SC cavity design and manufacturing

1. SC cavity design and manufacturing Material studies for SPL cavities at CERN Niobium raw material procurement ARNAU IZQUIERDO, Gonzalo

2. Intro • Niobium for superconducting cavities • Production of high RRR niobium • Niobium raw material procurement for SPL beta=1 cavities • Shapes and Quantities • Material specification • Order follow up and QC • Inspection and follow up at CERN • Alternative suppliers • Material studies of assemblies  see next presentation G. Arnau Izquierdo EN/MME

3. Intro • Use of Nb for superconducting cavities • High transition temperature Tc = 9,3 K and critical magnetic field Hc = 200 mT • Available in industrial shapes • Can be easily formed and machined, can be welded • Need of high purity ( high RRR) niobium • Reduce defects and impurities acting as normal conductive clusters • High thermal conductivity to keep T< Tc around normal conductive clusters and avoid propagation of normal conductive state (quench)  thermal stability • Impurities and lattice defects act as scatter centres that reduce both thermal and electrical conductivity at low temperature. • Measuring the RRR is a practical way to evaluate purity and low temperature thermal conductivity of a material K (W/mK) F.Koechlin, and B.Bonin G. Arnau Izquierdo EN/MME

4. Intro • Production of high RRR niobium • Main impurity from the ore is Ta • Main impurities reducing RRR are interstitial elements O, N, C and H. • Key points: • Refining by several electron beam remeltings under high vacuum. • Clean handling during forge, hot and cold rolling. • Final annealing 1-2 h at 700-800 °C in good vacuum. R. Grill et al. Plansee-Heraeus G. Arnau Izquierdo EN/MME

5. Shapes and quantities • Price Inquiry (restricted by FI to member states) • Plansee /AT with Heraeus /DE as supplier for ingots and subcontractor for smaller tubes G. Arnau Izquierdo EN/MME

6. Material Specification. Antecedents • Antecedents • DESY (W. Singer, D. Proch) • Technical Specification for Niobium Applied for the Fabrication of 1.3 GHz Superconducting cavities RRR 300 • FERMILAB (P. Bauer, C. Antoine) • Technical Specification for High RRR Grade Niobium Sheet and Rod for use in Superconducting Cavities • International standards • No EN standards for niobium • SAE AMS7850, Columbium Sheet, Strip, Plate and Foil • ASTM, Standard Specification for Niobium and Niobium Alloy ... • B391-09 ... Ingots • B392-09 ... Bar, Rod, and Wire • B393-09 ... Strip, Shit, and Plate The only standard dealing with a high RRR grade G. Arnau Izquierdo EN/MME

7. Material Specification. ASTM B393-09 • ASTM B393-09 • The only standard dealing with a high RRR grade • UNS R04220, Type 5 G. Arnau Izquierdo EN/MME

8. Material Specification. ASTM B393-09 G. Arnau Izquierdo EN/MME

9. Material Specification. CERN Tech. Specs. • Two Material Technical Specifications for RRR>300 and RRR>40 issued for the Price Inquiry • General characteristics • Chemical composition • Microstructure • Mechanical properties • Electrical properties • Surface defects • Bulk defects • Manufacturing process • Dimensions and tolerances • Quality control • Packing G. Arnau Izquierdo EN/MME

10. Order follow up and QC • Quality Control program defined in hte specification • A batch is defined as parts from the same melt, having followed the same forging and rolling and that have been annealed in the same charge G. Arnau Izquierdo EN/MME

11. Order follow up and QC • Order placed to Plansee /AT (procurement of ingots and production of smaller tubes subcontracted to Heraeus /DE) • Delivery schedule announced in the bid: 16–18 weeks (subject to prior sales!) • Order placed Aug 2010 • Order confirmation Dec 2010 • First sheets received Oct 2011 • Last item received next week hopefully... • Five visits • Discussion of CERN results on qualification samples • Pushing up in view of continuous delays • Ensuring strict respect of QC program and traceability • Various reasons given along the + 1 year for the cumulating delays G. Arnau Izquierdo EN/MME

12. Order follow up and QC • Chemical composition • Effect on electrical and thermal conductivity. Most sensitive is RRR measurement • Specified: • Analysis of interstitials on final product because of risk of pick up during process • Obtained: OK G. Arnau Izquierdo EN/MME

13. Order follow up and QC Cross-secton of qualification samples. • Microstructure • Homogeneous and fine, to avoid heterogeneous behaviour on forming (ie. orange peel on deep drawing, not so critical for spinning) • Very high purity makes difficult to master the cast grain size because of few nucleation sites • Specified • Completely recrystallized • Homogeneous grain size G  6 (45 µm), locally G  4 (90 µm) • Obtained Not fully recrystalized. Regions of coarse grains QC on sheets delivered. Worst cases found by the firm and by CERN: G. Arnau Izquierdo EN/MME

14. Order follow up and QC • Mechanical properties • Annealed product is required for forming. • Specified • Max of hardness • Band of yield strength (Rp0,2) • Min of ultimate strength (Rm) • Min of ductility (A) • Obtained Rm Rp0,2 A G. Arnau Izquierdo EN/MME

15. Order follow up and QC • Electrical properties • High RRR is (indirectly) required for cavity performance • Specified • RRR  300 @ 4.2 K • Obtained • 297 – 396 @ 4.2 K (estimated from measurements @ 9.3 K) • RRR check at CERN • Cryostat four point setup of TE/MCS. Measure just above Tc (9.3 to 10 K) • Samples 2x2x100 mm3, etched in a mixture of HF, HNO3 and H3PO4, kept below 15 °C to limit H2 pick up. Samples in the holder for chemical etching and etched Sample holder of the RRR measurement setup at CERN/TE/MSC G. Arnau Izquierdo EN/MME

16. Inspection and follow up at CERN • Square sheets • Visual inspection, marking, cutting of two corners for witness and sampling • Tests in progress • Microstructure • Hardness • Tensile • RRR • Roughness • Anodising as a means of assisting visual inspection was tried and abandoned. Not easy, added handling is risky and no obvious enhancement of the surface inclusions. • Tubes • Dimensional control  deviations • Roughness Anodising tests with different conditions on samples with metallic particlesembedded . Square sheet anodised G. Arnau Izquierdo EN/MME

17. Alternative suppliers • Alternative producers • Wah Chang /US • Tokyo Denkai /JP • Ningxia Group /CN, represented in Europe by Elite Material Solution /UK • Most propose only sheets • Prices are similar • A qualification sample from Ningxia has been tested satisfactory • RRR, microstructure, hardness, tensile test (on small specimen) G. Arnau Izquierdo EN/MME

18. Conclusions • All shapes and quantities required will be procured with satisfactory quality • Most firms have made the effort of qualifying for previous and ongoing Nb SC projects and are now mature for sheet production • Seamless tubes required specific development not completely mastered for tight tolerances • Keeping the schedule is a concern, at least with a relatively small order, not standard dimensions and a producer for which Nb is a very minor share of activity • Grain size G 6 is tight for sheets of 3.6 mm • RRR measurement is not a widespread in house technique amongst Nb producers • Anodising for visual inspection do not seems to be advantageous for as received sheet G. Arnau Izquierdo EN/MME