G. J. Colyer A. A. Schekochihin F. I. Parra C. M. Roach M. A. Barnes Y. C. Ghim W. Dorland
In electrostatic simulations of MAST plasma at electron-gyroradius scales, using the local flux-tube gyrokinetic code GS2 with adiabatic ions, we find that the longtime saturated electron heat flux (the level most relevant to energy transport) decreases as the electron collisionality decreases. At early simulation times, the heat flux quasisatura…
Preprint PublishedJ.C. Hillesheim D. Dickinson C.M. Roach S. Saarelma R. Scannell A. Kirk N.A. Crocker W.A. Peebles H. Meyer The MAST Team
Measurements of local density and magnetic field fluctuations near the pedestal top, conditionally-averaged over the ELM cycle, have been made in MAST. A Doppler backscattering (DBS) system installed at MAST was used to measure intermediate-k (k ? _i _ 3 - 4) density fluctuations at the top of the pedestal. A novel diagnostic technique combining DB…
Preprint PublishedS. S. Henderson L. Garzotti F.J. Casson D. Dickinson M. O'Mullane A. Patel C.M. Roach H.P. Summers H. Tanabe M. Valovic MAST team
Carbon and nitrogen impurity transport coefficients are determined from gas puff experiments carried out during repeat L-mode discharges on the Mega-Amp Spherical Tokamak (MAST) and compared against a previous analysis of helium impurity transport on MAST. The impurity density profiles are measured on the lowfield side of the plasma, therefore this…
Preprint PublishedD. Dickinson C. M. Roach J. M. Skipp H. R. Wilson
Solutions to a model 2D eigenmode equation describing micro-instabilities in tokamak plasmas are presented that demonstrate a sensitivity of the mode structure and stability to plasma profiles. In narrow regions of parameter space, with special plasma profiles, a maximally unstable mode is found that balloons on the outboard side of the tokamak. Th…
PublishedA.R. Field D. Dunai Y-C Ghim P. Hill B. Mcmillan C.M. Roach S. Saarelma A.A. Schekochihin S. Zoletnik The Mast Team
Observations of ion-scale density turbulence of relative amplitude are available on the Mega Amp Spherical Tokamak (MAST) using a 2D (8 radial × 4 poloidal channel) imaging Beam Emission Spectroscopy (BES) diagnostic. Spatial and temporal characteristics of this turbulence, i.e., amplitudes, correlation times, radial and perpendicular correlation …
PublishedM.D.J. Cole S.L. Newton S.C. Cowley N.F. Loureiro D. Dickinson C. Roach J.W. Connor
We have extended our study of the competition between the drive and stabilization of plasma microinstabilities by sheared flow to include electromagnetic effects at low plasma ß (the ratio of plasma to magnetic pressure). The extended system of characteristic equations is formulated, for a dissipative fluid model developed from the gyrokinetic equ…
PublishedA. Kirk D. Dunai M. Dunne G. Huijsmans S. Pamela M. Becoulet J.R. Harrison J. Hillesheim C. Roach S. Saarelma The Mast Team
The type I ELMy H-mode is the baseline operating scenario for ITER. While it is known that the type I ELM ultimately results from the peeling-ballooning instability, there is growing experimental evidence that a mode grows up before the ELM crash that may modify the edge plasma, which then leads to the ELM event due to the peeling-ballooning mode. …
PublishedS. S. Henderson L. Garzotti F. J. Casson D. Dickinson M. F. J. Fox M. O’Mullane A. Patel C. M. Roach H. P. Summers M. Valovic The Mast Team
Time-dependent helium gas puff experiments have been performed on the Mega Ampere Spherical Tokamak (MAST) during a two point plasma current scan in L-mode and a confinement scan at 900 kA. An evaluation of the He II spectrum line induced by charge exchange suggests anomalous rates of diffusion and inward convection in the outer regions of both L-m…
PublishedL. Garzotti J. Figueiredo C. M. Roach M. Valovic D. Dickinson G. Naylor M. Romanelli R. Scannell G. Szepesi The Mast Team
Reactor grade plasmas are likely to be fuelled by pellet injection. This technique transiently perturbs the profiles, driving the density profile hollow and flattening the edge temperature profile. After the pellet perturbation, the density and temperature profiles relax towards their quasi-steady-state shape. Microinstabilities influence plasma co…
PublishedS. Saarelma M.N.A. Beurskens D. Dickinson L. Frassinetti M.J.Leyland C.M. Roach EFDA-JET Contributors
The pedestal profile measurements in high triangularity JET plasmas show that with low fuelling the pedestal width decreases during the ELM cycle and with high fuelling it stays constant. In the low fuelling case the pedestal pressure gradient keeps increasing until the ELM crash and in the high fuelling case it initially increases then saturates d…
Published