Cryomodule Observations and Status
TomPeterson
Collectingour latest cryomodule information
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Outline
Cryomodule observations and status, 5/4/2018
New issue – two cracked bellowsStatus just prior to discovery of bellows problem – QC and fastener remediationCracked bellows – observations from F1.3-06Possible sources of bellows motion and stressLatest thoughts on this component failureNext steps
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F1.3-6 New Issue and Responses
Issue: In addition to the(likely) BPMleak, a major crack/tear was found on two cold coupler bellows ofF1.3-6 upon return to Fermilab.Cav4 and Cav5 coupler bellows both leak – the rest of the cavity string is leaktight.Same location of cracks on both bellows (3 or 9 o’clock)G-10 supports (for all cold couplers) showed signs of excessive rubbing from unanticipated motionPEEK support on warm coupler also showedwear.Shipping of J1.3-1 (JLab toFNAL, cold test, back to JLab)did notresult in vacuum leaks.Response: Investigation of coupler support, use of temporary shipping restraints and/or modifications to shipping frame/transportDamage to F1.3-6 coupler bellowslikely dueto inadequate restraint of upper cold mass by transportcaps.Results from latest J1.3-7 shipping tests will be incorporated into whatever changes areproposed.
Cryomodule observations and status, 5/4/2018
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LCLS-IICryomodule – inner coupler bellows failure
Cryomodule observations and status, 5/4/2018
RF power coupler cold end assembly
Cryomodule observations and status, 5/4/2018
Cracked inner bellowsconvolution here
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F1.3-06 – Summary of Observations as of April 19
Cryomodule observations and status, 5/4/2018
When F1.3-06 arrived atSLAC in January,it was found that the beamline vacuum had been ventedSuspected source of the beamline vacuum loss was that the BPM (after transport) had loose/missing feedthrough flangeboltsIn addition, some loose hardware was found on the bottom of the thermal shield (mechanical fasteners)Data from shock loggers showed relatively few excursions above the 1.5g shock specificationData gathered on low frequency vibrations waslimitedDisassemblyand further leak checking at SLAC wasnot practical, andso full examination had to wait untilF1.3-06was returned to FNAL
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F1.3-6 Issues andResponses
For BPM, Grade 2 Ti socket head cap screws (SHCS) used as opposed to Grade 5 Ti stud/SS nut combination as used on EU-XFEL (Design and QC issue)Design has been changed to match EU-XFELExisting production CMs will be retrofit with Grade 5 Ti stud/SS nut fastenersFor F1.3-06 BPM, SHCS were installed without washers (QC issue)This is the only BPM found to not have washersSince this CM will be totally rebuilt, washers will be addedFasteners on UCM were notall installed by the vendor per spec’s (vendor QCissue)Developed fastener spreadsheet listing critical parameters including torqueProcedures updated to add additional QC steps and fastener requirementsFasteners on all CMs will be checked for correct torque/use of Loctite as requiredTransportation is being closely reexaminedAdditional instrumentation has been added to capture vibration spectraThree additional transport tests performed (concrete CM, F1.3-06 return trip, andJ1.3-07)– data being analyzedTest results will drive changes to transport fixture and transportation specificsCommissioned both Design and QA/QC Reviews (project & internal)Project Design Review compared EU-XFEL designs to LCLS-IIProject QA/QC Review focused on travelers, specifications and documentationInternal QA/QC review focused on Fermilab process improvementsReview recommendations used to establish conditions for restart
Cryomodule observations and status, 5/4/2018
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Cryomodule Assembly/Test Status
Cryomodule observations and status, 5/4/2018
Cryomodule production status at the time of production stopJLab – 7 complete assemblies, 4 in assembly, of 19+2 totalFNAL – 7 complete assemblies, 5 in assembly, of 17+2 totalFollowing implementation of corrective actions:Both labs have been given approval to restartRetrofit of existing CMs and assembly of new CMs will proceed in parallel (extra staff added as required)CM testing drives completion so to reduce schedule delaysMinimal retest of retrofit CMsFully incorporate LERF capabilitiesDecrease install / removal duration
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LCLS-II-4.5-ES-0403, Cold Button Beam Position Monitor
Cryomodule observations and status, 5/4/2018
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The rough ride continues
Cryomodule observations and status, 5/4/2018
F1.3-06 returned to Fermilab on April 8On April 23 we learned that a leak check of the cavity string revealed leaks other than the likely BPM seal leaks.Cracks were found in two bellowsInner coupler bellows of cavities 4 and 5Subsequent leak checking showed these to be the only leaks other than the BPM bottom flange where bolts had come loose.
