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Ström, P., Petersson, P., Rubel, M., Bergsåker, H., Bykov, I., Frassinetti, L., . . . et al., . (2019). Analysis of deposited layers with deuterium and impurity elements on samples from the divertor of JET with ITER-like wall. Journal of Nuclear Materials, 516, 202-213
Open this publication in new window or tab >>Analysis of deposited layers with deuterium and impurity elements on samples from the divertor of JET with ITER-like wall
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2019 (English)In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 516, p. 202-213Article in journal (Refereed) Published
Abstract [en]

Inconel-600 blocks and stainless steel covers for quartz microbalance crystals from remote corners in the JET-ILW divertor were studied with time-of-flight elastic recoil detection analysis and nuclear reaction analysis to obtain information about the areal densities and depth profiles of elements present in deposited material layers. Surface morphology and the composition of dust particles were examined with scanning electron microscopy and energy-dispersive X-ray spectroscopy. The analyzed components were present in JET during three ITER-like wall campaigns between 2010 and 2017. Deposited layers had a stratified structure, primarily made up of beryllium, carbon and oxygen with varying atomic fractions of deuterium, up to more than 20%. The range of carbon transport from the ribs of the divertor carrier was limited to a few centimeters, and carbon/deuterium co-deposition was indicated on the Inconel blocks. High atomic fractions of deuterium were also found in almost carbon-free layers on the quartz microbalance covers. Layer thicknesses up to more than 1 micrometer were indicated, but typical values were on the order of a few hundred nanometers. Chromium, iron and nickel fractions were less than or around 1% at layer surfaces while increasing close to the layer-substrate interface. The tungsten fraction depended on the proximity of the plasma strike point to the divertor corners. Particles of tungsten, molybdenum and copper with sizes less than or around 1 micrometer were found. Nitrogen, argon and neon were present after plasma edge cooling and disruption mitigation. Oxygen-18 was found on component surfaces after injection, indicating in-vessel oxidation. Compensation of elastic recoil detection data for detection efficiency and ion-induced release of deuterium during the measurement gave quantitative agreement with nuclear reaction analysis, which strengthens the validity of the results.

Keywords
Fusion, Tokamak, Plasma-wall interactions, ToF-ERDA, NRA, SEM
National Category
Fusion, Plasma and Space Physics
Research subject
Physics
Identifiers
urn:nbn:se:kth:diva-240616 (URN)10.1016/j.jnucmat.2018.11.027 (DOI)000458897100020 ()2-s2.0-85060313456 (Scopus ID)
Note

QC 20190125

Available from: 2018-12-20 Created: 2018-12-20 Last updated: 2019-10-29Bibliographically approved
Vasilopoulou, T., Bergsåker, H., Bykov, I., Frassinetti, L., Garcia Carrasco, A., Hellsten, T., . . . Zychor, I. (2019). Improved neutron activation dosimetry for fusion. Fusion engineering and design, 139, 109-114
Open this publication in new window or tab >>Improved neutron activation dosimetry for fusion
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2019 (English)In: Fusion engineering and design, ISSN 0920-3796, E-ISSN 1873-7196, Vol. 139, p. 109-114Article in journal (Refereed) Published
Abstract [en]

Neutron activation technique has been widely used for the monitoring of neutron fluence at the Joint European Torus (JET) whereas it is foreseen to be employed at future fusion plants, such as ITER and DEMO. Neutron activation provides a robust tool for the measurement of neutron fluence in the complex environment encountered in a tokamak. However, activation experiments previously performed at JET showed that the activation foils used need to be calibrated in a real fusion environment in order to provide accurate neutron fluence data. Triggered by this challenge, an improved neutron activation method for the evaluation of neutron fluence at fusion devices has been developed. Activation assemblies similar to those used at JET were irradiated under 14 MeV neutrons at the Frascati Neutron Generator (FNG) reference neutron field. The data obtained from the calibration experiment were applied for the analysis of activation foil measurements performed during the implemented JET Deuterium-Deuterium (D-D) campaign. The activation results were compared against thermoluminescence measurements and a satisfactory agreement was observed. The proposed method provides confidence on the use of activation technique for the precise estimation of neutron fluence at fusion devices and enables its successful implementation in the forthcoming JET Deuterium-Tritium (D-T) campaign.

