402 IEEE TRANSACTIONS ON PLASMA SCIENCE, VOL. 42, NO. 3, MARCH 2014 MAST Accomplishments and Upgrade for Fusion Next-Steps William Morris, Joe Milnes, Tom Barrett, Clive Challis, Ian Chapman, Martin Cox, Geof Cunningham, Fahim Dhalla, Geoff Fishpool, Philippe Jacquet, Ioannis Katramados, Andrew Kirk, Ken McClements, Richard Martin, Hendrik Meyer, Michele Romanelli, Samuli Saarelma, Sergei Sharapov, Vaughan Thompson, Martin Valoviˇ c, Glenn Whitfield, and Dan Wolff Abstract—The Mega Amp Spherical Tokamak (MAST) pro- gram and a major upgrade are aimed at using MASTs capa- bilities and parameter ranges to address specific issues for ITER physics, help find solutions for DEMO (in particular plasma exhaust), and develop a credible physics basis for possi- ble ST-based Component Test Facilities/Fusion Nuclear Science Facilities. MAST also provides an attractive access point for scientists and engineers joining fusion. The general approach is to combine experiments, theory, and modeling intimately to help create usable predictive models for future devices. Physics results include edge-localized mode (ELM) mitigation with the flexible resonant magnetic perturbation coils (up to n = 6), where smaller, more frequent ELMs are generated, challenging conventional 2-D stability theory. Gyrokinetic theory and models are combined with experiments in the areas of pedestal stability, pellet fueling optimization, and impurity transport. Fast particle stability and confinement are used to optimize scenarios and neutral beam geometry. Exhaust modeling includes turbulence processes that enhance cross-field transport to help ease the power handling. The first major phase of the upgrade program is well under way, to increase the toroidal field and the transformer flux swing and especially implement the flexible exhaust physics platform by means of 17 new poloidal field coils and a closed pumpable divertor. Changes in the neutral beam systems (off-axis as well as on-axis) and new diagnostics especially of the divertor complete the present upgrade scope. Index Terms— Cyanate ester, divertor, machine protection, MAST, neutral beam, pellet and gas fueling, sliding joints, solenoid, spherical tokamak, super-X, vertical stabilization. I. I NTRODUCTION T HE Mega Amp Spherical Tokamak (MAST) is a flexible diverted medium-sized tokamak ( R ∼ 0.85 m, a ∼ 0.6 m) with cross section comparable with those of devices, such as DIII-D, ASDEX Upgrade, EAST, and KSTAR, but at a tight aspect ratio, like NSTX [1]. The research program, as on the Manuscript received August 1, 2013; accepted December 25, 2013. Date of current version March 6, 2014. This work was supported in part by the RCUK Energy Programme under Grant EP/I501045 and in part by the European Communities under the Contract of Association between EURATOM and CCFE. To obtain further information on the data and models underlying this paper please contact PublicationsManager@ccfe.ac.uk. The views and opinions expressed herein do not necessarily reflect those of the European Commission. The authors are with EURATOM/CCFE Fusion Association, Culham Sci- ence Centre, Abingdon OX14 3DB, U.K. (e-mail: william.morris@ccfe.ac.uk; joe.milnes@ccfe.ac.uk). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TPS.2014.2299973 Fig. 1. Cross section of the MAST upgrade showing the 17 new shaping and divertor coils and the new closed divertor. The ELM coils are also visible, and the two cryopumps are in the corners of the vessel behind the divertor structure. other devices, is wide ranging. Recent research is described in [2] and [3]. The upgrade is outlined in [2] and [4] and references therein, and shown in Fig. 1. In the present device, special capabilities include a very flexible arrangement of small internal coils to make resonant magnetic perturbations (RMPs), with toroidal mode number n up to 6 with the ability to change the field structure during a pulse. These have been used for edge-localized mode (ELM) mitigation studies, with closely coupled theory and modeling: this has formed a major part of the recent research program motivated by the decision process for the installation of ELM coils on ITER and their later exploitation. MAST is also equipped with a pellet injector with the option for injection on the high field side, and into ELM-mitigated plasmas. Comparison of experimental results with gyrokinetic modeling is starting to reveal the processes that determine the balance of inward versus outward transport of the pellet fuel. Fast ion behavior is important in many devices—MAST and future STs, such as Fusion Nuclear 0093-3813 © 2014 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.