Cavity fabrication and preparation sequences for the TESLA / TTF cavities at DESY

1st ILC workshop at KEK Tsukuba Japan A.Matheisen

for DESY and the TESLA Collaboration

•Introduction•Cavity Production steps

Example and overview tablecomments on cavity fabrication

•Cavity Preparation stepsExample and overview tablecomments on cavity fabrication

•Conclusion and remarks

Since 1990 DESY and the TESLA collaboration have put a lot of activities in the Since 1990 DESY and the TESLA collaboration have put a lot of activities in the field of srf cavities to study and prepare the build up of a TEV superconducting field of srf cavities to study and prepare the build up of a TEV superconducting linear accelerator / TESLAlinear accelerator / TESLA

The choice was made on 1.3 Ghz 9 cell geometryThe choice was made on 1.3 Ghz 9 cell geometry

State of the art of acceleration field gradient was 5 MV/m for multi-cell cavity in State of the art of acceleration field gradient was 5 MV/m for multi-cell cavity in “medium” scale production“medium” scale production

Lots of promising attempts and receipts on single cell were around ( HPP-Cornell / Lots of promising attempts and receipts on single cell were around ( HPP-Cornell / closed BCP /-SACLAY/ HPR - CERNclosed BCP /-SACLAY/ HPR - CERN

Within the TESLA collaboration a test and preparation facility was set up at DESYWithin the TESLA collaboration a test and preparation facility was set up at DESY

IntroductionIntroduction

Decision was made toDecision was made toOrder Cavities in Industry, qualify companies,Order Cavities in Industry, qualify companies,learn on large scale production learn on large scale production Preparation und testing at DESY Preparation und testing at DESY

( ( multiple choice of preparation/ no clear receipt /multiple choice of preparation/ no clear receipt / no specified facility available)no specified facility available)

Cavity fabrication

• Cavity fabrication was set up in close connection with industrial companies

• Each company had its characteristic in manufacturing and specially in welding technique

General fabrication steps applied in all companies are presented here

Cavity (9 Zeller)

Endhalbzell-Endrohr- Einheit

kurz

Endhalbzell- Endrohr- Einheit

lang

Flansch(Hauptkoppler-

Stutzen)

Flansch(Endflansch)

HOM-Kopplerkurze Seite

Rippe RippeAnbindung(end-kurz-lang)

Endhalbzellekurz

AntennenflanschNW 12

HOM-KopplerDESY

End-kurz-lang

Formteil F

Bordscheibelange Seite

Endhalbzellelang

Flansch(end-kurz-lang)

HOM-Kopplerlange Seite

Flansch(Endflansch)

Antennenstutzenlang

Endrohrlang

AntennenflanschNW 12

Formteil Flang

HOM-KopplerDESY

End-kurz-lang

Hauptkoppler-stutzen

Endrohrkurz

Cavity (9 cell TESLA /TTF design)

End group 1 End group 2Hantel

Normalhalb-Zelle

Normalhalb-Zelle

Stützring

Nb-BlechNormalhalelle

Nb-BlechNormalhalbzelle

Dumb-bell

Overview over cavity fabrication

Cavity (9 Zeller)

Cavity (9 Zeller)

Hantel

Normalhalb-Zelle

Normalhalb-Zelle

Stützring

Nb-BlechNormalhalelle

Nb-BlechNormalhalbzelle

dumb bell

Overview over cavity fabrication

Cavity fabrication : Example dumb bell / Cavity

7. Welding of Iris 8. Welding of stiffening rings9. Mechanical measurement of dumb-bells10. Reshaping of dumb bell if needed11. Cleaning 12. Rf measurement of dumb-bell13. Trimming of dumb-bells ( Equator regions )14. Cleaning 15. Intermediate chemical etching ( BCP /20- 40 µm )+ Rinsing16. Visual Inspection of the inner surface of the dumb-belllocal grinding if needed + (second chemical treatment + inspection )

Dumb- bell

1. Mechanical measurement2. Cleaning (by ultra sonic [us] cleaning +rinsing)3. Trimming of iris region and reshaping of cups if needed4. Cleaning 5. Rf measurement of cups 6. Buffered chemical polishing + Rinsing (for welding of Iris)

Dumb-bell ready for cavity

cups Dumb-bell pipes flanges Cone HOM coupler

Forming byForming by Deep drawing

trimming milling milling milling milling

Reshaping Reshaping Yes Yes Yes

Geometry checkGeometry check Yes Yes Yes Yes Yes Yes

cleaningcleaning Yes Yes Yes Yes Yes Yes

Rf measurementRf measurement Yes Yes Yes

trimmingtrimming Yes Yes Yes

cleaningcleaning Yes Yes Yes Yes Yes Yes

BCP for weldsBCP for welds Yes Yes Yes Yes Yes Yes

EB WeldingEB Welding Yes Yes Yes Yes Yes Yes

Geometry checkGeometry check Yes Yes Yes Yes

Rf measurementRf measurement Yes Yes Yes

shaping / trimmingshaping / trimming Yes Yes Yes Yes Yes Yes

BCP for visual BCP for visual inspectioninspection

Yes Yes Yes

grindinggrinding Yes Yes Yes Yes

Overview on fabrication steps for cavity subunits

Cavity welding: the general way There are differences of welding processes in industry

