Protoplanets with core masses below the critical mass fill in their Roche lobe

(2011)

Authors:

Caroline Terquem, Tobias Heinemann

Overview of physics results from MAST

Nuclear Fusion 51:9 (2011)

Authors:

B Lloyd, RJ Akers, F Alladio, S Allan, LC Appel, M Barnes, NC Barratt, N Ben Ayed, BN Breizman, M Cecconello, CD Challis, IT Chapman, D Ciric, G Colyer, JW Connor, NJ Conway, M Cox, SC Cowley, G Cunningham, A Darke, M De Bock, E Delchambre, G De Temmerman, RO Dendy, P Denner, MD Driscoll, B Dudson, D Dunai, M Dunstan, S Elmore, AR Field, G Fishpool, S Freethy, L Garzotti, KJ Gibson, MP Gryaznevich, W Guttenfelder, J Harrison, RJ Hastie, NC Hawkes, TC Hender, B Hnat, DF Howell, MD Hua, A Hubbard, G Huysmans, D Keeling, YC Kim, A Kirk, Y Liang, MK Lilley, M Lisak, S Lisgo, YQ Liu, GP Maddison, R Maingi, SJ Manhood, R Martin, GJ McArdle, J McCone, H Meyer, C Michael, S Mordijck, T Morgan, AW Morris, DG Muir, E Nardon, G Naylor, MR O'Brien, T O'Gorman, J Pláeník, A Patel, SD Pinches, MN Price, CM Roach, V Rozhansky, S Saarelma, SA Sabbagh, A Saveliev, R Scannell, SE Sharapov, V Shevchenko, S Shibaev, D Stork, J Storrs, W Suttrop, A Sykes, P Tamain, D Taylor, D Temple, N Thomas-Davies, A Thornton, MR Turnyanskiy, M Valovic, RGL Vann, G Voss, MJ Walsh, SEV Warder, HR Wilson, M Windridge

Abstract:

Major developments on the Mega Amp Spherical Tokamak (MAST) have enabled important advances in support of ITER and the physics basis of a spherical tokamak (ST) based component test facility (CTF), as well as providing new insight into underlying tokamak physics. For example, L-H transition studies benefit from high spatial and temporal resolution measurements of pedestal profile evolution (temperature, density and radial electric field) and in support of pedestal stability studies the edge current density profile has been inferred from motional Stark effect measurements. The influence of the q-profile and E × B flow shear on transport has been studied in MAST and equilibrium flow shear has been included in gyro-kinetic codes, improving comparisons with the experimental data. H-modes exhibit a weaker q and stronger collisionality dependence of heat diffusivity than implied by IPB98(y,2) scaling, which may have important implications for the design of an ST-based CTF. ELM mitigation, an important issue for ITER, has been demonstrated by applying resonant magnetic perturbations (RMPs) using both internal and external coils, but full stabilization of type-I ELMs has not been observed. Modelling shows the importance of including the plasma response to the RMP fields. MAST plasmas with q > 1 and weak central magnetic shear regularly exhibit a long-lived saturated ideal internal mode. Measured plasma braking in the presence of this mode compares well with neo-classical toroidal viscosity theory. In support of basic physics understanding, high resolution Thomson scattering measurements are providing new insight into sawtooth crash dynamics and neo-classical tearing mode critical island widths. Retarding field analyser measurements show elevated ion temperatures in the scrape-off layer of L-mode plasmas and, in the presence of type-I ELMs, ions with energy greater than 500 eV are detected 20 cm outside the separatrix. Disruption mitigation by massive gas injection has reduced divertor heat loads by up to 70%. © 2011 IAEA, Vienna.

Saturn: storm-clouds brooding on towering heights.

Nature 475:7354 (2011) 44-45

Thermal structure and dynamics of Saturn's northern springtime disturbance.

Science 332:6036 (2011) 1413-1417

Authors:

Leigh N Fletcher, Brigette E Hesman, Patrick GJ Irwin, Kevin H Baines, Thomas W Momary, Agustin Sanchez-Lavega, F Michael Flasar, Peter L Read, Glenn S Orton, Amy Simon-Miller, Ricardo Hueso, Gordon L Bjoraker, Andrei Mamoutkine, Teresa del Rio-Gaztelurrutia, Jose M Gomez, Bonnie Buratti, Roger N Clark, Philip D Nicholson, Christophe Sotin

Abstract:

Saturn's slow seasonal evolution was disrupted in 2010-2011 by the eruption of a bright storm in its northern spring hemisphere. Thermal infrared spectroscopy showed that within a month, the resulting planetary-scale disturbance had generated intense perturbations of atmospheric temperatures, winds, and composition between 20° and 50°N over an entire hemisphere (140,000 kilometers). The tropospheric storm cell produced effects that penetrated hundreds of kilometers into Saturn's stratosphere (to the 1-millibar region). Stratospheric subsidence at the edges of the disturbance produced "beacons" of infrared emission and longitudinal temperature contrasts of 16 kelvin. The disturbance substantially altered atmospheric circulation, transporting material vertically over great distances, modifying stratospheric zonal jets, exciting wave activity and turbulence, and generating a new cold anticyclonic oval in the center of the disturbance at 41°N.

Plasma rotation and transport in MAST spherical tokamak

Nuclear Fusion 51:6 (2011)

Authors:

AR Field, C Michael, RJ Akers, J Candy, G Colyer, W Guttenfelder, YC Ghim, CM Roach, S Saarelma

Abstract:

The formation of internal transport barriers (ITBs) is investigated in MAST spherical tokamak plasmas. The relative importance of equilibrium flow shear and magnetic shear in their formation and evolution is investigated using data from high-resolution kinetic- and q-profile diagnostics. In L-mode plasmas, with co-current directed NBI heating, ITBs in the momentum and ion thermal channels form in the negative shear region just inside qmin. In the ITB region the anomalous ion thermal transport is suppressed, with ion thermal transport close to the neo-classical level, although the electron transport remains anomalous. Linear stability analysis with the gyro-kinetic code GS2 shows that all electrostatic micro-instabilities are stable in the negative magnetic shear region in the core, both with and without flow shear. Outside the ITB, in the region of positive magnetic shear and relatively weak flow shear, electrostatic micro-instabilities become unstable over a wide range of wave numbers. Flow shear reduces the linear growth rates of low-k modes but suppression of ITG modes is incomplete, which is consistent with the observed anomalous ion transport in this region; however, flow shear has little impact on growth rates of high-k, electron-scale modes. With counter-NBI ITBs of greater radial extent form outside qmin due to the broader profile of E × B flow shear produced by the greater prompt fast-ion loss torque. © 2011 IAEA, Vienna.