| 1. |
- Murari, A., et al.
(författare)
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A control oriented strategy of disruption prediction to avoid the configuration collapse of tokamak reactors
- 2024
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Ingår i: Nature Communications. - 2041-1723 .- 2041-1723. ; 15:1
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Tidskriftsartikel (refereegranskat)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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| 2. |
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| 3. |
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| 4. |
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| 5. |
- Joffrin, E., et al.
(författare)
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Overview of the JET preparation for deuterium-tritium operation with the ITER like-wall
- 2019
-
Ingår i: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 59:11
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Forskningsöversikt (refereegranskat)abstract
- For the past several years, the JET scientific programme (Pamela et al 2007 Fusion Eng. Des. 82 590) has been engaged in a multi-campaign effort, including experiments in D, H and T, leading up to 2020 and the first experiments with 50%/50% D-T mixtures since 1997 and the first ever D-T plasmas with the ITER mix of plasma-facing component materials. For this purpose, a concerted physics and technology programme was launched with a view to prepare the D-T campaign (DTE2). This paper addresses the key elements developed by the JET programme directly contributing to the D-T preparation. This intense preparation includes the review of the physics basis for the D-T operational scenarios, including the fusion power predictions through first principle and integrated modelling, and the impact of isotopes in the operation and physics of D-T plasmas (thermal and particle transport, high confinement mode (H-mode) access, Be and W erosion, fuel recovery, etc). This effort also requires improving several aspects of plasma operation for DTE2, such as real time control schemes, heat load control, disruption avoidance and a mitigation system (including the installation of a new shattered pellet injector), novel ion cyclotron resonance heating schemes (such as the three-ions scheme), new diagnostics (neutron camera and spectrometer, active Alfven eigenmode antennas, neutral gauges, radiation hard imaging systems...) and the calibration of the JET neutron diagnostics at 14 MeV for accurate fusion power measurement. The active preparation of JET for the 2020 D-T campaign provides an incomparable source of information and a basis for the future D-T operation of ITER, and it is also foreseen that a large number of key physics issues will be addressed in support of burning plasmas.
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| 6. |
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| 7. |
- Labit, B., et al.
(författare)
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Dependence on plasma shape and plasma fueling for small edge-localized mode regimes in TCV and ASDEX Upgrade
- 2019
-
Ingår i: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 59:8
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Tidskriftsartikel (refereegranskat)abstract
- © 2019 Institute of Physics Publishing. All rights reserved. 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 (ne,sep/nG ∼ 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.
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| 8. |
- Coda, S., et al.
(författare)
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Physics research on the TCV tokamak facility: From conventional to alternative scenarios and beyond
- 2019
-
Ingår i: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 59:11
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Tidskriftsartikel (refereegranskat)abstract
- The research program of the TCV tokamak ranges from conventional to advanced-tokamak scenarios and alternative divertor configurations, to exploratory plasmas driven by theoretical insight, exploiting the device's unique shaping capabilities. Disruption avoidance by real-time locked mode prevention or unlocking with electron-cyclotron resonance heating (ECRH) was thoroughly documented, using magnetic and radiation triggers. Runaway generation with high-Z noble-gas injection and runaway dissipation by subsequent Ne or Ar injection were studied for model validation. The new 1 MW neutral beam injector has expanded the parameter range, now encompassing ELMy H-modes in an ITER-like shape and nearly non-inductive H-mode discharges sustained by electron cyclotron and neutral beam current drive. In the H-mode, the pedestal pressure increases modestly with nitrogen seeding while fueling moves the density pedestal outwards, but the plasma stored energy is largely uncorrelated to either seeding or fueling. High fueling at high triangularity is key to accessing the attractive small edge-localized mode (type-II) regime. Turbulence is reduced in the core at negative triangularity, consistent with increased confinement and in accord with global gyrokinetic simulations. The geodesic acoustic mode, possibly coupled with avalanche events, has been linked with particle flow to the wall in diverted plasmas. Detachment, scrape-off layer transport, and turbulence were studied in L- and H-modes in both standard and alternative configurations (snowflake, super-X, and beyond). The detachment process is caused by power 'starvation' reducing the ionization source, with volume recombination playing only a minor role. Partial detachment in the H-mode is obtained with impurity seeding and has shown little dependence on flux expansion in standard single-null geometry. In the attached L-mode phase, increasing the outer connection length reduces the in-out heat-flow asymmetry. A doublet plasma, featuring an internal X-point, was achieved successfully, and a transport barrier was observed in the mantle just outside the internal separatrix. In the near future variable-configuration baffles and possibly divertor pumping will be introduced to investigate the effect of divertor closure on exhaust and performance, and 3.5 MW ECRH and 1 MW neutral beam injection heating will be added.
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| 9. |
- Moiseenko, V. E., et al.