1. Degreasing and rinsing of parts2. Drying under clean condition3. Chemical etching at the welding area ( Equator)4. Careful and intensive rinsing with ultra pure water5. Dry under clean conditions6. Install parts to fixture under clean conditions7. Install parts into electron beam (eb) welding chamber

( no contamination on the weld area allowed)8. Install vacuum in the eb welding chamber <= 1E-5 mbar9. Welding and cool down of Nb to T< 60 C before venting10.Leak check of weld

1 1 pieces 3 1 piece2 7 pieces

Fabrication:1. Sequences need to be adopted to the company hardware2. Companies need to be trained an stay trained

learning curve to stable production 3. Control on subcontractors4. Dependency on major products of company training of personal

Experiences on cavity fabrication:

Deep drawing:1. Reproducibility depends on tool design and tool material specification – investigation in tooling2. Dependency on Nb supplier found 3. Different shape from ingot to ingot found (Hardness / grain size) Better quality control + specification reproducibility

Measurements: 1. Rf measurement of cups / dumb bells Time consuming2. Mechanical measurements of sub units Time consuming

( F part HOM tube / flanges /dumb-bell 3 D measurement complex

combination of mechanical and rf measurement possible ? ( 3 D imaging of units)

Cavity preparation

O Some steps of the preparation are related to the specific hardware With a modified hardware they might be eliminated

Example: Entering procedure for cleanroomProcedureCar wash + Ultrasonic cleaning + ultra pure water rinsing+ drying inside cleanroom

They will be display as

O Some steps are common for all processes independent on BCP or EP processing

They will be outlined by =

Actually more than 50 steps are in the line

General comment

italic letters

Cavity PreparationCavity Preparation

Standard treatment used forTTF Modules 1-5(BCP treatments +1400 C titanium post purification)

BCP

Standard treatment used forTTF Modules 1-5(BCP treatments +1400 C titanium post purification)

EP / 1

Treatment sequence used for the first batch of cavities electro-polishedin collaboration with KEKCombination ofBCP (80- 160 µm)+ EP (80- 100µm) at KEK+EP (20-50 µm) at DESYPart of production1400 C titanium post purified

EP / 2

Treatment sequence under study at DESYNo 1400 C Ti post purification Only EP applied (200 µm) Improved handling sequences

Actually there are 3 general lines

The preparation process can be split up into 4 major steps

Preparation step BFinal cleaning and assembly for vertical test

Preparation step CWelding of connection to He vessel / He vessel welding

Preparation step DFinal cleaning and assembly for module / horizontal test

Preparation step ARemoval of demage layer / post purification / tuning

Cavity preparation (BCP)

As example the BCP treatment use for sequence Module 1-5 at TTFTreatment includes post-purification by Titanium at 1400 C

Part A of preparation

1. Rf measurements and mechanical inspection

2. Chemical etching of cavity inside (CP 80 µm + clean water rinsing) 3. Chemical etching of cavity outside (>20 µm+ clean water rinsing)4. Annealing and H2 outgasing in UHV oven at 800 C

5. Rinsing in ultra pure water 6. Insertion to 1400 C UHV oven ( inside DESY cleanroom )7. Chemical etching (Removal of Titanium surface layer)

cavity inside (CP 80 µm + clean water rinsing) outside ( 40 µm+ clean water rinsing)

Part B of preparation

1. Tuning of field profile

2. Chemical etching of cavity inside (“final” BCP [ 20 µm ] + clean water rinsing)

3. High pressure rinsing4. Drying in class 10 clean room air 12 h5. Assembly of auxiliaries6. Vacuum leak check of flange connections 7. Venting and dismount pumping flange ( beampipe )8. 1st high pressure9. 2nd high pressure rinse10. Drying over night in class 10 cleanroom11. Install antenna for vertical rf measurements

Rf Measurement at 2 K

Cavity preparation (BCP)

1. Enter cleanroom after rf test

2. Venting of cavity3. Removal of variable Antenna 4. Installation of pumping valve5. Install Argon atmosphere inside cavity6. Transport for welding of interconnection ring NB to

Titanium

7. Venting of cavity8. Removal of flanges (beampipe / Input coupler port)9. Measure and install fieldprofile10.Weld helium vessel11. Leak check of vessel welds

Rf Measurement at 2 K

Cavity preparation (BCP)

Part C of preparationHere major differences for BCP and EP cavities appear !!!

