Conceptual design of in vessel mid-plane saddle coils for fast AC operation in ASDEX Upgrade

The ASDEX Upgrade tokamak is operating to prepare the physics base for ITER and DEMO. In the framework of the enhancement activities of the ASDEX Upgrade experiment, a set of 24 in vessel saddle coils will be investigated as a next step. This coil set consists of three groups of coils poloidally and toroidally distributed inside the vessel. The aim of these coils is to generate a non axisymmetric error field to control MHD instabilities. Upper and lower ring coils are under manufacturing and will be partially mounted for the next campaign, while the coils in the middle position, the so called A-coils, are presently undergoing the detail design phase. The large bandwidth of these coils requires addressing different problems: parasitic currents in surrounding coil structures, which are to be minimized, and the presence of alternating currents in permanent magnetic field which is inducing oscillating forces that may excite strong resonances of the structures. The aim of this paper is to introduce the design of such coils and to present the actual status of the supporting analyses which have been carried out so far to find technical solutions to the aforementioned issues.