Place, publisher, year, edition, pages
ELSEVIER SCIENCE SA, 2019
Keywords
Neutron activation, Neutron dosimetry, JET, Fusion
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-269598 (URN)10.1016/j.fusengdes.2019.01.002 (DOI)000458939100015 ()2-s2.0-85059692263 (Scopus ID)
Note

QC 20200401

Available from: 2020-04-01 Created: 2020-04-01 Last updated: 2020-04-01Bibliographically approved
Joffrin, E., Bergsåker, H., Bykov, I., Frassinetti, L., Fridström, R., Garcia Carrasco, A., . . . et al., . (2019). Overview of the JET preparation for deuterium-tritium operation with the ITER like-wall. Nuclear Fusion, 59(11), Article ID 112021.
Open this publication in new window or tab >>Overview of the JET preparation for deuterium-tritium operation with the ITER like-wall
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2019 (English)In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 59, no 11, article id 112021Article in journal (Refereed) Published
Abstract [en]

For the past several years, the JET scientific programme (Pamela et al 2007 Fusion Eng. Des. 82 590) has been engaged in a multi-campaign effort, including experiments in D, H and T, leading up to 2020 and the first experiments with 50%/50% D-T mixtures since 1997 and the first ever D-T plasmas with the ITER mix of plasma-facing component materials. For this purpose, a concerted physics and technology programme was launched with a view to prepare the D-T campaign (DTE2). This paper addresses the key elements developed by the JET programme directly contributing to the D-T preparation. This intense preparation includes the review of the physics basis for the D-T operational scenarios, including the fusion power predictions through first principle and integrated modelling, and the impact of isotopes in the operation and physics of D-T plasmas (thermal and particle transport, high confinement mode (H-mode) access, Be and W erosion, fuel recovery, etc). This effort also requires improving several aspects of plasma operation for DTE2, such as real time control schemes, heat load control, disruption avoidance and a mitigation system (including the installation of a new shattered pellet injector), novel ion cyclotron resonance heating schemes (such as the three-ions scheme), new diagnostics (neutron camera and spectrometer, active Alfven eigenmode antennas, neutral gauges, radiation hard imaging systems...) and the calibration of the JET neutron diagnostics at 14 MeV for accurate fusion power measurement. The active preparation of JET for the 2020 D-T campaign provides an incomparable source of information and a basis for the future D-T operation of ITER, and it is also foreseen that a large number of key physics issues will be addressed in support of burning plasmas.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD, 2019
Keywords
fusion power, JET, tritium, isotope
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-260157 (URN)10.1088/1741-4326/ab2276 (DOI)000484122200001 ()2-s2.0-85070875113 (Scopus ID)
Note

QC 20190926

Available from: 2019-09-26 Created: 2019-09-26 Last updated: 2019-10-04Bibliographically approved
Garzotti, L., Frassinetti, L., Stefániková, E., Bergsåker, H., Bykov, I., Garcia Carrasco, A., . . . Zychor, I. (2019). Scenario development for D-T operation at JET. Nuclear Fusion, 59(7), Article ID 076037.
Open this publication in new window or tab >>Scenario development for D-T operation at JET
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2019 (English)In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 59, no 7, article id 076037Article in journal (Refereed) Published
Abstract [en]

The JET exploitation plan foresees D-T operations in 2020 (DTE2). With respect to the first D-T campaign in 1997 (DTE1), when JET was equipped with a carbon wall, the experiments will be conducted in presence of a beryllium-tungsten ITER-like wall and will benefit from an extended and improved set of diagnostics and higher additional heating power (32 MW neutral beam injection + 8 MW ion cyclotron resonance heating). There are several challenges presented by operations with the new wall: a general deterioration of the pedestal confinement; the risk of heavy impurity accumulation in the core, which, if not controlled, can cause the radiative collapse of the discharge; the requirement to protect the divertor from excessive heat loads, which may damage it permanently. Therefore, an intense activity of scenario development has been undertaken at JET during the last three years to overcome these difficulties and prepare the plasmas needed to demonstrate stationary high fusion performance and clear alpha particle effects. The paper describes the status and main achievements of this scenario development activity, both from an operational and plasma physics point of view.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD, 2019
Keywords
tokamaks, magnetic confinement fusion, nuclear fusion power
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-262997 (URN)10.1088/1741-4326/ab1cca (DOI)000471317000001 ()2-s2.0-85069038696 (Scopus ID)
Note

