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- Murari, A., et al.
(author)
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A control oriented strategy of disruption prediction to avoid the configuration collapse of tokamak reactors
- 2024
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In: Nature Communications. - 2041-1723 .- 2041-1723. ; 15:1
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Journal article (peer-reviewed)abstract
- The objective of thermonuclear fusion consists of producing electricity from the coalescence of light nuclei in high temperature plasmas. The most promising route to fusion envisages the confinement of such plasmas with magnetic fields, whose most studied configuration is the tokamak. Disruptions are catastrophic collapses affecting all tokamak devices and one of the main potential showstoppers on the route to a commercial reactor. In this work we report how, deploying innovative analysis methods on thousands of JET experiments covering the isotopic compositions from hydrogen to full tritium and including the major D-T campaign, the nature of the various forms of collapse is investigated in all phases of the discharges. An original approach to proximity detection has been developed, which allows determining both the probability of and the time interval remaining before an incoming disruption, with adaptive, from scratch, real time compatible techniques. The results indicate that physics based prediction and control tools can be developed, to deploy realistic strategies of disruption avoidance and prevention, meeting the requirements of the next generation of devices.
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- Kirov, K. K., et al.
(author)
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Analysis of the fusion performance, beam-target neutrons and synergistic effects of JET's high-performance pulses
- 2021
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In: Nuclear Fusion. - JET, EUROfus Consortium, Culham Sci Ctr, Abingdon OX14 3DB, Oxon, England. [Kirov, K. K.; Belonohy, E.; Challis, C. D.; Garzotti, L.; Keeling, D.; King, D.; Lomas, P. J.; Rimini, F. G.] Culham Sci Ctr, Culham Ctr Fus Energy, United Kingdom Atom Energy Author, Abingdon OX14 3DB, Oxon, England. [Eriksson, J.] Uppsala Univ, Dept Phys & Astron, SE-75120 Uppsala, Sweden. [Frigione, D.] ENEA CR Frascati, Unita Tecn Fus, Via E Fermi 45, I-00044 Rome, Italy. [Giacomelli, L.] CNR, IFP, Via R Cozzi 53, I-20125 Milan, Italy. [Hobirk, J.; Kappatou, A.] Max Planck Inst Plasma Phys, D-85748 Garching, Germany. [Lerche, E.; Van Eester, D.] Lab Plasma Phys, KMS ERM Renaissancelaan,30 Ave Renaissance, B-1000 Brussels, Belgium. [Nocente, M.] Univ Milano Bicocca, Piazza Sci 3, I-20126 Milan, Italy. [Reux, C.] CEA, IRFM, F-13108 St Paul Les Durance, France. [Sips, A. C. C.] European Commiss, B-1049 Brussels, Belgium. : Institute of Physics Publishing (IOPP). - 0029-5515 .- 1741-4326. ; 61:4
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Journal article (peer-reviewed)abstract
- Achieving high neutron yields in today's fusion research relies on high-power auxiliary heating in order to attain required core temperatures. This is usually achieved by means of high neutral beam (NB) and radio frequency (RF) power. Application of NB power is accompanied by production of fast beam ions and associated beam-target (BT) reactions. In standard JET operational conditions, deuterium (D) NBs are injected into D plasmas. The injected beams comprise D atoms at full, one-half and one-third injected energy. Typically, the full energy of the injected D beams is between 90 and 120 keV, providing 1.4-2.0 MW of heating, which is about half of the injected power. Half-energy D beams carry about one-third of the injected power and the rest of the power is carried by the third energy fraction of D beams. Under these conditions, thermal fusion reactions, i.e. those between plasma ions, and BT reactions are of the same order of magnitude. This study addresses important issues regarding the impact of density, central electron and ion temperatures and their ratio, T-i(0)/T-e(0), on fusion performance, measured by the total neutron yield and BT neutron counts. NB/RF synergistic effects are discussed as well. It is demonstrated that thermal fusion gain increases linearly with normalised plasma pressure, beta(N), and confinement, B-t tau. The BT neutrons are, however, more difficult to predict and this task in general requires numerical treatment. In this study, BT neutrons in JET's best-performing baseline and hybrid pulses are analysed and the underlying dependencies discussed. Central fast ion densities are found to decrease with increased density and density peaking. This is attributed to poorer beam penetration at high density. The BT reactions however are unchanged and can even increase if operating at higher core temperatures. An increase in the central ion temperature and T-i(0)/T-e(0) ratio leads to higher total and BT reaction rates whilst simultaneously the ratio of the BT to total neutron decreases significantly. NB/RF synergistic effects are found to have a negligible impact on total neutron rate. This can be explained by the reduced beam penetration in high-density conditions leading to lower central fast ion density.
