The non-perturbative MHD-kinetic hybrid code MARS-K (Liu et al 2014 Phys. Plasmas21 056105) is updated to include relativistic effects for kinetic fast particles, enabling the code to model excitation of Alfvén eigenmodes (AEs) by runaway electrons (REs) in post-disruption tokamak plasmas. Applying the updated code to RE beams in both DIII-D and ITER, a zoo of AE modes triggered by trapped REs due to precessional drift-kinetic resonances is computed while scanning the RE energy. At fixed RE energy, multiple unstable roots are also excited. These AE modes possess radially different eigenmode structures, ranging from global modes to core-localized ones. The computed mode frequency is in the Alfvén frequency range, increasing with the assumed RE energy in a staircase fashion and quantitatively matching the experimental measurement (in DIII-D). At the (more relevant) high-frequency range (above 1 MHz), the modeled eigenmodes are identified as compressional AEs (CAEs) in DIII-D and a mixture of CAE and shear Alfvén waves in ITER.
This paper presents a model that simulates how runaway electrons in tokamak plasmas can excite Alfvén eigenmodes, which are oscillations in the magnetic field. The model was applied to the DIII-D and ITER tokamaks, and it was found that these modes can have different structures and frequencies depending on the energy of the runaway electrons.