(författare)
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Stellator research at IPP KIPT : Status and prospects
- 2019
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Ingår i: PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY. - : KHARKOV INST PHYSICS & TECHNOLOGY. - 1562-6016. ; :1, s. 3-8
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Tidskriftsartikel (refereegranskat)abstract
- Features of the recent Uragan-2M campaign are reviewed together with some theoretical advances. They include experiments with B4C limiter, studies of various 1. . . 20 kHz oscillations, development of a new in-situ diagnostics for wall conditions, i.e. the thermal desorption probe, the improved numerical model of RF plasma production in stellarators in the ion cyclotron and electron-cyclotron frequency ranges, a new positive-definite form of time-harmonic Maxwell's equations and plasma start-up studies.
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| 10. |
- Moiseenko, V. E., et al.
(författare)
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Research on stellarator-mirror fission-fusion hybrid
- 2014
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Ingår i: Plasma Physics and Controlled Fusion. - : IOP Publishing. - 0741-3335 .- 1361-6587. ; 56:9, s. 094008-
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Tidskriftsartikel (refereegranskat)abstract
- The development of a stellarator-mirror fission-fusion hybrid concept is reviewed. The hybrid comprises of a fusion neutron source and a powerful sub-critical fast fission reactor core. The aim is the transmutation of spent nuclear fuel and safe fission energy production. In its fusion part, neutrons are generated in deuterium-tritium (D-T) plasma, confined magnetically in a stellarator-type system with an embedded magnetic mirror. Based on kinetic calculations, the energy balance for such a system is analyzed. Neutron calculations have been performed with the MCNPX code, and the principal design of the reactor part is developed. Neutron outflux at different outer parts of the reactor is calculated. Numerical simulations have been performed on the structure of a magnetic field in a model of the stellarator-mirror device, and that is achieved by switching off one or two coils of toroidal field in the Uragan-2M torsatron. The calculations predict the existence of closed magnetic surfaces under certain conditions. The confinement of fast particles in such a magnetic trap is analyzed.
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| 11. |
- Moiseenko, V. E., et al.
(författare)
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Fast ion motion in the plasma part of a stellarator-mirror fission-fusion hybrid
- 2016
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Ingår i: Plasma Physics and Controlled Fusion. - : IOP Publishing. - 0741-3335 .- 1361-6587. ; 58:6
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Tidskriftsartikel (refereegranskat)abstract
- Recent developments of a stellarator-mirror (SM) fission-fusion hybrid concept are reviewed. The hybrid consists of a fusion neutron source and a powerful sub-critical fast fission reactor core. The aim is transmutation of spent nuclear fuel and safe fission energy production. In its fusion part, a stellarator-type system with an embedded magnetic mirror is used. The stellarator confines deuterium plasma with moderate temperature, 1-2 keV. In the magnetic mirror, a hot component of sloshing tritium ions is trapped. There, the fusion neutrons are generated. A candidate for a combined SM system is a DRACON magnetic trap. A basic idea behind an SM device is to maintain local neutron production in a mirror part, but at the same time eliminate the end losses by using a toroidal device. A possible drawback is that the stellarator part can introduce collision-free radial drift losses, which is the main topic for this study. For high energy ions of tritium with an energy of 70 keV, comparative computations of collisionless losses in the rectilinear part of a specific design of the DRACON type trap are carried out. Two versions of the trap are considered with different lengths of the rectilinear sections. Also the total number of current-carrying rings in the magnetic system is varied. The results predict that high energy ions from neutral beam injection can be satisfactorily confined in the mirror part during 0.1-1 s. The Uragan-2M experimental device is used to check key points of the SM concept. The magnetic configuration of a stellarator with an embedded magnetic mirror is arranged in this device by switching off one toroidal coil. The motion of particles magnetically trapped in the embedded mirror is analyzed numerically with use of motional invariants. It is found that without radial electric field particles quickly drift out of the SM, even if the particles initially are located on a nested magnetic surface. We will show that a weak radial electric field, which would be spontaneously created by the ambipolar radial particle losses, can make drift trajectories closed, which substantially improves particle confinement. It is remarkable that the improvement acts both for positive and negative charges.
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| 12. |
- Moiseenko, V. E., et al.
(författare)
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Fast Trapped Particle Motion In Uragan-2M Stellarator With Embedded Magnetic Mirror
- 2014
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Ingår i: Problems of Atomic Science and Technology. - 1562-6016. ; :6, s. 26-29
-
Tidskriftsartikel (refereegranskat)abstract
- The magnetic configuration of a stellarator with an embedded magnetic mirror is arranged in the Uragan-2M experimental device by switching off one toroidal coil. The motion of particles magnetically trapped in the embedded mirror is analyzed numerically with use of motional invariants. It is found that without electric field the particle quickly drift out of the mirror. Sufficiently small radial electric field can make the drift trajectories closed that substantially improve particle confinement. It is remarkable that the improvement acts both for positive and negative charges.
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| 13. |
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| 14. |
- Zaborowski, AM, et al.
