A. Kirk J. Harrison Yueqiang Liu E. Nardon I. T. Chapman P. Denner The Mast Team
The application of nonaxisymmetric resonant magnetic perturbations (RMPs) with a toroidal mode number n . 6 in the MAST tokamak produces a significant reduction in plasma energy loss associated with type-I edge localized modes (ELMs), the first such observation with n>3 . During the ELM mitigated stage clear lobe structures are observed in visible-…
PublishedIT Chapman NR Walkden JP Graves C Wahlberg
Sheared toroidal rotation is found to increase the ideal external kink stability limit, thought to be the ultimate performance limit in fusion tokamaks. However, at rotation speeds approaching a significant fraction of the Alfv´en speed, the toroidal rotation shear drives a Kelvin-Helmholtzlike global plasma instability. Optimising the rotation pr…
PublishedI T Chapman J P Graves T Johnson O Asunta P Bonoli M Choi E F Jaeger M Jucker O Sauter
Numerical modelling of the effects of ion cyclotron resonance heating (ICRH) on the stability of the internal kink mode suggests that ICRH should be considered as an essential sawtooth control tool in ITER. Sawtooth control using ICRH is achieved by directly affecting the energy of the internal kink mode rather than through modification of the magn…
PublishedJ W S Cook R O Dendy S C Chapman
We report a first principles study of the coupled evolution of energetic ions, background majority ions, electrons and electromagnetic fields in magnetised plasma during the linear phase of the lower hybrid drift instability. A particle-incell code, with one spatial and three velocity space co-ordinates, is used to analyse the evolving distribution…
PublishedW A Cooper J P Graves O Sauter S P Hirshman I T Chapman M Gobbin L Marrelli P Martin I Predebon D Terranova
Magnetohydrodynamic equilibrium states with a three-dimensional helical core are computed to model the MAST spherical tokamak and the RFX-mod reversed field pinch. The boundary is fixed as axisymmetric. The MAST equilibrium state has the appearance of an internal kink mode and is obtained under conditions of weak reversed central shear. The RFX-mod…
PublishedIT Chapman MP Gryaznevich DF Howell YQ Liu The Mast Team
Resistive wall mode stability limits have been probed by MHD spectroscopy and numerical modelling. MAST plasmas have operated up to βN = 5.7, well above the predicted ideal kink no-wall limit or measured resonant field amplification limits due to a combination of rotation and kinetic damping. By varying the density, both the rotation and the fast …
PublishedJ W S Cook S C Chapman R O Dendy
We present particle-in-cell (PIC) simulations of minority energetic protons in deuterium plasmas, which demonstrate a collective instability responsible for emission near the lower hybrid frequency and its harmonics. The simulations capture the lower hybrid drift instability in a regime relevant to tokamak fusion plasmas, and show further that the …
PublishedV. Igochine I. T. Chapman V. Bobkov S. Günter M. Maraschek D. Moseev G. Pereversev M. Reich J. Stober Asdex Upgrade Team
It is often observed that large sawteeth trigger the neoclassical tearing mode (NTM) well below the usual threshold for this instability. At the same time, fast particles in the plasma core stabilize sawteeth and provide these large crashes. The paper presents results of first experiments in ASDEX Upgrade for destabilization of fast particle stabil…
PublishedA. Kirk Yueqiang Liu E. Nardon P. Tamain P. Cahyna I. Chapman P. Denner H. Meyer S. Mordijck D. Temple The Mast Team
Experiments have been performed on MAST using internal (n=3) resonant magnetic perturbation coils. The application of the RMPs to L-mode discharges has shown a clear density pump out when the field line pitch angle at the low field side of the plasma is sufficiently well aligned with the applied field. The application of the RMPs before the L-H tra…
PublishedI.T. Chapman
The sawtooth instability in tokamak plasmas results in a periodic reorganization of the core plasma. A typical sawtooth cycle consists of a quiescent period, during which the plasma density and temperature increase, followed by the growth of a helical magnetic perturbation, which in turn is followed by a rapid collapse of the central pressure. The …
Published