Optimization of magnetic perturbation spectra for the COMPASS tokamak

The present contribution describes preparatory calculations for producing controlled resonant magnetic perturbations (RMPs) using the set of saddle coils of the COMPASS tokamak, recently transferred from UKAEA Culham to IPP Prague. In the future experimental programme of COMPASS we plan to focus on studies of RMPs, especially in view of their application as an ELM control mechanism and their planned use in ITER. We computed the spectra of perturbations for several different equilibria simulated by MHD equilibrium and transport codes and determined the positions and sizes of the resulting islands. The adaptation of coil configuration to a particular equilibrium is necessary because of varying safety factor profiles among the equilibria. It is shown how the saddle coils of COMPASS can be adapted to our equilibria to obtain good island overlap at the edge, which is believed to be a key component in the ELM mitigation effect. The mutual relation between the nonlinear plasma response and the perturbation field is discussed, using results of a cylindrical reduced MHD code. (author)