(författare)
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Microsatellite instability in young patients with rectal cancer: molecular findings and treatment response
- 2022
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Ingår i: The British journal of surgery. - : Oxford University Press (OUP). - 1365-2168 .- 0007-1323. ; 109:3, s. 251-255
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Tidskriftsartikel (refereegranskat)abstract
- In this study of 400 patients with early-onset rectal cancer, 12.5 per cent demonstrated microsatellite instability (MSI). MSI was associated with a reduced likelihood of nodal positivity, an increased rate of pathological complete response, and improved disease-specific survival.
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| 15. |
- Kotenko, V. G., et al.
(författare)
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Magnetic Surfaces of a Combined Magnetic System
- 2012
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Ingår i: PROBL ATOM SCI TECH. - 1562-6016. ; :6, s. 22-24
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Tidskriftsartikel (refereegranskat)abstract
- The existence of closed magnetic surfaces in a model of the combined magnetic system is shown by numerical simulations. The numeric model contains a magnetic system of the l = 2 torsatron with the coils of an additional toroidal magnetic field and the mirror-type magnetic system. The mirror-type magnetic system is realized by switching off one of the coils of an additional toroidal magnetic field.
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| 16. |
- Kovtun, Yurii, V, et al.
(författare)
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ICRF Plasma Production with Hydrogen Minority Heating in Uragan-2M and Large Helical Device
- 2023
-
Ingår i: Plasma and Fusion Research. - : Japan Society of Plasma Science and Nuclear Fusion Research. - 1880-6821. ; 18:2402042
-
Tidskriftsartikel (refereegranskat)abstract
- This report compares results ion-cyclotron range of frequencies (ICRF) plasma production at hydrogen mi-nority regime in Uragan-2M (U-2M) and Large Helical Device (LHD). The condition of the presence of the fundamental harmonic ion cyclotron resonance zone for the hydrogen inside the plasma column should be ful-filled for this method. The scenario is successful at both machines and weakly sensitive to the variation of the hydrogen concentration in the H2+He gas mixture. It should be noted that at LHD the start up is slower than at U-2M. The comparison of plasma production in ICRF with hydrogen minority at U-2M and LHD indicate that this scenario can be scaled to larger stellarator devices. The experiments made are the base for the proposal for usage this scenario for plasma production in ICRF at Wendelstein 7-X at magnetic field reduced to 1.7 T.
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| 17. |
- Moiseenko, V. E., et al.
(författare)
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Stellarator-mirror fusion-fission hybrid - a fast route to clean and safe nuclear energy
- 2023
-
Ingår i: Journal of Plasma Physics. - : Cambridges Institutes Press. - 0022-3778 .- 1469-7807. ; 89:4
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Tidskriftsartikel (refereegranskat)abstract
- The multiple-recycle fuel cycle for uranium-238 considered here, if practically realized, can bring revolutionary changes in nuclear energy. A full use of uranium-238 implies a practically infinite resource for power generation. Besides the energy, the fuel cycle net output is only fission products, which are co-products rather than waste. For the same amount of energy produced, the amount of fission products is two orders of magnitude less compared with the amount of spent nuclear fuel generated in currently exploited nuclear energy production scenarios. Using the simplest isotope balance model, key features of the multiple-recycle fuel cycle for uranium-238 are investigated. The repetition of this cycle results in smooth transformation of the initial fuel to 'stationary' fuel without strong variations in the fractional isotope content. Deficit of delayed neutrons is a threat of the fuel cycle considered as well as other fuel cycles that use plutonium. It has a dramatic impact on reactor controllability and safety. A solution to this threat could be a subcritical nuclear reactor with an external neutron source. In this paper, use of a stellarator-mirror (SM) fusion-fission hybrid for the multiple-recycle fuel cycle for uranium-238 is analysed. A summary of the experimental and theoretical studies on the SM hybrid is given. Preliminary results for principal design of a SM hybrid nuclear reactor for the multiple-recycle fuel cycle for uranium-238 are presented.
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| 18. |
- Chernitskiy, S. V., et al.
(författare)
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A fuel cycle for minor actinides burning in a stellarator-mirror fusion-fission hybrid
- 2017
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Ingår i: PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY. - : KHARKOV INST PHYSICS & TECHNOLOGY. - 1562-6016. ; :1, s. 36-39
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Tidskriftsartikel (refereegranskat)abstract
- The MCNPX Monte-Carlo code has been used to model a concept of a fusion-fission stellarator-mirror hybrid aimed for transmutation transuranic content from the spent nuclear fuel. A fuel cycle for the subcritical fusion-fission hybrid is investigated and discussed.
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| 19. |
- Chernitskiy, S. V., et al.
(författare)
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Minor actinides burning in a stellarator-mirror fusion-fission hybrid
- 2015
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Ingår i: Problems of Atomic Science and Technology. - 1562-6016. ; :1, s. 20-23
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Tidskriftsartikel (refereegranskat)abstract
- The MCNPX Monte-Carlo code has been used to model a compact concept of a fusion-fission reactor based on a combined stellarator-mirror trap for transmutation transuranic elements from the spent nuclear fuel. Calculation results for fission rates for transuranic elements are presented.
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| 20. |
- Chernitskiy, S. V., et al.
