The global build-up to intrinsic edge localized mode bursts seen in divertor full flux loops in JET

A global signature of the build-up to an intrinsic edge localized mode (ELM) is found in the temporal analytic phase of signals measured in full flux azimuthal loops in the divertor region of JET. Toroidally integrating, full flux loop signals provide a global measurement proportional to the voltage induced by changes in poloidal magnetic flux; they are electromagnetically induced by the dynamics of spatially integrated current density. We perform direct time-domain analysis of the high time-resolution full flux loop signals VLD2 and VLD3. We analyze plasmas where a steady H-mode is sustained over several seconds during which all the observed ELMs are intrinsic; there is no deliberate intent to pace the ELMing process by external means. ELM occurrence times are determined from the Be II emission at the divertor. We previously [Chapman et al., Phys. Plasmas 21, 062302 (2014); Chapman et al., in 41st EPS Conference on Plasma Physics, Europhysics Conference Abstracts (European Physical Society, 2014), Vol. 38F, ISBN 2-914771-90-8] found that the occurrence times of intrinsic ELMs correlate with specific temporal analytic phases of the VLD2 and VLD3 signals. Here, we investigate how the VLD2 and VLD3 temporal analytic phases vary with time in advance of the ELM occurrence time. We identify a build-up to the ELM in which the VLD2 and VLD3 signals progressively align to the temporal analytic phase at which ELMs preferentially occur, on a ∼2−5ms timescale. At the same time, the VLD2 and VLD3 signals become temporally phase synchronized with each other, consistent with the emergence of coherent global dynamics in the integrated current density. In a plasma that remains close to a global magnetic equilibrium, this can reflect bulk displacement or motion of the plasma. This build-up signature to an intrinsic ELM can be extracted from a time interval of data that does not extend beyond the ELM occurrence time, so that these full flux loop signals could assist in ELM prediction or mitigation

Modelling of combined ICRF and NBI heating in JET hybrid plasmas

During the 2015-2016 JET campaigns many efforts have been devoted to the exploration of high performance plasma scenarios envisaged for ITER operation. In this paper we model the combined ICRF+NBI heating in selected key hybrid discharges using PION. The antenna frequency was tuned to match the cyclotron frequency of minority hydrogen (H) at the center of the tokamak coinciding with the second harmonic cyclotron resonance of deuterium. The modelling takes into account the synergy between ICRF and NBI heating through the second harmonic cyclotron resonance of deuterium beam ions which allows us to assess its impact on the neutron rate RNT. We evaluate the influence of H concentration which was varied in different discharges in order to test their role in the heating performance. According to our modelling, the ICRF enhancement of RNT increases by decreasing the H concentration which increases the ICRF power absorbed by deuterons. We find that in the recent hybrid discharges this ICRF enhancement was in the range of 10-25%. Finally, we extrapolate the results to D-T and find that the best performing hybrid discharges correspond to an equivalent fusion power of ∼7.0 MW in D-T.This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014-2018 under grant agreement No 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission. Dani Gallart would like to thank “La Caixa” for support of his PhD studies.Peer ReviewedPostprint (published version

Diagnosing Fuel Ions in Fusion Plasmas using Neutron Emission Spectroscopy

Neutron emission spectra, measured with the time of flight spectrometer TOFOR, at the joint European torus (JET) are presented in this thesis. TOFOR has been in use since 2005, routinely measuring the neutron emission from JET plasmas. The work in the thesis mainly concerns the modeling of the signatures in the neutron spectrum that reveal different parts of the fuel ion distribution, such as the thermal bulk plasma as well as energetic ions from neutral beam and ion cyclotron heating. Parametric models of the signatures, using plasma parameters as input, are employed to generate trial neutron spectra. The parameters, such as the fuel ion temperature or the fast ion distribution function, are deduced by iteratively fitting the trial spectra to the measured data. Measurements with TOFOR have been made and the models were applied. The studies are mainly on neutrons from d(d, n)3 He reactions(DD), although the emission from reactions with the plasma impurity 9 Be and triton burn up is covered as well. This has allowed for detailed studies of e.g. the physics ICRF heating as well as the interactions between energetic ions and plasma instabilities, such as toroidal Alfvé Eigenmodes

