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8 results on '"FUSION REACTIONS"'

1. Conceptual design of DIII-D experiments to diagnose the lifetime of spin polarized fuel

Author

A.V. Garcia, W.W. Heidbrink, and A.M. Sandorfi

Subjects
spin polarized fusion, DIII-D, charged fusion products, fusion reactions, Nuclear and particle physics. Atomic energy. Radioactivity, QC770-798
Abstract

In magnetic fusion experiments, the cross sections for the D-T and D- ^3 He fusion reactions are increased by as much as 50% if the fuel remains spin polarized parallel to the magnetic field. The goal of this study is to assess the feasibility of lifetime measurements of spin polarization, in magnetic fusion relevant conditions, on the DIII-D tokamak using relative changes in charged fusion product (CFP) loss measurements that depend upon the differential fusion cross section d σ /dΩ. Relative measurements that capture changes in the escaping CFP pitch, poloidal, and energy distributions are studied in two realistic TRANSP calculated plasma scenarios: (a) vector-polarized ^3 He and D pellets are injected into a hot hydrogen plasma to produce thermonuclear reactions, and (b) a tensor-polarized deuterium pellet is injected into an L-mode hydrogen background plasma that includes unpolarized ^3 He neutral beam injection. Ideal CFP signals in both scenarios show substantial pitch sensitivity to polarization for 14.7 MeV proton detection at a poloidal angle of $-56^{\circ}$ (on the outer wall in the ion $\nabla B$ direction), and strong sensitivity to polarization for 3.6 MeV alpha flux detection by an array of poloidal detectors. Energy-resolved measurements of 14.7 MeV protons are also sensitive to the degree of polarization for the $-56^{\circ}$ port in the beam-plasma scenario. A realistic assessment of CFP signals in the thermonuclear scenario show count rates in the range of $2\times10^4$ cps for pitch-resolved proton detection and $2\times10^5$ cps for alpha flux measurements. Reduced chi-squared $\chi^{\,2}_\mathrm r$ calculations show polarization lifetime measurements are feasible for either proton or alpha detection of both enhanced or suppressed polarization for the thermonuclear scenario. Measurements of gamma rays produced in the weak $\textrm{D} + {}^{3}\textrm{He} \rightarrow \gamma+ {}^5\textrm{Li}$ branch complement the CFP measurements.

Published
2023
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2. First results from third harmonic ion cyclotron acceleration of deuterium beams in EAST ion heating studies experiments

Author

G. Zhu, W. Zhang, X. Zhang, G. Zhong, C. Qin, L. Liu, H. Yang, L. Liao, Y. Cheng, Y. Mao, S. Yuan, Y. Wang, H. Li, and J. Luo

Subjects
third harmonic ICRF, fishbone instabilities, ICRF-NBI synergy, neutron yield, fusion reactions, Nuclear and particle physics. Atomic energy. Radioactivity, QC770-798
Abstract

Recent Experimental Advanced Superconductivity Tokamak experiments have been dedicated to the studies of increasing ion temperature using Neutral Beam Injection (NBI) in synergy with radio-frequency waves in the Ion Cyclotron Range of Frequencies (ICRFs) in third harmonic. They showed that this scenario effectively accelerates fast deuterium ions and produces a larger tail of fast neutrons with E > 3.0 MeV, as measured by Neutron Energy Spectrum. Comparing to the scenario with 2.2 MW NBI alone, adding an addition of 0.3 MW ICRF power leads to an enhancement of fusion yield by 67% (from ${\text{0}}{{.73 \times 1}}{{\text{0}}^{{\text{14}}}}{\text{ n}}\;{{\text{s}}^{ - {\text{1}}}}$ to ${\text{1}}{{.22 \times 1}}{{\text{0}}^{{\text{14}}}}{\text{ n}}\;{{\text{s}}^{ - 1}}$ ) and an increase of core ion temperature by $\Delta {T_{\text{i}}}\sim 7{\text{80 eV}}$ . Besides, the simulation results of TRANSP show that the neutron yield produced by 0.2 MW ICRF in third harmonic with NBI synergy is roughly consistent with the experimental results. Meanwhile, the 80 keV fast ion tail generated by NBI can be heated up to 400 keV and 600 keV by the 0.2 MW and 1.0 MW ICRF with the synergistic effect, respectively. In addition, it is observed for the first time that this ICRF-NBI synergy leads to the excitation of fishbone instabilities with characteristic frequencies of (10–20) kHz. Furthermore, parameter scans of ICRF/NBI power and plasma density were performed for third harmonic ICRF and NBI synergetic heating schemes. It is found that the neutron yield increases nonlinearly as the ICRF power or plasma density increases.