(författare)
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Neutronic Model Of A Fusion Neutron Source
- 2013
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Ingår i: Problems of Atomic Science and Technology. - 1562-6016. ; :1, s. 61-63
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Tidskriftsartikel (refereegranskat)abstract
- The MCNPX numerical code has been used to model a fusion neutron source based on a combined stellarator-mirror trap. Calculation results for the neutron spectrum near the inner wall and radial leakage of neutrons through the mantle surface of the fusion neutron source are presented.
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| 21. |
- Chernitskiy, S. V., et al.
(författare)
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Neutronic Model of a Stellarator-Mirror Fusion-Fission Hybrid
- 2012
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Ingår i: PROBL ATOM SCI TECH. - 1562-6016. ; :6, s. 58-60
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Tidskriftsartikel (refereegranskat)abstract
- The MCNPX numerical code has been used to model a compact concept for a fusion-fission reactor based on a combined stellarator-mirror trap. Calculation results for the radial leakage of neutrons through the mantle surface of the fission reactor are presented.
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| 22. |
- Chernitskiy, S. V., et al.
(författare)
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Neutronic Model of a Stellarator-Mirror Fusion-Fission Hybrid
- 2013
-
Ingår i: Fusion science and technology. - 1536-1055 .- 1943-7641. ; 63:1T, s. 322-324
-
Tidskriftsartikel (refereegranskat)abstract
- The MCNPX numerical code has been used to model the neutron transport in a mirror based fusion-fission reactor. The purpose is to find a principal design of the fission mantle which fits to the neutron source and to calculate the leakage of neutrons through the mantle surface of the fission reactor. The fission reactor part has a cylindrical shape with an outer radius 1.66 m and a 4 m length. The fuel has the isotopic composition of the spent nuclear fuel from PWR after uranium-238 removal. Inside the fission reactor core is a vacuum chamber with a radius 0.5 m containing a 4 m long hot plasma producing fusion neutrons. To sustain the hot ion plasma which is responsible for the fusion neutron production, neutral beam injection is considered. Calculation results for the radial leakage of neutrons through the mantle surface of the fission reactor are presented. These calculations predict that the power released with neutrons from the reactor to outer space would be small and will not exceed the value of 6 kW while the reactor thermal power is 1 GWth.
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| 23. |
- Chernitskiy, S. V., et al.
(författare)
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Static neutronic calculation of a subcritical transmutation stellarator-mirror fusion-fission hybrid
- 2014
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Ingår i: Annals of Nuclear Energy. - : Elsevier BV. - 0306-4549 .- 1873-2100. ; 72, s. 413-420
-
Tidskriftsartikel (refereegranskat)abstract
- The MCNPX Monte-Carlo code has been used to model the neutron transport in a sub-critical fast fission reactor driven by a fusion neutron source. A stellarator-mirror device is considered as the fusion neutron source. The principal composition for a fission blanket of a mirror fusion-fission hybrid is devised from the calculations. Heat load on the first wall, the distribution of the neutron fields in the reactor, the neutron spectrum and the distribution of energy release in the blanket are calculated. The possibility of tritium breeding inside the installation in quantities that meet the needs of the fusion neutron source is analyzed. The portion of the plasma column generates fusion neutrons that mainly do not reach the fission reactor core is proposed to be surrounded by a vessel filled with borated water to absorb the flying out neutrons. The flux of the neutrons escaping from the device to surrounding space is also calculated.
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| 24. |
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| 25. |
- Kovtun, Yurii V., et al.
(författare)
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ICRF plasma production at hydrogen minority regime in LHD
- 2023
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Ingår i: Nuclear Fusion. - : Institute of Physics Publishing (IOPP). - 0029-5515 .- 1741-4326. ; 63:10
-
Tidskriftsartikel (refereegranskat)abstract
- This study aim is to develop further an ion cyclotron range of frequencies (ICRF) method of plasma production in stellarators based on the minority heating. The previous studies demonstrate production of low density plasma (9.5 × 1017m−3) at low power of up to 0.2 MW. The higher ICRF heating power experiments become possible after introducing a programmable ICRF power ramp up at the front of the ICRF pulse. With this trick, all the shots went with the antenna voltage within the safe range. Increase of the ICRF power predictably results in increase of the density of produced plasma. Without pre-ionization the plasma density achieved was 6 × 1018 m−3 which is 6 times higher than in previous experiments. However, the electron temperature was not high, the light impurities were hot fully stripped, and there were no recombination peaks after termination of the ICRF pulse. Plasma density is too low to provide good conditions for efficient plasma heating. For the reference, the ICRF heating of high density cold plasma prepared by electron cyclotron resonance heating is performed. Both electrons and ions were heated to high temperatures, and this plasma state is sustained. The antenna–plasma coupling was much better which result in larger heating power with the lower antenna voltage.
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| 26. |
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| 27. |
- Ågren, Olov, et al.
