Finite-Orbit-Width Effects on Energetic-Particle-Induced Geodesic Acoustic Mode∗)

We identify linear properties of the energetic-particle-induced geodesic acoustic mode (EGAM) using eigenmode analysis based on the gyrokinetic theory. From the perturbed gyrokinetic equation with energetic particles, we derive a dispersion relation of the EGAM. The behaviors of the roots vary depending on the safety factor. Taking into account of the finite-orbit-width (FOW) effects, we examine variations of the growth rates of the EGAM for various beam intensities. The analyses indicate that the FOW effects are small, within several percent of the growth rates, for experimentally relevant radial wave numbers.