Efforts to improve the assembly
work of SRF cavities in the cleanroom to suppress field emission
加速器学会
2022/10/21

Mathieu OMET
応用超伝導加速器イノベーションセンター
高エネルギー加速器研究機構

Contents• Introduction• Clean room survey• Study on particle generation during assembly• Assembly work planning, documentation, and analysis• Further measures to reduce field emission• FE statistics• SummaryMathieu OMET, 2022/10/21

Efforts to improve the assembly work of SRF cavities in the clean room to suppress field emission

2Motivation• Our R&D goal: Achieve as high as possible quality
factors Q0 and maximal accelerating voltages Eacc within 1.3 GHzsuperconducting radio frequency (SRF) cavities
MT-4

Mathieu OMET, 2022/10/21

Efforts to improve the assembly work of SRF cavities in the clean room to suppress field emission

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Example Workflow of Cavity Treatment before Test
Bulk Electro Polishing

InspectionAnnealing

Inspection / Grinding

Tuning / Straightening

AssemblyBaking

Mathieu OMET, 2022/10/21

Electro PolishingHigh Pressure Rinsing

High Pressure Rinsing

Vertical Test

Efforts to improve the assembly work of SRF cavities in the clean room to suppress field emission

4Motivation• Since field emission (FE) degrades
the cavity performance, it has tobe avoided• Thus, pollution of the inner cavity
surface with particulates has to beavoided• Sources of particulates:

Degradation dueto heavy FE• Environment• Generation during assembly process→ We have to understand bothMathieu OMET, 2022/10/21

Efforts to improve the assembly work of SRF cavities in the clean room to suppress field emission

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Clean Room SurveyNormal Light• Turned off all ambient lighting in STF class 1000 clean room (C1000CR) andclass 10 clean room (C10CR)• Used spotlight to illuminate surfaces in C1000CR

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Efforts to improve the assembly work of SRF cavities in the clean room to suppress field emission

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C10CR Airlock South Door

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Efforts to improve the assembly work of SRF cavities in the clean room to suppress field emission

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C10CR Airlock North Door

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Dust and Fiber Particles on Table
Beside Pumping Station

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Efforts to improve the assembly work of SRF cavities in the clean room to suppress field emission

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Clean Room Survey
D light• Evaluate the capability of the D light to find dust in the clean room
• Evaluate the dust in the clean room using D light• Light source used:

Mathieu OMET, 2022/10/21

Efforts to improve the assembly work of SRF cavities in the clean room to suppress field emission

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Check on Dependence of Angle

Left

Top right
Mathieu OMET, 2022/10/21

Top left

RightTop• No dependence fromleft, top, right• Little dependence
when in direction or
opposite direction ofthe camera

Efforts to improve the assembly work of SRF cavities in the clean room to suppress field emission

11Confirm that we actually do see Dust
• Sample surface: housing of HELEN (Helium leak detector)• Initial situation• Air blow, wipe with alcohol,
air blow again• Final situation• A lot of dust was removed• It is indeed dust we see
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Efforts to improve the assembly work of SRF cavities in the clean room to suppress field emission

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Checking other Surfaces with Cleaning(Air Blowing)• Sample surface: valve of pumping station (ion pump)• Initial situation
Final situation after air blowing

Mathieu OMET, 2022/10/21

Efforts to improve the assembly work of SRF cavities in the clean room to suppress field emission

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STF Changing Room Door to Air Lock

Mathieu OMET, 2022/10/21

Efforts to improve the assembly work of SRF cavities in the clean room to suppress field emission

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COI C1000CR –Air Lock

Mathieu OMET, 2022/10/21Efforts to improve the assembly work of SRF cavities in the clean room to suppress field emission

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COI C1000CR –Pumping Station

Mathieu OMET, 2022/10/21

Efforts to improve the assembly work of SRF cavities in the clean room to suppress field emission

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COI C1000CR –Cavity Stored in the CR

Mathieu OMET, 2022/10/21

Efforts to improve the assembly work of SRF cavities in the clean room to suppress field emission

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COI C1000CR –Items Stored in Shelf

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Efforts to improve the assembly work of SRF cavities in the clean room to suppress field emission

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COI C1000CR –Items Stored in Shelf

Mathieu OMET, 2022/10/21

Efforts to improve the assembly work of SRF cavities in the clean room to suppress field emission

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COI C10CR –Keyence Ion Gun

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Efforts to improve the assembly work of SRF cavities in the clean room to suppress field emission

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STF C1000CR –Tray with Tools

Mathieu OMET, 2022/10/21

Efforts to improve the assembly work of SRF cavities in the clean room to suppress field emission

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COI C10CR –Tray with Tools

Mathieu OMET, 2022/10/21

Efforts to improve the assembly work of SRF cavities in the clean room to suppress field emission

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STF C1000CR - Window of Air Lockbetween C1000CR and C10CR
Before cleaning

Mathieu OMET, 2022/10/21

After cleaning

Efforts to improve the assembly work of SRF cavities in the clean room to suppress field emission

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Conclusion of Clean Room Survey• Using a spotlight or using D-light both allow a survey of dust and dirt on
surfaces of the clean room
• D-light is a bit more versatile• In some areas cleaning was necessary and was applied• It was not feasible to clean every last corner → avoid whirling up dust fromthere• Areas behind shelfs, which are used for storage• Torque wrenches• Etc.

