena : experiments in the low-keV region, using optical and collector methods
- 1979
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Energetic ions bombarding the surface of a solid result in a manifold of processes. An ion with sufficient energy can penetrate into the solid. The slowing-down process represents a transfer of energy to the lattice atoms. Part of this energy is deposited on the target surface and may result in sputtering, the release of particles from the target. Emitted particles are to some extent excited and by detecting the photon intensity and relating this intensity to the surface concentration of a particular element, depth concentrations have been measured. The results represents measurements of mean projected ranges and straggling. By measuring the depth concentrations before and after annealing migration studies have been performed. Dose-dependent effects, blistering and flaking, have also been investigated by this method as well as by replica studies. The released particles have been collected on a semi-circular collector made by high-purity aluminum. Quantitative measurements of the angular distribution of sputtered particles have been performed. Deviations from a cosine distribution were observed, probably as a result of grain orientation effects in polycrystalline targets. By the use of an applied electric field the fraction of charged particles could be measured in the case of sputtering of a tungsten target.
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| 8. |
- Emmoth, Birger, et al.
(författare)
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Particle collection at the plasma edge by a fast reciprocating probe at the TEXTOR tokamak
- 2003
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Ingår i: Journal of Nuclear Materials. - 0022-3115 .- 1873-4820. ; 313, s. 729-733
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Tidskriftsartikel (refereegranskat)abstract
- A fast reciprocating probe system capable of transferring different types of heads has been constructed and implemented at the TEXTOR tokamak for diagnosing the plasma edge. It gives the possibility of using a particle collector technique to extend studies of material transport from the scrape-off layer to the near plasma edge. For the first time, the system was used for exposures of graphite samples (pure and coated with a-C:H or W) at positions both within and outside the last closed flux surface. Various surface analysis methods were applied to investigate the probe morphology and, by this, to determine radial deposition profiles of boron impurities and deuterium. The profiles for boron are remarkably flat whilst those for deuterium are characterised by a steep decay with the e-folding length of approximately 15 mm. On tungsten-coated samples almost no deuterium was found, most likely because of little carbon co-deposition, shallow implantation and low trapping coefficient of deuterons in the tungsten layer. Reconstruction of experimental results by means of a multifluid TECXY code helped to identify the contribution of impurity sources (limiters, wall) to the observed radial distribution of species.
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| 9. |
- Gasior, P., et al.
(författare)
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Laser-induced removal of co-deposits from graphitic plasma-facing components : Characterization of irradiated surfaces and dust particles
- 2009
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Ingår i: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115 .- 1873-4820. ; 390-91, s. 585-588
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Tidskriftsartikel (refereegranskat)abstract
- Laser-induced fuel desorption and ablation of co-deposited layers on limiter plates from the TEXTOR tokamak have been studied. Gas phase composition was monitored in situ, whereas the ex situ studies have been focused on the examination of irradiated surfaces and broad analysis of dust generated by ablation of co-deposits. The size of the dust grains is in the range of few nanometers to hundreds of micrometers. These are fuel-rich dust particles, as determined by nuclear reaction analysis. The presence of deuterium in dust indicates that not all fuel species are transferred to the gas phase during irradiation. This also suggests that photonic removal of fuel and the ablation of co-deposit from plasma-facing components may lead to the redistribution of fuel-containing dust to surrounding areas.
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| 10. |
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| 11. |
- Kreter, A., et al.
(författare)
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Deuterium retention in different carbon materials exposed in TEXTOR :
- 2008
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Ingår i: PROCEEDINGS OF THE 17TH INTERNATIONAL VACUUM CONGRESS/13TH INTERNATIONAL CONFERENCE ON SURFACE SCIENCE/INTERNATIONAL CONFERENCE ON NANOSCIENCE AND TECHNOLOGY. - Bristol : IOP PUBLISHING LTD. ; , s. 062024-
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Konferensbidrag (refereegranskat)abstract
- CFC NB31, CFC DMS780 and fine-grain graphite EK98 were simultaneously exposed in the SOL of TEXTOR in order to measure the retention of deuterium in the material bulk. After exposure, the samples were analysed by thermal desorption spectrometry and nuclear reaction analysis with a conventional beam as well as with a microbeam. The deuterium retention amounts (2-4).10(21) D/m(2) for the incident fluence of similar to 2.10(25) D/m(2). The retention values are similar for both CFC materials and lower by similar to 20-40% for EK98. The retention in all three materials scales roughly with a square root of incident fluence without saturation for the range of fluences obtained. The majority of deuterium is stored in a surface layer of <8 mu m. However, in NB31 deuterium is detectable as deep as 80 mu m. The in-bulk retention estimated for a TEXTOR experimental campaign of approximate to 7500 s of plasma has a contribution of approximate to 10% to the total retention, which is dominated by deuterium-carbon co-deposition.
