Kinetic ballooning mode (KBM) was simulated and studied numerically by means of a full electromagnetic theory that retains all three gyroscopic fields: , and . The destabilizing influence of the parallel magnetic field fluctuation on the KBM was reported. When is neglected, the maximum growth rate decreases by approximately 5% for the magnetohydrodynamic-like ballooning mode (BM), and the growth rates in the higher β region decrease significantly for KBMs with a moderate safety factor (q). These are due to the partial cancellation of the stabilizing component of the drift by introduction of effect. Here, β is the ratio of the thermal pressure to magnetic pressure, and is the toroidal magnetic field. The destabilizing effect of on KBM is weaker for higher q. Under the influence of toroidal effect, the introduction of the results in the expansion of the KBM instability window. Compared to the main body of the KBM instability, the extended instability shows partially different features in both the mode- and spectral-structures. For the case of , the KBM is always unstable in almost the entire region of low shear for a smaller pressure gradient, and the stability boundary in plane is much wider than that for the case of . Moreover, the stability boundary of the KBM changes slightly in the plane when is included in the model. All the evidences indicated that β affects KBM through both and , and the fundamental properties of KBM are determined by the two gyroscopic fields: and , while a new ion drift is introduced by including to modify the mode characteristics to some extent.
This paper investigates the impact of parallel magnetic field fluctuations on kinetic ballooning modes (KBMs) in tokamaks using gyrokinetic simulations. It shows that including these fluctuations can significantly affect the stability and characteristics of KBMs, especially at higher plasma pressure. The findings are important for understanding plasma stability and turbulence in fusion devices.