Published
2023
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3. Comparison of JET-C DD neutron rates independently predicted by the ASCOT and TRANSP Monte Carlo heating codes

Author

H. Weisen, P. Sirén, J. Varje, null JET Contributors, École Polytechnique Fedérale de Lausanne, University of Helsinki, Department of Applied Physics, Aalto-yliopisto, and Aalto University

Subjects
Monte Carlo orbit code, Physics, Nuclear and High Energy Physics, Jet (fluid), Monte Carlo method, BEAMS, Condensed Matter Physics, 01 natural sciences, 010305 fluids & plasmas, Nuclear physics, neutron deficit, FUSION, fusion reactions, neutron rate, Physics::Plasma Physics, JET, 0103 physical sciences, Neutron, 010306 general physics
Abstract

Simulations of the DD neutron rates predicted by the ASCOT and TRANSP Monte Carlo heating codes for a diverse set of JET-C (JET with carbon plasma facing components) plasmas are compared. A previous study (Weisen et al 2017 Nucl. Fusion 57 076029) of this data set using TRANSP found that the predicted neutron rates systematically exceeded the measured ones by factors ranging between 1 and 2. No single explanation for the discrepancies was found at the time despite a large number of candidates, including anomalous fast ion loss mechanisms, having been examined. The results shed doubt on our ability to correctly predict neutron rates also in the deuterium–tritium plasmas expected in the JET D–T campaign (DTE2). For the study presented here the calculations are independently repeated using ASCOT with different equilibria and independent mapping of the profiles of temperature and density to the computational grid. Significant differences are observed between the results from the investigations with smaller systematic differences between neutron rates measurements and predictions for the ones using ASCOT. These are traced back not to intrinsic differences between the ASCOT and TRANSP codes, but to the differences in profiles and equilibria used. These results suggest that the discrepancies reported in reference (Weisen et al 2017 Nucl. Fusion 57 076029) do not require invoking any unidentified plasma processes responsible for the discrepancies and highlight the sensitivity of such calculations to the plasma equilibrium and the necessity of a careful mapping of the profiles of the ion and electron densities and temperatures.

Published
2021
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4. Fusion product losses due to fishbone instabilities in deuterium JET plasmas

Author

Barcelona Supercomputing Center, Kiptily, V.G., Fitzgerald, M., Goloborodko, V., Sharapov, S.E., Challis, C.D., Frigione, D., Graves, J., Mantsinen, Mervi, Beaumont, P., Garcia-Munoz, M., Perez von Thun, C., Rodriguez, J.F.R., Darrow, D., Keeling, D., King, D., McClements, K.G., Solano, E.R., Schmuck, S., Sips, G., Szepesi, G., JET Contributors, Barcelona Supercomputing Center, Kiptily, V.G., Fitzgerald, M., Goloborodko, V., Sharapov, S.E., Challis, C.D., Frigione, D., Graves, J., Mantsinen, Mervi, Beaumont, P., Garcia-Munoz, M., Perez von Thun, C., Rodriguez, J.F.R., Darrow, D., Keeling, D., King, D., McClements, K.G., Solano, E.R., Schmuck, S., Sips, G., Szepesi, G., and JET Contributors

