SPS DOUBLEQUARTER WAVE CRAB CAVITIES DISCUSSION ON CAVITY

SPS DOUBLE-QUARTER WAVE CRAB CAVITIES DISCUSSION ON CAVITY PREPARATION PROCEDURES (REVIEWED) Silvia Verdú-Andrés, Toohig fellow at BNL on behalf of DQW crab cavity design team CERN, 11 November 2015

Cavity preparation - procedures • • Cavity assembly BCP & HPR High-T baking Tuning and RF measurements Silvia Verdú-Andrés, BNL | CERN, 28 October 2015 | Slide 2

Cavity assembly

Cavity assembly procedure (modified – bead pull before light BCP) BC-20 -QA BC-21 -QC BC-22 -QC BC-23 -QC BC-24 -QC BC-25 -QA BC-26 -QC BC-27 -QC BC-28 -QA BC-29 -QA BC-30 -QA BC-31 -QA BC-32 -QA BC-33 -QA BC-34 -QC BC-35 -QA BC-36 -QC BC-37 -QC BC-38 -QA BC-39 -QA BC-40 -QA BC-41 -QA BC-42 -QA BC-43 -QA BC-44 -QA BC-45 -QA BC-46 -QA BC-47 -QC BC-48 -QC BC-49 -QC BC-50 -QC Final EB weld of the cavity Visual examination Helium leak tightness test Radiographic examination Dimensional + thickness control Fabrication of fixture for cavity tuning Tuning with frequency check Dimensional control (Dimesnions for He vessel) and pre BCP thickness measurement Bead pull measurement Optical inspection Fabrication of stiffening frame for cavity chemistry and cold test Design and fab of BCP hardware (Teflon/HDPE flanges, o-rings, mounting fixture) Thickness measurement Bulk chemical polishing Visual examination Thickness measurement Resonator frequency check Bead pull measurement with FPC (dummy) and/or HOM couplers Heat treatment Light chemical polishing Thickness measurement Visual examination Procurement of Nb coated flanges, RF gaskets, bellows, tuning linkage, assembly hardware Fabrication of FPC and Pick. Up for vertical cold test Test probe calibration Manual HPR High pressure water rinse Cleanroom assembly Evacuation and helium leak test 120 C low temperature bake RF acceptance tests at cold temperature (without and with HOM couplers) Silvia Verdú-Andrés, BNL | CERN, 28 October 2015 | Slide 4

Cavity assembly procedure - to do • Upload latest version of document in EDMS

BCP and HPR

Cavity prototype Silvia Verdú-Andrés, BNL | CERN, 28 October 2015 | Slide 7

BCP & HPR at JLab facility • Discussions on progress; JLab was given the funds to perform BCP & HPR for CCs • BCP facility at Jlab uses cabinet • Inlet at the bottom • Outlet at the top BCP cabinet • Possibility to use rotating capabilities of EP facility to perform BCP • • avoid iterations cavity completely filled with acid avoid fumes interaction with freshly-polished, reactive Nb Silvia Verdú-Andrés, BNL | CERN, 28 October 2015 | Slide 8

BCP & HPR at JLab facility Bulk BCP CONFIGURATION (standard procedure) (about 150 mm removal) Silvia Verdú-Andrés, BNL | CERN, 28 October 2015 | Slide 9

BCP & HPR at JLab facility Light BCP CONFIGURATION (standard procedure) (about 30 mm removal) • If BCP is not made in rotating facility, Action define thickness removal at different heights of cavity • Wish: include at least 4 thickness gauges with active readout during BCP. Currently only 1 thickness gauge available. Silvia Verdú-Andrés, BNL | CERN, 28 October 2015 | Slide 10

Preferred location for thickness gauges during BCP at JLab If only one gauge available: (Wish) At least 4 gauges: (for monitoring on high freq sensitivity regions) • one on each inductive plate • one on each capacitive plate = thickness gauge Silvia Verdú-Andrés, BNL | CERN, 28 October 2015 | Slide 11

