ANL Proposal to Perform Electropolishing for the ILC 6/24/2018 ANL Proposal to Perform Electropolishing for the ILC Speaker: Mike Kelly December 5-7, 2005 Test

Joint ANL/FNAL Cavity Processing Facility

Electropolishing at Argonne Argonne has electropolished ~150 SC niobium cavities Cavity performance at ANL using EP is directly relevant to ILC Experience with various geometries is directly applicable to ILC Major infrastructure for EP of large SC cavities is in place

Cavity Processing at ANL Cavity Performance Outline Cavity Processing at ANL Cavity Performance An ANL Proposal for the ILC Technical Issues with 9-cell EP

I. Cavity Processing: High Performance SC Structures for RIA 6/24/2018 I. Cavity Processing: High Performance SC Structures for RIA 345 MHz =0.40 Double-spoke 115 MHz =0.15 Steering-Corrected QWR 172.5 MHz =0.26 HWR 345 MHz =0.62 Triple-spoke 57.5 MHz QWR-based structures 0.03<  <0.14 Recent work focused on set of drift-tube cavities for RIA Quarter-, half-, multispoke cavities. Similar to elliptical cell structures- large cavities, high RRR niobium, geometry optimized in 3D to minimize B field Large extended region of high magnetic field We are used to thinking about processing of new shapes 345 MHz =0.5 Triple-spoke 1 m Test

I. Cavity Processing: High-Pressure Water Rinsing 6/24/2018 I. Cavity Processing: High-Pressure Water Rinsing Horizontal HPR Development Manual HPR Full cavity processing capability In close touch with developments at DESY, KEK and JLab Optimize flow patterns for relatively complicated spoke geometry Automated HPR: RIA Triple-Spoke Automated HPR: RIA Half-wave Test

I. Cavity Processing: Clean Room Assembly Goal: Minimize or eliminate field emission from particulates using a simple, practical and effective curtained clean area Coupler & pumping lines mounted in class 100 (or better) area Simplicity is crucial; cavity connections ideally made in seconds Work performed below & downstream from open cavity Hardware must be compatible with clean conditions Half-wave for RIA

Cavity Processing: Clean room assembly

I. Cavity Processing: ANL Recipe for EP with TEM Cavities Electropolishing has been a mainstay at ANL Based on the Siemens process Cavity (anode) - observed no polishing rate sensitivity to electrical connection point even for large cavities High purity Al cathode (3003 series) tailored to the cavity Acid composition 85:10 mixture of 96% H2SO4, 40% HF, reagent grade Temperature 28-32o C (chilled water through the cathode) Average anode current density ~40 mA/cm2, acid replaced when value drops below 30 mA/cm2

I. Cavity Processing: Niobium Geometries Electropolished at ANL 6/24/2018 I. Cavity Processing: Niobium Geometries Electropolished at ANL Quarter-wave We believe that electropolishing is a key step in our fabrication process. Smaller parts use same technique as for elliptical cavity half cells Long center conductors are rotated in the electrolyte bath with the aluminum cathode around outside Most challenging spoke geometry – large surface area housing – critical spoke region required good polishing with no stagnant areas in the electrolyte Devised a washing machine action together with a set of impellers – dealt with issue of moving electrical connections Co-axial half-wave Important EP Technical Issues: Temperature gradients and stability Acid flow patterns Double spoke Test

I. Cavity Processing: ANL b=0.63 Triple-Spoke Cavity, Area ~1.5 m2

I. Cavity Processing: High RRR & Hydrogen Q-disease Test #2 after 48 h @ 110-140 K Issue: Hydrogen is introduced during fabrication Has been shown that in high RRR cavities hydrides form preferentially at surface, grain boundaries, lattice imperfections Data clearly indicate the presence of hydrogen Q-disease

I. Cavity Processing: Hydrogen Degassing FY06 program to bake out all high RRR cavities for RIA 600 oC bake for 10 hours to degas hydrogen has been performed 10 mm chemical polish, high-pressure rinse, clean assembly (Furnace is also suitable for 9-cell cavities)

II. Cavity Performance: Beta=0.63 Multi-Spoke Cavities 6/24/2018 II. Cavity Performance: Beta=0.63 Multi-Spoke Cavities Q-disease was observed; hydrogen degassing at 600 oC was performed at ANL 2 K surface resistance decreased substantially after 600 0C bake. No X-rays T = 4.2 K (unchanged after bake) Test results for the three multi-spoke cavities developed for RIA are shown here. The two spoke cavity results shown here at the left easily exceed the initial RIA design goal. Recent tests of the beta=0.5 and beta=0.63 triple spoke resonators at 4.2 K shown here in red also exceed the RIA design goal even though the development is not yet complete. In particular, the first time we looked for hydrogen Q-disease in one of the cavities by hold in the hydride formation temperature region we strong effect with the beta=0.63 cavity. Performance may yet increase after hydrogen degassing which will be performed. Test