(författare)
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Steady-state fusion fission reactor concepts based on stellarator-mirror and mirror machines
- 2015
-
Ingår i: Problems of Atomic Science and Technology. - 1562-6016. ; :1, s. 3-7
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Tidskriftsartikel (refereegranskat)abstract
- Neutron sources and hybrid reactors offer a possibility for application of fusion in a not too distant future. Steady-state operation on a time scale of a year without interruption is essential for such applications. In response to this need, our studies are focused on concepts which are not limited by pulsed operation. Special attention is put on mirror machines and a stellarator-mirror concept with localized neutron production. Reactor safety, magnetic coils, power amplification by fission, plasma heating, a radial constant of motion which provides a bounded radial motion in the collision free approximation are some of the issues addressed.
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| 28. |
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| 29. |
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| 30. |
- Hagnestål, Anders, et al.
(författare)
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Coil System For a Mirror-Based Hybrid Reactor
- 2012
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Ingår i: Fusion for Neutrons and Subcritical Nuclear Fission. - : AIP. - 9780735410381 ; , s. 217-223
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Konferensbidrag (refereegranskat)abstract
- Two different superconducting coil systems for the SFLM Hybrid study - a quadrupolar mirror based fusion-fission reactor study - are presented. One coil system is for a magnetic field with 2 T at the midplane and a mirror ratio of four. This coil set consists of semi-planar coils in two layers. The alternative coil system is for a downscaled magnetic field of 1.25 T at the midplane and a mirror ratio of four, where a higher beta is required to achieve sufficient the neutron production. This coil set has one layer of twisted 3D coils. The 3D coils are expected to be considerably cheaper than the semiplanar, since NbTi superconductors can be used for most coils instead of Nb3Sn due to the lower magnetic field.
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| 31. |
- Moiseenko, V. E., et al.
(författare)
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Curl-free positive definite form of time-harmonic Maxwell's equations well-suitable for iterative numerical solving
- 2021
-
Ingår i: Plasma Physics and Controlled Fusion. - : Institute of Physics Publishing (IOPP). - 0741-3335 .- 1361-6587. ; 63:12
-
Tidskriftsartikel (refereegranskat)abstract
- A new form of time-harmonic Maxwell's equations is developed on the base of the standard ones and proposed for numerical modeling. It is written for the magnetic field strength H, electric displacement D, vector potential A and the scalar potential phi. There are several attractive features of this form. The 1st one is that the differential operator acting on these quantities is positive. The 2nd is absence of curl operators among the leading order differential operators. The Laplacian stands for leading order operator in the equations for H, A and phi, while the gradient of divergence stands for D. The 3rd feature is absence of space varied coefficients in the leading order differential operators that provides diagonal domination of the resulting matrix of the discretized equations. A simple example is given to demonstrate the applicability of this new form of time-harmonic Maxwell's equations.
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| 32. |
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| 33. |
- Moiseenko, Vladimir E., et al.
(författare)
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Multiple recycle fuel cycle for spent nuclear fuel components incineration in fusion-fission hybrid
- 2022
-
Ingår i: Problems of Atomic Science and Technology. - : Problems of Atomic Science and Technology. - 1562-6016. ; :6, s. 40-43
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Tidskriftsartikel (refereegranskat)abstract
- A multiple recycle fuel cycle (MRFC) is analyzed using a simple numerical model. A straightforward approach to MRFC has some unfavorable features like strong variation of the neutron multiplication factor and accumulation of americium isotopes which would likely hamper its practical usage. A solution proposed here is addition of 238U both to initial fuel and the recycled fuel.
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| 34. |
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| 35. |
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| 36. |
- Moiseenko, V. E., et al.
(författare)
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Second harmonic cyclotron heating of sloshing ions in a straight field line mirror
- 2007
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Ingår i: Fusion science and technology. - 1536-1055 .- 1943-7641. ; 51:2T, s. 160-163
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Tidskriftsartikel (refereegranskat)abstract
- The second harmonic heating in mirrors is explicated. A new coordinate-independent form of the second harmonic term in the plasma dielectric response is derived. The second harmonic heating in the WKB limit is addressed and compared with minority heating. A newly developed three-dimensional model for the time-harmonic boundary problem for Maxwell's equations is used for second harmonic heating modeling in the reactor-scale straight field line mirror device. Computations show that the antenna Q is low and the regime of global resonance overlapping is in effect. Only a small portion of the wave energy transits through the cyclotron layer and penetrates to the central part of the trap. The power deposition is peaked at the plasma core.
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| 37. |
- Moiseenko, V. E., et al.
(författare)
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Stellarator-Mirror Hybrid with Neutral Beam Injection
- 2013
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Ingår i: Fusion science and technology. - 1536-1055 .- 1943-7641. ; 63:1T, s. 119-122
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Tidskriftsartikel (refereegranskat)abstract
- A stellarator-mirror fusion-fission hybrid has recently been proposed. Neutral beam injection (NBI) is here studied numerically for this hybrid using a two-dimensional kinetic code, KNBIM The code accounts for Coulomb collisions between the hot ions and the background plasma. The geometry of the confining magnetic field is arbitrary for the code and is accounted for via a numerical bounce averaging procedure. Along with the kinetic calculations the neutron production intensity is computed. The calculated hot ion distribution function from NBI is used in power balance estimates for the whole system. The requirement that the fast neutrals should be efficiently captured in the plasma is imposed to restrict the range of plasma parameters. The results of the power balance calculations are close to results obtained previously with a bi-Maxwellian ion distribution function. The calculated parameters for a power producing stellarator mirror device are within modern top technical capabilities. The parameters of plasma and NBI characteristics seem also attainable. The calculated fusion Q is within a range with potential for energy production in a hybrid reactor.
