| 1. |
- Chapman, I. T., et al.
(author)
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Overview of MAST results
- 2015
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In: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 55:10
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Journal article (peer-reviewed)abstract
- The Mega Ampere Spherical Tokamak (MAST) programme is strongly focused on addressing key physics issues in preparation for operation of ITER as well as providing solutions for DEMO design choices. In this regard, MAST has provided key results in understanding and optimizing H-mode confinement, operating with smaller edge localized modes (ELMs), predicting and handling plasma exhaust and tailoring auxiliary current drive. In all cases, the high-resolution diagnostic capability on MAST is complemented by sophisticated numerical modelling to facilitate a deeper understanding. Mitigation of ELMs with resonant magnetic perturbations (RMPs) with toroidal mode number n(RMP) = 2, 3, 4, 6 has been demonstrated: at high and low collisionality; for the first ELM following the transition to high confinement operation; during the current ramp-up; and with rotating n(RMP) = 3 RMPs. n(RMP) = 4, 6 fields cause less rotation braking whilst the power to access H-mode is less with n(RMP) = 4 than n(RMP) = 3, 6. Refuelling with gas or pellets gives plasmas with mitigated ELMs and reduced peak heat flux at the same time as achieving good confinement. A synergy exists between pellet fuelling and RMPs, since mitigated ELMs remove fewer particles. Inter-ELM instabilities observed with Doppler backscattering are consistent with gyrokinetic simulations of micro-tearing modes in the pedestal. Meanwhile, ELM precursors have been strikingly observed with beam emission spectroscopy (BES) measurements. A scan in beta at the L-H transition shows that pedestal height scales strongly with core pressure. Gyro-Bohm normalized turbulent ion heat flux (as estimated from the BES data) is observed to decrease with increasing tilt of the turbulent eddies. Fast ion redistribution by energetic particle modes depends on density, and access to a quiescent domain with 'classical' fast ion transport is found above a critical density. Highly efficient electron Bernstein wave current drive (1 A W-1) has been achieved in solenoid-free start-up. A new proton detector has characterized escaping fusion products. Langmuir probes and a high-speed camera suggest filaments play a role in particle transport in the private flux region whilst coherence imaging has measured scrape-off layer (SOL) flows. BOUT++ simulations show that fluxes due to filaments are strongly dependent on resistivity and magnetic geometry of the SOL, with higher radial fluxes at higher resistivity. Finally, MAST Upgrade is due to begin operation in 2016 to support ITER preparation and importantly to operate with a Super-X divertor to test extended leg concepts for particle and power exhaust.
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| 2. |
- Iiyoshi, A., et al.
(author)
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Muon catalyzed fusion, present and future
- 2019
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In: Proceedings of the international conference on advances and applications in plasma physics (aapp 2019). - : American Institute of Physics (AIP). - 9780735419261
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Conference paper (peer-reviewed)abstract
- The novel proposal of the Muon Catalyzed Fusion (MCF) concept is brought to light employing recent results on its relevant cross sections. In 1993, Kino et al. proposed an innovative scheme of MCF, employing non-adiabatic calculations of muonic atom-nucleus collision in the energy range from 10-3 eV to 100 eV, whereby the fusion in flight along with the formation of muonic molecular resonances was revisited [1]. In 1994, Froelich independently calculated the cross section up to 2 keV, and found the behavior of like resonance [2]. In 1996, Kino et al. examined these resonances, and concluded that the resonances were not suitable for MCF [3]. As a result, the research has been continued to examine the possibility of non-resonant In-flight Muon Catalyzed Fusion (IFMCF) calculating the muonic atom-nucleus collision cross-section with an improved precision within the optical model for nuclear reactions. The resultant fusion cross section was 2000 barns at 1.4 keV [4] which should be good enough to be used as a fast neutron source [5]. A research program has been initiated to confirm these results theoretically as well as experimentally. For the sake of the theoretical analysis, a few-body computer code has been put forward to handle the nuclear reactions for nucleon transfer. In this paper, an innovative compact reactor concept is proposed, based on IFMCF. In this concept, muons are injected to a gas target of D2 and T2, which is pressurized aerodynamically by the Mach shock wave using a supersonic stream generated in a Laval nozzle [6], [7]. It generates the output power of 28 MW with 1019 cm-3s-1 of fusions by supplying fresh muons of 1016 cm-3s-1 providing 1000 times of catalyzed cycle of reactions. To maintain Q values > 1, assuming 30% efficiency for thermal to electric conversion, the energy supply for muon production can be as low as 8 GeV/muons. One of the possible applications of muon catalyzed fusion is transmutation of long-lived fission products (LLFPs).
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| 3. |
- Kirk, A., et al.
(author)
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Overview of recent physics results from MAST
- 2017
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In: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 57:10
-
Journal article (peer-reviewed)abstract
- New results from MAST are presented that focus on validating models in order to extrapolate to future devices. Measurements during start-up experiments have shown how the bulk ion temperature rise scales with the square of the reconnecting field. During the current ramp-up, models are not able to correctly predict the current diffusion. Experiments have been performed looking at edge and core turbulence. At the edge, detailed studies have revealed how filament characteristics are responsible for determining the near and far scrape off layer density profiles. In the core the intrinsic rotation and electron scale turbulence have been measured. The role that the fast ion gradient has on redistributing fast ions through fishbone modes has led to a redesign of the neutral beam injector on MAST Upgrade. In H-mode the turbulence at the pedestal top has been shown to be consistent with being due to electron temperature gradient modes. A reconnection process appears to occur during edge localized modes (ELMs) and the number of filaments released determines the power profile at the divertor. Resonant magnetic perturbations can mitigate ELMs provided the edge peeling response is maximised and the core kink response minimised. The mitigation of intrinsic error fields with toroidal mode number n > 1 has been shown to be important for plasma performance.
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