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Cecconello, Marco
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Publications (10 of 66) Show all publications
Sias, G., Cecconello, M., Klimek, I., Wodniak, I., Yadykin, D., Andersson Sundén, E., . . . Zychor, I. (2019). A locked mode indicator for disruption prediction on JET and ASDEX upgrade. Fusion engineering and design, 138, 254-266
Open this publication in new window or tab >>A locked mode indicator for disruption prediction on JET and ASDEX upgrade
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2019 (English)In: Fusion engineering and design, ISSN 0920-3796, E-ISSN 1873-7196, Vol. 138, p. 254-266Article in journal (Refereed) Published
Abstract [en]

The aim of this paper is to present a signal processing algorithm that, applied to the raw Locked Mode signal, allows us to obtain a disruption indicator in principle exploitable on different tokamaks. A common definition of such an indicator for different machines would facilitate the development of portable systems for disruption prediction, which is becoming of increasingly importance for the next tokamak generations. Moreover, the indicator allows us to overcome some intrinsic problems in the diagnostic system such as drift and offset. The behavior of the proposed indicator as disruption predictor, based on crossing optimized thresholds of the signal amplitude, has been analyzed using data of both JET and ASDEX Upgrade experiments. A thorough analysis of the disruption prediction performance shows how the indicator is able to recover some missed and tardy detections of the raw signal. Moreover, it intervenes and corrects premature or even wrong alarms due to, e.g., drifts and/or offsets.

Keywords
Tokamak, Disruption prediction, Locked mode signal, Disruption indicators, Feature extraction
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-377710 (URN)10.1016/j.fusengdes.2018.11.021 (DOI)000457663100032 ()
Note

For complete list of authors see http://dx.doi.org/10.1016/j.fusengdes.2018.11.021

Available from: 2019-03-08 Created: 2019-03-08 Last updated: 2019-03-08Bibliographically approved
Ström, P., Petersson, P., Rubel, M. J., Fortuna-Zaleśna, E., Widdowson, A. & Sergienko, G. (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 analysed 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 mu m were indicated, but typical values were on the order of a few hundred nm. 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 mu m 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
Identifiers
urn:nbn:se:uu:diva-379019 (URN)10.1016/j.jnucmat.2018.11.027 (DOI)000458897100020 ()
Funder
Swedish Foundation for Strategic Research , RIF14-0053Swedish Research Council, 821-2012-5144Swedish Research Council, 2015-04884Swedish Research Council, 2017-00643
Note

Authors listed as Contributor / bidragsgivare above are part of EUROfusion Consortium, JET, Culham Science Centre, UK.

Available from: 2019-03-12 Created: 2019-03-12 Last updated: 2019-04-24Bibliographically approved
Drenik, A., Andersson Sundén, E., Binda, F., Cecconello, M., Conroy, S., Dzysiuk, N., . . . Zychor, I. (2019). Analysis of the outer divertor hot spot activity in the protection video camera recordings at JET. Fusion engineering and design, 139, 115-123
Open this publication in new window or tab >>Analysis of the outer divertor hot spot activity in the protection video camera recordings at JET
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2019 (English)In: Fusion engineering and design, ISSN 0920-3796, E-ISSN 1873-7196, Vol. 139, p. 115-123Article in journal (Refereed) Published
Abstract [en]

Hot spots on the divertor tiles at JET result in overestimation of the tile surface temperature which causes unnecessary termination of pulses. However, the appearance of hot spots can also indicate the condition of the divertor tile surfaces. To analyse the behaviour of the hot spots in the outer divertor tiles of JET, a simple image processing algorithm is developed. The algorithm isolates areas of bright pixels in the camera image and compares them to previously identified hot spots. The activity of the hot spots is then linked to values of other signals and parameters in the same time intervals. The operation of the detection algorithm was studied in a limited pulse range with high hot spot activity on the divertor tiles 5, 6 and 7. This allowed us to optimise the values of the controlling parameters. Then, the wider applicability of the method has been demonstrated by the analysis of the hot spot behaviour in a whole experimental campaign.

