Overview of new MAST physics in anticipation of first results from MAST Upgrade
Review article, 2019

The mega amp spherical tokamak (MAST) was a low aspect ratio device (R/a = 0.85/0.65 ∼ 1.3) with similar poloidal cross-section to other medium-size tokamaks. The physics programme concentrates on addressing key physics issues for the operation of ITER, design of DEMO and future spherical tokamaks by utilising high resolution diagnostic measurements closely coupled with theory and modelling to significantly advance our understanding. An empirical scaling of the energy confinement time that favours higher power, lower collisionality devices is consistent with gyrokinetic modelling of electron scale turbulence. Measurements of ion scale turbulence with beam emission spectroscopy and gyrokinetic modelling in up-down symmetric plasmas find that the symmetry of the turbulence is broken by flow shear. Near the non-linear stability threshold, flow shear tilts the density fluctuation correlation function and skews the fluctuation amplitude distribution. Results from fast particle physics studies include the observation that sawteeth are found to redistribute passing and trapped fast particles injected from neutral beam injectors in equal measure, suggesting that resonances between the m = 1 perturbation and the fast ion orbits may be playing a dominant role in the fast ion transport. Measured D-D fusion products from a neutron camera and a charged fusion product detector are 40% lower than predictions from TRANSP/NUBEAM, highlighting possible deficiencies in the guiding centre approximation. Modelling of fast ion losses in the presence of resonant magnetic perturbations (RMPs) can reproduce trends observed in experiments when the plasma response and charge-exchange losses are accounted for. Measurements with a neutral particle analyser during merging-compression start-up indicate the acceleration of ions and electrons. Transport at the plasma edge has been improved through reciprocating probe measurements that have characterised a geodesic acoustic mode at the edge of an ohmic L-mode plasma and particle-in-cell modelling has improved the interpretation of plasma potential estimates from ball-pen probes. The application of RMPs leads to a reduction in particle confinement in L-mode and H-mode and an increase in the core ionization source. The ejection of secondary filaments following type-I ELMs correlates with interactions with surfaces near the X-point. Simulations of the interaction between pairs of filaments in the scrape-off layer suggest this results in modest changes to their velocity, and in most cases can be treated as moving independently. A stochastic model of scrape-off layer profile formation based on the superposition of non-interacting filaments is in good agreement with measured time-average profiles. Transport in the divertor has been improved through fast camera imaging, indicating the presence of a quiescent region devoid of filament near the X-point, extending from the separatrix to ψ n ∼ 1.02. Simulations of turbulent transport in the divertor show that the angle between the divertor leg on the curvature vector strongly influences transport into the private flux region via the interchange mechanism. Coherence imaging measurements show counter-streaming flows of impurities due to gas puffing increasing the pressure on field lines where the gas is ionised. MAST Upgrade is based on the original MAST device, with substantially improved capabilities to operate with a Super-X divertor to test extended divertor leg concepts. SOLPS-ITER modelling predicts the detachment threshold will be reduced by more than a factor of 2, in terms of upstream density, in the Super-X compared with a conventional configuration and that the radiation front movement is passively stabilised before it reaches the X-point. 1D fluid modelling reveals the key role of momentum and power loss mechanisms in governing detachment onset and evolution. Analytic modelling indicates that long legs placed at large major radius, or equivalently low at the target compared with the X-point are more amenable to external control. With MAST Upgrade experiments expected in 2019, a thorough characterisation of the sources of the intrinsic error field has been carried out and a mitigation strategy developed.