Part D of preparation

1. Entering the clean room after tank welding

2. Chemical etching of cavity inside (BCP 20 µm + clean water rinsing)3. High pressure rinsing4. Drying in class 10 clean room air 12 h5. Assembly of HOM Coupler / Pick Up probe / Flanges6. Vacuum leak check of flange connections 7. Venting and dismount pumping flange ( beampipe )8. 1st high pressure9. 2nd high pressure rinse10.Drying over night in class 10 cleanroom11.Mount pumping port for leack check and mass spectrometry12.Leak check13.Mount horizontal platform14.Vent cavity for coupler installation 15.dismount coupler port blind flange 16.Install power coupler17.Final leak check

Cavity preparation (BCP)

Part C of Cavity preparation has major differences for electro polished cavities qualified to 35 MV/m

Cavity preparation for electro polished cavitiesCavity preparation for electro polished cavities

But up to now no qualified and reproducible procedure for This preparation step on Electro-polishing of cavities

with tanks is available

This part of the preparation was set up on the basis that a final surface treatment can be don when the helium vessel is installed

Part A of cavity preparation BCP EP1a EP1b EP2

Field profile measurement /mechanical inspection

OK OK OK OK

Chemical etching of outside

+ clean water rinse

BCP >20 µm BCP >20 µm BCP >20 µm BCP >20 µm

etching of cavity inside

+ clean water rinse

BCP80 µm BCP80 µm BCP80 µm EP 160 µm

Annealing and H2 out-gassing in UHV oven at 800 C

OK OK OK OK

Rinsing with clean water ok ok ok ok

TI post purification

Oven inside DESY cleanroom

1400 C 1400 C NO NO

Removal of Titanium layer

Chemical etching

inside + clean water rinse

BCP 80 µm BCP 80 µm no no

Chemical etching

outside + clean water rinse

BCP >= 40 µm

BCP >= 40 µm

no No

Field profile measurement /mechanical inspection

ok ok ok ok

Summary table for Part A of cavity preparation

BCP EP 1a EP 1b EP 2

Final treatmentFinal treatment BCP 20 µm (DESY) EP 100 µm (KEK) EP 100 µm (KEK) EP 40 µm (DESY)

High pressure rinseHigh pressure rinse ok at KEK at KEK At DESY

TransportationTransportation Yes Yes

fieldprofilefieldprofile tuning tuning

HP rinsesHP rinses yes yes

Assembly Assembly auxiliaries auxiliaries auxiliaries auxiliaries

High pressure rinseHigh pressure rinse 2 times 3-5 time 3-8 times 6 times

Drying in cl 10 12h cl 10 cleanroom 12h cl 10 cleanroom 12h cl10 cleanroom 12h cl 10 cleanroom

Install antenna for vertical rf test for vertical rf test for vertical rf test for vertical rf test

120 C baking120 C baking No Yes Yes Yes

resultsresults On AC Cavities average

28,6 MV/m

(26-32 MV/m)

2 cavities

35 MV/m

2 cavities 23MV/m field emission loaded

4 cavities field emission loaded

2 cavities <26MV/m limit: fabrication error

2 Cavities

<30 MV/mLimit: material

Additional Additional treatmentstreatments

5 µm BCP

1 cavity 35 MV/m

5 µm BCP

1 cavity 35 MV/m EP 40 µm (DESY)

2 Cavity 37 MV/m

Summary table for Part B of cavity preparation

Cavity preparation for electro polishing EP 1Cavity preparation for electro polishing EP 1

Part C of Cavity preparationReentering cleanroom after rf test

Remove variable Antenna Install bead pull and measure field profile inside cleanroomAdjust fieldprofile (outside of cleanroom

Installation of antennas for mode spectrum controlHigh pressure rinsingInstall Argon atmosphere inside cavityTransport for welding of interconnection ring NB to Titanium

Venting of cavityRemoval of antennas Install bead pull and measure field profile inside cleanroomHigh pressure rinsingAdjust fieldprofile outside of cleanroom

Remove bead pull systemHigh pressure rinsinginstall of antennas for mode spectrum analysisWeld helium vessel Leak check of vessel welds

2 cavities lost gradient due to not well established manipulation

This procedures are much too complicated

Way out is to install bead pull and rf antennas that go with the cavity on that process ?

cavity interior sealed inside the cleanroomhermetically until preparation for Module / horizontal test ( under investigation)

Way out development of final treatment on dressed cavities ?Light BCP ?Oxi polishing ?Cavity ep with tank ?

conclusion

Cavity production in industry has to set up with good results

We learned .That the Production is depending on company specific ways Industry need training and sensitization for the cavity productionThe rise up time until stable production is company depending

Procedures for cavity treatment are available

We learned that - Only when the procedures are followed strictly the results are stable- Any missing step leads to cavity performance degradation- Errors in the sequence need a step back in the process- Any changes in the process, even small once have impact on others steps

and needs a reestablishing and a new qualification of the procedure- Cavity results on single cell are not one to one transferable to multi-cells- Changes in a procedure has to be qualified on 9 cell cavities - For Electro polished cavities investigations on the reproducibility of the process are needed- Investigations on final treatment after vertical measurements have to be made to have a smooth and reliable process after vertical measurements

conclusion