Keywords
JET, ITER-like wall, Plasma-wall interaction, Image analysis
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-378736 (URN)10.1016/j.fusengdes.2018.12.079 (DOI)000458939100016 ()
Note

For complete list of authors see http://dx.doi.org/10.1016/j.fusengdes.2018.12.079

Available from: 2019-03-11 Created: 2019-03-11 Last updated: 2019-03-11Bibliographically approved
Labit, B., Cecconello, M., Sperduti, A. & Zuin, M. (2019). Dependence on plasma shape and plasma fueling for small edge-localized mode regimes in TCV and ASDEX Upgrade. Nuclear Fusion, 59(8), Article ID 086020.
Open this publication in new window or tab >>Dependence on plasma shape and plasma fueling for small edge-localized mode regimes in TCV and ASDEX Upgrade
2019 (English)In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 59, no 8, article id 086020Article in journal (Refereed) Published
Abstract [en]

Within the EUROfusion MST1 work package, a series of experiments has been conducted on AUG and TCV devices to disentangle the role of plasma fueling and plasma shape for the onset of small ELM regimes. On both devices, small ELM regimes with high confinement are achieved if and only if two conditions are fulfilled at the same time. Firstly, the plasma density at the separatrix must be large enough (n(e,sep)/n(G) similar to 0.3), leading to a pressure profile flattening at the separatrix, which stabilizes type-I ELMs. Secondly, the magnetic configuration has to be close to a double null (DN), leading to a reduction of the magnetic shear in the extreme vicinity of the separatrix. As a consequence, its stabilizing effect on ballooning modes is weakened.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD, 2019
Keywords
H-mode, type-II ELMs, grassy ELMs, plasma triangularity, separatrix density, ballooning modes
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-390512 (URN)10.1088/1741-4326/ab2211 (DOI)000473079500003 ()
Note

For complete list of authors see http://dx.doi.org/10.1088/1741-4326/ab2211

Available from: 2019-08-12 Created: 2019-08-12 Last updated: 2019-08-12Bibliographically approved
Neverov, V. S., Andersson Sundén, E., Binda, F., Cecconello, M., Conroy, S., Dzysiuk, N., . . . Zychor, I. (2019). Determination of isotope ratio in the divertor of JET-ILW by high-resolution H alpha spectroscopy: H-D experiment and implications for D-T experiment. Nuclear Fusion, 59(4), Article ID 046011.
Open this publication in new window or tab >>Determination of isotope ratio in the divertor of JET-ILW by high-resolution H alpha spectroscopy: H-D experiment and implications for D-T experiment
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2019 (English)In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 59, no 4, article id 046011Article in journal (Refereed) Published
Abstract [en]

The data of the H alpha high-resolution spectroscopy, collected on the multiple lines of sight, which cover the entire divertor space in poloidal cross-section, during the recent hydrogen-deuterium experiments in JET-ILW (ITER-like wall), are processed. A strong spatial inhomogeneity of the hydrogen concentration, H/(H + D), in divertor is found in many pulses. Namely, the H/(H + D) ratio may be lower in the inner divertor than that in the outer divertor by the values of 0.15-0.35, depending on the conditions of gas puffing and plasma heating. This effect suggests the necessity of spatially-resolved measurements of isotope ratio in the divertor in the upcoming deuterium-tritium experiments. Also, separation of the overlapped T alpha and D alpha spectral lines is shown to be a challenging task especially when the local Doppler-broadened (Gaussian) line shapes are noticeably distorted by the net inward flux of fast non-Maxwellian neutral atoms. We use the respective, formerly developed model of an asymmetric spectral line shape, while analysing the data of the first deuterium-tritium experiment in JET-C (carbon wall), and test the model via comparing the isotope ratio results with another diagnostic's measurements. This model is shown to increase the accuracy of tritium concentration measurements in the divertor.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD, 2019
Keywords
tokamak diagnostics, spectral line shapes, inverse problems, isotope ratio
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-378618 (URN)10.1088/1741-4326/ab0000 (DOI)000458371300001 ()
Note