MAST

MAST Upgrade

spherical tokamak

Author

J.R. Harrison

Culham Science Centre

R. Akers

Culham Science Centre

S.Y. Allan

Culham Science Centre

J.S. Allcock

Culham Science Centre

J. O. Allen

University of York

L. Appel

Culham Science Centre

M. Barnes

Culham Science Centre

N. Ben Ayed

Culham Science Centre

W. Boeglin

Florida International University

C. Bowman

University of York

J. Bradley

University of Liverpool

P. Browning

University of Manchester

P. Bryant

University of Liverpool

M. Carr

Culham Science Centre

M. Cecconello

Uppsala University

C. Challis

Culham Science Centre

S. Chapman

The University of Warwick

I.T. Chapman

Culham Science Centre

G. Colyer

University of Oxford

S. Conroy

Uppsala University

N.J. Conway

Culham Science Centre

M. Cox

Culham Science Centre

G. Cunningham

Culham Science Centre

R.O. Dendy

Culham Science Centre

William D. Dorland

University of Oxford

Benjamin Dudson

University of York

Luke Easy

Culham Science Centre

S.D. Elmore

Culham Science Centre

T. Farley

Culham Science Centre

X. Feng

Durham University

A.R. Field

Culham Science Centre

A. Fil

University of York

G.M. Fishpool

Culham Science Centre

M. Fitzgerald

Culham Science Centre

K. Flesch

University of Wisconsin Madison

M.F.J. Fox

Culham Science Centre

H. Frerichs

University of Wisconsin Madison

S. Gadgil

The University of Warwick

D. Gahle

Culham Science Centre

Luca Garzotti

Culham Science Centre

Y.-C. Ghim

Culham Science Centre

S. Gibson

Culham Science Centre

K.J. Gibson

University of York

S. Hall

Culham Science Centre

C. Ham

Culham Science Centre

N. Heiberg

Culham Science Centre

S.S. Henderson

Culham Science Centre

Edmund Hood Highcock

University of Oxford

Chalmers, Physics, Subatomic and Plasma Physics

Bogdan Hnat

The University of Warwick

J. Howard

Australian National University

J. Huang

Chinese Academy of Sciences

S.W.A. Irvine

The University of Warwick

A.S. Jacobsen

Max Planck Society

O. Jones

Culham Science Centre

I. Katramados

Culham Science Centre

D. Keeling

Culham Science Centre

A. Kirk

Culham Science Centre

I. Klimek

Uppsala University

L. Kogan

Culham Science Centre

J. Leland

Culham Science Centre

B. Lipschultz

University of York

B. Lloyd

Culham Science Centre

J. Lovell

Oak Ridge National Laboratory

B. Madsen

Technical University of Denmark (DTU)

O. Marshall

University of York

R. Martin

Culham Science Centre

G. McArdle

Culham Science Centre

K. McClements

Culham Science Centre

B. McMillan

The University of Warwick

A. Meakins

Culham Science Centre

H.F. Meyer

Culham Science Centre

F. Militello

Culham Science Centre

J. Milnes

Culham Science Centre

S. Mordijck

College of William and Mary

A.W. Morris

Culham Science Centre

D. Moulton

Culham Science Centre

D. Muir

Culham Science Centre

K. Mukhi

Culham Science Centre

S. Murphy-Sugrue

Culham Science Centre

O. Myatra

University of York

G. Naylor

Culham Science Centre

P. Naylor

University of York

Sarah Newton

Culham Science Centre

T. O'Gorman

Culham Science Centre

John Omotani

Culham Science Centre

M.G. O'Mullane

University of Strathclyde

S. Orchard

Culham Science Centre

S.J.P. Pamela

Culham Science Centre

L. Pangione

Culham Science Centre

F. I. Parra

Culham Science Centre

R.V. Perez

Florida International University

L. Piron

Culham Science Centre

M. Price

Culham Science Centre

M. Reinke

Oak Ridge National Laboratory

F. Riva

Culham Science Centre

C. M. Roach

Culham Science Centre

D. Robb

University of Glasgow

D. Ryan

Culham Science Centre

S. Saarelma

Culham Science Centre

M. Salewski

Technical University of Denmark (DTU)

S. Scannell

Culham Science Centre

AA Schekochihin

University of Oxford

O. Schmitz

University of Wisconsin Madison

S. E. Sharapov

Culham Science Centre

R. Sharples

Durham University

S.A. Silburn

Culham Science Centre

S.F. Smith

Culham Science Centre

A. Sperduti

Uppsala University

R. Stephen

Culham Science Centre

N.T. Thomas-Davies

Culham Science Centre

A.J. Thornton

Culham Science Centre

M. Turnyanskiy

Culham Science Centre

Martin Valovic

Culham Science Centre

F van Wyk

Culham Science Centre

R.G.L. Vann

University of York

N. R. Walkden

Culham Science Centre

I. Waters

University of Wisconsin Madison

H.R. Wilson

Culham Science Centre

Nuclear Fusion

0029-5515 (ISSN)

Vol. 59 11 112011

Subject Categories

Meteorology and Atmospheric Sciences

Other Physics Topics

Fusion, Plasma and Space Physics

DOI

10.1088/1741-4326/ab121c

More information

Latest update

11/12/2021