An improved analytical theory of ion temperature gradient instability in tokamak plasmas

Abstract The ion temperature gradient (ITG) instability is a fundamental mechanism driving heat transport in magnetically confined plasmas. Previous analytical models often based on fluid-ion approximations, assuming | ω | ∼ | ω ∗ i | ≫ | ω d i | , are found to exhibit notable discrepancies when compared to numerical results obtained by gyrokinetic simulations and eigenvalue code. Here, ω denotes the mode frequency, ω ∗ i the ion diamagnetic drift frequency and ω d i the ion magnetic drift frequency due to magnetic field gradient and curvature. In this work, we have developed an improved analytical theory that assumes | ω | ∼ | ω ∗ i | ∼ | ω d i | . A new analytical ITG dispersion relation is first derived for adiabatic electrons and subsequently extended via perturbation theory to incorporate trapped electron effects. The resulting analytical predictions show excellent agreement with numerical results of simulation and eigenvalue codes. This improved analytical theory, thus, provides a robust theoretical approach for further studies of ITG instabilities in magnetically confined fusion devices.