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- Simpson, J., et al.
(author)
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Investigation of the dependence of p(e,ped) on n(e,sep) in JET H-Mode plasmas using integrated JETTO-MISHKA-FRANTIC simulations
- 2023
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In: Nuclear Materials and Energy. - : Elsevier BV. - 2352-1791. ; 34
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Journal article (peer-reviewed)abstract
- Experimentally, it has been observed in high-confinement (H-Mode) plasmas with Edge Localised Modes (ELMs) on JET that the pressure pedestal (p(e,ped)) is degraded by approximately a factor of two when there is a change in electron separatrix density, n(e,sep), from 1 - 4 x 10(19) m(-3). Previous work using the pedestal stability code EUROPED, has been able to predict the degradation of p(e,ped) but only for n(e,sep) = 1.5 x 10(19) m(-3). In this work, we apply a coupled code JETTO-MISHKA-FRANTIC, to self-consistently predict the transport in the pedestal region and neutral source with varying separatrix conditions. The code feeds back on the transport in the pedestal region to achieve profiles that are marginally stable to ideal MHD modes (continuous ELM model in JETTO). When accounting for the change in electron separatrix temperature (T-e,T-sep), ion separatrix temperature (T-e,T-sep) and the poloidally integrated neutral flux crossing the separatrix (Gamma(sep,neui)) as it changes with n(e,sep) (according to a scan in n(e,sep) in the edge code EDGE2D-EIRENE), no degradation in p(e,ped) was observed in JETTO-MISHKA-FRANTIC in contrast to experiment. Instead, an increase in p(e,ped) with n(e,sep) was observed which is driven by an increasing density pedestal (n(e,ped)). Within the presented JETTO-MISHKA-FRANTIC simulations, changing the pedestal width by a factor of two and a half in normalised poloidal flux (psi(n)) resulted in an approximately 40% degradation in p(e,ped) for n(e,sep) = 1 - 3 x 10(19) m(-3). This change in pedestal width was not supported by experimental data. A scan in the ratio of particle and energy transport in the pedestal (D/chi) was found to have a negligible effect on p(e,ped). Qualitative agreement between JETTO-MISHKA-FRANTIC with EUROPED was found when the input density profiles are identical.
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- Stancar, Z., et al.
(author)
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Experimental validation of an integrated modelling approach to neutron emission studies at JET
- 2021
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In: Nuclear Fusion. - : Institute of Physics Publishing (IOPP). - 0029-5515 .- 1741-4326. ; 61:12
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Journal article (peer-reviewed)abstract
- An integrated modelling methodology for the calculation of realistic plasma neutron sources for the JET tokamak has been developed. The computational chain comprises TRANSP plasma transport and DRESS neutron spectrum calculations, and their coupling to the MCNP neutron transport code, bridging plasma physics and neutronics. In the paper we apply the developed methodology to the analysis of neutron emission properties of deuterium and helium plasmas at JET, and validate individual modelling steps against neutron diagnostic measurements. Two types of JET discharges are modelled-baseline-like and three-ion radio-frequency scenarios-due to their diversity in plasma heating, characteristics of the induced fast ion population, and the imprint of these on neutron emission properties. The neutron emission modelling results are quantitatively compared to the total neutron yield from fission chambers, neutron emissivity profiles from the neutron camera, neutron spectra from the time-of-flight spectrometer, and neutron activation measurements. The agreement between measured and calculated quantities is found to be satisfactory for all four diagnostic systems within the estimated experimental and computational uncertainties. Additionally, the effect of neutrons not originating from the dominating D(D, n)He-3 reactions is studied through modelling of triton burnup DT neutrons, and, in mixed D-He-3 plasmas, neutrons produced in the Be-9(D, n gamma)B-10 reaction on impurities. It is found that these reactions can contribute up to several percent to the total neutron yield and dominate the neutron activation of samples. The effect of MeV-range fast ions on the neutron activation of In-115 and Al-27 samples is measured and computationally validated.
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