Optimization of Magnetic Perturbation Spectra for the COMPASS Tokamak

The COMPASS tokamak, recently transferred from UKAEA Culham to IPP Prague, is equipped with a set of saddle coils for producing controlled resonant magnetic perturbations (RMPs). 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. In the present contribution we describe the preparatory calculations for the planned experiments. We computed the spectra of perturbations for several different equilibra predicted by MHD simulations and determined the positions and sizes of the resulting islands. 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. Impact of the nonlinear plasma response on the perturbation field is discussed, using results of a cylindrical reduced MHD code.