For complete list of authors see http://dx.doi.org/10.1088/1741-4326/ab0000

Available from: 2019-03-11 Created: 2019-03-11 Last updated: 2019-03-11Bibliographically approved
Cecconello, M., Boeglin, W., Keeling, D., Conroy, S., Klimek, I. & Perez, R. ,. (2019). Discrepancy between estimated and measured fusion product rates on MAST using TRANSP/NUBEAM. Nuclear Fusion, 59(1), Article ID 016006.
Open this publication in new window or tab >>Discrepancy between estimated and measured fusion product rates on MAST using TRANSP/NUBEAM
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2019 (English)In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 59, no 1, article id 016006Article in journal (Refereed) Published
Abstract [en]

Experimental evidence is presented of a discrepancy between the predicted and measured D-D fusion product rates on MAST Both the neutron and proton production rates, measured independently with a neutron camera and charged fusion product detector array, are approximately 40% lower than those predicted by TRANSP/NUBEAM codes. This deficit is scenario independent and cannot be explained by uncertainties in the typical plasma parameters suspected for such discrepancies, such as electron temperature, the plasma effective charge and the injected neutral beam power. Instead, a possible explanation is an overestimate of the neutron emissivity due to the guiding centre approximation used in NUBEAM to model the fast ion orbits.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD, 2019
Keywords
spherical tokamak, MAST, fusion product deficit, TRANSP, NUBEAM
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-371111 (URN)10.1088/1741-4326/aaea19 (DOI)000450625000002 ()
Funder
Swedish Research CouncilEU, Horizon 2020, 633053
Available from: 2018-12-28 Created: 2018-12-28 Last updated: 2018-12-28Bibliographically approved
Trier, E., Cecconello, M., Wodniak, I., Yadykin, D. & Zuin, M. (2019). ELM-induced cold pulse propagation in ASDEX Upgrade. Plasma Physics and Controlled Fusion, 61(4), Article ID 045003.
Open this publication in new window or tab >>ELM-induced cold pulse propagation in ASDEX Upgrade
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2019 (English)In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 61, no 4, article id 045003Article in journal (Refereed) Published
Abstract [en]

In ASDEX Upgrade, the propagation of cold pulses induced by type-I edge localized modes (ELMs) is studied using electron cyclotron emission measurements, in a dataset of plasmas with moderate triangularity. It is found that the edge safety factor or the plasma current are the main determining parameters for the inward penetration of the T-e perturbations. With increasing plasma current the ELM penetration is more shallow in spite of the stronger ELMs. Estimates of the heat pulse diffusivity show that the corresponding transport is too large to be representative of the inter-ELM phase. Ergodization of the plasma edge during ELMs is a possible explanation for the observed properties of the cold pulse propagation, which is qualitatively consistent with non-linear magneto-hydro-dynamic simulations.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD, 2019
Keywords
ELMs, MHD instabilities, stochastic field, magnetic islands, cold pulse
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-378614 (URN)10.1088/1361-6587/aaf9c3 (DOI)000458986000002 ()
Note

For complete list of authors see http://dx.doi.org/10.1088/1361-6587/aaf9c3

Available from: 2019-03-11 Created: 2019-03-11 Last updated: 2019-03-11Bibliographically approved
Vasilopoulou, T., Andersson Sundén, E., Binda, F., Cecconello, M., Conroy, S., Dzysiuk, N., . . . 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.

Keywords
Neutron activation, Neutron dosimetry, JET, Fusion
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-378735 (URN)10.1016/j.fusengdes.2019.01.002 (DOI)000458939100015 ()
Note

For complete list of authors see http://dx.doi.org/10.1016/j.fusengdes.2019.01.002

Available from: 2019-03-08 Created: 2019-03-08 Last updated: 2019-03-08Bibliographically approved
Cecconello, M. (2019). Liquid Scintillators Neutron Response Function: A Tutorial. Journal of fusion energy, 38(3-4), 356-375
Open this publication in new window or tab >>Liquid Scintillators Neutron Response Function: A Tutorial
2019 (English)In: Journal of fusion energy, ISSN 0164-0313, E-ISSN 1572-9591, Vol. 38, no 3-4, p. 356-375Article in journal (Refereed) Published
Abstract [en]