Abstract

During development of a high-performance hybrid scenario for future deuterium–tritium experiments on the Joint European Torus, an increased level of fast ion losses in the MeV energy range was observed during the instability of high-frequency n = 1 fishbones. The fishbones are excited during deuterium neutral beam injection combined with ion cyclotron heating. The frequency range of the fishbones, 10–25 kHz, indicates that they are driven by a resonant interaction with the NBI-produced deuterium beam ions in the energy range ≤120 keV. The fast particle losses in a much higher energy range are measured with a fast ion loss detector, and the data show an expulsion of deuterium plasma fusion products, 1 MeV tritons and 3 MeV protons, during the fishbone bursts. An MHD mode analysis with the MISHKA code combined with the nonlinear wave-particle interaction code HAGIS shows that the loss of toroidal symmetry caused by the n = 1 fishbones affects strongly the confinement of non-resonant high energy fusion-born tritons and protons by perturbing their orbits and expelling them. This modelling is in a good agreement with the experimental data., 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 and from the RCUK Energy Programme [grant No EP/P012450/1]. To obtain further information on the data and models underlying this paper please contact PublicationsManager@ukaea.uk . The views and opinions expressed herein do not necessarily reflect those of the European Commission, Peer Reviewed, Postprint (author's final draft)

Published
2018

5. The 'neutron deficit' in the JET tokamak

Author

Weisen, H., Bergsåker, Henric, Bykov, Igor, Frassinetti, Lorenzo, Garcia-Carrasco, Alvaro, Hellsten, Torbjörn, Johnson, Thomas, Menmuir, Sheena, Petersson, Per, Rachlew, Elisabeth, Ratynskaia, Svetlana, Rubel, Marek, Stefanikova, Estera, Ström, Petter, Tholerus, Emmi, Tolias, Panagiotis, Olivares, Pablo Vallejos, Weckmann, Armin, Zhou, Yushun, Zychor, I., et al., Weisen, H., Bergsåker, Henric, Bykov, Igor, Frassinetti, Lorenzo, Garcia-Carrasco, Alvaro, Hellsten, Torbjörn, Johnson, Thomas, Menmuir, Sheena, Petersson, Per, Rachlew, Elisabeth, Ratynskaia, Svetlana, Rubel, Marek, Stefanikova, Estera, Ström, Petter, Tholerus, Emmi, Tolias, Panagiotis, Olivares, Pablo Vallejos, Weckmann, Armin, Zhou, Yushun, Zychor, I., and et al.

Abstract

The measured D-D neutron rate of neutral beam heated JET baseline and hybrid H-modes in deuterium is found to be between approximately 50% and 100% of the neutron rate expected from the TRANSP code, depending on the plasma parameters. A number of candidate explanations for the shortfall, such as fuel dilution, errors in beam penetration and effectively available beam power have been excluded. As the neutron rate in JET is dominated by beamplasma interactions, the ` neutron deficit' may be caused by a yet unidentified form of fast particle redistribution. Modelling, which assumes fast particle transport to be responsible for the deficit, indicates that such redistribution would have to happen at time scales faster than both the slowing down time and the energy confinement time. Sawteeth and edge localised modes are found to make no significant contribution to the deficit. There is also no obvious correlation with magnetohydrodynamic activity measured using magnetic probes at the tokamak vessel walls. Modelling of fast particle orbits in the 3D fields of neoclassical tearing modes shows that realistically sized islands can only contribute a few percent to the deficit. In view of these results it appears unlikely that the neutron deficit results from a single physical process in the plasma., 20200311

Published
2017
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6. Effects of island chains on transport through changes in the radial electric field (TJ-II stellarator)

Author

F. Auriemma, I. Predebon, R. Lorenzini, A. López-Fraguas, D. López-Bruna, and B. Momo

Subjects
Physics, History, Work (thermodynamics), Ambipolar diffusion, Flux, Radius, Mechanics, Plasma, Computer Science Applications, Education, law.invention, Physics::Plasma Physics, law, Electric field, Electric discharges, Scaling, Fusion reactions, Stellarator, Erbium
Abstract

