The Mega Ampère Spherical Tokamak (MAST) programme is strongly focused on addressing key physics issues in preparation for operation of ITER as well as providing solutions for DEMO design choices. In this regard, MAST has provided key results in understanding and optimizing H-mode confinement, operating with smaller edge localized modes (ELMs), predicting and handling plasma exhaust and tailoring auxiliary current drive. In all cases, the high-resolution diagnostic capability on MAST is complemented by sophisticated numerical modelling to facilitate a deeper understanding. Mitigation of ELMs with resonant magnetic perturbations (RMPs) with toroidal mode number n RMP = 2, 3, 4, 6 has been demonstrated: at high and low collisionality; for the first ELM following the transition to high confinement operation; during the current ramp-up; and with rotating n RMP = 3 RMPs. n RMP = 4, 6 fields cause less rotation braking whilst the power to access H-mode is less with n RMP = 4 than n RMP = 3, 6. Refuelling with gas or pellets gives plasmas with mitigated ELMs and reduced peak heat flux at the same time as achieving good confinement. A synergy exists between pellet fuelling and RMPs, since mitigated ELMs remove fewer particles. Inter-ELM instabilities observed with Doppler backscattering are consistent with gyrokinetic simulations of micro-tearing modes in the pedestal. Meanwhile, ELM precursors have been strikingly observed with beam emission spectroscopy (BES) measurements. A scan in beta at the L–H transition shows that pedestal height scales strongly with core pressure. Gyro-Bohm normalized turbulent ion heat flux (as estimated from the BES data) is observed to decrease with increasing tilt of the turbulent eddies. Fast ion redistribution by energetic particle modes depends on density, and access to a quiescent domain with ‘classical’ fast ion transport is found above a critical density. Highly efficient electron Bernstein wave current drive (1 A W−1) has been achieved in solenoid-free start-up. A new proton detector has characterized escaping fusion products. Langmuir probes and a high-speed camera suggest filaments play a role in particle transport in the private flux region whilst coherence imaging has measured scrape-off layer (SOL) flows. BOUT++ simulations show that fluxes due to filaments are strongly dependent on resistivity and magnetic geometry of the SOL, with higher radial fluxes at higher resistivity. Finally, MAST Upgrade is due to begin operation in 2016 to support ITER preparation and importantly to operate with a Super-X divertor to test extended leg concepts for particle and power exhaust.
New results from MAST are presented that focus on validating models in order to extrapolate to future devices. Measurements during start-up experiments have shown how the bulk ion temperature rise scales with the square of the reconnecting field. During the current ramp up models are not able to correctly predict the current diffusion. Experiments have been performed looking at edge and core turbulence. At the edge detailed studies have revealed how filament characteristic are responsible for determining the near and far SOL density profiles. In the core the intrinsic rotation and electron scale turbulence have been measured. The role that the fast ion gradient has on redistributing fast ions through fishbone modes has led to a redesign of the neutral beam injector on MAST Upgrade. In H-mode the turbulence at the pedestal top has been shown to be consistent with being due to electron temperature gradient modes. A reconnection process appears to occur during ELMs and the number of filaments released determines the power profile at the divertor. Resonant magnetic perturbations can mitigate ELMs provided the edge peeling response is maximised and the core kink response minimised. The mitigation of intrinsic error fields with toroidal mode number n>1 has been shown to be important for plasma performance.
A high-performance data acquisition (DAQ) system has been developed for steady-state fusion experiments at the Large Helical Device (LHD). Its significant characteristics are 110 MB s−1 continuous DAQ capability and the performance scalability using an unlimited number of DAQ units. Incoming data streams are first transferred temporarily onto the shared random access memory, and then cut into definite time chunks to be stored. They are also thinned out to 1/N to be served for the real-time monitoring clients. In LHD steady-state experiment, the DAQ cluster has established the world record for acquiring 90 GB/shot. The established technology of this steady-state acquisition and store can contribute to the ITER experiments whose data amount is estimated in the range 100 or 1000 GB/shot. This system also acquires experimental data from multiple remote sites through the fusion-dedicated virtual private network in Japan. The speed lowering problem in long-distance TCP/IP data transfer has been improved by the packet pacing optimization. The demonstrated collaboration scheme will be analogous to that of ITER and the supporting machines.
Synthesisof the Modifications of Ca2SiO4 and the Determination of their Powder X-ray Diffraction Patterns
This paper summarizes the characteristics of the spheromak .lasmas obtained during the past five-year operation period of S-1 experiments. The S-1 Spheromak device, which began operation in 1983, generates a compact toroid in which the self-generated toroidal field in the plasma is comparable to the poloidal field. The S-1 experiment is unique in that spheromak plasmas are formed by inductive transfer of magnetic flux from a toroidal-shaped "flux core", and plasma stability is maintained by shaping of the externally applied equilibrium field and using loose-fitting passive conductors. Without stabilizer coils, the plasma was unstable to gross MHD modes, with the tilt or shift being dominant. Significant improvements in plasma stability and parameters occurred after the installation of passive Figure-8 stabilization coils or funr.el-shaped conductor plates. Stable spheromaks with up to 550 kA
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