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CCFE-PR(16)652016
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…
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CCFE-PR(16)622016
Spherical tokamaks (STs) typically have lower magnetic fields than conventional tokamaks, but similar mass densities. Suprathermal ions with relatively modest energies, in particular beam-injected ions, consequently have speeds close to or exceeding the Alfven velocity, and can therefore excite a range of Alfvenic instabilities. STs heated with neu…
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CCFE-PR(16)402016
A non-steady-state orbit-following Monte-Carlo code has been developed. As part of the verification and validation of the code, calculations of time dependent neutron rates have been made for a specific shot in the Mega Amp Spherical Tokamak (MAST) using three-dimensional fields representing vacuum resonant magnetic perturbations (RMPs) and toroida…
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CCFE-PR(16)612016
In the last three years, magnetic reconnection research in the MAST spherical tokamak achieved major progress by use of new 32 chord ion Doppler tomography, 130 channel YAG and 300 channel Ruby Thomson scattering diagnostics. In addition to the previously achieved high power plasma heating during merging, detailed full temperature profile measureme…
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CCFE-PR(16)432016
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…
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CCFE-PR(16)312016
This paper describes a recent advances in merging/reconnection experiments in MAST, namely tomographic ion Doppler spectroscopy capability from 2013 which solves the problem of the absence of ion temperature profile measurement during the solenoid-less startup. Providing 32 channel line-integrated spectra from 0.25m< rtangential <1.1m are con…
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CCFE-PR(16)362016
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…
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CCFE-PR(16)122016
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…
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CCFE-PR(15)582015
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…
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CCFE-PR(15)852015
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…
Showing 51 - 60 of 143 UKAEA Paper Results