# Presentation: 564356

## LCLS Undulator Bellows Module 

- Soon-Hong Lee

**Internal Design Review**

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

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

**Contents**

## LayoutShort Break Diagnostic Section

##  Total angular rotation  0.5 

** ****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 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******** **

** ****Adjacent two undulators are tilted and/or in parallel**
** ****Quad center manual adjustment range = ******** 2.0 mm****  **
** ****Total lateral offset ******** ******** 2.0 mm**

## 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

## Specifications

| Flexibility | Allow  0.5 of Angular Stroke (Pitch and Yaw)
Allow  2.0 mm of Lateral Stroke (X & Y axes) 
Allow  5.0 mm of Axial Stroke (Z axis) |
| --- | --- |
| Life | At least 2,000 cycles |
| Vacuum | 1 x 10 –7 Torr |
| Low Beam Impedance
 | Electric continuity by RF fingers and RF seal ring or spring gasket 
across flange joint |
| Space Constraints | Minimize beam directional overall length of module (Z-axis)
Axial constraint mechanism for easy installation and maintenance |
| Thermal Loads
 | Bake at 200 C and Operation Heating
Contact Resistance Heating  |
| Structural Loads | Fatigue stress due to flexible strokes across the module
Gravity, vacuum force, and contact force  |
| Plating Requirements
 | 0.4 ~ 0.5 mils Silver plating on the RF-shielding fingers
0.2 ~ 0.3 mils Rhodium plating on the Stub tube/Spring fingers |

## Bellows Module

- Removable tie rods for restraints to prevent damages

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

- EVAC flanges with chain clamps for space limitation and easy maintenance

- RF-connections

## 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

## Materials for RF Fingers and Stub

**Materials for RF Fingers and Stub**

**Fingers**

**Stub Tube**

**Fingers**

**Flange**

**Need Heat Treatment after forming**

## RF Finger Stress Analysis

**RF Finger Stress Analysis**

- 3 mm at tip

## RF Finger Stress Analysis

**RF Finger Stress Analysis**

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

## Design Parameters

**Design Parameters**

- RF-finger root

- RF-finger tip

** ****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 **

- Spring finger

- Stub

## FEA Case Study

**FEA Case Study**

| 
Case | 
Contact | RF Fingers |  |  | Spring Finger |  | 
Thickness | 
Maximum Displacement | 
Maximum Stress | 
Z-travel    (± 5 mm ) |
| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
|  |  | No. of Fingers | Root angle | Tip angle | No. of Fingers | Fingerangle |  |  |  |  |
| 1 | 
Point Contact | 18 | 18o | 8o | 8 | 

45o | 

0.15mm | 3.85 mm | 225 MPa | Contracted |
| 2 |  | 9 | 36o | 16o | 8 |  |  | 3.82 mm | 397 MPa | Contracted |
| 3-1 |  | 16 | 20o | 8o | 8 |  |  | 3.79 mm | 226 MPa | Contracted |
| 3-2 |  | 16 | 20o | 8o | 8 |  |  | 2.87 mm | 144 MPa | Extended |
| 4 | 

Surface Contact | 18 | 18o | 8o | 8 |  |  | 3.13 mm | 281 MPa | Contracted |
| 5 |  | 18 | 18o | 10o | 9 | 40o |  | 3.04 mm | 304 MPa | Contracted |
| 6 |  | 15 | 22o | 10o | 9 | 40o | 0.30 mm | 3.38 mm | 553 MPa | Contracted |
| 7 |  | 9 | 36o | 18o | 9 | 40o | 0.15 mm | 3.84 mm | 423 MPa | Contracted |
| 8, 9 |  | 18 | - |  | - |  | 0.15 mm | 6.10 mm | 221 MPa | No Spring fingers |

** ****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)**

**-**** 2m****m**

**+**** 2m****m**

**+**** 5 m****m**

## Case 1

**Case 1**

## Case 3-1

**Case 3-1**

## Case 3-2

**Case 3-2**

## Case 8

**Case 8**

## Case 9

**Case 9**

## 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

## Bellows Module Assembly

## 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

|  | Materials | Size | Price | Vendors |
| --- | --- | --- | --- | --- |
| Stub  | OFE Cu Tube | 1⁄2 ̋ O.D. x 0.0625 ̋ THK x 1.5 ̋ LG |  | Copper and Brass Sales |
|  | OFE Cu Rod | 5/8 ̋ O.D. x 1.5 ̋ LG |  |  |
| Fixtures | OFE Cu Plate | 5/16 ̋ (or 1/4 ̋) x 12 ̋ x 72 ̋ |  |  |
| RF-fingers / Spring-fingers | BeCu 174-HT | Thickness: 0.15 mm
Width: 35 mm
Length: 55 mm | 1lb/ free sample | Brush Wellman, Inc. 
(1 lb free, $500 min. lot charge) |
|  | BeCu 25-1/2HT |  |  |  |
|  | GlidCop A-15 |  |  | Spot Welding Consultant, Inc. |
|  |  |  | $460.00  / min. 5 lb | J. L. Anthony & Company |
| Bellows | Stainless Steel 347 | P/N: 200-125-3-EE
Lateral offset: ±0.17 ̋ (4.3 mm)
Angular offset: ± 50° 
@ installed length of 1.59 ̋ | $ 271.00 /Ea | Standard Bellows Company |

## 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Bellows Testing

- Jim Morgan

## 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

- 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

- 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

- Set-up for dynamic axial Testing

## Enlarged View – Test Fixture

- Enlarged view

## Bellows Prototype Schedule

## 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