QC 20191025

Available from: 2019-10-25 Created: 2019-10-25 Last updated: 2019-10-25Bibliographically approved
Rachlew, E. (2018). Fragmentation of imidazole, pyrimidine and purine induced by core ionization: Significance of small-scale chamical environment. Journal of Photochemistry and Photobiology A: Chemistry, 356, 283-289, Article ID 2018.01.003.
Open this publication in new window or tab >>Fragmentation of imidazole, pyrimidine and purine induced by core ionization: Significance of small-scale chamical environment
2018 (English)In: Journal of Photochemistry and Photobiology A: Chemistry, ISSN 1010-6030, Vol. 356, p. 283-289, article id 2018.01.003Article in journal (Refereed) Published
Place, publisher, year, edition, pages
Elsevier, 2018
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-224641 (URN)10.1016/j.jphotochem.2018.01.003 (DOI)000428972800030 ()2-s2.0-85040358168 (Scopus ID)
Note

QC 20180327

Available from: 2018-03-21 Created: 2018-03-21 Last updated: 2020-03-09Bibliographically approved
Ding, B. J., Bergsåker, H., Bykov, I., Frassinetti, L., Garcia Carrasco, A., Hellsten, T., . . . Zychor, I. (2018). Review of recent experimental and modeling advances in the understanding of lower hybrid current drive in ITER-relevant regimes. Nuclear Fusion, 58(9), Article ID 095003.
Open this publication in new window or tab >>Review of recent experimental and modeling advances in the understanding of lower hybrid current drive in ITER-relevant regimes
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2018 (English)In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 58, no 9, article id 095003Article, review/survey (Refereed) Published
Abstract [en]

Progress in understanding lower hybrid current drive (LHCD) at high density has been made through experiments and modeling, which is encouraging given the need for an efficient off-axis current profile control technique in burning plasma. By reducing the wall recycling of neutrals, the edge temperature is increased and the effect of parametric instability (PI) and collisional absorption (CA) is reduced, which is beneficial for increasing the current drive efficiency. Strong single pass absorption is preferred to prevent CA and high LH operating frequency is essential for wave propagation to the core region at high density, presumably to mitigate the effect of PI. The dimensionless parameter that characterizes LH wave accessibility and wave refraction for the experiments in this joint study is shown to bracket the region in parameter space where ITER LHCD experiments will operate in the steady state scenario phase. Further joint experiments and cross modeling are necessary to understand the LHCD physics in weak damping regimes which would increase confidence in predictions for ITER where the absorption is expected to be strong.

Place, publisher, year, edition, pages
Institute of Physics (IOP), 2018
Keywords
lower hybrid current drive, magnetic fusion, ITER
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-270870 (URN)10.1088/1741-4326/aad0aa (DOI)000439338800001 ()2-s2.0-85051170151 (Scopus ID)
Note

QC 20200316

Available from: 2020-03-16 Created: 2020-03-16 Last updated: 2020-03-16Bibliographically approved
Takahashi, O., Kooser, K., Ha, D. T., Myllynen, H., Laksman, J., Rachlew, E. & Kukk, E. (2018). Site-selective bond scission of methylbenzoate following core excitation. Physical Chemistry, Chemical Physics - PCCP, 20(14), 9591-9599
Open this publication in new window or tab >>Site-selective bond scission of methylbenzoate following core excitation
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2018 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 20, no 14, p. 9591-9599Article in journal (Refereed) Published
Abstract [en]

The chemical bond scission of methylbenzoate (C6H5CO2CH3) following core excitation at the C and O K edges was examined from partial ion yield measurements across these edges using synchrotron radiation. Site-specific scission of the C-O bonds was observed at both edges. Theoretical X-ray absorption spectra (XAS) were obtained using density functional theory. Peak assignments in the observed spectra were found to be consistent with the theory. From core-excited state dynamics calculations, an elongation of the C-O bond was predicted and provides an explanation of the observed partial ion yield enhancement of CH3+ and C6H5CO+ at the core-excited resonances at both edges.

