Overview of physics results from MAST

H. Meyer, R.J. Akers, F. Alladio, L.C. Appel, K.B. Axon, N. Ben Ayed, P. Boerner, R.J. Buttery, A. Foster, MAST Team, NBI Team

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Abstract

Several improvements to the MAST plant and diagnostics have facilitated new studies advancing the physics basis for ITER and DEMO, as well as for future spherical tokamaks (STs). Using the increased heating capabilities PNBI ≤ 3.8 MW H-mode at Ip = 1.2 MA was accessed showing that the energy confinement on MAST scales more weakly with Ip and more strongly with Bt than in the ITER IPB98(y, 2) scaling. Measurements of the fuel retention of shallow pellets extrapolate to an ITER particle throughput of 70% of its original designed total throughput capacity. The anomalous momentum diffusion, χ, is linked to the ion diffusion, χi, with a Prandtl number close to P χ/χi 1, although χi approaches neoclassical values. New high spatial resolution measurements of the edge radial electric field, Er, show that the position of steepest gradients in electron pressure and Er (i.e. shearing rate) are coincident, but their magnitudes are not linked. The Te pedestal width on MAST scales with rather than ρpol. The edge localized mode (ELM) frequency for type-IV ELMs, new in MAST, was almost doubled using n = 2 resonant magnetic perturbations from a set of four external coils (n = 1, 2). A new internal 12 coil set (n ≤ 3) has been commissioned. The filaments in the inter-ELM and L-mode phase are different from ELM filaments, and the characteristics in L-mode agree well with turbulence calculations. A variety of fast particle driven instabilities were studied from 10 kHz saturated fishbone like activity up to 3.8 MHz compressional Alfvén eigenmodes. Fast particle instabilities also affect the off-axis NBI current drive, leading to fast ion diffusion of the order of 0.5 m2 s−1 and a reduction in the driven current fraction from 40% to 30%. EBW current drive start-up is demonstrated for the first time in a ST generating plasma currents up to 55 kA. Many of these studies contributed to the physics basis of a planned upgrade to MAST.
Original languageEnglish
Pages (from-to)104017-104030
Number of pages13
JournalNuclear Fusion
Volume49
Issue number10
DOIs
Publication statusPublished - Oct 2009

Keywords

  • energy confinement
  • fuel retention
  • results
  • mega ampere spherical tokamak
  • upgrade

Cite this

Meyer, H., Akers, R. J., Alladio, F., Appel, L. C., Axon, K. B., Ben Ayed, N., Boerner, P., Buttery, R. J., Foster, A., MAST Team, & NBI Team (2009). Overview of physics results from MAST. Nuclear Fusion, 49(10), 104017-104030. https://doi.org/10.1088/0029-5515/49/10/104017