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LCLS Undulator Bellows Module . Internal Design Review. Soon-Hong Lee . Contents. Layout General Requirements Specifications Conceptual Designs Materials for Bellows Module FE Stress Analysis Mechanical Failure Test Conclusions. Layout Short Break Diagnostic Section.

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lcls undulator bellows module

LCLS Undulator Bellows Module

Internal Design Review

Soon-Hong Lee

slide2

Contents

  • Layout
  • General Requirements
  • Specifications
  • Conceptual Designs
  • Materials for Bellows Module
  • FE Stress Analysis
  • Mechanical Failure Test
  • Conclusions
slide4

General Requirements

Bellows motion requirements

  • Baking temperature at ~200 C
  • Fabrication tolerance of chamber, BPM, Quad.
  • Longitudinal cradle motion constraint = 3.0 mm
  • Total axial travel  5.0 mm
  • Adjacent two undulators are tilted and/or in parallel
  • Quad center manual adjustment range =  2.0 mm
  • Total lateral offset   2.0 mm
  • Adjacent two undulators are tilted symmetrically
  • Angular stroke for bellows module = 2  tan–1 (height change/length between bellows module)  
  • Height change = 2 mm   (~2.5) + 2 mm   (~2.5) = 10 mm 2 x tan–1 (10/3800) = 0.3
  • Undulator segment pitch tolerance (rms) = 14 rad
  • Total angular rotation  0.5

From www.flexhose.com

general requirements
General Requirements
  • Mechanical Concept of Bellows Module
    • Consider axial travels/constraints for easy installation and maintenance
    • Consider lateral offset with flexible contact fingers and static stub
    • Consider maintenance cycle and material fatigue life
    • Consider mechanical restraints to prevent damages for bellows and fingers
  • RF Connections
    • Provide a sliding surface with good lubricity and good electric conductivity
      • RF fingers, spring fingers, and stub mechanism
      • RF seal ring or spring gasket across flange joints
    • 0.4 ~ 0.5 mils silver plating on the shield fingers
    • 0.2 ~ 0.3 mils rhodium plating on the stub
bellows module
Bellows Module

Removable tie rods for restraints to prevent damages

EVAC flanges with chain clamps for space limitation and easy maintenance

Welded Bellows (200-125-3-EE) Axial travel: 16~60 mm lateral offset:  4.3 mm angular offset: 50

RF-connections

bellows module exploded
Bellows Module - Exploded

RF Fingers (BeCu 174) with Ag-plating

Stub (OFE Cu) & Spring Fingers (BeCu) with Rd-plating

RF seal ring or spring gasket

slide9

Materials for RF Fingers and Stub

Need Heat Treatment after forming

Flange

Stub Tube

Fingers

Fingers

slide11

RF Finger Stress Analysis

324.8 MPa at root > Fatigue strength of BeCu (276MPa)

design parameters
Design Parameters
  • To investigate maximum stress at root
    • contact types (point contact or surface contact)
    • # of RF-fingers
    • # of Spring-fingers
    • shape of fingers to reduce the overlap damage
    • thickness and length of fingers

RF-finger root

Spring finger

Stub

RF-finger tip

fea case study
FEA Case Study

+ 2mm

  • Use Pro/Mechanica - Contact Analysis
  • - Surfaces of fingers & stub are contacted
  • - Applied ±2 mm (Y) for lateral offset, ± 5 mm (Z) for axial travel
  • Criteria
  • - Maximum Displacement < 8.0 mm
  • - Maximum Stress < 276 MPa
  • (based on fatigue strength of BeCu Alloy 174)

+ 5 mm

- 2mm

rf fingers
RF Fingers

0.15 mm thick 53.5 mm long 16 fingers

spring fingers
Spring Fingers

0.15 mm thick

29.5 mm long

8 fingers

slide22

Mechanical Failure Test

  • Object of failure test is to prove the part in the following conditions
  • 2,000 cycle actuation
  • ± 5.0 mm axial travel distance
  • ± 2.0 mm lateral offset movement
  •  0.5 of angular stroke
  • Ag- & Rd- plating thickness
conclusions
Conclusions
  • Established design specifications based on physics requirements, maintenance, and installation etc.
  • Conceptual design and drawings are completed.
  • Based on FE analysis (contact analysis) by use of Pro/Mechanica, max. stress on fingers is expected to have 226MPa which shows below fatigue strength (276 MPa) of BeCu Alloy 174.
  • Lubricity and mechanical failure tests are planned to investigate the Rd- & Ag-plating thickness and the performance of RF- & Spring-fingers.
rf fingers and stub plating and test requirements
RF Fingers and Stub Plating and Test Requirements
  • Plating Requirements
  • Maintain electric continuity and provide lubricity across the sliding joint ( RF fingers and Stub) during operations
  • Optimize plating performance
    • Avoid galling
    • Minimize loss of plating
    • Avoid loss of plating adhesion (flaking)
  • Testing Parameters for Bellows Assembly and Sliding Joint
    • Test at 10-7 torr
    • Allow visual inspection of sliding joint during the test
    • 2000 cycle test
    • ±5mm axial travel (static and dynamic)
    • ±2mm lateral offset (static and dynamic)
    • ±0.5° angular offset
approach
Approach

1. Plate RF Fingers and Stub with Rd and Ag according to specifications developed for the bellows for the PEP- II High Energy Ring*

2. Test fingers as assembled inside the bellows to insure acceptable performance at operating conditions for 2000 cycles

3. Change coating thicknesses if required

4. Optimize performance as budget and schedule allow

*Curt Besler, Jeffery Berg “High Current RF Shield for PEP-II Vacuum System Expansion Joint” LLNL

M.E. Nordby, N. Kurita “Bellows Design for PEP-II High Energy Ring Arc Chambers” SLAC

plating materials and initial thickness
Plating Materials and Initial Thickness

RF Fingers – 0.4 to 0.5 mils Ag

Stub – 0.2 to 0.3 mils Rd

Plating thickness can be changed to optimize performance.

Other possible materials for increased lubricity at the joint

include:

  • Dicronite – impregnated Tungsten Disulfide
  • Nanolube – nested nanoshpere structure Tungsten Disulfide
section thru test fixture
Section Thru Test Fixture

Set-up for dynamic axial Testing

bellows prototype costs
Bellows Prototype Costs
  • Material costs from current loaded schedule
    • Bellows $ 1,500
    • Test Equipment $ 4,000
    • Evaluation of plating $ 3,000
    • Rh plate stub $ 900
    • Ag plate fingers $ 3,000
    • Fabrication of small parts $ 600