Investigating fusion plasma instabilities in the Mega Amp Spherical Tokamak using mega electron volt proton emissions (invited)

Perez, R. V.; Boeglin, W.; Darrow, D. S.; Cecconello, M.; Klimek, Iwona; Allan, S.; Akers, R.; Keeling, D.; McClements, K. G.; Scannell, R.; Turnyanskiy, M.; Angulo, A.; Avila, Pierre; Leon, Omar; López, C.; Jones, O.; Conway, N. J.; Michael, Clive

doi:10.1063/1.4889736

Cited by 22 publications

(21 citation statements)

References 11 publications

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“…This diagnostic has a compact four-channel system of collimated and individually oriented silicon detectors, which probes different regions of the plasma by recording unconfined 3 MeV protons leaving the plasma on curved trajectories during neutral beam injection. Proton rates of up to 200 kHz were recorded with a time resolution of 1 ms, and time-resolved measurements in the four channels have been used to infer fusion reaction rate profiles in the poloidal plane before and after sawtooth crashes [79]. The effects of toroidal Alfvén eigenmodes (TAEs), fishbones and long-lived modes [80] on fusion proton fluxes in MAST have also been studied [81].…”

Section: Measuring Charged Fusion Productsmentioning

confidence: 99%

Overview of MAST results

et al. 2015

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The Mega Ampère 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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Section: Measuring Charged Fusion Productsmentioning

confidence: 99%

Overview of MAST results

et al. 2015

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“…Data are typically integrated over 1 ms, setting the temporal resolution of the measurements. The CFPD was installed on MAST to provide a complementary measurement to that provided by the NC [11]. Four detectors measured the flux of 3.02 MeV protons and 1.01 MeV tritons (the gyro-radii of these two fusion products being very nearly equal) produced by D-D fusion reactions.…”

Section: Description Of the Diagnosticsmentioning

confidence: 99%

Measurements and modelling of fast-ion redistribution due to resonant MHD instabilities in MAST

Jones

Cecconello

McClements

et al. 2015

Plasma Phys. Control. Fusion

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Abstract. The results of a comprehensive investigation into the effects of toroidicityinduced Alfvén eigenmodes (TAE) and energetic particle modes on the NBI-generated fast-ion population in MAST plasmas are reported. Fast-ion redistribution due to frequency-chirping TAE in the range 50 kHz to 100 kHz, and frequency-chirping energetic particle modes known as fishbones in the range 20 kHz to 50 kHz, is observed. TAE and fishbones are also observed to cause losses of fast ions from the plasma. The spatial and temporal evolution of the fast-ion distribution is determined using a fission chamber, a radially-scanning collimated neutron flux monitor, a fast-ion deuterium alpha spectrometer and a charged fusion product detector. Modelling using the global transport analysis code Transp, with ad hoc anomalous diffusion and fishbone loss models introduced, reproduces the coarsest features of the affected fast-ion distribution in the presence of energetic-particle-driven modes. The spectrally and spatially resolved measurements show however that these models do not fully capture the effects of chirping modes on the fast-ion distribution.

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“…Typically, from 4 to 6 plasma discharges are used to measure the neutron count rate profiles, taking advantage of the high repeatability of the plasma discharges in MAST. Additional fast ions diagnostic on MAST include a Fast Ion D α (FIDA) system, which provides information on which part of the fast ion velocity distribution is affected by MHD instabilities [7], and a charged fusion product detector [8]. A detailed comparison of the observations from these three diagnostics is outside the scope of this paper: the interested reader can find an initial comparison in [9].…”

Section: Introductionmentioning

confidence: 99%

TRANSP modelling of total and local neutron emission on MAST

et al. 2015

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The results of TRANSP simulations of neutron count rate profiles measured by a collimated neutron flux monitor–neutron camera (NC)—for different plasma scenarios on MAST are reported. In addition, the effect of various plasma parameters on neutron emission is studied by means of TRANSP simulation. The fast ion redistribution and losses due to fishbone modes, which belong to a wider category of energetic particle modes, are observed by the NC and modelled in TRANSP.

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Investigating fusion plasma instabilities in the Mega Amp Spherical Tokamak using mega electron volt proton emissions (invited)

Cited by 22 publications

References 11 publications

Overview of MAST results

Overview of MAST results

Measurements and modelling of fast-ion redistribution due to resonant MHD instabilities in MAST

TRANSP modelling of total and local neutron emission on MAST

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