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| 38. |
- Noack, Klaus, et al.
(författare)
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Comments on the power amplification factor of a driven subcritical system
- 2013
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Ingår i: Annals of Nuclear Energy. - : Elsevier BV. - 0306-4549 .- 1873-2100. ; 59, s. 261-266
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Tidskriftsartikel (refereegranskat)abstract
- The power amplification factor PAF of a driven subcritical system is defined as the ratio of the fission power output of the blanket to the power which the driver must deliver to sustain its neutron source intensity. This parameter decisively determines the effectiveness of the whole system independent of its special purpose as energy amplifier or as transmutation facility. The present note derives a refined analytical expression for the PAF which reveals more physical details than the expressions given by other authors. Moreover, the traditionally used forms of the static reactor eigenvalue equation and of its adjoint equation are rewritten for subcritical systems and used in the derivation of the expression for the PAF. The derived formula and the modified eigenvalue equations are discussed.
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| 39. |
- Thor, M., et al.
(författare)
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Inter-institutional analysis demonstrates the importance of lower than previously anticipated dose regions to prevent late rectal bleeding following prostate radiotherapy
- 2018
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Ingår i: Radiotherapy and Oncology. - : Elsevier BV. - 0167-8140. ; 127:1, s. 88-95
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: To investigate whether inter-institutional cohort analysis uncovers more reliable dose-response relationships exemplified for late rectal bleeding (LRB) following prostate radiotherapy. Material and methods: Data from five institutions were used. Rectal dose-volume histograms (DVHs) for 989 patients treated with 3DCRT or IMRT to 70-86.4 Gy@1.8-2.0 Gy/fraction were obtained, and corrected for fractionation effects (alpha/beta = 3 Gy). Cohorts with best-fit Lyman-Kutcher-Burman volume-effect parameter a were pooled after calibration adjustments of the available LRB definitions. In the pooled cohort, dose-response modeling (incorporating rectal dose and geometry, and patient characteristics) was conducted on a training cohort (70%) followed by final testing on the remaining 30%. Multivariate logistic regression was performed to build models with bootstrap stability. Results: Two cohorts with low bleeding rates (2%) were judged to be inconsistent with the remaining data, and were excluded. In the remaining pooled cohorts (n = 690; LRB rate = 12%), an optimal model was generated for 3DCRT using the minimum rectal dose and the absolute rectal volume receiving less than 55 Gy (AUC = 0.67; p = 0.0002; Hosmer-Lemeshow p-value, p(HL) = 0.59). The model performed nearly as well in the hold-out testing data (AUC = 0.71; p < 0.0001; p(HL) = 0.63), indicating a logistically shaped dose-response. Conclusion: We have demonstrated the importance of integrating datasets from multiple institutions, thereby reducing the impact of intra-institutional dose-volume parameters explicitly correlated with prescription dose levels. This uncovered an unexpected emphasis on sparing of the low to intermediate rectal dose range in the etiology of late rectal bleeding following prostate radiotherapy. (C) 2018 Elsevier B. V. All rights reserved. Radiotherapy and Oncology 127 (2018) 88-95
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| 40. |
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| 41. |
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| 42. |
- Ågren, Olov, et al.
(författare)
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Hybrid Reactor Studies Based on the Straight Field Line Mirror
- 2013
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Ingår i: Fusion science and technology. - 1536-1055 .- 1943-7641. ; 63:1T, s. 52-57
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Tidskriftsartikel (refereegranskat)abstract
- The straight field line mirror (SFLM) hybrid reactor studies aim to identify a concept where the safety of fission power production could be enhanced. A fusion neutron source could become a mean to achieve this. The SFLM studies address critical issues such as reactor safety, natural circulation of coolants, steady state operation for a year or more and means to avoid too strong material loads by a proper geometrical arrangement of the reactor components. A key result is that power production may be possible with a fusion Q factor as low as 0.15. This possibility arises from the high power amplification by fission, which within reactor safety margins may exceed a factor of 100. The requirements on electron temperature are dramatically lower for a fusion hybrid compared to a stand-alone fusion reactor. This and several other factors are important for our choice to select a mirror machine for the fusion hybrid reactor studies.
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| 43. |
- Ågren, Olov, et al.
