A detailed cross-device investigation on the role of filamentary dynamics in high-density regimes has been performed within the EUROfusion framework, comparing the ASDEX Upgrade (AUG) and TCV tokamaks. Both devices run density ramp experiments at different levels of plasma current, keeping the toroidal field or q95 constant in order to disentangle the role of the parallel connection length and the current. During the scan at a constant toroidal field, in both devices the scrape-off layer (SOL) profiles tend to develop a clear SOL density shoulder at a lower edge density whenever the current is reduced. Different current behaviour is substantially reconciled in terms of the edge density normalized to the Greenwald fraction. During the scan at constant q95 AUG exhibits similar behaviour, whereas in TCV no upstream profile modification signature has been observed at lower current levels. The latter behaviour has been ascribed to the lack of target density rollover. The relation between the upstream density profile modification and detachment condition has been investigated. For both devices the relation between blob size and the SOL density e-folding length is found independent of the plasma current, with the observation of a clear increase in blob size and the edge density normalized to a Greenwald fraction. ASDEX Upgrade has also explored filamentary behaviour in the H-mode. The experiments in AUG have focused on the role of neutrals, performing discharges with and without cryogenic pumps, highlighting how high neutral pressure, not only in the divertor but also at the midplane, is needed in order to develop an H-mode SOL profile shoulder in AUG.

PB - IOP Publishing VL - 60 UR - http://eprints.whiterose.ac.uk/152047/1/Vianello_2019_NF_manuscript.pdf IS - 1 U1 -FP

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U5 - 2391efbf0432454f26047770a55623d8 ER - TY - JOUR T1 - Physics research on the TCV tokamak facility: from conventional to alternative scenarios and beyond JF - Nuclear Fusion Y1 - 2019 A1 - Coda, S. A1 - Agostini, M. A1 - Albanese, R. A1 - Alberti, S. A1 - Alessi, E. A1 - Allan, S. A1 - Hogeweij, G. M. D. A1 - Perek, A. A1 - Ravensbergen, T. A1 - Vijvers, W. A. J. A1 - Allcock, J. A1 - Ambrosino, R. A1 - Anand, H. A1 - Andrebe, Y. A1 - EUROfusion MST1 Team A1 - et al. AB - The research program of the TCV tokamak ranges from conventional to advanced-tokamak scenarios and alternative divertor configurations, to exploratory plasmas driven by theoretical insight, exploiting the device's unique shaping capabilities. Disruption avoidance by real-time locked mode prevention or unlocking with electron-cyclotron resonance heating (ECRH) was thoroughly documented, using magnetic and radiation triggers. Runaway generation with high-Z noble-gas injection and runaway dissipation by subsequent Ne or Ar injection were studied for model validation. The new 1 MW neutral beam injector has expanded the parameter range, now encompassing ELMy H-modes in an ITER-like shape and nearly non-inductive H-mode discharges sustained by electron cyclotron and neutral beam current drive. In the H-mode, the pedestal pressure increases modestly with nitrogen seeding while fueling moves the density pedestal outwards, but the plasma stored energy is largely uncorrelated to either seeding or fueling. High fueling at high triangularity is key to accessing the attractive small edge-localized mode (type-II) regime. Turbulence is reduced in the core at negative triangularity, consistent with increased confinement and in accord with global gyrokinetic simulations. The geodesic acoustic mode, possibly coupled with avalanche events, has been linked with particle flow to the wall in diverted plasmas. Detachment, scrape-off layer transport, and turbulence were studied in L- and H-modes in both standard and alternative configurations (snowflake, super-X, and beyond). The detachment process is caused by power 'starvation' reducing the ionization source, with volume recombination playing only a minor role. Partial detachment in the H-mode is obtained with impurity seeding and has shown little dependence on flux expansion in standard single-null geometry. In the attached L-mode phase, increasing the outer connection length reduces the in–out heat-flow asymmetry. A doublet plasma, featuring an internal X-point, was achieved successfully, and a transport barrier was observed in the mantle just outside the internal separatrix. In the near future variable-configuration baffles and possibly divertor pumping will be introduced to investigate the effect of divertor closure on exhaust and performance, and 3.5 MW ECRH and 1 MW neutral beam injection heating will be added. VL - 59 IS - 11 U1 - FP U2 - PEPD U5 - d50a5905a84255c86ad6d49b1cfa1569 ER - TY - JOUR T1 - Modification of SOL profiles and fluctuations with line-average density and divertor flux expansion in TCV JF - Nuclear Fusion Y1 - 2017 A1 - Vianello, N. A1 - Tsui, C. A1 - Theiler, C. A1 - Allan, S. A1 - Boedo, J. A1 - Labit, B. A1 - Reimerdes, H. A1 - Verhaegh, K. A1 - Vijvers, W. A. J. A1 - Walkden, N. A1 - Costea, S. A1 - Kovacic, J. A1 - Ionita, C. A1 - Naulin, V. A1 - Nielsen, A. H. A1 - J. Juul Rasmussen A1 - Schneider, B. A1 - Schrittwieser, R. A1 - Spolaore, M. A1 - Carralero, D. A1 - Madsen, J. A1 - Lipschultz, B. A1 - Militello, F. A1 - TCV team A1 - EUROfusion MST1 Team VL - 57 IS - 11 U1 -FP

