Gyrokinetic investigations of the electromagnetic geodesic acoustic mode

Abstract

The linear characteristics of the electromagnetic geodesic acoustic mode (GAM) are investigated numerically with the gyrokinetic code GEM. The results indicate that the electromagnetic effect has little influence on the frequency and damping rate of GAM. The results also show that both m=1 and m=2 poloidal magnetic components of GAM exist, and the m=1 magnetic component has comparable sine and cosine components, while the m=2 magnetic component is dominated by the sine component, where m is the poloidal mode number. In addition, the amplitudes of various magnetic components increase with respect to the ratio of plasma pressure to magnetic pressure β and safety factor q. Most importantly, the amplitude of m=1 magnetic component is comparable to or even slightly larger than that of m=2 magnetic component. It is also found that the trapped electron effect may be important for the magnetic components. Furthermore, the various magnetic components are compared with the previous analytical results and some discussions are given.

The first observation of GAM induced by negative biasing in J-TEXT tokamak

“…GAM is an electrostatic mode, however, theoretical [42][43][44][45][46][47][48] and experimental [49][50][51][52][53] works have confirmed the magnetic component of the GAM. In this experiment, the reciprocating probe is equipped with a 3D magnetic probe positioned inside the LCFS, which successfully measures the magnetic fluctuation component of L-GAM, as shown in figure 6, here δ Bθ and δ Br represent the fluctuations in the differential signal of poloidal and radial magnetic fields, respectively.…”