MAP Assembly Investigation A project summary for discussion during 4/11/2014 meeting

Summary During assembly and RF test it was noted that the cavities behavior was not as designed, and varied with changes in end plate fastener torque. – For details of the behavior, see the summary by Daniel Bowring Priorities for recovery of the modular cavity 3/24/14 A meeting was held on 4/2/2014 to discuss the current findings, the proposed actions, and prioritize those actions agreed upon.

Planned Actions for SLAC In simplified form – Measure flange distortion as clamped – Measure flange distortion assembled but with relaxed fasteners – Remove one end plate Visually examine installed end plate, try to obtain photos, perhaps using borescope – Cause no harm during inspection – Remove other endplate and: Measure cavity flanges Endplate flatness and RF contact features Take photos – Prepare gaskets of fully annealed copper (~.03” thick) Provide details so that the geometry can be simulated if desired – Assemble and cold test w/o the helicoflex vacuum gaskets – Review results establish additional steps as needed Defer adapter and window tests until the soft gasket assembly cold tests are reviewed.

Results and Proposed Plan Revisions A summary of measurements are presented on the next few slides The measurements are followed by some mechanical simulation results Discussion of next steps sequence/schedule of work etc. is then open for discussion

Review of Existing Geometry Note key points

View of Assy

Measurements of Clamped Assembly Datum Structure established as shown

Distance to Face of Water Rings Nominal 1.5” spacing measures flat w/in.007 on one end and flat w/in.003” on the other

Distance to Cavity and Clamp Flanges The measurement is somewhat compromised by the tapered distortion and probe access but roughly the dimensions are: measures measures to 2.912

Profile along outside of Clamped Flanges CMM measurements confirm significant flange distortion Image shows OD of cavity “flange” on the lower left and the OD and end face of the clamp ring (called “endplate”) The red lines show deviation from a perfect cylinder with perpendicular end face (shown in black) The ~.015” of flex over ~1” of end plate indicates ~1° of flex

Profile along outside of Released Flanges CMM measurements confirm significant plastic distortion Image shows OD of cavity “flange” on the lower left and the OD and end face of the clamp ring (called “endplate”) The red lines show deviation from a perfect cylinder with perpendicular end face (shown in black) The roughly.005” over 1” on the end plane indicates ~.3° residual flex

Flange Contact Feature Measurement The profile of the cavity flange was measured at several points around the circumference Measurements are consistent with a expected plastic deformation

Circumferential Distortion The flange rotation is constrained at the two support arm attachment points resulting in “problematic” local distortion

End Plate RF contact marks Will need to obtain stylus measurements and high magnification images Inspection by loupe reveals variation and areas of little/no? marking

Mechanical Simulations Initial simple model to see how bad things were RF and Helicoflex loads applied as pressures on annular areas Clamp bolt load applied as a traction load on the flange bolt holes, so the model doesn’t account for clamp bolt bending stiffness which would lessen the flange rotation Very large flange rotation that would completely unload RF seal

Diagnostic Assembly Desire is to verify system geometry and RF “seal” Approach is to reduce the required flange loads by assembling with a “soft” RF gasket and without the Helicoflex vacuum seal Concerns include: – We don’t know precisely the relationship between clamp conditions and cavity performance (low pressure, periodic opens, fissures, etc.) – We do have some experience with clamped cavities and do “know” that the transition from quite poor contact to design contact can occur rather suddenly implying that relatively small contact deficiencies are significant – Want very compliant RF gasket, thickness is limited to ~.04” thick – Maximum variation for RF seal is still a maximum of ~.007” (probably considerably less) – Variation at support ties may be very significant. It is conceivable that that local variation in stiffness is a “spoiler” – We will be clamping to RF performance with still very springy components.

Potential Solution After considering various constraints a possible solution was simulated Stiffen the cavity flange with external rings pre-clamped to the cavity flange, separate clamp bolts to close the end plates – This works very well with only RF contact loads – Simulation shows that this approach is limited by the 24 available cavity ring threaded holes. Significant improvement may be made by welding a stiffener ring to the cavity flange – The approach is detailed in the following slides Two rings: – Extender ring welded at ID to existing flange – Clamp ring bolted through extender to existing flange 24x and to extender ring 24x – RF contact and Helicoflex joints closed with 48 clamp screws bearing against the back of the cavity end plate – OD of new rings extended to keep joint between the extender and clamp rings closed under the cavity end plate clamping reaction

Axial Displacement (Uy)

Contact surfaces remain closed (good)

Pre-weld test assembly with RF contact pressure only

Pre-weld test assembly with RF and Helicoflex contact pressure

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