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| 12. |
- Litnovsky, Andrey, et al.
(författare)
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Carbon transport, deposition and fuel accumulation in castellated structures exposed in TEXTOR
- 2007
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Ingår i: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115 .- 1873-4820. ; 367, s. 1481-1486
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Tidskriftsartikel (refereegranskat)abstract
- In order to maintain the thermo-mechanical durability of ITER it is proposed to castellate the interior surface of the first wall and divertor by splitting them into small-size cells [W. Daener et a]., Fusion Eng. Des. 61&62 (2002) 61]. A concern is the accumulation of fuel in the gaps of the castellation. In TEXTOR, molybdenum limiters were exposed in the scrape-off layer (SOL) plasma to assess fuel accumulation. The first limiter was exposed under deposition-dominated conditions. Carbon deposits were formed both on top surfaces and in the gaps. About 0.12% of the impinging D-fluence was found in the gaps. Another castellated limiter was exposed under erosion-dominated conditions. Deposited layers were found only on the plasma shadowed areas of the gaps. A significant amount of molybdenum from the limiter was found intermixed in the deposit. The gaps contained similar to 0.03% of the impinging D-fluence. Modeling was performed to simulate carbon transport into the gaps.
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| 13. |
- Litnovsky, A., et al.
(författare)
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Direct comparative test of single crystal and polycrystalline diagnostic mirrors exposed in TEXTOR in erosion conditions
- 2005
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Ingår i: 32nd EPS Conference on Plasma Physics 2005, EPS 2005, Held with the 8th International Workshop on Fast Ignition of Fusion Targets. - 9781622763320 ; , s. 1726-1729
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Konferensbidrag (refereegranskat)abstract
- First direct comparative test of single crystal and polycrystalline diagnostic mirror materials under erosion conditions has been made in TEXTOR. Before exposure in TEXTOR, glow discharge cleaning has efficiently restored the reflectivity of initially oxidized mirrors. After the exposure, no significant changes in total reflectivity were observed. Drastic increase of diffuse reflectivity was measured for polycrystalline molybdenum mirror, but not for the single crystal. Thus, specular reflectivity of single crystal is significantly higher than of polycrystalline one. The most affected wavelength range is 250-1000 nm, no significant changes of reflectivity was noticed in the range 1000-2000 nm. No or negligible effect of erosion on polarization characteristics of mirrors was measured.
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| 14. |
- Litnovsky, A., et al.
(författare)
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Experimental investigations of castellated monoblock structures in TEXTOR
- 2005
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Ingår i: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115 .- 1873-4820. ; 337-39:1-3, s. 917-921
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Tidskriftsartikel (refereegranskat)abstract
- To insure the thermo-mechanical durability of ITER it is planned to manufacture the castellated armour of the divertor i.e. to split the armour into cells [W. Daener et al., Fusion Eng. Des. 61T62 (2002) 61]. This will cause an increase of the surface area and may lead to carbon deposition and tritium accumulation in the gaps in between cells. To investigate the processes of deposition and fuel accumulation in gaps, a castellated test-limiter was exposed to the SOL plasma of TEXTOR. The geometry of castellation used was the same as proposed for the vertical divertor target in ITER [W. Daener et al., Fusion Eng. Des. 61T62 (2002) 61]. After exposure the limiter was investigated with various surface diagnostic techniques. Deposited layers containing carbon, hydrogen, deuterium and boron were found both on top plasma-facing surfaces and in the gaps. The amount of deuterium in the gaps was at least 30% of that found on the top surfaces.
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| 15. |
- Litnovsky, A., et al.
