We present a comprehensive study of the multiple electrostatic and electromagnetic electron temperature gradient (ETG) modes with a significant upgrading of the gyrokinetic code HD7. Specifically, the non-adiabaticity of all particle species and the electromagnetic effects are taken into account in the upgraded version. Multiple electrostatic ETG (ES-ETG) modes with conventional and unconventional ballooning mode structures are found to be excited by large temperature gradients. The unconventional modes with mode-index >0 (where represents peak number as well as parity in ballooning space) have comparable growth rates with the conventional mode under the specific condition, e.g. , indicating that unconventional modes are significant in L-mode or pedestal top of H-mode. In addition, different from the phenomenon of ES-ETG, multiple electromagnetic ETG (EM-ETG) modes can be excited with and the transition of the dominant eigenstate is observed. The EM-ETG mode has an excited threshold of (the ratio of electron pressure over magnetic pressure), indicating that the electromagnetic effect plays a key role in high (the ratio of thermal pressure to magnetic pressure) condition. Similar to the typical ES-ETG mode, the novel EM-ETG mode is destabilized by large and suppressed by sufficiently large (either positive or negative) magnetic shear. Talking about the transport capability, the simulation result reveals that EM-ETG mode induced particle flux is quite low () while the energy flux is non-negligible compared to that induced by ion temperature gradient driven mode. Possible relevance of the results with the transport physics in transport barriers is discussed.
This paper investigates different types of electron temperature gradient (ETG) modes and their impact on plasma transport in tokamak devices. It explores both electrostatic and electromagnetic ETG modes, including unconventional modes, and their dependence on plasma parameters like temperature gradient and magnetic shear. The study reveals that electromagnetic ETG modes can significantly contribute to energy transport, even though particle transport is relatively low.