(författare)
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On improved confinement in mirror plasmas by a radial electric field
- 2017
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Ingår i: Plasma Physics and Controlled Fusion. - : IOP Publishing. - 0741-3335 .- 1361-6587. ; 59:11
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Tidskriftsartikel (refereegranskat)abstract
- A weak radial electric field can suppress radial excursions of a guiding center from its mean magnetic surface. The physical origin of this effect is the smearing action by a poloidal E x B rotation, which tend to cancel out the inward and outward radial drifts. A use of this phenomenon may provide larger margins for magnetic field shaping with radial confinement of particles maintained in the collision free idealization. Mirror fields, stabilized by a quadrupolar field component, are of particular interest for their MHD stability and the possibility to control the quasi neutral radial electric field by biased potential plates outside the confinement region. Flux surface footprints on the end tank wall have to be traced to avoid short-circuiting between biased plates. Assuming a robust biasing procedure, moderate voltage demands for the biased plates seems adequate to cure even the radial excursions of Yushmanov ions which could be locally trapped near the mirrors. Analytical expressions are obtained for a magnetic quadrupolar mirror configuration which possesses minimal radial magnetic drifts in the central confinement region. By adding a weak controlled radial quasi-neutral electric field, the majority of gyro centers are predicted to be forced to move even closer to their respective mean magnetic surface. The gyro center radial coordinate is in such a case an accurate approximation for a constant of motion. By using this constant of motion, the analysis is in a Vlasov description extended to finite beta. A correspondence between that Vlasov system and a fluid description with a scalar pressure and an electric potential is verified. The minimum B criterion is considered and implications for flute mode stability in the considered magnetic field is analyzed. By carrying out a long-thin expansion to a higher order, the validity of the calculations are extended to shorter and more compact device designs.
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| 44. |
- Ågren, Olov, et al.
(författare)
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On MHD stability, ellipticity, omnigenuity, constants of motions and a modified thermal barrier of a straight field line mirror
- 2007
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Ingår i: Fusion science and technology. - 1536-1055 .- 1943-7641. ; 51:2T, s. 200-203
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Tidskriftsartikel (refereegranskat)abstract
- The straight field line mirror field(1) is the unique field which gives the lowest ellipticity of the flux tube of an MHD stable minimum B mirror field. In this particular vacuum field, each gyro center bounces back and forth on a single magnetic field line, and a pair of two new constants of motion is associated with this property(2). Using these invariants in the Vlasov equation, it can be shown that the radial gyro center magnetic drift is absent to first order in the plasma beta, and the equilibrium is omnigenous. The neoclassical increase of the radial transport may thus be avoided without an axisymmetrization of this single cell mirror. A scheme to improve end confinement of ions, and simultaneously create an electric potential barrier for the electrons and a sloshing ion component, has been proposed. The end plugging transforms ions under way to escape into the loss cone into sloshing ions by ion cyclotron resonance heating. Numerical studies on sloshing ion production by RF heating(4) demonstrate strong absorption of the RF field near the fundamental gyro frequency resonance of the minority deuterium ions as well as near the tritium second harmonic gyro frequency resonance. The scenario indicates a possibility to achieve a high energy gain factor in this kind of single cell mirror with the proposed modified thermal barrier.
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| 45. |
- Ågren, Olov, et al.
(författare)
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Possibilities for transmutation of nuclear waste and energy production with a "straight field line mirror" neutron source
- 2009
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Ingår i: Fusion science and technology. - 1536-1055 .- 1943-7641. ; 55:2T, s. 46-51
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Tidskriftsartikel (refereegranskat)abstract
- A pure fusion mirror device suffers from the predicted low values of the Q factor (energy gain factor). A much higher energy production may be achieved in a fusion-fission reactor, where the fusion plasma neutron source is surrounded by a fission mantle. The fusion neutrons are capable of initiating energy producing fission reactions in the surrounding mantle. A mirror machine can probably be designed to provide sufficient space for a 1.1 m wide fission mantle inside the current coils, and the power production from the fission reactions can in such a case exceed the fusion power by more than two orders of magnitude ( P-fis / P-fus approximate to 150), suggesting a realistic reactor regime for a mirror based fusion-fission device. An energy producing device may operate with an electron temperature around 1 keV Transmutation of long-lived radio active isotopes (minor actinides) from spent nuclear fuel from fission reactors can reduce geological storage from 100 000 years to only 300 years. Since the energy of D-T fusion neutrons are above the threshold for the most important transmutation reactions desired for treatment of nuclear waste, there may be an interest for a mirror transmutation device even if no net energy is produced. Recent theoretical simulations have considered the possibility to use the Gas Dynamic Trap (GDT) at Novosibirsk as a subcritical burner for transmutation by fusion neutrons. In the present work, possibilities for mirror based fusion-fission machines are discussed Means to achieve sufficient end confinement for a straight field line mirror fusion-fission system with a thermal barrier are briefly analyzed End leakage can alternatively be avoided by connecting the ends of a magnetic mirror with a stellerator tube, while the fusion neutrons are produced in the mirror part where a high energy sloshing ion component is confined. A zero dimensional model for such a mirror-stellarator system has been developed. The computed results indicate some possible parameter regimes for industrial transmutation and power production.
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| 46. |
- Ågren, Olov, et al.
