Energy transport by locally trapped electrons during ECRH in Stellarators

An increase in the energy transport by locally trapped electrons in the electron-cyclotron resonance heating (ECRH) is considered as a cause of fast power losses. Two-dimensional Fokker-Planck equation is used to describe the evolution of the distribution of trapped electrons due to ECRH and Coulomb collisions. The quasi-linear diffusion coefficient incorporates the magnetic field inhomogeneity, relativistic effects, spatial wave damping, and a finite width of the electromagnetic beam. The numerical calculations show that the effect under consideration can enhance the power losses in the case of an off-axis heating and moderate single-pass collisionless wave damping