Fluctuations and Discrete Particle Noise in Gyrokinetic Simulation of Drift Waves
Authors: Thomas G. Jenkins and W.W. Lee
The relevance of the gyrokinetic fluctuation-dissipation theorem (FDT) to thermal equilibrium and non-equilibrium states of the gyrokinetic plasma is explored, with particular focus being given to the contribution of the weakly damped normal modes to the fluctuation spectrum. It is found that the fluctuation energy carried in the normal modes exhibits the proper scaling with particle count (as predicted by the FDT in thermal equilibrium) even in the presence of drift waves which grow linearly and attain a nonlinearly saturated steady state. This favorable scaling is preserved, and the saturation amplitude of the drift wave unaffected, for parameter regimes in which the normal modes become strongly damped and introduce a broad spectrum of discreteness-induced background noise in frequency space. The relationship of the present work to the more general issue of discrete particle noise in particle-in-cell simulations is discussed.
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Physics of Plasmas 14, 032307 (March 2007)
doi: 10.1063/1.2710808
© (2007) American Institute of Physics.
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