MULTILAYERS C Antoine Irfu SACLAY CEADSMIrfuSACMLesar Claire Antoine

MULTILAYERS C. Antoine, Irfu, SACLAY) CEA/DSM/Irfu/SACM/Lesar Claire Antoine – 2011 - 12 - TTC Meeting Beijing 1

SRF limitations in (brief) summary Superheating field vs Vortex nucleation Nb~ 55 MV/m Nb 3 Sn ~ 95 MV/m Nb<50 MV/m + magn. screening Calculation for the superheating model valid only near TC “perfect material” (no surface defects) In real life : penetration of vortex faster @ low temperature (why? ) early penetration of vortex possible @ surface defects Nb : the best because of its high HC 1 ? Either we are able to produce 0 defect surfaces, either we screen the surface with multilayers ! More theoretical and exp. work needed CEA/DSM/Irfu/SACM/Lesar Claire Antoine – 2011 - 12 - TTC Meeting Beijing 2

Local magnetometry (1) 3 rd harmonic measurement, local measurement : sample size >> excitation/measuring coil b 0 cos (wt) applied in the coil temperature ramp third harmonic signal appears @ BC 1 Differential Locking Amplifier Excitation/Detection coil (small/sample) increasing I = increasing B TCi at Bi = T/Tc Sample SL : third harmonic signal for various b 0 CEA/DSM/Irfu/SACM/Lesar Claire Antoine – 2011 - 12 - TTC Meeting Beijing 4

B (m. T) T (K) CEA/DSM/Irfu/SACM/Lesar Claire Antoine – 2011 - 12 - TTC Meeting Beijing

Local magnetometry (3) 60 ML 4 SL 50 Nb Ref Field (m. T) 40 30 20 10 0 0 5 10 T 15 20 ML sample : 250 nm Nb + (14 nm Mg. O + 25 nm Nb. N) x 4 NEW ! Multilayer tested for the first time BC 1 > 55 m. T @ 8 K ! CEA/DSM/Irfu/SACM/Lesar Claire Antoine – 2011 - 12 - TTC Meeting Beijing 6

Participation to Eucard 2 WP 11. 2: Thin Film Niobium on copper (µm) (CERN) After ~ 20 years stagnation : new revolutionary deposition techniques (e. g. HPIMS) Great expectations in cost reduction No improved performances/ bulk Nb k tas b Su 2 Higher Tc material (µm) (CERN) Based on superheating model. Higher field and lower Q 0 expected Superheating model questionable @ 2 K, type II SC Higher Tc material (nm), multilayer (CEA+ INPG) Based on trapped vortices model (Gurevich) Higher field and lower Q 0 expected Recent experimental evidences Specific characterization tools needed Local magnetometry (CEA) Sample cavity (HZB) Better understanding of SRF physics needed CEA/DSM/Irfu/SACM/Lesar Claire Antoine – 2011 - 12 - TTC Meeting Beijing Subtask 3 k tas b Su 4 k tas b Su 1 8