Overview of MAST results

Chapman, I. T. and Adamek, J. and Akers, R. J. and Allan, S. and Appel, L. and Asunta, O. and Barnes, M. and Ayed, N. Ben and Bigelow, T. and Boeglin, W. and Bradley, J. and Brünner, J. and Cahyna, P. and Carr, M. and Caughman, J. and Cecconello, M. and Challis, C. and Chapman, S. and Chorley, J. and Colyer, G. and Conway, N. and Cooper, W. A. and Cox, M. and Crocker, N. and Crowley, B. and Cunningham, G. and Danilov, A. and Darrow, D. and Dendy, R. and Diallo, A. and Dickinson, D. and Diem, S. and Dorland, W. and Dudson, B. and Dunai, D. and Easy, L. and Elmore, S. and Field, A. and Fishpool, G. and Fox, M. and Fredrickson, E. and Freethy, S. and Garzotti, L. and Ghim, Y. C. and Gibson, K. and Graves, J. and Gurl, C. and Guttenfelder, W. and Ham, C. and Harrison, J. and Harting, D. and Havlickova, E. and Hawke, J. and Hawkes, N. and Hender, T. and Henderson, S. and Highcock, E. and Hillesheim, J. and Hnat, B. and Holgate, J. and Horacek, J. and Howard, J. and Huang, B. and Imada, K. and Jones, O. and Kaye, S. and Keeling, D. and Kirk, A. and Klimek, I. and Kocan, M. and Leggate, H. and Lilley, M. and Lipschultz, B. and Lisgo, S. and Liu, Y. Q. and Lloyd, B. and Lomanowski, B. and Lupelli, I. and Maddison, G. and Mailloux, J. and Martin, R. and McArdle, G. and McClements, K. and McMillan, B. and Meakins, A. and Meyer, H. and Michael, C. and Militello, F. and Milnes, J. and Morris, A. W. and Motojima, G. and Muir, D. and Nardon, E. and Naulin, V. and Naylor, G. and Nielsen, A. and O'Brien, M. and O'Gorman, T. and Ono, Y. and Oliver, H. and Pamela, S. and Pangione, L. and Parra, F. and Patel, A. and Peebles, W. and Peng, M. and Perez, R. and Pinches, S. and Piron, L. and Podesta, M. and Price, M. and Reinke, M. and Ren, Y. and Roach, C. and Robinson, J. and Romanelli, M. and Rozhansky, V. and Saarelma, S. and Sangaroon, S. and Saveliev, A. and Scannell, R. and Schekochihin, A. and Sharapov, S. and Sharples, R. and Shevchenko, V. and Silburn, S. and Simpson, J. and Storrs, J. and Takase, Y. and Tanabe, H. and Tanaka, H. and Taylor, D. and Taylor, G. and Thomas, D. and Thomas-Davies, N. and Thornton, A. and Turnyanskiy, M. and Valovic, M. and Vann, R. and Walkden, N. and Wilson, H. and Wyk, L. V. and Yamada, T. and Zoletnik, S. (2015) Overview of MAST results. Nuclear Fusion, 55 (10). pp. 1-19. 104008. ISSN 0029-5515

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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 nRMP = 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 nRMP = 3 RMPs. nRMP = 4, 6 fields cause less rotation braking whilst the power to access H-mode is less with nRMP = 4 than nRMP = 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.