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Publications (10 of 128) Show all publications
Schnabel, G. & Sjöstrand, H. (2019). A first sketch: Construction of model defect priors inspired by dynamic time warping. Paper presented at WONDER 2018: 5th International Workshop On Nuclear Data Evaluation for Reactor applications, 8-12 October 2018, Aix-en-Provence, France. EPJ Web of Conferences, 211, Article ID 07005.
Open this publication in new window or tab >>A first sketch: Construction of model defect priors inspired by dynamic time warping
2019 (English)In: EPJ Web of Conferences, E-ISSN 2100-014X, Vol. 211, article id 07005Article in journal (Refereed) Published
Abstract [en]

Model defects are known to cause biased nuclear data evaluations if they are not taken into account in the evaluation procedure. We suggest a method to construct prior distributions for model defects for reaction models using neighboring isotopes of 56Fe as an example. A model defect is usually a function of energy and describes the difference between the model prediction and the truth. Of course, neither the truth nor the model defect are accessible. A Gaussian process (GP) enables to define a probability distribution on possible shapes of a model defect by referring to intuitively understandable concepts such as smoothness and the expected magnitude of the defect. Standard specifications of GPs impose a typical length-scale and amplitude valid for the whole energy range, which is often not justified, e.g., when the model covers both the resonance and statistical range. In this contribution, we show how a GP with energy-dependent length-scales and amplitudes can be constructed from available experimental data. The proposed construction is inspired by a technique called dynamic time warping used, e.g., for speech recognition. We demonstrate the feasibility of the data-driven determination of model defects by inferring a model defect of the nuclear models code TALYS for (n,p) reactions of isotopes with charge number between 20 and 30. The newly introduced GP parametrization besides its potential to improve evaluations for reactor relevant isotopes, such as 56Fe, may also help to better understand the performance of nuclear models in the future.

Keywords
Bayesian statistics, Gaussian processes, optimization
National Category
Accelerator Physics and Instrumentation
Research subject
Physics with specialization in Applied Nuclear Physics
Identifiers
urn:nbn:se:uu:diva-379182 (URN)10.1051/epjconf/201921107005 (DOI)
Conference
WONDER 2018: 5th International Workshop On Nuclear Data Evaluation for Reactor applications, 8-12 October 2018, Aix-en-Provence, France
Available from: 2019-03-13 Created: 2019-03-13 Last updated: 2019-08-22Bibliographically approved
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
Kumar, D., Sjöstrand, H., Bahauddin Alam, S., Palau, J.-M. & De Saint Jean, C. (2019). Analysis of the Prior Nuclear Data Correlation and Its Effect on the Adjustment in Bayesian Inference. In: : . Paper presented at International Conference on Nuclear Data for Science and Technology, Beijing, China, May 19-24, 2019.
Open this publication in new window or tab >>Analysis of the Prior Nuclear Data Correlation and Its Effect on the Adjustment in Bayesian Inference
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2019 (English)Conference paper, Oral presentation with published abstract (Other academic)
Abstract [en]

High-quality nuclear data is of prime importance while considering the design of advanced fast reactors. The quantification of nuclear data uncertainties is always required for the safety calculations of nuclear power plants. Using reliable nuclear data and its correlation are of great importance for the quality of uncertainty analysis. Nuclear data is usually evaluated using mathematical models and is improved by using integral experiments. To utilize the past critical experimental data to the reactor design work, a typical procedure for the nuclear data adjustment is based on the Bayesian theory (least-square technique or Monte-Carlo). Using Bayesian theorem, the nuclear model parameters are optimized by the inclusion of experimental information. The posterior data and its covariance are evaluated from the optimized model parameters. In this process, the prior data, its covariance and the integral experimental data are provided to the optimizer as input. The selection of integral experiments is based on the availability of well-documented specifications and experimental uncertainties. The prior covariance matrix used for the adjustment is usually very large as it contains correlation information between energy groups, nuclear reactions and isotopes considered for the adjustment. Often, due to the choices made for adjustment; the prior correlation matrix is encountered as negative definite or singular. These situations affect the accuracy of the adjustment heavily. Hence, in the adjustment process, it is very important to avoid the prior matrix as singular or negative definite. In this work, using principal component analysis, the size of the prior nuclear data (and its correlation) is first reduced to ensure the non-singularity in the prior. Further, the reduced parameters are used in Bayesian inference for the posterior calculation. Furthermore, the influence of each individual ingredient (experiment/nuclear data) will be analyzed using the concept of Cook’s distance. First, JEZEBEL (239Pu, 240Pu and 241Pu) will be considered and the transposition of the result on ASTRID Fast reactor concept will be discussed.