Place, publisher, year, edition, pages
Royal Society of Chemistry, 2018
National Category
Chemical Sciences Physical Sciences
Identifiers
urn:nbn:se:kth:diva-226759 (URN)10.1039/c7cp08428e (DOI)000429205700058 ()29578226 (PubMedID)2-s2.0-85045112931 (Scopus ID)
Note

QC 20180503

Available from: 2018-05-03 Created: 2018-05-03 Last updated: 2018-05-03Bibliographically approved
Huber, A., Bergsåker, H., Bykov, I., Elevant, T., Frassinetti, L., Garcia Carrasco, A., . . . Zychor, I. (2017). Comparative H-mode density limit studies in JET and AUG. Nuclear Materials and Energy, 12, 100-110
Open this publication in new window or tab >>Comparative H-mode density limit studies in JET and AUG
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2017 (English)In: Nuclear Materials and Energy, E-ISSN 2352-1791, Vol. 12, p. 100-110Article, review/survey (Refereed) Published
Abstract [en]

Identification of the mechanisms for the H-mode density limit in machines with fully metallic walls, and their scaling to future devices is essential to find for these machines the optimal operational boundaries with the highest attainable density and confinement. Systematic investigations of H-mode density limit plasmas in experiments with deuterium external gas fuelling have been performed on machines with fully metallic walls, JET and AUG and results have been compared with one another. Basically, the operation phases are identical for both tokamaks: the stable H-mode phase, degrading H-mode phase, breakdown of the H-mode with energy confinement deterioration usually accompanied by a dithering cycling phase, followed by the l -mode phase. The observed H-mode density limit on both machines is found close to the Greenwald limit (n/n GW = 0.8-1.1 in the observed magnetic configurations). The similar behavior of the radiation on both tokamaks demonstrates that the density limit (DL) is neither related to additional energy losses from the confined region by radiation, nor to an inward collapse of the hot discharge core induced by overcooling of the plasma periphery by radiation. It was observed on both machines that detachment, as well as the X-point MARFE itself, does not trigger a transition in the confinement regime and thus does not present a limit on the plasma density. It is the plasma confinement, most likely determined by edge parameters, which is ultimately responsible for the transition from H-to L-mode. The measured Greenwald fractions are found to be consistent with the predictions from different theoretical models [16,30] based on MHD instability theory in the near-SOL.

Place, publisher, year, edition, pages
Elsevier, 2017
Keywords
Density limit, H-mode, Detachment, Greenwald fraction, JET, ASDEX Upgrade
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-270872 (URN)10.1016/j.nme.2017.01.005 (DOI)000417293300013 ()2-s2.0-85019677025 (Scopus ID)
Note

QC 20200316

Available from: 2020-03-16 Created: 2020-03-16 Last updated: 2020-03-16Bibliographically approved
Frassinetti, L., Saarelma, S., Lomas, P., Nunes, I., Rimini, F., Beurskens, M. N., . . . Stefániková, E. (2017). Dimensionless scalings of confinement, heat transport and pedestal stability in JET-ILW and comparison with JET-C. Plasma Physics and Controlled Fusion, 59(1), Article ID 014014.
Open this publication in new window or tab >>Dimensionless scalings of confinement, heat transport and pedestal stability in JET-ILW and comparison with JET-C
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2017 (English)In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 59, no 1, article id 014014Article in journal (Refereed) Published
Abstract [en]

Three dimensionless scans in the normalized Larmor radius rho*, normalized collisionality nu* and normalized plasma pressure beta have been performed in JET with the ITER-like wall (JET-ILW). The normalized energy confinement and the thermal diffusivity exhibit a scaling with rho* consistent with the earlier results obtained in the carbon wall JET (JET-C) and with a gyro-Bohm scaling. In the pedestal, experimental results show that the stability is not dependent on rho*, qualitatively in agreement with the peeling-ballooning (P-B) model. The nu* dimensionless scaling shows that JET-ILW normalized confinement has a stronger dependence on collisionality than JET-C. This leads to a reduction of the difference in the confinement between JET-ILW and JET-C to approximate to 10% at low nu*. The pedestal stability shows an improvement with decreasing nu*. This is ascribed to the increase of the bootstrap current, to the reduction of the pedestal width and to the reduction of the relative shift between pedestal density and temperature position. The beta dimensionless scan shows that, at low collisionality, JET-ILW normalized confinement has no clear dependence with beta, in agreement with part of the earlier scalings. At high collisionality, a reduction of the normalized confinement with increasing beta is observed. This behaviour is driven mainly by the pedestal where the stability is reduced with increasing beta. The P-B analysis shows that the stability reduction with increasing beta at high nu* is due to the destabilizing effect of the increased relative shift.

