HWR Cavity Parting and Fabrication

Design and Fabrication of a 162.5 MHz HWR cryomodule for Project X

Speaker: Mike Kelly

March 5, 2012

Considerations for Fabrication and Processing

1. Niobium material and parting

2. Forming, cutting machining

3. Tuning

4. Surface processing – S. Gerbick

5. Testing

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ANL SRF Group

Quality Control

Coordination

Nb procurement,

Mechanical & EM

design

Chemistry

Clean processing &

assembly

Testing

ANL Shops

Adron

Wire EDM niobium

cutting

AES

Sciaky

Roark

Niobium tooling and forming –

FEA

Electron beam welding

Meyer Tool

Numerical Precision

Stainless and niobium

machining

Fermilab, JLab

Furnace and various

expertise

Niobium-to-stainless

braze

ANL Approach to Cavity Fabrication

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162.5 MHz Half-wave Cavity

Exploded View

Niobium Assembly

8+1 total units

Starting point for cavities is EM model together with niobium parting/forming

Stainless jacket

48 inches

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162.5 MHz Half-wave Niobium Sheet Layout

Units are inches, sheets are 0.125 inches thick, RRR>250

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Niobium Parts Forming in US Industry

Upper housing Center conductor Re-entrant nose

Bottom dome Toroid top side Toroid inside

Doubler plate Lower housing Coupling port

Cavity Port Braze Assemblies

Niobium-to-stainless braze using pure copper

Conflat flange is machined into stainless blanks

Bellows attached (welded) to cavity flange and also helium vessel

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Niobium Wire Cutting in US Industry

Wire EDM Sinker EDM

Cavity re-entrant nose (beam port nose) assemblies

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Parts received from forming vendor

Doubler OD is trimmed to size with wire EDM Cooling holes added

Doublers are beam welded to re-entrant nose

Beam port braze assembly is welded to nose assembly

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Electron Beam Welding in US Industry

Seam weld Seam weld

Doubler weld Beam port weld

Re-entrant nose weld Housing assembly weld

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Electron Beam Welding in US Industry

Completed niobium assembly

Electron Beam Welding/Tuning

Major sub-assembly before closure weld

Final niobium assembly

Two circumferential welds and two

longitudinal welds to close cavity

Final closure weld on the HWR’s ‘trickier’ than for QWR’s Weld beads on closure weld cross at 90 degrees Fit tolerance challenging on outer housing Risk (has been) mitigated by testing on weld samples

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Example of tuning steps for QWR

Cavity Tuning by Clamping and Wire EDM

Small rings removed from center conductor and housing

Clamping subcomponents for frequency checking

Final ‘cold’ frequency

Initial frequency before welding subcomponents

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Stainless Steel Helium Jacket Fabrication in US Industry

Backfilling cavity with Argon gas prior to welding

Argon purge in He space for welding

Final TIG weld Final weld joining cavity to stainless (low total heat relative to TIG)

600 C Hydrogen Degassing is planned

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FNAL High-vacuum furnace

Half-wave Cavity Testing in ANL 2 K – 4 K Cryostat

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All crygenics connections

– 1.8 K to 4.6 K operation

Diagnostics

– Phase-lock electronics

– Thermometry

– 2nd Sound Detection

– Microphonics measurements

400 Watts RF power at 162.5 Mhz

– Will require a new amplifier for high-power testing

Timeline for Prototype Fabrication

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16 months timescale to finish testing of a prototype consistent with recent experience with 72 MHz QWR

Prototyping is to establish specific fixturing and manufacturing details to guide production ― Time is not allocated to address fundamental performance issues such

as failure to make gradient due to e.g. bad niobium or problems in EM design

30% schedule float in ID 24 and 50% in ID 26 to account for conflicts with ARRA upgrade

Summary of Fabrication

Nearly all fabrication techniques are similar or identical for QWR’s and HWR’s and are well understood

Small differences in fabrication techniques will be addressed in the prototyping, e.g., – Crossing weld beads

– ‘Clam shell’ outer housing

– Facilities for processing and testing cavities exist and require modest fixturing for HWR work

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