Biennial Report 2005-2007 - Saha Institute of Nuclear Physics

Material Physics 185The Kekuchi line in the micrograph suggests that the film is essentially single crystalline.NR Ray, AK Srivastava†, Rambabu†PP5.2.1.4 Ion acceleration and heating by MHD activity in the SINP tokamak plasmaThe acceleration of ions and electrons to high energy is common in astrophysical plasmas and isbelieved to be due to the magnetic reconnection process. In the laboratory, electron accelerationcoherent with magnetic activity has been observed in fusion devices. Similar observations for ionsare very rare. In the SINP tokamak, we find that bulk ions are accelerated to high energies in thepresence of a strong MHD mode, believed to be caused by the electric field associated with themagnetic reconnection process. Further, the hard x-ray bremsstralung from the core of the plasmaand the hard x-ray emanating from the limiter appear to have a relative time delay at certain times,suggesting different transport mechanisms.SK Saha, AK Hui, Santwana Raychaudhuri, S Chowdhury, D BanikPP5.2.1.5 Non-diffusive transport in the SINP tokamakThe outward transport of particles in a plasma confined by a magnetic field is usually by a diffusionprocess. However, experimental measurements and simulations reveal that the particle flux occursin narrow and random bursts rather than as a steady flow. Such bursts are observed in the densityas well as the temperature in the scrape-off layer of the SINP tokamak. This has been interpretedin terms of the formation and propagation of plasma structures. We have made measurementson these structures using conditional averaging technique. These structures are elongated in thepoloidal direction, have both poloidal and radial propagations and convect as much as 30-40% ofthe total particle flux in the SOL region of the tokamak. The picture of plasma transport in thefar SOL of tokamaks is therefore dominantly a non-diffusive one.SK Saha, S ChowdhuryPP5.2.1.6 Edge Biasing of SINP-TOKAMAK Plasma in High-q regimeIn SINP-TOKAMAK device both high/normal q and very low q regimes can be achieved. Recentlyin this machine in very low q regime fast edge biasing experiment revealed a change in plasmacurrent profile at edge region leading to better confinement and longer duration of plasma current.It is now planned to extend this experiment to high/normal q regime. For this purpose, as before,a tungsten electrode assembly with 6 mm diameter rod will be biased by a pulsed power supply.