Inelastic neutron scattering from carbon, iron, yttrium and lead

Double-differential cross sections and angular distributions of inelastic neutron scattering on 12C, 56Fe, 89Y and 208Pb have been measured at 96 MeV at The Svedberg Laboratory, Uppsala, Sweden. Results on elastic neutron scattering at 96 MeV from these nuclei have been reported previously [1–3]. To obtain the inelastic cross sections, a forward-folding technique has been applied. A physically reasonable trial spectrum has been folded with the response function of the detector system and the output has been compared with the experimental data. To create the trial spectrum, a Gaussian has been used for the elastic part and the PRECO code [4–7] for the inelastic part. Other models were tested for the pre-equilibrium contribution and the method was found to be model independent. The response function of the detector setup has been obtained experimentally at the smallest possible angle, in this case at 9 deg. The resulting preliminary inelastic scattering data cover an excitation energy range up to 45 MeV and the angular intervals 28 to 58 degrees for 12C, 26 to 65 degrees for 56Fe and 26 to 52 degrees for 89Y and 208Pb. The preliminary results are discussed and compared to several model codes as well as existing experimental data for (n,n′x), (n,p′x) and (p,p′x). Possible improvements of the analysis are also discussed

Development of a PhD course in verification of nuclear test explosions under AMC

Under the AMC, a range of activities covering education, research and outreach are foreseen. One of them concerns education and the build-up of competence related to disarmament, and for that reason collaborative efforts have been ongoing during 2021 and 2022 to develop a PhD-level course in verification of nuclear test explosions, and to offer it during September-October 2022.  The course has developed by Uppsala University and the Swedish Defence Reserach Agency (FOI) and corresponds to 7.5 credits. It is a cross-disciplinary course that spans over several disciplines. It introduces the participants to treaties and verification regimes governing nuclear weapons and it explains identification, calculation and analysis of signatures from nuclear weapon explosions. Furthermore, effort has been made to let the participants actively work with data collection, aggregation, analysis and with the interpretation and evaluation of data. The course includes also both a laboratory exercise on detection of radionuclides, and a project work in which the participants analyze a test explosion scenario and summarize their findings and conclusions in a manner very similar to how this is done in reality. This poster will describe the details of the course and its content. Since the course is planned to be offered just before this conference, we also hope to provide some information on its execution, as well as feedback from the participants

Analysis of resonant fast ion distributions during combined ICRF and NBI heating with transients using neutron emission spectroscopy

ICRF heating at the fundamental cyclotron frequency of a hydrogen minority ion species also gives rise to a partial power absorption by deuterium ions at their second harmonic resonance. This paper studies the deuterium distributions resulting from such 2nd harmonic heating at JET using neutron emission spectroscopy data from the time of flight spectrometer TOFOR. The fast deuterium distributions are obtained over the energy range 100 keV to 2 MeV. Specifically, we study how the fast deuterium distributions vary as ICRF heating is used alone as well as in combination with NBI heating. When comparing the different heating scenarios, we observed both a difference in the shapes of the distributions as well as in their absolute level. The differences are most pronounced below 0.5 MeV. Comparisons are made with corresponding distributions calculated with the code PION. We find a good agreement between the measured distributions and those calculated with PION, both in terms of their shapes as well as their amplitudes. However, we also identified a period with signs of an inverted fast ion distribution, which showed large disagreements between the modeled and measured results. Resonant interactions with tornado modes, i.e. core localized toroidal alfven eigenmodes (TAEs), are put forward as a possible explanation for the inverted distribution

Development of a PhD course in verification of nuclear test explosions under AMC

Under the AMC, a range of activities covering education, research and outreach are foreseen. One of them concerns education and the build-up of competence related to disarmament, and for that reason collaborative efforts have been ongoing during 2021 and 2022 to develop a PhD-level course in verification of nuclear test explosions, and to offer it during September-October 2022.  The course has developed by Uppsala University and the Swedish Defence Reserach Agency (FOI) and corresponds to 7.5 credits. It is a cross-disciplinary course that spans over several disciplines. It introduces the participants to treaties and verification regimes governing nuclear weapons and it explains identification, calculation and analysis of signatures from nuclear weapon explosions. Furthermore, effort has been made to let the participants actively work with data collection, aggregation, analysis and with the interpretation and evaluation of data. The course includes also both a laboratory exercise on detection of radionuclides, and a project work in which the participants analyze a test explosion scenario and summarize their findings and conclusions in a manner very similar to how this is done in reality. This poster will describe the details of the course and its content. Since the course is planned to be offered just before this conference, we also hope to provide some information on its execution, as well as feedback from the participants