C100 summary of performance degradation - VTA to Cryomodule Ari Deibert Palczewski SRF Scientist July 5, 2016

Acknowledgements JLab staff Mike Drury – most of the slides Kurt Macha Rongli Geng Andrew B. Burrill – SLAC John Mammosser – SNS I did not perform any data analysis or create any plots used in this talk

Outline Measurement Hardware FE Onset – Definitions Overall Statistics Known assembly issues VTA (cavity test) to CMTF (module test)

Cavity Each cryomodule contains a string of eight 7-cell low-loss SRF 1497 MHz cavities Each Cavity undergoes an rigorous qualification process 160 µ M BCP 600 C Bake 24 hours – Hydrogen removal- Eliminates Q 0 disease 30 µ M Electropolish – Reduce Q 0 Slope Multiple High Pressure Rinses 120 C Bake for 24 hours Vertical Test at 2.07 K Cavity String assembled in a “Class ” Clean room Cavities must deliver an Average Maximum Operating gradient of 19.2 MV/m with average Q 0 of 7.2E9 at 2.07 K 96% exceeded requirement

Measurement Hardware Vertical Test Area (VTA) –Single Ion Chamber installed inside Dewar lid (~ 7 feet above cavity and ~2 feet off axis) CANBERRA AM-IP100 Cryomodule Test Facility –Octirad – 8 channels of GM tubes In use in CMTF until C100-5 tests –Decarad – 10 channels of GM tubes In use during Commissioning tests (tunnel) beginning with C100-1 In use in CMTF starting with C100-6 Comparisons made between two systems during C100-7 tests – this was a final verification test.

GM Tube Locations Top Center WG2 WG3 WG6 WG4/5 WG7 WG8 WG1 BL Sup BL Ret BL Sup BL Ret WG tubes and Top Center = Radial BL Supply and Return = BL Top Center WG3/4/5 WG4/5/6WG7/8 WG1/2 DecaRad OctiRad

OctiRad / DecaRad Comparison Cavity C on 06/01/12 Similar behavior for other cavities Compared beamline tube positions and top center tube position Relatively good agreement up to about 100 mR/hr Octirad tubes saturate at much lower dose rates Onset Gradients derived from octirad data tends to be higher by ~1 MV/m

DecaRad Calibration Two tubes co-located with ion chamber on Test Cave Wall – ion chamber in VTS identical to this one.

FE Onset Definition CMTF Decarad Channels have noise floor at just above or below 1 mR/hr Onset defined as the gradient at which slope intercepts 1mR/hr line

FE Onset Definition VTA VTA Noise floor ≤ 1E-2 mR/hr VTA Onset = 1 st Gradient ≥ 1E-2 mR/hr For comparisons in this presentation – using the CMTF definition

VTA Onsets Using the CMTF definition results in higher average onset gradient for VTA data x2 cavities that do not have FE onsets by definition

VTA and CMTF Onsets 1 mR/hr definition Average Onset drops by 6 MV/m from VTA to CMTF Number of Cavities with no Field Emission drops by more than half

R.L. Geng, 2016 CEBAF StayTreat, June 28-30, 2016  Many leaks detected in the C100 strings. o 80 Serpentine seals, 7 leaks o 56 BL radial wedge seals, 0 leaks o 20 BL cavity to valve seals, 1 leak o 204 HOM/ FP seals, 1 repaired with using a higher torque  7 (out of 10) Cryomodules had leaks. o Serpentine seal leak sizes ranged from 3e-9 TL/s to 4e-7 TL/s o The one beam line leak at the VAT valve was 4e-6 TL/s Cavity String Assembly Slide 13

known possible issues – VTA to module “Slow pumpdown” of string was in general ~ 8X higher (initial flow rate) than vertical cavity testing and ~20X higher than ILC R&D rate. Most string assemblies were performed in old cleanroom which was spec’d to class 1000, unlike VTA assembly which had secondary class 100/10 tents within cleanroom for final assembly. Worst module c100-4 was not fully disassembled and re-hpr’ed when a cavity needed to be swapped mid string assembly (no nitrogen JLab during string assembly)

backup Questions? Mini-workshop on beam-line field-emitter particulates in CEBAF SRF linacs Located in link below has other information about topic as well

C100-3 Evolution Two Cavities in this module have little or no measurable FE after two years after install Gains from He Processing tend to be small in comparison with early performance

C100-4 Evolution During String Assembly – original cavity at position 3 was swapped out First Acceptance Test showed low FE onset gradients – between 6 MV/m and 11 MV/m Also several cavities with very low quench gradients Helium Processing used to recover gradient After processing –Onset gradients between 9 MV/m and 16 MV/m

R.L. Geng, 2016 CEBAF StayTreat, June 28-30, 2016 Ion chamber used in VTA and CMTF: CANBERRA AM-IP100. Detector Sensitivities 0.4 μ R/Pulse. Detector Range: 100 μ R/h R/h. Energy Range 50 keV to 3 MeV. (data retrieved specification sheet published on vendor website) Geiger-Muller (GM) tubes used with OctiRad DAQ: Thermo Scientific HP Gamma Sensitivity: ~1200 cpm/mR/h (137Cs). Detector range: from back ground to 100 mR/h for non dead time corrected instruments or up to 3 R/h for those equipped with dead time correction capability. Energy Range: 20 keV to 1 MeV. (data retrieved specification sheet published on vendor website) GM tubes used with DecaRad DAQ: LND, INC 714 Gamma Detector. Gamma Sensitivity: 90 cpm/mR/h (60Co). Detector Range: 2 mR/h R/h (60Co). Energy Range: 40 keV to 500 keV. (Information provided by Omar Garza of Engineering Division, JLAB. Range data retrieved from information provided by Bill Lehnert of LND, Inc.) Slide 18