Thermal fluctuations in gyrokinetic plasma at finite beta

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Abstract
A covariant gyrokinetic fluctuation-dissipation theorem is used to predict unusual thermal-equilibrium fluctuation spectra for weakly electromagnetic gyrokinetic plasma in the limit of weak coupling. Wave number spectra are derived both by exact integrations of the frequency spectra and by resonance integrations over weakly damped normal modes. The former reduce in the electrostatic limit to previous heuristic results and are interpreted in terms of the concept of a ‘‘gyrokinetic vacuum.’’ The latter are interpreted in terms of a new form for the gyrokinetic energy conservation law and a new formula for the gyrokinetic plasmon action density.