1. Thin Films for Superconducting Cavities HZB

2. Outline Introduction to Superconducting Cavities The Quadrupole Resonator Commissioning Outlook 2

3. Basics of RF Cavities Acceleration of charged particles using a radio frequency field There are normal conducting and superconducting (sc) cavities Q nc ≈ 10 5 vs. Q sc ≈ 10 10 The needed power for operation is about a factor of 200 less than for superconducting cavities 3

4. Materials for sc Cavities Niobium (from sheet) – Critical temperature T c = 9.2K – Accelerating gradients reaching the theoretical limit (≈45MV/m) due to improved treatment techniques – Expensive Niobium on copper – 1-2μm niobium on copper cavity – Less need of niobium – Accelerating gradients up to 10MV/m 4

5. Where can we improve? 5 Understanding the dominant loss mechanisms in niobium Reducing losses Improving the performance of niobium films Reducing material costs Finding new materials ? ?

6. How can we improve? Power consumption in a superconducting cavity is proportional to its surface resistance R S R S shows a complex behavior on external parameters, such as temperature, frequency, magnetic and electric field 6 Systematic studies on cavities are no option

7. The Quadrupole Resonator 7 361 mm The Quadrupole Resonator enables RF characterization of small, flat samples over a wide parameter range Samples of 75mm diameter are welded to a niobium cylinder with flange so that they can be mounted to the host cavity

8. Field Configuration & Features Resonant frequencies: 400MHz, 800MHz, 1.2 GHz Almost identical magnetic field configuration Ratio between peak magnetic and electric field proportional to frequency B׀׀B׀׀ 0 max 50 mm 1 E. Mahner et al. Rev. Sci. Instrum., Vol. 74, No. 7, July 2003 2 T. Junginger et. al Rev. Sci. Instrum., Vol. 83, No. 6, June 2012 8

9. DC Heater Quadrupole Resonator Thermometry Chamber Heat Flow The Calorimetric Technique Measuring the temperature on the sample surface Precise Calorimetric measurements over wide temperature range Temperature Sensors Temperature Sensors Sample Surface 9

10. time Temperature Bath Temperature of Interest P DC,1 P DC,2 P RF Power DC onRF on ≈60 s≈40 s Temperature Sensors Temperature Sensors DC Heater Heat Flow The Calorimetric Technique Measured directly Measurement of transmitted power P t P t =c∫H 2 ds, c from computer code Measurement of transmitted power P t P t =c∫H 2 ds, c from computer code 10

11. Imperfect Meissner Effect Meissner effect Trapped magnetic flux 11

12. Flux Trapping in the Quadrupole Resonator Sample DC Coil 12

13. Flux Trapping in the Quadrupole Resonator DC Coil 13

14. First test with trapped flux 14

15. R S (B) at 400MHz, 2-4K 15

16. Trapped Flux at 400MHz and 4K 16

17. Outlook MgB 2 from Superconductor Technologies, Inc. – T c = 39K, B c up to 1T – expected: E acc > 75MV/m, R BCS (4K,500MHz) = 2.5nΩ HiPIMS: Nb/Cu from CERN and Berkeley – Dense film, low cost, but competitive to bulk Nb? ECR: Nb/Cu from Jlab – High RRR, low cost, but competitive to bulk Nb? 17

19. Recent Cavity Projects European XFEL: – 800 9-cell cavities, E acc = 24MV/m ESS: – 170 5-cell cavities, 15-18MV/m ILC: – 16900 9-cell cavities, 35MV/m LHeC ERL: – 944 5-cell cavities, 20MV/m Plenty of other projects with more than 1000 cavities and gradients between 5 and 25MV/m 19