E. G. Highcock M. Barnes A. A. Schekochihin F. I. Parra C. M. Roach S.C. Cowley
The effect of flow shear on turbulent transport in tokamaks is studied numerically in the experimentally relevant limit of zero magnetic shear. It is found that the plasma is linearly stable for all nonzero flow shear values, but that subcritical turbulence can be sustained nonlinearly at a wide range of temperature gradients. Flow shear increases …
PublishedS. A. Arshad J. G. Cordey D. C. Mcdonald J. Farthing E. Joffrin M. Von Hellermann C. M. Roach J. Svensson
Principal techniques and trends in the validation and analysis of data in magnetic fusion research are described and examples of applications are given. Wellestablished methods to obtain key physical quantities are outlined, as well as newer techniques employing integrated analysis of multiple diagnostics to improve quality and extract additional i…
PublishedD.J. Applegate C.M. Roach S.C. Cowley W.D. Dorland N. Joiner R.J. Akers N.J. Conway A.R. Field A. Patel M. Valovic M.J. Walsh
Gyrokinetic microstability analyses, with and without electromagnetic effects, are presented for a spherical tokamak plasma equilibrium closely resembling that from a high confinement mode ( H mode ) discharge in the mega-ampere spherical tokamak ( MAST ) [ A. Sykes et al. , Nucl. Fusion 41 , 1423 ( 2001 )] . Electrostatic ion temperature gradient …
PublishedG. Manfredi C. M. Roach
The generation of zonal flows and their interplay with drift wave turbulence is studied numerically using a model based on the Hasegawa–Mima equation, with an electron response depending only on the fluctuating part of the electrostatic potential. In regimes dominated by the diamagnetic velocity, large-amplitude nonlinear oscillations are observe…
PublishedA. Sykes R. J. Akers L. C. Appel P. G. Carolan J.W. Connor N. J. Conway G. F. Counsell A. Dnestrovskij Yu.N. Dnestrovskij M. Gryaznevich P. Helander M. P. S. Nightingale C. Ribeiro C. M. Roach M. Tournianski M. J. Walsh H. R. Wilson The S
H -mode operation has been achieved in high current I p . 200 kA plasmas in the START spherical tokamak for both neutral-beam-injection-heated and Ohmic discharges. The transition to H mode features the development of well-defined edge pedestals in density and temperature, which signifies the formation of an edge-transport barrier, and associated e…
PublishedC. M. Bishop C. M. Roach
Neural networks provide a new tool for the fast solution of repetitive nonlinear curve fitting problems. In this article we introduce the concept of a neural network, and we show how such networks can be used for fitting functional forms to experimental data. The neural network algorithm is typically much faster than conventional iterative approach…
Published