Superconducting Magnets and Materials: Superconducting Materials for RF Applications Lance Cooley – Head, SRF Materials Group Fermilab General Accelerator Development Review January 24-26, 2011

History and Scope Over the past ~7 years, Technical Division has built up expertise in SRF materials to support cavity development, primarily for ILC  Materials science of niobium  QA/QC, diagnostics, and specifications (sheets)  Small-scale acid processing (3.9 GHz, coupons)  University collaborations, other interactions (e.g. TTC) Vendor and process qualification added emphasis on single-cell activities  Single-cell cavities are analog to wire “short samples”  ICPA conceived in 2007 for in-house processing R&D  Mechanical polishing also conceived ~2007  Cavity-level diagnostics and repairs Lance Cooley, Fermilab – General Accelerator Development Review January 24-26, 20112

Present Goals and Approaches Support Project Needs and Improve Gereric SRF Understanding Materials – Coupons and Cut-outs  Understand the best niobium surface for Q 0, E Acc  Study how processing changes the surface  Understand how changes affect SRF properties  Seek better fabrication and processing approaches ICPA & Mechanical Polishing – Cavities  Extend materials understanding to practical implementation using single-cell cavities  Sized to accommodate 9-cell 1.3 GHz cavity  Conduct processing R&D and process validation  Rapidly evaluate new ideas by real cavity tests  Pilot scale aids transfer of ideas to projects & industry Lance Cooley, Fermilab – General Accelerator Development Review January 24-26, 20113

Accomplishments (FY09-10) – Materials Techniques [1] to replicate cavity topography Repair of large pits by laser melting [2] New model [3] indicated equal contribution of roughness and contamination to Q-slope at high E Raman spectroscopy of EP solutions gave new insights about fluorine activity [4] Auto-focus and automated acquisition of optical inspection images was developed [5] Lance Cooley, Fermilab – General Accelerator Development Review January 24-26, * * * * Transferred to ILC 9-cell activities 1 – M. Ge (IHEP post doc) et al., SuST – M. Ge, G. Wu, et al. Proc. SRF – A Dzyuba (Ph.D student) et al., SuST – C Thompson (chemist) with Perkin-Elmer 5 – E Toropov (Ph.D. student) and D. Sergatskov

Accomplishments - Materials New coupon EP tool Cold work was shown to promote weld pitting  Welds should be stress-relieved  Cells should be annealed before EP EP also breaks down in meniscus regions  Avoid reduction of EP solution viscosity, keep T < 40 °C Lance Cooley, Fermilab – General Accelerator Development Review January 24-26, Full SRF Materials Group result, Published in LD Cooley et al., IEEE Trans ASC 2011 Rolled Nb from W Starch, FSUWelding J Rathke, AES

Present model of the Nb surface Up to 40% hydrogen is at Nb surface after BCP or EP [1]  Acid polishing loads Nb with H   ’ must be present, besides  H clusters (  ’) are favored at dislocations [2] & vacancies [3]  Clusters lead to lossy  phase, origin of “Q sickness” & Q slope High-temp. anneal “resets” Nb Final bake mobilizes  ’, but comes with oxygen penalty [4] Lance Cooley, Fermilab – General Accelerator Development Review January 24-26, °C VacClean Nb Light EP / BCP  ’’ 120°C Vac  0.2% Oxy This surface is > 35 MV/m ! Heavy EP / BCP  ’’ [1] Romanenko (Peoples Fellow) He atom recoil spectroscopy with U.Mich. & W.Ontario, also Ricker Myneni J.Res.NIST 2010 [2] Romanenko Ph.D. Thesis – Cornell, SEM + EBSD, and Visentin et al, e+ / e- annihilation, SRF2009 [3] D. Ford (NWU Ph.D. student) DFT + VASP at Fermilab [4] Casalbuoni et al, Nuc.Inst.Meth.PR-A 538, 45 (2005) 90°C 160°C -70°C  ′′ 

Integrated Cavity Processing Apparatus and Mechanical Polishing Mech. Polish Chemical Polish (EP) HPR water plant Class 10 With HPR tool 1000°C Vac. Furnace Complete infrastructure to process 1.3 GHz 1-cell (and 9-cell) R&D cavities from receipt to test! Lance Cooley, Fermilab – General Accelerator Development Review January 24-26, Many FNAL divisions and sections contributed to the success of this project

ICPA Project Management Lance Cooley, Fermilab – General Accelerator Development Review January 24-26, Three Main Stages (Lance Cooley Manager, Charlie Cooper Engineer)  Infrastructure Upgrade (Gary Lorenz – Task manager)  Installation of Equipment (Main Technicians – Dan Assell, Todd Thode)  System Integration & Operational Readiness Preparation

ICPA Project Management (cont.) Lance Cooley, Fermilab – General Accelerator Development Review January 24-26, Microsoft Office Controls Project Timeline

Accomplishments - ICPA Lance Cooley, Fermilab – General Accelerator Development Review January 24-26, Constr. & assembly completed FY10 HPR tool operations 12/10/2010 EP tool in ORC process Jan 2011  Expect shake-down operations March 2011  Expect first acid process May 2011 C Cooper TD Instrum. & Ctrl. Grp. TD Cavity Processing Grp.

