The Effect of Trapped Electrons on the Collisionless Damping of the Geodesic Acoustic Mode

The effect of deeply trapped electrons on the collisionless damping of geodesic acoustic modes is studied in the simple toroidal configuration assuming that omega(de) << omega(be), where omega(de) and omega(be) are the geodesic drift frequency and bounce frequency of the trapped electrons. The rate of the damping induced by the trapped electrons is found to be an increasing function of the safety factor q until the edge of the tokamak plasma is reached. In the low q range, the rate of the damping caused by the circulating ions is larger than that of the damping caused by the trapped electrons, but as q increases, the latter becomes comparable with and even exceeds the former at the edge of the tokamak plasma.