Gyrokinetic simulation study on the energetic-particle-induced geodesic acoustic mode

Miki, Kazuhiro; Idomura, Yasuhiro   

From the perturbed gyrokinetic equation, we derive linear growth rates and real frequencies of the energetic-particle-induced geodesic acoustic mode (EGAM). Representing bump-on-tail distributions as the beam injection, we close the system together with the quasi-neutrality. Obtained dispersion relation, in which the finite-orbit-width (FOW) is taken, deduces the linear parameters depending on q-values, beam intensities, and plasma machine sizes. For experimentally-relevant parameters, the FOW effects are small, within several percent of the growth rates. The results are confirmed also in plasma size scan using the full-f gyrokinetic Eulerian code GT5D. We further introduce a slowing-down distribution function to compared with the DIII-D results and hybrid code simulation results. The comparison results in consistency.