Place, publisher, year, edition, pages
Culham Sci Ctr, EUROfus Consortium, JET, Abingdon OX14 3DB, Oxon, England. [Frassinetti, L.; Stefanikova, E.] KTH Royal Inst Technol, Div Fus Plasma Phys, SE-10691 Stockholm, Sweden. [Saarelma, S.; Lomas, P.; Rimini, F.; Drewelow, P.; Flanagan, J.; Garzotti, L.; Giroud, C.; Hawks, N.; Joffrin, E.; Kempenaars, M.; Kim, Hyun-Tae; Kruezi, U.; Lupelli, I.; Maggi, C. F.; Menmuir, S.; Romanelli, M.] Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England. [Nunes, I.; Meneses, L.] Univ Lisbon, Inst Plasmas & Fusao Nucl, IST, P-1049001 Lisbon, Portugal. [Beurskens, M. N. A.] Max Planck Inst Plasma Phys, D-17491 Greifswald, Germany. [Boom, J. E.] Max Planck Inst Plasma Phys, Boltzmannstr 2, D-85748 Garching, Germany. [de la Luna, E.] CIEMAT, Lab Nacl Fus, Madrid 28040, Spain. [Delabie, E.] Oak Ridge Natl Lab, Oak Ridge, TN 37831 USA. [Loarte, A.] ITER Org, Plasma Operat Directorate, F-13115 St Paul Les Durance, France. [Lomanowski, B.] Aalto Univ, TEKES, Espoo, Finland. [Bilkova, P.; Peterka, M.] AS CR, Vvi, Inst Plasma Phys, Prague, Czech Republic. [Rachlew, E.] KTH Royal Inst Technol, Dept Phys, SE-10691 Stockholm, Sweden.: , 2017
Keywords
JET-ILW, dimensionless scaling, pedestal, confinement, pedestal stability, heat transport
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-196967 (URN)10.1088/0741-3335/59/1/014014 (DOI)000386594300014 ()2-s2.0-85006117570 (Scopus ID)
Note

QC 20161213

Available from: 2016-12-13 Created: 2016-11-28 Last updated: 2019-12-10Bibliographically approved
Wiesen, S., Bergsåker, H., Bykov, I., Elevant, T., Frassinetti, L., Garcia Carrasco, A., . . . Zychor, I. (2017). Plasma edge and plasma-wall interaction modelling: Lessons learned from metallic devices. Nuclear Materials and Energy, 12, 3-17
Open this publication in new window or tab >>Plasma edge and plasma-wall interaction modelling: Lessons learned from metallic devices
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2017 (English)In: Nuclear Materials and Energy, E-ISSN 2352-1791, Vol. 12, p. 3-17Article, review/survey (Refereed) Published
Abstract [en]

Robust power exhaust schemes employing impurity seeding are needed for target operational scenarios in present day tokamak devices with metallic plasma-facing components (PFCs). For an electricity-producing fusion power plant at power density P-sep/R > 15 MW/m divertor detachment is a requirement for heat load mitigation. 2D plasma edge transport codes like the SOLPS code as well as plasma-wall interaction (PWI) codes are key to disentangle relevant physical processes in power and particle exhaust. With increased quantitative credibility in such codes more realistic and physically sound estimates of the life-time expectations and performance of metallic PFCs can be accomplished for divertor conditions relevant for ITER and DEMO. An overview is given on the recent progress of plasma edge and PWI modelling activities for (carbon-free) metallic devices, that include results from JET with the ITER-like wall, ASDEX Upgrade and Alcator C-mod. It is observed that metallic devices offer an opportunity to progress the understanding of underlying plasma physics processes in the edge. The validation of models can be substantially improved by eliminating carbon from the experiment as well as from the numerical system with reduced degrees of freedom as no chemical sputtering from amorphous carbon layers and no carbon or hydro-carbon transport are present. With the absence of carbon as the primary plasma impurity and given the fact that the physics of the PWI at metallic walls is less complex it is possible to isolate the crucial plasma physics processes relevant for particle and power exhaust. For a reliable 2D dissipative plasma exhaust model these are: cross-field drifts, complete kinetic neutral physics, geometry effects (including main-chamber, divertor and sub-divertor structures), SOL transport reflecting also the non-diffusive nature of anomalous transport, as well as transport within the pedestal region in case of significant edge impurity radiation affecting pedestal pressure and hence P-sep.

Place, publisher, year, edition, pages
Elsevier, 2017
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-270871 (URN)10.1016/j.nme.2017.03.033 (DOI)000417293300003 ()2-s2.0-85016571978 (Scopus ID)
Note

QC 20200316

Available from: 2020-03-16 Created: 2020-03-16 Last updated: 2020-03-16Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0001-7389-5501

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