(författare)
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Radial constant of motion for particles in magnetic mirror fields
- 2014
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Ingår i: Plasma Physics and Controlled Fusion. - : IOP Publishing. - 0741-3335 .- 1361-6587. ; 56:9, s. 095026-
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Tidskriftsartikel (refereegranskat)abstract
- It is crucial for magnetic fusion devices that particle confinement occurs for long periods in a magnetic flux tube, and radial loss from the flux tube by a collision-free radial drift needs to be eliminated. Longitudinal, as well as radial, confinement is required. Two standard constants of motion, the energy and the magnetic moment of the gyrating particle, provide longitudinal confinement. A third constant of motion, which implies bounded radial motion, would be sufficient for radial confinement, but it is often impossible to identify such an invariant. A closed form expression for a radial invariant is derived for magnetic mirrors with a stabilizing quadrupolar field. A weak radial electric field, controlled by electrically biased endplates, is a tool for making a collision-free motion radially bounded in open systems. Experimental results in such magnetic confinement schemes indicate a qualitative agreement with our predictions for the existence of a radial invariant. Voltage and power requirements for the biased endplates are vanishingly small if the magnetic drifts are minimized in the magnetic field design. The power requirements to sustain the biased potentials are expected to be vanishingly small for a gross stable plasma.
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| 47. |
- Ågren, Olov, et al.
(författare)
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Radial Drift Invariant In Long-Thin Mirrors
- 2012
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Ingår i: Fusion for Neutrons and Subcritical Nuclear Fission. - : AIP. - 9780735410381 ; , s. 255-258
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Konferensbidrag (refereegranskat)abstract
- In omnigenous systems, the guiding centers are constrained to move on magnetic surfaces. Since a magnetic surface is determined by a constant radial Clebsch coordinate, omnigenuity implies that the guiding center radial coordinate (the Clebsch coordinate) is constant. Near omnigenuity is probably a requirement for high quality confinement and in such systems only small oscillatory radial banana guiding center excursions from the average drift surface occur. The guiding center radial coordinate is then the leading order term for a more precise radial drift invariant I-r, where higher order corrections arise from the oscillatory "banana ripple" associated with the excursions from the mean drift magnetic surface. An analytical expression for the radial invariant is derived for long-thin quadrupolar mirror equilibria. The formula for the invariant is then used in a Vlasov distribution function. To model radial density profiles, it is necessary to use the radial invariant (the parallel invariant is insufficient for this). The results are also compared with standard fluid approaches. In several aspects, the fluid and Vlasov system with the radial invariant give analogous formulas. One difference is that the parallel current associated with finite banana widths could be derived from the radial invariant.
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| 48. |
- Ågren, Olov, et al.
(författare)
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The Hybrid Reactor Project Based On The Straight Field Line Mirror Concept
- 2012
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Ingår i: Fusion for Neutrons and Subcritical Nuclear Fission. - : AIP. - 9780735410381 ; , s. 173-185
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Konferensbidrag (refereegranskat)abstract
- The straight field line mirror (SFLM) concept is aiming towards a steady-state compact fusion neutron source. Besides the possibility for steady state operation for a year or more, the geometry is chosen to avoid high loads on materials and plasma facing components. A comparatively small fusion hybrid device with "semi-poor" plasma confinement (with a low fusion Q factor) may be developed for industrial transmutation and energy production from spent nuclear fuel. This opportunity arises from a large fission to fusion energy multiplication ratio, Q(r) = P-fis/P-fus >> 1. The upper bound on Q(r) is primarily determined by geometry and reactor safety. For the SFLM, the upper bound is Q(r)approximate to 150, corresponding to a neutron multiplicity of k(eff) =0.97. Power production in a mirror hybrid is predicted for a substantially lower electron temperature than the requirement T-e approximate to 10 keV for a fusion reactor. Power production in the SFLM seems possible with Q approximate to 0.15, which is 10 times lower than typically anticipated for hybrids (and 100 times smaller than required for a fusion reactor). This relaxes plasma confinement demands, and broadens the range for use of plasmas with supra-thermal ions in hybrid reactors. The SFLM concept is based on a mirror machine stabilized by qudrupolar magnetic fields and large expander tanks beyond the confinement region. The purpose of the expander tanks is to distribute axial plasma loss flow over a sufficiently large area so that the receiving plates can withstand the heat. Plasma stability is not relying on a plasma flow into the expander regions. With a suppressed plasma flow into the expander tanks, a possibility arise for higher electron temperature. A brief presentation will be given on basic theory for the SFLM with plasma stability and electron temperature issues, RF heating computations with sloshing ion formation, neutron transport computations with reactor safety margins and material load estimates, magnetic coil designs as well as a discussion on the implications of the geometry for possible diagnostics. Reactor safety issues are addressed and a vertical orientation of the device could assist passive coolant circulation. Specific attention is put to a device with a 25 m long confinement region and 40 cm plasma radius in the mid-plane. In an optimal case (k(eff) = 0.97) with a fusion power of only 10 MW, such a device may be capable of producing a power of 1.5 GW(th).
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| 50. |
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