Surface impedance of superconductors in magnetic fields

by Prof. Ruggero Vaglio (Prof. ordinario Università di Napoli Federico II)

Wednesday 13 Jul 2016, 11:00 → 13:00 Europe/Rome

Rostagni meeting room (INFN-LNL)

The FCC-hh is presently under study at CERN. From the available information the beam will run in a 100 km ring collider inside a beam screen of 20 mm diameter operating in the temperature range 40-60K. The beam screen will be exposed to magnetic fields up to 20 T and support an average current of 1A (with peaks up to 25A ) with a frequency spectrum from DC to about 1.5GHz. The beam could be realized in copper-coated (~80µm) stainless steel as in LHC, however at the foreseen operating temperatures the overall beam impedance would be too high, posing severe problems on the overall accelerator design. A possible solution considered at CERN is to reduce the impedance by internally coating the internal copper beam screen surface by a thin film of High Temperature Superconductor (HTS). In the present lecture the theory of the superconductor surface resistance in the presence of high magnetic fields is reviewed, and new results are presented in the frequency regime below the so called “depinning frequency” The effective possible advantages of the HTS proposed solution over simple Cu coating are finally discussed.