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U5 - e6fbf10944c346e164a89755f84348fd ER - TY - JOUR T1 - Overview of MAST results JF - Nuclear Fusion Y1 - 2015 A1 - Chapman, I.T. A1 - Adamek, J. A1 - Akers, R. J. A1 - Allan, S. A1 - Appel, L. A1 - Asunta, O. A1 - Barnes, M. A1 - N. Ben Ayed A1 - Hawke, J. A1 - Bigelow, T. A1 - Boeglin, W. A1 - Bradley, J. A1 - Brünner, J. A1 - Cahyna, P. A1 - Carr, M. A1 - Caughman, J. A1 - Cecconello, M. A1 - Challis, C. A1 - Chapman, S. A1 - Chorley, J. A1 - Colyer, G. A1 - Conway, N. A1 - Cooper, W. A. A1 - Cox, M. A1 - Crocker, N. A1 - Crowley, B. A1 - Cunningham, G. A1 - Danilov, A. A1 - Darrow, D. A1 - Dendy, R. A1 - Diallo, A. A1 - Dickinson, D. A1 - Diem, S. A1 - Dorland, W. A1 - Dudson, B. A1 - Dunai, D. A1 - Easy, L. A1 - Elmore, S. A1 - Field, A. A1 - Fishpool, G. A1 - Fox, M. A1 - Fredrickson, E. A1 - Freethy, S. A1 - Garzotti, L. A1 - Ghim, Y. C. A1 - Gibson, K. A1 - Graves, J. A1 - Gurl, C. A1 - Guttenfelder, W. A1 - Ham, C. A1 - Harrison, J. A1 - Harting, D. A1 - Havlickova, E. A1 - Hawkes, N. A1 - Hender, T. A1 - Henderson, S. A1 - Highcock, E. A1 - Hillesheim, J. A1 - Hnat, B. A1 - Holgate, J. A1 - Horacek, J. A1 - Howard, J. A1 - Huang, B. A1 - Imada, K. A1 - Jones, O. A1 - S. Kaye A1 - Keeling, D. A1 - Kirk, A. A1 - Klimek, I. A1 - Kocan, M. A1 - Leggate, H. A1 - Lilley, M. A1 - Lipschultz, B. A1 - Lisgo, S. A1 - Liu, Y. Q. A1 - Lloyd, B. A1 - Lomanowski, B. A1 - Lupelli, I. A1 - Maddison, G. A1 - J. Mailloux A1 - Martin, R. A1 - McArdle, G. A1 - McClements, K. A1 - McMillan, B. A1 - Meakins, A. A1 - Meyer, H. A1 - Michael, C. A1 - Militello, F. A1 - Milnes, J. A1 - Morris, A. W. A1 - Motojima, G. A1 - Muir, D. A1 - Nardon, E. A1 - Naulin, V. A1 - Naylor, G. A1 - Nielsen, A. A1 - O'Brien, M. A1 - O'Gorman, T. A1 - Ono, Y. A1 - Oliver, H. A1 - Pamela, S. A1 - Pangioni, L. A1 - Parra, F. A1 - Patel, A. A1 - Peebles, W. A1 - Peng, M. A1 - Perez, R. A1 - Pinches, S. A1 - Piron, L. A1 - Podesta, M. A1 - Price, M. A1 - Reinke, M. A1 - Ren, Y. A1 - Roach, C. A1 - Robinson, J. A1 - Romanelli, M. A1 - Rozhansky, V. A1 - Saarelma, S. A1 - Sangaroon, S. A1 - Saveliev, A. A1 - Scannell, R. A1 - Schekochihin, A. A1 - Sharapov, S. A1 - Sharples, R. A1 - Shevchenko, V. A1 - Silburn, S. A1 - J. Simpson A1 - Storrs, J. A1 - Takase, Y. A1 - Tanabe, H. A1 - Tanaka, H. A1 - Taylor, D. A1 - Taylor, G. A1 - Thomas, D. A1 - Thomas-Davies, N. A1 - Thornton, A. A1 - Turnyanskiy, M. A1 - Valovic, M. A1 - Vann, R. A1 - Walkden, N. A1 - Wilson, H. A1 - Wyk, L. V. A1 - Yamada, T. A1 - Zoletnik, S. A1 - MAST Team A1 - MAST Upgrade Teams VL - 55 IS - 10 U1 - FP U2 - TP U5 - 9d7b191e90422e8ed8bcf2078b75987f ER - TY - JOUR T1 - Overview of physics results from MAST JF - Nuclear Fusion Y1 - 2011 A1 - Lloyd, B. A1 - Akers, R. J. A1 - Alladio, F. A1 - Allan, S. A1 - Appel, L. C. A1 - Barnes, M. A1 - Barratt, N. C. A1 - N. Ben Ayed A1 - Breizman, B. N. A1 - Cecconello, M. A1 - Challis, C. D. A1 - Chapman, I.T. A1 - Ciric, D. A1 - Colyer, G. A1 - Connor, J. W. A1 - Conway, N. J. A1 - Cox, M. A1 - Cowley, S. C. A1 - Cunningham, G. A1 - Darke, A. A1 - De Bock, M. A1 - Delchambre, E. A1 - De Temmerman, G. A1 - Dendy, R. O. A1 - Denner, P. A1 - Driscoll, M. D. A1 - Dudson, B. A1 - Dunai, D. A1 - Dunstan, M. A1 - Elmore, S. A1 - Field, A. R. A1 - Fishpool, G. A1 - Freethy, S. A1 - Garzotti, L. A1 - Gibson, K. J. A1 - Gryaznevich, M. P. A1 - Guttenfelder, W. A1 - Harrison, J. A1 - Hastie, R. J. A1 - Hawkes, N. C. A1 - Hender, T. C. A1 - Hnat, B. A1 - Howell, D. F. A1 - Hua, M. D. A1 - Hubbard, A. A1 - Huysmans, G. A1 - Keeling, D. A1 - Kim, Y. C. A1 - Kirk, A. A1 - Liang, Y. A1 - Lilley, M. K. A1 - Lisak, M. A1 - Lisgo, S. A1 - Liu, Y. Q. A1 - G. P. Maddison A1 - Maingi, R. A1 - Manhood, S. J. A1 - Martin, R. A1 - McArdle, G. J. A1 - McCone, J. A1 - Meyer, H. A1 - Michael, C. A1 - Mordijck, S. A1 - Morgan, T. A1 - Morris, A. W. A1 - Muir, D. G. A1 - Nardon, E. A1 - Naylor, G. A1 - O'Brien, M. R. A1 - O'Gorman, T. A1 - Palenik, J. A1 - Patel, A. A1 - Pinches, S. D. A1 - Price, M. N. A1 - Roach, C. M. A1 - Rozhansky, V. A1 - Saarelma, S. A1 - Sabbagh, S. A. A1 - Saveliev, A. A1 - Scannell, R. A1 - Sharapov, S. E. A1 - Shevchenko, V. A1 - Shibaev, S. A1 - Stork, D. A1 - Storrs, J. A1 - Suttrop, W. A1 - Sykes, A. A1 - Tamain, P. A1 - Taylor, D. A1 - Temple, D. A1 - Thomas-Davies, N. A1 - Thornton, A. A1 - Turnyanskiy, M. R. A1 - Valovic, M. A1 - Vann, R. G. L. A1 - Voss, G. A1 - Walsh, M. J. A1 - Warder, S. E. V. A1 - Wilson, H. R. A1 - Windridge, M. A1 - Wisse, M. A1 - Zoletnik, S. KW - MODEL KW - TRANSPORT AB -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 x 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(gamma, 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%.

VL - 51 SN - 0029-5515 IS - 9 N1 - ISI Document Delivery No.: 818DPTimes Cited: 0Cited Reference Count: 60SI U1 -PSI

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