UKAEA Journals

Showing 1 - 10 of 22 Journals Results
2016
CCFE-PR(16)65

In this paper we have developed a fluid model to study the radial mode structure of the reactive energetic geodesic acoustic modes (reactive EGAMs), a branch of GAM that becomes unstable in the presence of a cold fast ion beam. We have solved the resulting dispersion relationship, a second order ODE, both analytically in restricted cases and numeri…

Preprint Published
2016
CCFE-PR(16)43

The sandpile paradigm is widely used to model aspects of the phenomenology of magnetically confined fusion (MCF) plasmas, including enhanced confinement, edge pedestals and, potentially, the impulsive energy and particle release process known as ELMing. Here we identify new points of contact between ELMing and the systemwide avalanches in a sandpil…

Preprint Published
2016
CCFE-PR(16)36

A number of tools have recently been developed to study equilibrium and stability in tokamaks with pressure anisotropy. Here we apply these tools to a Mega Ampere Spherical Tokamak (MAST) discharge to calculate equilibrium, Alfven continua and eigenmodes, through to linear growth and nonlinear saturation of a toroidal Alfven eigenmode (TAE); this i…

Preprint Published
2016
CCFE-PR(16)12

We use the HAGIS code to compute the nonlinear stability of the Q=10 ITER baseline scenario to toroidal Alfveneigenmodes (TAE) and the subsequent effects of these modes on fusion alpha-particle redistribution. Our calculations build upon an earlier linear stability survey [Rodrigues, P. et al. (2015). Nuclear Fusion, 55(8), 083003] which provides a…

Preprint Published
2015
CCFE-PR(15)58

Extending the ideal MHD stability code MISHKA, a new code, MISHKA-A, is developed to study the impact of pressure anisotropy on plasma stability. Based on full anisotropic equilibrium and geometry, the code can provide normal mode analysis with three fluid closure models: the single adiabatic model (SA), the double adiabatic model (CGL) and the inc…

Preprint Published
2015
CCFE-PR(15)85

An unstable branch of energetic geodesic acoustic mode (EGAM) is found using the fluid theory with fast ions characterised by their narrow width in energy distribution and collective transit along field lines. This mode, with a frequency much lower than the thermal GAM frequency !GAM, is now confirmed as a new type of unstable EGAM : a reactive in…

Preprint Published
2015
CCFE-PR(15)33

In this work, we generalise linear magnetohydrodynamic (MHD) stability theory to include equilibrium pressure anisotropy in the uid part of the analysis. A novel `single-adiabatic' (SA) uid closure is presented which is complementary to the usual `double-adiabatic' (CGL) model and has the advantage of naturally reproducing exactly the MHD spectrum …

Preprint Published
2012

In this paper, current profiles for plasma discharges on the mega-ampere spherical tokamak are directly calculated from pickup coil, flux loop, and motional-Stark effect observations via methods based in the statistical theory of Bayesian analysis. By representing toroidal plasma current as a series of axisymmetric current beams with rectangular cr…

Published
2012

The transport of injected beam ions due to toroidal magnetic field ripple in the mega-ampere spherical tokamak (MAST) is quantified using a full orbit particle tracking code, with collisional slowing-down and pitch-angle scattering by electrons and bulk ions taken into account. It is shown that the level of ripple losses is generally rather low, al…

Published