News from MAST - February 2005

The 3rd MAST Results Review and Research Forum was held on the 1st and 2nd of February to review the proposed experimental programme for 2005, in the light of existing results and high priority R & D needs for both ITER and future spherical tokamaks. Facilities for remote participation were made available and many international collaborators tuned in from a number of locations around the world. Constructive comments on the presentations were received from a number of remote participants in the days following the forum. Stan Kaye (PPPL) attended the forum and delivered presentations on the NSTX research programme and NSTX-MAST collaboration opportunities. Over 120 experimental proposals have been submitted for 2005 including a number from international collaborators.

The 2005 campaign is based around eight main subject areas. Campaign Drivers have been appointed to co-ordinate experimental proposals and drive the programme forward in each of these areas.

MAST operation resumed in January following the short engineering break. After a period of conditioning and diagnostic commissioning, the main physics programme began on 15th February. Vessel boronisation was carried out on Wednesday 16th February.

Initial experiments have included start-up studies, locked mode threshold scaling experiments, H-mode threshold studies and HELIOS validation experiments. Non-solenoid start-up is a key strategic issue for burning STs, which cannot accommodate a central solenoid. Franco Alladio and colleagues from ENEA Frascati are working with the MAST team on this important issue and participated remotely in the recent start-up experiments. Locked mode threshold studies are being carried out using the error field correction coil system installed in 2004 and contribute to the ITPA-IEA joint experiment on low beta error field studies (MDC-6). H-mode threshold studies are focussing on further optimisation of H-mode access with the new MAST divertor and PF coil configuration. HELIOS validation experiments are being carried out by Iain Paton of the University of Strathclyde in conjunction with the MAST team. The HELIOS (HELium Injection & Optical Spectroscopy) diagnostic is based on the measurement of helium line ratios to give electron temperature and density profiles near the plasma separatrix. Careful comparison with high spatial resolution Thomson scattering measurements allows a stringent test of the underlying atomic physics modelling.

In parallel with the on-going physics programme, improvements to the MAST plant and diagnostics continue to be implemented. For example, plasma radial position control, based on real-time optical data from a new Dα linear camera, has recently been successfully deployed. The system, known as HOMER (High-resolution Optical Measurements of Edge Radiation) was developed by John Storrs together with John Dowling, Glenn Counsell and Graham McArdle. Typical output is shown in Fig 1 for shot 12467 at 154ms. The red plot is the raw emission, the black after applying a low-envelope filter which deals with most reflections and with spikes. The vertical red line is the detected raw data peak. The adjacent vertical green line is the Abel inversion peak, here very close to the raw data peak though this is not always the case. Outboard is to the left. The camera uses a 2048 pixel CCD, with a 1ms exposure period. Frame processing takes around 500μs. The edge radius and a status flag are sent for every frame to the digital plasma control system where the radial position feedback control is done.

Collaboration Activities

Alexander Saveliev of the A F Ioffe Physico-Technical Institute, St. Petersburg, Russia, is visiting Culham to work on electron Bernstein wave numerical modelling and benchmarking of calculations with U.S. collaborators Gary Taylor (PPPL) and Bob Harvey (CompX).

Elise Delchambre attended the Tore-Supra mid-term programme workshop on 24 - 25 Feb at Cadarache and participated in discussions with the Tore-Supra team on issues of common interest. Elise also visited the University of Marseille.

Martin Valovic visited General Atomics in January to prepare for ITPA-IEA joint experiments (NSTX/MAST/DIII-D) on aspect ratio confinement scaling (CDB-6, TP-9) and subsequently participated in DIII-D experiments remotely.

Anthony Field visited Princeton Plasma Physics Laboratory (PPPL), General Atomics (GA) and the Massachusetts Institute of Technology (MIT) in February for discussions on fluctuation diagnostics and also (in the case of PPPL) to progress analysis of ITPA-IEA joint experiments on internal transport barriers (TP-8.1) together with members of the NSTX team.

Anthony Field gave a presentation on "MAST developments towards high beta steady state operation" at the IEA Workshop (W59) on 'Shape and Aspect Ratio Optimisation for a High Beta Steady State Tokamak' at General Atomics, in February.

Andrew Kirk and Ben Dudson visited the Lawrence Livermore National Laboratory (LLNL) in January to work on the BOUT code and its application to MAST data. Andrew also visited General Atomics to participate in pedestal similarity experiments (MAST/NSTX/DIII-D) working with Max Fenstermacher and Tom Osborne of the DIII-D team, as well as Rajesh Maingi (ORNL) from the NSTX team. These studies (PEP-9) are part of the co-ordinated programme of ITPA-IEA joint experiments.

Publications

"Structure of ELMs in MAST and the implications for energy deposition"
A Kirk et al 2005, Plasma Phys. Contr. Fusion 47 315.