Overview of physics results from MAST

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 P NBI ⩽ 3.8 MW H-mode at I p = 1.2 MA was accessed showing that the energy confinement on MAST scales more weakly with I p and more strongly with B t 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, χϕ, is linked to the ion diffusion, χi, with a Prandtl number close to P ϕ ≈ χϕ/χi ≈ 1, although χi approaches neoclassical values. New high spatial resolution measurements of the edge radial electric field, E r , show that the position of steepest gradients in electron pressure and E r (i.e. shearing rate) are coincident, but their magnitudes are not linked. The T e 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.

Ebw Physics of Ece in NSTX

“…Relevant publications: [11,12,[15][16][17][18][19][20][21][22] By means of the coupled ray-tracing and Fokker-Planck simulations, using AMR with LUKE, we have thoroughly investigated electron Bernstein wave heating and current drive prospects for spherical tokamaks, particularly for four typical present and planned plasmas: NSTX Land H-mode, MAST Upgrade and NHTX [11,12]. Figure 5 - Figure 8 show the current drive efficiency for the NSTX L-and H-mode, for MAST Upgrade and for NHTX.…”

Increasing current drive efficiency in DEMO by induction of counter-rotation

“…This is also relevant for alternative methods of driving counter-rotation, which will also introduce torque at the edge of the plasma (Section 4). Modelling was carried out assuming the Prandtl number (the ratio of the angular momentum and ion thermal diffusivities) was = 1 [10]. For the profiles assumed, this gave m 2 s −1 .…”

The use of Bayesian inversion to resolve plasma equilibrium

“…1 MAST is also equipped with an array of precision diagnostics, 12 including a high spatial resolution, single-time point, ruby TS system, a multitime point Nd:YAG TS system with a coarser spatial resolution, motional Stark effect ͑MSE͒, charge exchange recombination, and fast magnetics. This has enabled plasma performance to be routinely lifted above ␤ n Ϸ 5, which was reported in 2005.…”