National Category
Probability Theory and Statistics
Identifiers
urn:nbn:se:uu:diva-396768 (URN)
Conference
International Conference on Nuclear Data for Science and Technology, Beijing, China, May 19-24, 2019
Available from: 2019-11-08 Created: 2019-11-08 Last updated: 2019-11-11Bibliographically 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
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
Kumar, D., Alam, S. B., Sjöstrand, H. & De Saint Jean, C. (2019). Influence of nuclear data parameters on integral experiment assimilation using Cook's distance. Paper presented at 5th edition of the International Workshop On Nuclear Data Evaluation for Reactor Applications (WONDER-2018), Aix en Provence, France, October 8-12, 2018. EPJ Web of Conferences, 211, Article ID 07001.
Open this publication in new window or tab >>Influence of nuclear data parameters on integral experiment assimilation using Cook's distance
2019 (English)In: EPJ Web of Conferences, ISSN 2101-6275, E-ISSN 2100-014X, Vol. 211, article id 07001Article in journal (Other academic) Published
Abstract [en]

Nuclear data used in designing of various nuclear applications (e.g., core design of reactors) is improved by using integral experiments. To utilize the past critical experimental data to the reactor design work, a typical procedure for the nuclear data adjustment is based on the Bayesian theory (least-square technique or Monte-Carlo). In this method, the nuclear data parameters are optimized by the inclusion of the experimental information using a Bayesian inference. The selection of integral experiments is based on the availability of well-documented specifications and experimental data. Data points with large uncertainties or large residuals (outliers) may aect the accuracy of the adjustment. Hence, in the adjustment process, it is very important to study the influence of experiments as well as of the priori nuclear data on the adjusted results. In this work, the influence of each individual ingredient (related to nuclear data) is analyzed using the concept of Cook’s distance. First, JEZEBEL (Pu239, Pu240 and Pu241) integral experiment is considered for data assimilation and then the transposition of results on ASTRID fast reactor concept is discussed.

Place, publisher, year, edition, pages
EDP Sciences, 2019
National Category
Subatomic Physics
Identifiers
urn:nbn:se:uu:diva-378672 (URN)10.1051/epjconf/201921107001 (DOI)
Conference
5th edition of the International Workshop On Nuclear Data Evaluation for Reactor Applications (WONDER-2018), Aix en Provence, France, October 8-12, 2018
Funder
Swedish Research Council
Available from: 2019-03-08 Created: 2019-03-08 Last updated: 2019-10-10Bibliographically approved
Sjöstrand, H., Schnabel, G. & Rochman, D. (2019). Integral adjustment of nuclear data libraries: finding unrecognized systematic uncertainties and correlations. In: Conference program & Abstract book: 2019 International Conference on Nuclear Data for Science and Technology, May 19-24, 2019, Beijing, China. Paper presented at 2019 International Conference on Nuclear Data for Science and Technology, May 19-24, 2019, Beijing, China (pp. 212-212).
Open this publication in new window or tab >>Integral adjustment of nuclear data libraries: finding unrecognized systematic uncertainties and correlations
2019 (English)In: Conference program & Abstract book: 2019 International Conference on Nuclear Data for Science and Technology, May 19-24, 2019, Beijing, China, 2019, p. 212-212Conference paper, Oral presentation with published abstract (Other academic)
Abstract [sv]

To reduce the uncertainties and obtain a better predictive power, integral adjustment of nuclear data libraries is one powerful option. Databases with integral experiments, such as the ICSBEP contain a large amount of data. When adjusting nuclear data using these integral experiments, it is important to not only include reported experimental uncertainties but also to account for the possibility of unreported experimental uncertainties and correlations between experiments, and calculation uncertainties. Unreported uncertainties and correlations can be identified and possibly quantified using marginal likelihood optimization (MLO). MLO has previously been tested for integral adjustment. In this paper, a method for including more information from the full likelihood space is pursued. It is shown that MLO can be an effective tool in addressing unknown uncertainties and correlations for a selected number of integral experiments. Results in terms of obtained parameter estimates as well as of posterior uncertainties and correlations are reported. The results are validated against an independent set of integral experiments. The findings are important for large-scale ND evaluations that heavily rely on automatization, such as TENDL, but also for any integral adjustment where a complete knowledge of all uncertainty components is out of reach. The authors believe that this is always the case.

National Category
Subatomic Physics
Identifiers
urn:nbn:se:uu:diva-396767 (URN)
Conference
2019 International Conference on Nuclear Data for Science and Technology, May 19-24, 2019, Beijing, China
Available from: 2019-11-08 Created: 2019-11-08 Last updated: 2019-11-11Bibliographically approved
Schnabel, G., Sjöstrand, H., Rochman, D. & J. Koning, A. (2019). Interfacing TALYS with a Bayesian treatment of model defects and inconsistent data. In: : . Paper presented at International Conference on Nuclear Data for Science and Technology, 2019, Beijing, China, May 19-24, 2019.
Open this publication in new window or tab >>Interfacing TALYS with a Bayesian treatment of model defects and inconsistent data
2019 (English)Conference paper, Oral presentation with published abstract (Other academic)
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-396398 (URN)
Conference
International Conference on Nuclear Data for Science and Technology, 2019, Beijing, China, May 19-24, 2019
Available from: 2019-11-04 Created: 2019-11-04 Last updated: 2019-11-11Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-7595-8024

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