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One of two cracked inner coupler bellows
Cryomodule observations and status, 5/4/2018
We do not knowwhenthese otherleaksopened up,duringshipmenttoSLAC orduringtravel back toFNAL.
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CAD model cross section at RF power coupler
Cryomodule observations and status, 5/4/2018
Coupler tuning mechanism is anchored to the vacuum vessel and restrains the cold part of the coupler in the coupler axial direction. Relative motion of cavity string and coupler are taken via the inner coupler bellows.Inner and outer bellows have supports underneath which limit downward motion. Normally about 1 mm clearance.
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G-10 support block observations
Cryomodule observations and status, 5/4/2018
Black dust on all 8G-10 blocks
Abrasion on G-10 block indicates motion of at least several mm and parallel to coupler axis, perpendicular to cavity string axis. This would correspond to the cavity string swinging side-to-side.It appears that bellows cracked due to large and/or frequent motion of cavity string relative to the vacuum vessel.
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Cryomodule shipping end caps
Cryomodule observations and status, 5/4/2018
Initial shipping constraint design goal was to support the cold mass against axial load, for which only the central support post provides supportEnd support posts are free to move axially for thermal contractionTry not to overload the support posts by applying a downward or lateral load via these shipping constraintsHowever, the cold mass is free to rock sideways from the top (next slide) if not laterally constrainedAn interference was noted in F1.3-06 between the shipping end caps and the new cavity #1 gate valve support. There is some evidence that for this or other reasons, shipping caps might not have been fully engaged.
The image shows the 300 mm pipewith shipping plug insert, downstreamend.The LCLS-II shipping end plugs differsomewhat from those forEu-XFEL dueto slightly different vacuum flangedesign.A careful comparison andstudy of our system resistance tolateral loading is underway.
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Cavity motionwhich could resultfrom support motion
Cryomodule observations and status, 5/4/2018
~774 mm
~476 mm
Ratio of cavity motionto support bolt lift isabout 1.6. Cavitymotion up at about a17 degree (0.3 radian)angle.Motion in the direction shown would lift the G-10 support block into contact with the coupler.
Cold mass is notlocked down at thetop. Rests hereon verticalalignmentbolts.
RF power couplerassembly – other possible motion
Cryomodule observations and status, 5/4/2018
This mass is suspended between inner and outer bellows.Vibrationof this unit between bellows will be measured during the J1.3-07 shipping tests. Thecoupler tuningmechanism (adjustment knob on the left) constrains axial motion of this central unit.Downward motion is limited by PEEK and G-10 supports.Onecould stillhave upward andlateral motion.
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Thermal shieldvibration – another “noise” source
Cryomodule observations and status, 5/4/2018
In addition to the above described motions, the thermal shield showed signs of shock loading and bumping against the vacuum vessel.Thermal shield motion is anticipated and bumpers are provided to limit thermal shield motion.Thermal shield motion could induce vibration in other parts of the cold mass system.Although no damage has been attributed to thermal shield motion,further constrainingthermal shield motion for shipment might be prudent.
Bumpers to limit thermal shield travel. We can see marks from their bumping the vacuum vessel during shipping.
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Trailer camber andshimming – possible vibration source
Cryomodule observations and status, 5/4/2018
Theupward front-to-back camber of the shipping trailer results in the shipping frame only contacting the trailer in the middle.Thisproblem was recognized and shims were placed under the front and back of the shippingframe for cryomodule shipments.However, flexing of the trailer may still provide motion or shocks due to the center of the trailer carrying the load or loss of contact at the center with all the load on the shims.The result could be a source of vibration.