Accomplishments – Mechanical Polishing Order-of-magnitude improvement in surface finish over EP – This is a transformational alternative! 40 MV/m in single cell, 9-cell repaired to R a = 14 nm R a ~ 100 nm R a ~ 3,000 nm Lance Cooley, Fermilab – General Accelerator Development Review January 24-26, C Cooper et al.

Planned Work - Coupon Cavity 1.3 GHz cavity fitted with integrated coupon ports can be placed directly into processing tools  Allows material to be studied at any processing stage  First two will be delivered ~March Lance Cooley, Fermilab – General Accelerator Development Review January 24-26, 2011

Planned Work FY11-FY13 - Materials Identify how hydrogen, hydrides, oxygen, and niobium defects interact at each processing step  Simulated processes on coupons + real processing for cavity cut-outs and coupon cavity  Electron microscopy, He recoil, µ-SR (with collaborators)  Computational modeling plus property measurements Expand understanding of the roles played by dislocations and cold work  Repeat Casalbuoni experiments* on CW Nb rod  B c3 measurements to estimate  just under surface  Dislocations should accelerate changes Support collaborations and fundamental studies  FNAL is a main supplier of coupons to others Lance Cooley, Fermilab – General Accelerator Development Review January 24-26, *Casalbuoni Nuc. Inst. Meth. PR-A 538, 45 (2005)

Planned Work FY11-FY13 - ICPA FY11: start chemical operations, qualify with 4-6 single cell cavities using standard parameters FY12 – EP process R&D:  Add water cooling, study cooled EP  Water cooling permits temperature control to be decoupled from flow rate of electrolyte  EP solution is pumped at ~10 L / min now!  Annealed single-cell cavities – 10 delivered FY2011  Expect annealed state to improve EP results  Investigate spectroscopy of fluorine ion, HFSO 3  Consider buffered EP, titrating fluorine dose FY12-13: Also qualify cavity vendors, supply single-cells with benchmark EP for other R&D  FNAL is a main supplier of cavities to others Lance Cooley, Fermilab – General Accelerator Development Review January 24-26,

Planned Work – Mechanical Polishing FY11 – FY12:  Optimize final polishing route for elliptical cavities – Can cavity processing become acid-free?  Improve media / slurry combinations  Incorporate cooling with process  Transfer to “production” projects, e.g. ILC  Correlate R a with Q(E) and BCS resistance  Lack of correlation clarifies role(s) of contamination FY12 – FY13:  Explore mech. polishing of ~2 low-loss / re-entrant cavs.  Is mechanical polishing a routine processing route for ~60 MV/m niobium cavities?  Prepare cavities for thin films (LBNL) and coatings (ANL)  Consider design changes for other frequencies Lance Cooley, Fermilab – General Accelerator Development Review January 24-26,

Long Range Plans Apply materials science to eliminate Q losses in ~ 5 years  Example: Prevent H and O uptake  Anneal (ultrasonic annealing?)  Mechanical polish with high pH  Bake at 800 °C (is this needed?)  Vacuum-process interior (e.g. plasma)  Cap interior (e.g. ALD)  HPR & assemble (is HPR needed?)  No 120°C bake?  Do this on 60 MV/m re-entrant cavity! Explore films and tailored coatings  Mechanical polish is ideal starting point  In ~5 years: Nb on Cu, multilayers, Nb 3 Sn Lance Cooley, Fermilab – General Accelerator Development Review January 24-26, Clean Nb Clean, protected Nb At BCS limit for Q? CP Nb Cu

Connections to Other Programs Materials R&D for ILC R&D program, Project X Collaborations with ANL, U Ill.- Chi., U Chicago, Northwestern, IIT, NHMFL / Fla. St., West Va. U, TRIUMF, Michigan, Mich. St., Western Ontario  Strong interaction with SRF University collaboration Interactions with raw materials suppliers, cavity vendors, processing vendors, and diagnostics / scientific tool companies (too many to list…) Lance Cooley, Fermilab – General Accelerator Development Review January 24-26, publications conference plenary presentation Invited talks at PACs, SRF, ASC Focus areas of TTC EP tool design won Siemens 2011 Design Award for 3-D Engineering Publications, Presentations, & Awards

Personnel and Budget Scientific  Cooley, Cooper, Romanenko (Peoples Fellow), Sergatskov, Wu (to ANL), Ge (Postdoc, now at Cornell)  5 Ph.D. students supported together with Accel. Phys. Ph.D. program Technical  5 FTE technician / engineer Lance Cooley, Fermilab – General Accelerator Development Review January 24-26, FY11: GAD: 5.8 FTE SWF ILC and other: 4.0 FTE SWF

Answering the GAD Charge High-quality, high-impact work  Transformational approaches  Basic understanding that underpins design and engineering of future HEP machines New tools, including mechanical and chemical processing apparati, and growth of expertise make proposed work exciting! Management coordinates project needs with fundamental research  Interactions with ILC, PX require engineering deliverables that make R&D relevant to end use  Interactions with university collaborations are of mutual benefit and bring in resources not otherwise available to Fermilab or GAD Lance Cooley, Fermilab – General Accelerator Development Review January 24-26,