Proposals for impedance measurements at CERN

2. Proposals for impedance measurements at CERN Sergio Calatroni, Sergey Arsenyev, Daniel Schulte Sergio Calatroni

3. The context Sergio Calatroni • Innovative surface treatments are being studied such as : • a-C coatings • LESS • HTS • Innovative vacuum components are in development such as: • Novel RF fingers design • New joining techniques for vacuum chambers • These are relevant both for the HL-LHC project and the FCC study • CERN lacks at present a facility for characterizing impedance of real vacuum components at low temperature

4. The scope Sergio Calatroni • Sergey has already discussed available results and possible interpretations on LESS • We need to move some steps ahead: • Impedance measurements as a function of temperature 300 K <-> 4.2 K (1.9 K) • In presence of a multi-T magnetic field • In a frequency range of interest for beam impedance (MHz <-> GHz for resistive wall & TMCI. TCBI is sensitive to KHz and probably not affected by LESS – and HTS should be good enough at low frequency) • On real components (ie tube-like as a beam screen)

5. Multi-T field Sergio Calatroni LHC: 8.66 T HL-LHC: 11 T FCC: 16 T FRESCA: a facility in TE-MSC generating a 11T dipole field in a 88 mm free bore

6. FRESCA Contacts: Daniel Schoerling, Jerome Fleiter, Amalia Ballarino Sergio Calatroni

7. Frequency range Test surface Sergio Calatroni MHz <-> GHz range needs RF Baseline proposal: two-rods, which excite two different TEM modes with different field configuration

8. From Sergey An absolute measurement precision of a few % was achieved in the past (F. Caspers, M. Morvillo and F. Ruggiero - LHC Project Report 115, 1997) with this technique when measuring Rs of copper at cryogenic temperatures. It is of extreme importance to attain such and better accuracies in the case we want to measure HTS coatings Sergio Calatroni

9. Possible variant (Fritz) Sergio Calatroni Work as a dielectric loaded waveguide, with end couplings only 40 mm diameter -> 0 = 4.39 GHz cutoff for circular waveguide. Sapphire loading =10 ->  0 /3 Better dielectrics could be found, with higher  and still very low tan 

10. Possible implementation in FRESCA Sergio Calatroni

11. Staged work Sergio Calatroni We focus on exploiting existing large scale infrastructure thus minimizing cost. It is agreed with the Cryolab (Johannes Bremer) that the RF configuration will be studiedon an existing cryostat in order to finalize the design of the system

12. Next stage(s) Sergio Calatroni Based on this evaluation, and partly in parallel with it, an anti-cryostat has to be designed and manufactured, adapted to the FRESCA facility. This will ultimately allow for example characterization of realistic beam screens segments up to ~500 mmlong Temperature range 300 K <-> 4.2 K (1.9 K) will be inherently built-in Prospective to make use of the FRESCA2 test stand as well: 13 T (15 T), 100 mm bore, 1.5 m long Possible developments: multipacting measurement at cold, B-field quality measurement due to persistent currents in HTS

13. Final note Sergio Calatroni • Impedance test system for real-size vacuum components, following needs of HL-LHC and FCC • Based on large existing infrastructure, still sizable investment are needed (anti-cryostat, RF test infrastructure) • Complementaritywith ALBA-ICMAB should be fostered • @CERN: • Sergio & Daniel: coordination • TE-VSC: owner of the device • Sergey: RF simulation and measurements • TE-VSC Fellow: cryostat integration, RF measurements • TE-MSC: Cryolab + FRESCA • BE-RF: Support for design & simulation, test • BE-ABP: Support for simulation & studies • EN-MME: support for design & manufacturing