Mathieu OMET, 2022/10/21

Efforts to improve the assembly work of SRF cavities in the clean room to suppress field emission

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Study Particulates created during theAssembly• Study performed together withSHIN NIPPON AIR TECHNOLOGIES
CO.,LTD (SNK)• Ambient lighting is turned off• Green laser light is transmitted
through the area of interest• Laser light is scattered by particles• Scattered light is recorded by avideo camera
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Masking of the Clean Room Windows

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Efforts to improve the assembly work of SRF cavities in the clean room to suppress field emission

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Clean Blowing

シャフト
カメラ
光源

C-10

加速器
A/S

C-1,000
A/S

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Efforts to improve the assembly work of SRF cavities in the clean room to suppress field emission

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Release of Bolts of Blind Flange

シャフト
カメラ
光源

C-10

加速器
A/S

C-1,000
A/S

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Efforts to improve the assembly work of SRF cavities in the clean room to suppress field emission28

Tightening Bolts of Attachment

シャフト
カメラ
光源

C-10

加速器
A/S

C-1,000
A/S

Mathieu OMET, 2022/10/21

Efforts to improve the assembly work of SRF cavities in the clean room to suppress field emission

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Work Plan for Assembly• Detailed assembly procedure isdescribed• Written for every single assembly• Discussed with supporting
technical staff before theassembly• Document is accessible during theassembly via tablet in theC1000CR

Mathieu OMET, 2022/10/21

Efforts to improve the assembly work of SRF cavities in the clean room to suppress field emission

30Documentation during Assembly with
Head-mounted Camera

Picture courtesy of T. Dohmae

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Analysis of Assembly Work
• After the assembly divergence from the work plan are noted down
• Recorded pictures and videos are shared with all group members via
internal services (picture gallery, cloud storage, electronical logbook)• A work report is compiled (typically a Power Point presentation) anddiscussed with all group members during the weekly group meeting• The work reports are accessible on the internal meeting webpage

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Further Measures to Suppress FieldEmission• Iris grinding of cavities
Example of iris grinding on 3-cell cavity
Picture courtesy of H. Araki→MT-4 (9-cell cavity)
1-2 iris, θ = 0 deg.

→MT-4 (9-cell cavity)
3-4 iris, θ = 162 deg.
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Further Measures to Suppress Field
Emission• Exchange ion gun from TOP GUN to KEYENCE SJ-L005G with filter→
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Further Measures to Suppress Field
Emission• Exchange the scroll pump with dry pump in clean room and at VT stand→→Mathieu OMET, 2022/10/21

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History of Field Emission insingle-cell Cavities
All Eacc_max and Eacc_onset (final π-mode at 2 K)

No radiation onset

Number of VTs
VTs with radiation
VTs w/o radiation
Mean Eacc_onset
Mean ratio (onset/max)
Mathieu OMET, 2022/10/21

112
37 (33.0%)
75 (67.0%)
27.3 MV/m
0.832

Efforts to improve the assembly work of SRF cavities in the clean room to suppress field emission

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History of Field Emission in
3-cell Cavities
All Eacc_max and Eacc_onset (final π-mode at 2 K)

No radiation onset

Number of VTs
VTs with radiation
VTs w/o radiation
Mean Eacc_onset
Mean ratio (onset/max)
Mathieu OMET, 2022/10/21

147 (50.0%)
7 (50.0%)
22.7 MV/m
0.688

Efforts to improve the assembly work of SRF cavities in the clean room to suppress field emission

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History of Field Emission in
9-cell Cavities
All Eacc_max and Eacc_onset (final π-mode at 2 K)

No radiation onset

Number of VTs
VTs with radiation
VTs w/o radiation
Mean Eacc_onset
Mean ratio (onset/max)
Mathieu OMET, 2022/10/21

5241 (78.9%)
11 (21.2%)
28.8 MV/m
0.637

Efforts to improve the assembly work of SRF cavities in the clean room to suppress field emission

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FE Comparison

Mathieu OMET, 2022/10/21

Efforts to improve the assembly work of SRF cavities in the clean room to suppress field emission

39Summary• Clean room survey• Understanding of assembly environment• Spotlight / D light (more versatile)• Improvement possible by cleaning and/or not whirling up dust in certain corners• Study on particles created during assembly• Understanding of particle creation and movement• Deduct rules for behavior during assembly(e.g. slow movement, clean up well after every assembly step, etc.)• Assembly work planning, documentation, and analysis• Similar to a Plan, Do, Check, Act (PDCA) cycle, which is a well-established tool in quality management• Allows to easily share information among group members• Further measures to reduce field emission• Iris grinding• Exchange of ion gun for assembly• Exchange of pump for rough pumping system• Field emission statistics• Clear improvements over the last 3 years for 3- and 9-cell cavities• With on all points above, we are improving the quality of our assembly processes• Thank you very much for your attention! Questions?
Mathieu OMET, 2022/10/21

Efforts to improve the assembly work of SRF cavities in the clean room to suppress field emission

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