Improved Analysis of Measured MHD Activity and the Use of Toroidicity Induced Alfvén Eigenmodes to Constrain Current Density Profile Reconstruction in the ASDEX Upgrade Tokamak PDF Download

Author: Karl D. Sassenberg
Publisher:
ISBN:
Category : Nuclear engineering
Languages : en
Pages : 151

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Book Description
In a tokamak plasma, knowledge of the thermal particle and supra-thermal ion populations, and their dynamics is essential for controlled operation as the plasma pressure and current gradients provide the energy required to trigger various types of (MagnetoHydroDynamic) MHD instabilities that act to degrade plasma control and performance. Therefore studying the behaviour of MHD instabilities will reveal considerable information about the various particle populations in the plasma. In particular, a sensitive and readily excitable class of MHD instability in a tokamak plasma is the Toroidicity induced Alfvén Eigenmode (TAE). This mode is excited by supra-thermal ions and its frequency depends on the magnetic field strength, mass density profile, safety factor and the major radius of a tokamak, making it a rich source of information. At ASDEX Upgrade plasma ions are accelerated to energies of 1MeV and higher by Ion Cyclotron Resonance Heating. The interactions between TAEs and the resulting supra-thermal ion population is used to infer the effects that TAEs will have on fusion-born {uF061}-particles in a thermonuclear fusion reactor. This is of paramount importance to ITER and any future fusion devices, as {uF061}-particles are envisioned to be the main source of energy used to maintain a burning plasma. The aim of this research was to characterise typically observed fast ion excited TAEs at ASDEX Upgrade, to study the stability of fast ion excited TAEs at ASDEX Upgrade, to demonstrate that such TAEs could be driven by ICRF (Ion Cyclotron Radio Frequency) beat waves, and to improve equilibrium reconstructions using TAE derived safety factor information. To this end all milestones were achieved demonstrating that the techniques developed to drive TAEs with ICRF beat waves provides the basis for a new diagnostic, which complements existing safety factor profile diagnostics.