The excitation of modes in the toroidal Alfvén eigenmodes (TAE) gap by an external antenna can be modelled by a driven damped harmonic oscillator. By performing a frequency scan it is possible to determine the damping rate of the mode through the quality factor. This method has been employed in recent Joint European Torus (JET) experiments dedicated to scenario development for the observation of alpha-driven instabilities in JET DT plasmas (i.e. plasmas composed by Deuterium and Tritium). However, the toroidal mode number n of the mode for which the measurements were performed could not be determined experimentally. The value of the damping obtained through experimental measurements for a selected time slice is then compared with those obtained from calculations performed by numerical codes for different modes with frequencies close to the experimental frequency of the antenna. This paper describes the modelling method and presents the numerical simulations carried out using a suite of codes to calculate the damping of TAE, which are compared with the value measured experimentally. The radial structures of these modes are first calculated with the ideal magnetohydrodynamic (MHD) code MISHKA. For each of these modes, the damping on thermal ions and thermal electrons and the contribution to the mode growth rate resulting from the resonant interaction with the ion cyclotron resonance heating (ICRH) accelerated ion population are calculated using the drift-kinetic code CASTOR-K. The radiative damping is calculated by using a complex resistivity in the resistive MHD code CASTOR code and the continuum damping is estimated using also the CASTOR code through the standard method of making the real part of the resistivity tend to zero. It was found the radiative damping is largely dominant over all other effects, except for the n = 3 TAE. The overall damping calculated numerically is consistent with the damping measured experimentally.

TAE stability calculations compared to TAE antenna results in JET

R. Fresa;
2018

Abstract

The excitation of modes in the toroidal Alfvén eigenmodes (TAE) gap by an external antenna can be modelled by a driven damped harmonic oscillator. By performing a frequency scan it is possible to determine the damping rate of the mode through the quality factor. This method has been employed in recent Joint European Torus (JET) experiments dedicated to scenario development for the observation of alpha-driven instabilities in JET DT plasmas (i.e. plasmas composed by Deuterium and Tritium). However, the toroidal mode number n of the mode for which the measurements were performed could not be determined experimentally. The value of the damping obtained through experimental measurements for a selected time slice is then compared with those obtained from calculations performed by numerical codes for different modes with frequencies close to the experimental frequency of the antenna. This paper describes the modelling method and presents the numerical simulations carried out using a suite of codes to calculate the damping of TAE, which are compared with the value measured experimentally. The radial structures of these modes are first calculated with the ideal magnetohydrodynamic (MHD) code MISHKA. For each of these modes, the damping on thermal ions and thermal electrons and the contribution to the mode growth rate resulting from the resonant interaction with the ion cyclotron resonance heating (ICRH) accelerated ion population are calculated using the drift-kinetic code CASTOR-K. The radiative damping is calculated by using a complex resistivity in the resistive MHD code CASTOR code and the continuum damping is estimated using also the CASTOR code through the standard method of making the real part of the resistivity tend to zero. It was found the radiative damping is largely dominant over all other effects, except for the n = 3 TAE. The overall damping calculated numerically is consistent with the damping measured experimentally.
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11563/134664
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