(författare)
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Overview of material migration and mixing, fuel retention and cleaning of ITER-like castellated structures in TEXTOR
- 2011
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Ingår i: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115 .- 1873-4820. ; 415:1, s. S289-S292
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Tidskriftsartikel (refereegranskat)abstract
- Plasma-facing components (PFCs) in ITER will be castellated by splitting them into small-size blocks to maintain the thermo-mechanical stability. However, there are concerns in particular on retention of codeposited radioactive fuel in the gaps. An R&D program is underway in TEXTOR addressing this acute issue of castellation. Material migration and fuel inventory are investigated using long- and short-term discharge-resolved experiments with castellated structures in TEXTOR. Significant impurity transport to the gaps was detected and results were in part quantitatively reproduced with 3D-GAPS code. Deposits containing up to 70 at.% of tungsten on the gap areas closest to the plasma were detected in recent experiments. Deposition in the gaps accompanied by metal mixing demand for development of effective cleaning techniques. In experiments with ITER-like castellation, the gaps were cleaned from carbonaceous deposits using oxygen plasmas at 350 degrees C. This contribution contains an overview of experimental and modeling results along with recommendations for PFCs in ITER.
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| 16. |
- Pisarev, A., et al.
(författare)
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Deuterium accumulation in carbon materials at high fluence
- 2009
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Ingår i: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115 .- 1873-4820. ; 390-91, s. 677-680
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Tidskriftsartikel (refereegranskat)abstract
- D retention in fine grain graphite MPG-8 and carbon fiber composite NB31 after exposure to plasma was investigated by means of thermal desorption spectroscopy. It was observed, that deuterium accumulation in the two materials was similar in the region of the fluence of 10(22)-4 x 10(24) D+/m(2), though NB31 retains about twice as much. The retention in MPG-8 reveals no saturation at high fluences and no flux dependence in the range of (0.5-3.5) x 10(20) D+/m(2) s. The difference between polished and unpolished samples, as well as between samples kept in air for various times after irradiation was within the experimental uncertainty.
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| 17. |
- Popov, V., et al.
(författare)
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Morphology of PZT-PMN films grown from airflow
- 2003
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Ingår i: Integrated Ferroelectrics. - : Informa UK Limited. - 1058-4587 .- 1607-8489. ; 54, s. 575-584
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Tidskriftsartikel (refereegranskat)abstract
- Lead zirconate titanate-lead magnesium niobate (PZT-PMN) films with thicknesses in the range 5 to 200 mum were fabricated by deposition from airflow at room temperature. Precursor powders of PZT and PMN were mixed in a ball mill and entrained in an airflow generated by a commercial jet-mill ( Micron-Master 02-506 ). Films were grown at a rate of 1 mum/minute onto the Ni and tungsten carbide substrates exposed to the air-powder mixture. Unfired, poled PZT-PMN films provided an audio acoustic response and form translucent 20-30 mum thick layers. Full density of the air-flow deposited materials has been achieved at temperatures 450degreesC lower than that typical for ball milled bulk PZT-PMN ceramics. After sintering for 2 hours at 850degreesC PZT-PMN ceramics with relative density of 99.5%, epsilon similar to 2170, tan delta similar to 0.009 @1 kHz and acceptable piezoelectric properties was obtained. Films sintered 2 hours at 1000degreesC showed remnant polarization P-r = 26 muC/cm(2) , P-s = 36 muC/cm(2) @95 kV/cm, and 50 Hz ac electric breakdown field as high as 120-170 kV/cm. Unusual grain morphology governs improved sinterability and enhanced properties of ferroelectric ceramics. Optical and AFM micrographs revealed needle-like grains preferentially oriented parallel to the air-powder stream. As-deposited films were found to be very non-uniform across the thickness: glass-like and with tensile strain on the contact surface. This strain is released and film microcrystalline structure becomes uniform in annealed film.
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| 18. |
- Ratynskaia, Svetlana V., et al.
(författare)
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Capture by aerogel-characterization of mobile dust in tokamak scrape-off layer plasmas
- 2009
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 49:12
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this letter is to demonstrate the feasibility and potential of the novel in situ dust diagnostic method-capture by aerogel targets. Aerogel, a highly porous material with a density of a few tens of kg m(-3), allows capturing of dust particles present during the discharge without destroying them. The first exposures in the TEXTOR scrape-off layer plasma showed that such targets are able to capture both slow and fast particles with sizes in the range from submicrometre to similar to 100 mu m. The technique provides information on dust velocity and size distribution as well as dust flux estimates. The composition and texture of the captured dust can also be studied in detail to shed light on dust formation processes.
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| 19. |
- Rubel, Marek J., 1953-, et al.
