MAST News Bulletin - December 2003

	News from MAST - December 2003 Welcome to the first of a regular series of news bulletins from MAST. The MAST project is presently in a major engineering break, which started in early July and will last until Spring 2004. Physics operation of MAST began in Jan 2000 and initially alternated with operation of the COMPASS-D tokamak. However, since May 2001 the MAST tokamak has operated almost continuously apart from short engineering breaks in Nov/Dec 2001 (NBI modifications), Aug/Sep 2002 (Electron Bernstein Wave antenna installation) and Jan/Feb 2003 (TF maintenance). MAST Developments During the present engineering break a number of major improvements to the MAST device are being implemented, as well as many smaller developments. The main improvements are: installation of an improved, more robust, and slightly longer central solenoid upgrade of the vessel armour and installation of an improved divertor modifications to the neutral beam injectors to allow reliable long pulse operation at full power The NBI upgrade is being carried out in two stages. The South injector will be upgraded during the present engineering break, whilst the South-West injector will be upgraded towards the end of 2004 (see MAST Operating Schedule below). To match the new longer solenoid, the positions of the internal upper and lower P2 poloidal field coils are also being re-optimised. The effect of the load assembly changes is illustrated schematically below.
	Changes to MAST for the 2004 experimental campaign (M4)
	The present engineering break is proceeding to plan:
	New centre column being lowered into position	MAST engineers inside the vessel installing the centre column armour
	New divertor structure - the lower divertor structure illustrated is replicated at the top of the machine	Upper divertor imbricated tiles installed
	A digital plasma control system has now been implemented on MAST. During the final few weeks of the 2003 experimental campaign (M3), MAST was routinely operated with digital plasma control. NBI system upgrade for reliable long pulse operation at high power, P = 5MW, > 5s: JET-style PINI sources New calorimeters and residual ion dumps employing hypervapotrons Diagnostic Developments A significant number of new diagnostics and diagnostic improvements have been implemented on MAST during the last experimental campaign. These include: increase in the ruby Thomson scattering system (single pulse) to 300 spatial points incorporation of additional Nd:YAG lasers in the multi-pulse Thomson scattering system to allow 200Hz operation (collaboration with Dublin City University) 16-channel bolometer array built with the assistance of IPP Garching 2D high resolution visible Bremsstrahlung diagnostic for Zeff measurements implementation of a poloidal and toroidal scanning capability on the neutral particle analyzer (on loan from PPPL) fast infra-red camera for study of divertor and chamber power loads during transient events new magnetic coils allowing detection of fast particle driven instabilities up to 5MHz and toroidal mode identification up to \|n\| = 20 fission chambers (on loan from PPPL) for neutron measurements x-ray crystal spectrometer for additional ion temperature measurements (a CXRS diagnostic is already in operation for ion temperature and rotation measurements) 2-D beam emission imaging system for diagnosis of neutral beam deposition a lower hybrid wave probe for detection of parametric decay products during electron Bernstein wave heating (with Ioffe Institute, St Petersburg) reflectometry and timing systems projects with IST Lisbon spatially imaging vacuum UV survey spectrometer (with Dublin City University) erosion diagnostics including impurity doping of plasma facing components combined with atomic physics analysis (ADAS) of the resulting plasma emission Experimental/Analysis Highlights The MAST programme is focussed on key ITER physics issues and on establishing the spherical tokamak concept as a potential fusion power plant and/or component test facility. Highlights of the 2003 experimental campaign include: Improved access to high confinement regimes through optimisation of fuelling (inboard puffing) and magnetic configuration. Demonstration of internal transport barriers in both the ion and electron channels with ion and electron thermal diffusivities reaching ion neo-classical levels. The TRANSP code (developed at PPPL) is now in routine use for analysis of MAST data. Demonstration of good confinement with edge localised modes (ELMs) which exhibit a type III character. Comprehensive studies of the structure of ELMs, their effects on the edge pedestal and their impact on plasma facing components. Fast imaging diagnostics, exploiting the excellent diagnostic access in MAST, have been used to capture a global image of ELM structure.
	Fast visible image of an ELM in MAST
	Measurements of neo-classical island evolution appearing to confirm the strong stabilising role of field curvature effects. By avoidance of neo-classical tearing modes normalised beta values up to ?N = 5.3 have been achieved, close to the ideal no-wall stability limit. Extensive exhaust studies demonstrating favourable power balance between upper and lower divertors and inboard/outboard strike points. The use of divertor biasing to reduce target power loads has been successfully demonstrated on MAST. MAST Operating Schedule The present MAST operating schedule is shown below. Following installation of the new divertor and centre column, and upgrade of the South beam line, the 2004 physics campaign is expected to run from May - Sep/Oct. There will then be a short engineering break to upgrade the second (South West) beam line. MAST Research Forum A MAST Research Forum will be held on 22nd/23rd Jan. 2004, at the Culham Science Centre, to review experimental proposals and plan the 2004 campaign (M4). Although the Forum is intended primarily for the MAST Team and close collaborators, other participants are very welcome. Anyone interested in attending should contact Kathy Patton (+44-1235-466635). If you would like to find out more details of the Forum or discuss the MAST programme please contact Brian Lloyd (+44-1235-466325) or Alan Sykes (+44-1235-466473). 9th International Spherical Tokamak Workshop The 9th International Spherical Tokamak Workshop was held at Culham in September and attended by ~ 50 scientists and engineers, including participants from the U.S., Russia, China, Japan and Europe. For more information, including the workshop presentations online, click here. Below: ST Workshop participants Back to MAST home page