Modified sixth order wave equations from a finite temperature expansion of the linearized Vlasov-Maxwell equations in the ion cyclotron range of frequencies are constructed for modelling the power deposition of the fast magnetosonic wave whenever a majority or high concentration minority fundamental cyclotron resonance resides in a plasma. The negative absorption sometimes observed around the cyclotron resonance in the solutions of the equations obtained by a rigorous perturbation expansion to second order in ion Larmor radius is avoided.
Alava, M., Heikkinen, J., Hellsten, T., Pavlov, I., & Scherbinin, O. (1994). On the modelling of fundamental ion cyclotron absorption by finite Larmor radius wave equations. Physica Scripta, 50(3), 275-282. https://doi.org/10.1088/0031-8949/50/3/010