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Motion in the cryomodule axial direction
Cryomodule observations and status, 5/4/2018
Given the observation of bellows cracks at 3:00/9:00 o’clock, my first impression was that motion was likely in the cryomodule axial direction.However, wear markson the G-10 coupler support blocks indicate motion in the direction of the coupler axis, at least when in contact with theG-10.Nevertheless, to complete the description of this possibility if it were to occur:Motion in the cryomodule axial direction could result from play in various parts of the invar rod clamping assemblies, both at the cavities and at the central invar rod anchor.Play at this latter location would result in the cavity string free to move axially as a unit.Observation of the invar rod clamps upon return of F1.3-06 to Fermilab did not indicate problems with invar rod clamps.
Clamps holding invar rod
Cavity post in clamp
Summary: motion which exercises the inner coupler bellows
Cryomodule observations and status, 5/4/2018
If the shipping support end caps allowedcavity stringlateral motion or displacement.Cavitystring side motionrelative to the vacuum vesselwouldbe taken by the coupler inner bellows.Anoffset,misalignment, orstretch of the bellowscouldresult inenhancedstresses within the bellowswhen combined with motion.Other lateral play in the cavity string support pathThe posts through support arms and roller bearings look quite stiff. (Also, cavity #1 needlebearing supports outwardsand magnetneedle bearing supportsarelocked with side clamps during shipment.)We are checking the design again, do not yet see an issue.(Less likely the problem) Axial motion due to invar rod support clamps slipping(Less likely the problem) Themass between two bellows (which includes a lot of stuff with the 45 K flange, center conductor, etc.) may oscillate laterally relative to the coupler axis.This is not known to be different fromEu-XFEL but could have contributed to the wear marks on the G-10 and/or to bellows fatigue.Motioncould beup, down to the supports,or in the cryomodule axial direction.The assembly may have a low natural frequency activated by shipping, and/or motion driven also by the thermal shield movement.Wear marks indicate motion along the cavity axis, not motion lateral to the coupler.
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Alignment requirements
Cryomodule observations and status, 5/4/2018
Cavity strings are aligned at the partner labs, and data referenced to vacuum vessel fiducials provide cavity positions with respect to the vacuum vessel. Tunnel alignment sets vacuum vessel position so as to place cavities, quad, and BPM on the beamline. Thus, offsets during shipping result in errors regarding our knowledge of cavity position and should be small, (e.g., tenths of a mm).
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F1.3-06post-shipment survey results – X (lateral) offset
Cryomodule observations and status, 5/4/2018
+1.5 mmat down-streamend at SLAC
-2.0 mmat down-streamend upon returnto Fermilab.These dataindicateinadequatesupport of thecold massduring shipping.
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Next steps – design and materials considerations
Cryomodule observations and status, 5/4/2018
Analysis of bellows failuresDeterminewhether fatigue fracture or other mechanismCheck that material thickness and composition matches specificationsCheck support post alignment bolt issues (sliding support shown at left, see also slide 15)This area is easily accessible after shippingWear seen on F1.3-06, some of which naturally occurs with thermal contraction from cold testingCheck procedures for installation and tightening – Fermilab and Jefferson Lab experience
Next steps – shipping considerations
Cryomodule observations and status, 5/4/2018
Shipping tests:Ashort shipping test ofJ1.3-07 was done, April 27-28.Configuration: whatwe havenow. This cryomodule has not been upgraded per the new fastener requirements. IncludesTigrade 2 bolts (but with washers) on the BPM fasteners.Careful installation of shipping end caps and plugs for restraint of the cold mass.Vacuum remained good. Little wear on G-10 support blocks. A few loose fasteners in locations we know need attention. Analyses of shipping test data are ongoing.A longer shipping test to SLACPresent cryomodule configuration, but with any necessary upgrades for the shipping hardware and extensive instrumentation (details to be determined based on short shipping test results)Thermal shield bracing for shipping (under consideration)Review of shipping configurationShipping caps fit and plug fit into the 300 mm pipeAdequacy of lateral constraint of motionComparison withEu-XFEL shipping constraint designFrame mounting on trailerSuccessful shipping of ~100Eu-XFEL cryomodules and of the JLab prototype cryomodule, combined with the understanding of the F1.3-06 shipping issues gained from our shipping tests and studies, give us confidence that we will fix these problems found in the F1.3-06 shipment and deliver LCLS-II cryomodules successfully to SLAC.
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Acknowledgements
Cryomodule observations and status, 5/4/2018
Thanks to many people in the LCLS-II collaboration for slides, images, and information in this presentation.
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