(författare)
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Fuel removal from plasma-facing components by oxidation-assisted technique : An overview of surface morphology after oxidation
- 2007
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Ingår i: Journal of Nuclear Materials. - : Elsevier. - 0022-3115 .- 1873-4820. ; 363-365, s. 877-881
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Tidskriftsartikel (refereegranskat)abstract
- Oxygen-assistedfuelremoval is reported for laboratory-prepared a-C:D films and for layers obtained by boronisation in a tokamak and then exposed to a helium–oxygen glow discharge in TEXTOR. Oxidation of thick mixed-material co-deposits under laboratory conditions is also presented. The essential results are following: (i) laboratory-prepared amorphous deuterated carbon (a-C:D) layers are decomposed efficiently by the He–O2 glow: D and C contents are decreased by a factor of 45–220 and 25–60, respectively; (ii) the same treatment of the boronised films leads to the release of D but no removal of carbon is observed; (iii) the thermal oxidation (at 300 °C in air under laboratory conditions) of co-deposits on PFC and probes exposed to the SOL reduces the D content by a factor of 4–5 after 2 h, whereas nearly complete fuelremoval (98%) occurs after 10 h at 300 °C. The study shows that the fuelremoval efficiency is dependent on the overall composition of the mixed layer. It is high from pure a-C:D films but distinctly less efficient from real co-deposits.
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| 20. |
- Rubel, Marek J., et al.
(författare)
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Graphite-tungsten twin limiters in studies of material mixing processes on high heat flux components
- 2000
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Ingår i: Journal of Nuclear Materials. - 0022-3115 .- 1873-4820. ; 283, s. 1089-1093
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Tidskriftsartikel (refereegranskat)abstract
- Graphite-tungsten twin limiters have been used at the TEXTOR tokamak for testing of high-Z metals as plasma facing materials and, in particular, for studies of the local and global transport of tungsten. The emphasis was on the change in surface morphology of limiters: the formation and properties of multicomponent co-deposits and the trapping characteristics of fuel on carbon and high-Z substrates exposed to the plasma under various operation conditions, i.e., heating scenarios, configuration of limiters, etc. Vast quantities of tungsten have been found to be locally transported to the adjacent graphite surfaces. Ion beam analysis also indicated strong intermixing of carbon, tungsten and boron on the hottest parts of the limiters. The results are discussed in terms of various mechanisms involving the transport of tungsten-containing species, possibilities of oxide production and formation of mixed (W-C-B) compounds.
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| 21. |
- Wienhold, P., et al.
(författare)
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Exposure of metal mirrors in the scrape-off layer of TEXTOR
- 2005
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Ingår i: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115 .- 1873-4820. ; 337-39:03-jan, s. 1116-1120
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Tidskriftsartikel (refereegranskat)abstract
- Large molybdenum mirrors have been exposed in the SOL of TEXTOR in order to simulate conditions relevant for ITER optical components. Distortions of the reflectivity - increase as well as decrease - are found in the erosion and deposition dominated areas, respectively. The changes are most pronounced in the near UV and level off in the IR and can partly be attributed to observed surface changes. A novel periscope system was installed and mirrors exposed in a pilot experiment to simulate the transmission of light to distant sensors in ITER.
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| 22. |
- Åkermark, Torbjörn, et al.
(författare)
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Laser annealing in combination with mass spectroscopy, a technique to study deuterium on tokamak carbon samples, a tool for detritiation
- 2006
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Ingår i: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115 .- 1873-4820. ; 359:3, s. 220-226
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Tidskriftsartikel (refereegranskat)abstract
- In this study, a method is presented based on mass spectroscopy to measure the a real density of deuterium on a graphite surface exposed to tokamak discharges. The studied sample was cut from a bumper limiter exposed in the TEXTOR tokamak and annealed by a 1 J Excimer laser (KrF). The energy used was 400 mJ cm(-2), which is below the threshold for ablation. 1 J cm(-2). The release of HD and D, was measured by a mass spectroscopy set-up and no other species released from the sample were detected in this experiment. The amount of D released from the sample after 20 laser pulses was measured to 7 x 10(16) D atoms per cm(-2) (for this particular sample) and most of the hydrogen at the surface was released in the first pulse, as checked by nuclear reaction analysis (NRA) techniques, which gave changes of the amount of deuterium before and after laser annealing. The sensitivity in this experiment was 5 x 10(14) atoms per cm(-2) for HD and 5 x 10(13) atoms per cm(-2) for D-2.
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