J.W.S. Cook S.C. Chapman
We present first principles simulations of the direct collisionless coupling of the free energy of fusionborn ions into electron current in a magnetically confined fusion plasma. These simulations demonstrate, for the first time, a key building block of some ‘‘alpha channeling’’ scenarios for tokamak experiments. Spontaneously excited obliq…
PublishedI. T. Chapman R. Scannell W. A. Cooper J. P. Graves R. J. Hastie G. Naylor A. Zocco
Thomson scattering measurements with subcentimeter spatial resolution have been made during a sawtooth crash in a Mega Ampere Spherical Tokamak fusion plasma. The unparalleled resolution of the temperature profile has shed new light on the mechanisms that underlie the sawtooth. As magnetic reconnection occurs, the temperature gradient at the island…
PublishedYueqiang Liu M.S. Chu W.F. Guo F. Villone R. Albanese G. Ambrosino M. Baruzzo T. Bolzonella I.T. Chapman A.M. Garofalo C.G. Gimblett R.J. Hastie T.C. Hender G.L. Jackson R.J. La Haye M.J. Lanctot Y.K. In G. Machiori M. Okabayashi R. Pac
Two issues of the resistive wall mode (RWM) control code maturity are addressed: the inclusion of advanced mode damping physics beyond the ideal MHD description, and the possibility of taking into account the influence of 3D features of the conducting structures on the mode stability and control. Examples of formulations and computational results a…
PublishedM-D Hua IT Chapman AR Field RJ Hastie SD Pinches The Mast Team
Plasma rotation in tokamaks is of special interest for its potential stabilising effect on micro- and macro instabilities, leading to increased confinement. In MAST, the torque from Neutral Beam Injection (NBI) can spin the plasma to a core velocity ~ 300km.s -1 (Alfven Mach number ~ 0.3). Low density plasmas often exhibit a weakly non-monotonic sa…
PublishedIT Chapman M-D Hua SD Pinches RJ Akers AR Field JP Graves RJ Hastie CA Michael The Mast Team
MAST plasmas with a safety factor above unity and a profile with either weakly reversed shear, or broad low shear regions, regularly exhibit long-lived saturated ideal magnetohydrodynamic (MHD) instabilities. The toroidal rotation is flattened in the presence of such perturbations and the fast ion losses are enhanced. These ideal modes, distinguish…
PublishedIT Chapman JP Graves C Wahlberg The Mast Team
The sensitivity of the stability of the ideal n = 1 internal kink mode to variations in the plasma profiles is analysed both analytically and numerically in rotating tokamak plasmas. These stability analyses have been carried out including the centrifugal effects of toroidal plasma rotation upon the equilibrium, and also inconsistently when the equ…
PublishedR.M.Nicol S.C.Chapman R.O.Dendy
Wepresentgeneralizedstructurefunction(GSF)analysisof magneticandvelocityfieldfluctuationsmeasured insituinthesolarwindat ~ 1 AUwiththeACEspacecraft.Wedecomposethefluctuationsintodirectionsparalleland perpendiculartothemeanlocalbackgroundmagneticfield.GSFplotsbasedonthesequantitiesareshowntoprovideaclear indicatorofthespectralbreakbetweentheinertial…
PublishedJ. P. Graves I. Chapman S. Coda L.-G. Eriksson T. Johnson
The sawtooth control mechanism in plasmas employing off-axis toroidally propagating ion cyclotron resonance waves in tokamaks is reinvestigated. The radial drift excursion of energetic passing ions distributed asymmetrically in the velocity parallel to the magnetic field determines stability when the rational q 1/4 1 surface resides within a narrow…
PublishedC. Wahlberg I. T. Chapman J. P. Graves
Analytical theory and two different magnetohydrodynamical stability codes are used in a study of the effects of toroidal plasma rotation on the stability of the ideal, internal kink mode in tokamaks. The focus of the paper is on the role that the centrifugal effects on the plasma equilibrium play for the stability of this mode, and results from one…
PublishedI. T. Chapman M. F. De Bock S. D. Pinches M. R. Turnyanskiy Mast Team V. G. Igochine M. Maraschek G. Tardini Asdex Upgrade Team
Sawtooth behavior has been investigated in plasmas heated with off-axis neutral beam injection in ASDEX Upgrade [A. Herrmann and O. Gruber, Fusion Sci. Technol. 44 , 569 (2003)] and the Mega-Ampere Spherical Tokamak MAST [A. Sykes and et al. , Nucl. Fusion 41 , 1423 (2001)]. Provided that the fast ions are well confined, the sawtooth period is foun…
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