II. Cavity Performance: Residual Surface Resistance vs. BPEAK 6/24/2018 II. Cavity Performance: Residual Surface Resistance vs. BPEAK (Best b=0.61 Cavity) Residual RF Surface Resistance (Ohms) Lower is better Test results for the three multi-spoke cavities developed for RIA are shown here. The two spoke cavity results shown here at the left easily exceed the initial RIA design goal. Recent tests of the beta=0.5 and beta=0.63 triple spoke resonators at 4.2 K shown here in red also exceed the RIA design goal even though the development is not yet complete. In particular, the first time we looked for hydrogen Q-disease in one of the cavities by hold in the hydride formation temperature region we strong effect with the beta=0.63 cavity. Performance may yet increase after hydrogen degassing which will be performed. Peak Surface Magnetic Field (Gauss) Test

III. An ANL Proposal for the ILC: Electropolishing Motivation It has been generally agreed that a U.S.-based technical capability to build, process and operate high-performance 9-cell elliptical cavities is required for the proposed International Linear Collider Proposal To leverage the existing infrastructure and expertise at Argonne to build a complete electropolish apparatus for ILC-type 9-cell elliptical cavities and perform electropolishing on 9-cell cavities Deliverables FY06: An operational electropolishing facility for ILC 9-cell cavities Resources Required FY06: 1.5 FTE (0.75 Scientist, 0.75 Designer/Technician); $135K M&S

III. An ANL Proposal for the ILC: Electropolishing FY07 Activities Electropolish cavities obtained through the ILC collaboration Study technical issues and optimize operating parameters Document procedures and train personnel Near term plan Generate at ANL together with Tajima (LANL) a technical plan and drawings (2 months) Take this plan out for design review by technical experts at Fermilab, JLab, KEK and DESY Fabricate and test the apparatus using a test cavity obtained though ILC collaboration Pre-rinse possibly at ANL, seal cavities in the joint clean room facility. Final HPR at Fermilab

III. An ANL Proposal for the ILC: Capability at Argonne Comprehensive chemical processing capability suitable for several cavities per week Primary infrastructure: A pair of large chemistry rooms A large air scrubber Three clean room areas for post-processing (high-pressure rinsing) A large volume de-ionized water system Procedures for procurement, storage, handling, disposal Hardware: power supplies, acid pumps, water chiller

III. An ANL Proposal for the ILC: Resources for ILC EP 60 feet EP Power Supplies 10 kW Chiller 32 l/m DI Water

III. An ANL Proposal for the ILC: A “Closed Loop” EP Flow Diagram AIR/ N2 INTAKE

III. An ANL Proposal for the ILC: A 9-cell Cavity in the ANL Chemistry Room 16 feet Floor Plan 16 feet Side View

IV. Technical Issues: Horizontal and Vertical Polishing Direct ANL experience indicates the following issues are important: Orientation of the niobium surface: Horizontal downward facing Nb surfaces polish faster than horizontal upward facing surfaces. Hydrogen bubbles: Streaming from the cathode can cause grooves, streaks in the cavity. Increasing bubble density raises resistivity of the electrolyte bath Uneven polishing: Differential polishing in elliptical cavities is not a cathode proximity effect; however is likely due to flow rate/temperature effects

IV. Technical Issues: Orientation of the Niobium Surface Horizontal-downward facing surfaces polish faster than horizontal upward surfaces Uneven polishing will be difficult to avoid in with a 9-cell cavity oriented vertically Polishing Rate at 3 Different Points on a Cavity Cavity flipped after every 50 cycles Surface facing down Surface facing up

IV. Technical Issues: Differential Iris/Equator Polishing Cathode Distance vs. Bath Potential Relevant niobium EP information contained in the literature Hydrogen bubbles shown to lead to an increase in the electrolyte resistivity Reference: Diepers et al, Research Laboratories of Siemens (1971) Data implies that the cathode distance is not critical Horizontal elliptical cavities should polish uniformly, however not so in practice

IV. Technical Issues: Differential Iris/Equator Polishing Test: Cathode distance vs. polishing rate Impeller Anode Cathode Anode – 12”x7/8”x1/8” RRR=250 Nb (Wah Chang) Cathode – 3 Turns 3/8” 3003 Series Aluminum Anode/Cathode voltage = 16 V Temperature = 28-30 oC Time = 1 hour, continuous Acid flow rate ~ 1 cm/s at the cathode 13 inches

IV. Technical Issues: Differential Iris/Equator Polishing Cathode Distance vs. Polishing Rate Sample 1 EP removal rate mm/minute Sample 2 Distance to Cathode (cm) NO RATE DEPENDENCE ON CATHODE PROXIMITY NO MASKING OR COMPLITCATED SHAPES NEEDED FOR 1.3 GHz CAVITIES

IV. Technical Issues: The ANL Proposal Would Address… Uneven polishing 4 flow rate effect? 4 separate flow rate from temp. stability by direct (water) cooling of cavity The perceived need to polish without a He vessel Temperature stability 4 use high-purity Al heat exchanger coil rather than Teflon

Concluding Statement ANL is eager to contribute to the ILC collaboration in an area of strong technical expertise and capability at this laboratory, namely, electropolishing