First results from MAST

Abstract

MAST is one of the new generation of large, purpose-built spherical tokamaks (STs) now becoming operational, designed to investigate the properties of the ST in large, collisionless plasmas. The first six months of MAST operations have been remarkably successful. Operationally, both merging-compression and the more usual solenoid induction schemes have been demonstrated, the former providing over 400 kA of plasma current with no demand on solenoid flux. Good vacuum conditions and operational conditions, particularly after boronization in trimethylated boron, have provided plasma current of over 1 MA with central plasma temperatures (ohmic) of order 1 keV. The Hugill and Greenwald limits can be exceeded and H mode achieved at modest additional NBI power. Moreover, particle and energy confinement show an immediate increase at the L-H transition, unlike the case of START, where this became apparent only at the highest plasma currents. Halo currents are small, with low toroidal peaking factors, in accordance with theoretical predictions, and there is evidence of a resilience to the major disruption.

Anomalous transport of energetic particles in ITER relevant scenarios

“…An apparent confirmation of these theoretical conclusions was found on early experiments at the Tokamak Fusion Test Reactor (TFTR) [7][8][9][10], where an upper limit for fast ion diffusivities was found at 0.1 m 2 · s −1 , an order of magnitude smaller than that of thermal ions. Recently, however, there has been renewed interest, triggered by experimental observations of anomalous redistribution of NBI ions at the Axial Symmetric Divertor EXperiment (ASDEX) Upgrade [11,12], at the Joint European Torus (JET) [13,14], at the Mega-Ampere Spherical Tokamak (MAST) [15,16], and at DIII-D [17,18].…”

Internal Kink Mode Dynamics in High-beta NSTX Plasmas

“…The National Spherical Torus Experiment (NSTX) [2] and the Mega-Ampere Spherical Tokamak (MAST) [3] are presently the largest ST devices in the world fusion program. These devices have achieved both high confinement [4,5] and high β. NSTX has achieved both high toroidal-β, β T ≡ 2µ 0 p /B 2 T 0 up to 35%, and high normalized-β, β N ≡ β T aB T 0 /I P up to 6.5% mT/MA [6,7] using up to 7MW of deuterium Neutral Beam Injection (NBI) heating.…”

High Speed Imaging of Edge Turbulence in NSTX

“…Wide angle images taken using fast cameras on NSTX [17] and MAST [21] have also shown that the edge light fluctuations in the plasma have a very long (many meter) correlation length along the magnetic field and a short (few-cm-scale) correlation length across the magnetic field B, similar to previous tokamak images on TFTR [22] and ASDEX [23]. Very long parallel correlation lengths have also been seen with probes in the scrape-off layer on JET [24].…”