Thickness removal – task list Request filling rate Define average and maximum thickness removal for bulk and light BCP Perform simulations for different BCP configurations provide cavity model to T. Jones Define ancillary for BCP and HPR at Jlab: Frame for installation in HPR cabinet available from Jlab Rotating crane to allow required tilting for draining and drying Clean blank-off flanges to cap off ports after cleaning

BCP & HPR at JLab facility HPR CONFIGURATION Silvia Verdú-Andrés, BNL | CERN, 28 October 2015 | Slide 13

BCP & HPR at JLab facility DRAINING & DRYING CONFIGURATION Angle a is 10. 6 degrees tilting needed to avoid stagnation in high H-field region Silvia Verdú-Andrés, BNL | CERN, 28 October 2015 | Slide 14

High-T baking

High-T baking procedure “Universal” (very similar around facilities) Main points: • Cavity degreased and bagged; no stiffening frame to avoid contamination • Pump down until vacuum is 10 -6 mbar • T ~ 600°C for about 10 h; monitor RGA (max. 9 elements) • Let cavity cool down in furnace • Cavity is ready when RGA levels are below 3 x 10 -6 mbar • Temperature ramp rates up and down shall not exceed 75°C/hour • Furnace must be clean of any residue that might evaporate at this temperature and then adhere to the component surfaces. Requested CERN procedure for comparison purposes Write document Any ancillary? Silvia Verdú-Andrés, BNL | CERN, 28 October 2015 | Slide 16

Tuning

Tuning procedure Thanks to Kurt Artoos, Graeme Burt and Carlo Zanoni for reviewing the draft document Document contents: Explains how “warm” model was generated from ideal RF design accounting from frequency shifts of thermal contraction and chemistry Collects frequency sensitivity to manufacturing and assembly tolerances used to assess preparation of functional drawing (August 2014) Describes tuning mechanisms, sensitivity and range Provides tuning strategy, incl. trimming and goal frequency after final weld Lists steps where frequency shift is expected Define ancillary (for pre-tuning when He vessel is not assembled yet to cavity) Define coupler used for low RF power measurements for frequency checks If elastic deformation for pre-tuning, design for stiffening frame needed that fixes cavity plates. Frame can be used for cold tests of bare cavity. Silvia Verdú-Andrés, BNL | CERN, 28 October 2015 | Slide 18

Tuning procedure – frequency sensitivity to welds Weld B Weld A Weld D Weld C Type No. Df/weld [k. Hz] Df [k. Hz] A 2 70 140 B 2 99 198 C 2 23 46 D 4 70 280 664 Non-negligible; however, values here discussed represent the worst-case scenario: chemical polishing procedures will smooth down the weld sagging • Welding can lead to some shrinkage of the sheets effect not accounted in this study • Must be taken into account in the tuning strategy and compensated before the last weld of the cavity assembly or during pre-tuning • Option: grind the welds before any chemical surface treatment to reduce the sagging but grinding can introduce residues • Note that grinding will only be possible for all welds but the last one (weld A). Question are all welds performed from the outside? • Silvia Verdú-Andrés, BNL | CERN, 28 October 2015 | Slide 19

Tuning procedure – frequency shifts * Frequency shift due to BCP is computed assumed uniform thickness removal for all cavity surface… not realistic! Silvia Verdú-Andrés, BNL | CERN, 28 October 2015 | Slide 20

Tuning procedure – goal frequency Silvia Verdú-Andrés, BNL | CERN, 28 October 2015 | Slide 21

Tuning procedure – tuning mechanisms, sensitivity and range Trimming 2. 4 MHz/mm when reducing the length of extra material in only one of the bowls Silvia Verdú-Andrés, BNL | CERN, 28 October 2015 | Slide 22

Tuning procedure – tuning mechanisms, sensitivity and range 1. 24 Silvia Verdú-Andrés, BNL | CERN, 28 October 2015 | Slide 23

Tuning procedure – frequency sensitivity to welds