This tutorial is devoted to the understanding of the different components that are present in the neutron light output pulse height distribution of liquid scintillators in fusion relevant energy ranges. The basic mechanisms for the generation of the scintillation light are briefly discussed. The different elastic collision processed between the incident neutrons and the hydrogen and carbon atoms are described in terms of probability density functions and the overall response function as their convolution. The results from this analytical approach is then compared with those obtained from simplified and full Monte Carlo simulations. Edge effect, finite energy resolution, light output and transport and competing physical processes between neutron and carbon and hydrogen atoms and their impact on the response functions are discussed. Although the analytical treatment here presented allows only for a qualitative comparison with full Monte Carlo simulations it enables an understanding of the main features present in the response function and therefore provides the ground for the interpretation of more complex response functions such those measured in fusion plasmas. Although the main part of this tutorial is focused on the response function to mono-energetic 2.45 MeV neutrons a brief discussion is presented in case of broad neutron energy spectra and how these can be used to infer the underlying properties of fusion plasmas via the application of a forward modelling method.

Place, publisher, year, edition, pages
SPRINGER, 2019
Keywords
Fusion reactions, Neutron, Liquid scintillator, Response function, Elastic scattering, Probability density function, Convolution, Energy resolution, Efficiency, Forward modelling
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-391293 (URN)10.1007/s10894-019-00212-w (DOI)000476509600008 ()
Funder
Swedish Research Council, 2015-03869EU, Horizon 2020, 633053
Available from: 2019-08-22 Created: 2019-08-22 Last updated: 2019-08-22Bibliographically approved
Eriksson, J., Hellesen, C., Binda, F., Cecconello, M., Conroy, S., Ericsson, G., . . . Tardocchi, M. (2019). Measuring fast ions in fusion plasmas with neutron diagnostics at JET. Plasma Physics and Controlled Fusion, 61(1), Article ID 014027.
Open this publication in new window or tab >>Measuring fast ions in fusion plasmas with neutron diagnostics at JET
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2019 (English)In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 61, no 1, article id 014027Article in journal (Refereed) Published
Abstract [en]

Fast ions in fusion plasmas often leave characteristic signatures in the neutron emission from the plasma. In this paper, we show how neutron measurements can be used to study fast ions and give examples of physics results obtained on present day tokamaks. The focus is on measurements with dedicated neutron spectrometers and with compact neutron detectors used in each channel of neutron profile monitors. A measured neutron spectrum can be analyzed in several different ways, depending on the physics scenario under consideration. Gross features of a fast ion energy distribution can be studied by applying suitably chosen thresholds to the measured spectrum, thus probing ions with different energies. With this technique it is possible to study the interaction between fast ions and MHD activity, such as toroidal Alfven eigenmodes (TAEs) and sawtooth instabilities. Quantitative comparisons with modeling can be performed by a direct computation of the neutron emission expected from a given fast ion distribution. Within this framework it is also possible to determine physics parameters, such as the supra-thermal fraction of the neutron emission, by fitting model parameters to the data. A detailed, model-independent estimate of the fast ion distribution can be obtained by analyzing the data in terms of velocity space weight functions. Using this method, fast ion distributions can be resolved in both energy and pitch by combining neutron and gamma-ray measurements obtained along several different sightlines. Fast ion measurements of the type described in this paper will also be possible at ITER, provided that the spectrometers have the dynamic range required to resolve the fast ion spectral features in the presence of the dominating thermonuclear neutron emission. A dedicated high-resolution neutron spectrometer has been designed for this purpose.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD, 2019
Keywords
fast ions, tokamaks, neutron diagnostics, plasma heating, MHD instabilities
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-371109 (URN)10.1088/1361-6587/aad8a6 (DOI)000450981300009 ()
Available from: 2018-12-20 Created: 2018-12-20 Last updated: 2018-12-20Bibliographically approved
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