The opening of island chains in magnetically confined fusion plasma is a natural, quite common process. The effects on transport, however, are difficult to assess because of the complexity of the phenomenon, which often happens in a dynamic way. In this work we investigate a basic way in which transport may be altered due to the presence of magnetic islands: the modification of the ambipolar radial electric field Er due to the distortion of the flux surfaces and the presence of a separatrix. For the latter, we modify the flux-surface averaged metric coefficients of an ideal magnetic configuration consisting of nested tori. The new radial coordinate excludes the island region. Once the geometry is modified, we also perturb the original Er with a neoclassical scaling taken from Shaing's theory [Phys. Plasmas 9 3470 (2002)]. Figure 1 shows an example application to TJ-II plasmas in a configuration-scan discharge where the 5/3 low-order rational of the rotational transform moves through the plasma minor radius. From the experimental data, the variations of electron temperature with respect to the mean indicate an increment around the resonant location (left), while the model indicates a decrement (right). It is suggested that a more profound modification of transport properties is necessary in order to explain the experimental results.

Published
2018
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7. Modelling third harmonic ion cyclotron acceleration of deuterium beams for JET fusion product studies experiments

Author

Barcelona Supercomputing Center, Schneider, M., Johnson, T., Dumont, R., Eriksson, L.-G., Giacomelli, L., Girardo, J.-B., Hellsten, T., Khilkevitch, E., Kiptily, V.G., Koskela, T., Mantsinen, M., Nocente, M., Salewski, M., Sharapov, S.E., Shevelev, A.E., Jet Contributors, Barcelona Supercomputing Center, Schneider, M., Johnson, T., Dumont, R., Eriksson, L.-G., Giacomelli, L., Girardo, J.-B., Hellsten, T., Khilkevitch, E., Kiptily, V.G., Koskela, T., Mantsinen, M., Nocente, M., Salewski, M., Sharapov, S.E., Shevelev, A.E., and Jet Contributors

Abstract

Recent JET experiments have been dedicated to the studies of fusion reactions between deuterium (D) and Helium-3 (3He) ions using neutral beam injection (NBI) in synergy with third harmonic ion cyclotron radio-frequency heating (ICRH) of the beam. This scenario generates a fast ion deuterium tail enhancing DD and D3He fusion reactions. Modelling and measuring the fast deuterium tail accurately is essential for quantifying the fusion products. This paper presents the modelling of the D distribution function resulting from the NBI+ICRF heating scheme, reinforced by a comparison with dedicated JET fast ion diagnostics, showing an overall good agreement. Finally, a sawtooth activity for these experiments has been observed and interpreted using SPOT/RFOF simulations in the framework of Porcelli's theoretical model, where NBI+ICRH accelerated ions are found to have a strong stabilizing effect, leading to monster sawteeth., 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., Peer Reviewed, Postprint (author's final draft)

Published
2016

8. Nuclear Astrophysics with the Trojan Horse Method

Author

M. Gulino, M. La Cognata, R. G. Pizzone, M. L. Sergi, G. G. Rapisarda, Silvio Cherubini, R. Sparta, Livio Lamia, A. Tumino, S. Romano, Claudio Spitaleri, and S. M. R. Puglia

Subjects
Physics, History, 010308 nuclear & particles physics, LOW-ENERGY, FUSION REACTIONS, REACTION-RATES, Trojan horse, 01 natural sciences, Computer Science Applications, Education, Nuclear physics, 0103 physical sciences, Nuclear astrophysics, 010306 general physics
Abstract

In this review, we discuss the new recent results of the Trojan Horse Method that is used to determine reaction rates for nuclear processes in several astrophysical scenarios. The theory behind this technique is shortly presented. This is followed by an overview of some new experiments that have been carried out using this indirect approach.

Published
2016
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