# Presentation: 855244

## LH2 Absorber Window R & D Program

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- Mary Anne Cummings
- MUTAC Review
- LBL
- April 26, 2005

## Topics

- Review
- Window design and test history
- FNAL test requirements
- Current program
- FEA (finite element analysis)
- MICE cooling channel windows
- New window tests – and improvements
- Comments

## Thin windows in cooling channels

- Absorbers, Vacuum and RF windows

- KEK Convection Absorber at MTA

- Forced-Flow Absorber with external cooling loop
- And secondary window

- MICE Convection Absorber in AFC module (and containment)

- MICE  201 MHz
- RF (Be window)

## Thin Windows Design 

- Thin Windows Design

- Cooling and safety  issues are in the window profile

- 500 to 120 m reduction

- Originally..

- Window design independent of particular cooling channel configuration

- Tapered torispherical
- Black, Cummings

- “Bellows”
- Lau, Black

- “Thinned Bellows”
- Lau, Black, Yang

- Modified torispherical
- FNAL, Cummings

- Interface/integration
- engineering  issues are in the flange design

## Evaluating the “thinnest” thickness

- Want windows confirmed** **as **safe**
- Different radii of curvature on either side of window
- Machined sides possibly not concentric
**What is the critical measurement?**

- If not at the center, where?

**180 microns**

**1mm**

**ASME vessel design definitions:**
- Design by Rule:
- Based on maximum Stress Theory
- Standard shapes, equations
- Design by Analysis          Must do destructive tests!
- Based on maximum Shear Stress
- Use FEA to determine MAWP for non-standard windows

## FNAL Safety requirements

- _FNAL Requirements:_
- _Vacuum_
- Burst test 5 vacuum windows at room temp. to demonstrate a burst pressure of at least 75 psid for all samples. (pressure exerted on interior side of vacuum volume).
- Non-destructive tests at room temperature:
- External pressure to 25 psid to demonstrate no failures: no creeping, yielding, elastic collapse/buckling or rupture
- Other absorber vacuum jacket testing to ensure its integrity
- _Absorber _
- Room temp test:  pressurize to burst ~  4 X MAWP (25 psi at FNAL)
-  Cryo test:
- 	a) pressure to below elastic limit to confirm consistency
- 	     with FEA results
-       b) pressure to burst (cryo temp – LN2) ~ 5 X MAWP
-                from   ASME:   UG 101 II.C.3.b.(i)

## MICE Safety Review for Windows

- RAL window pressure test requirements (Absorber and Vacuum)

- Test Pressure** **

- Test temperature

- # of tests required

- Remarks

- 96 psi(4 x design P)

- @ 293K

- 3

- Test to rupture. Windows to subject to thermal cycling before the test

- > 96 psi(5 X design P)

- @ 77K

- 1 or 2

- Test to rupture. If shrapnel is evident, one further test will be needed. The additional test will have the safety mesh fitted to verify that shrapnel doesn’t reach the safety window.

- 25 psi

- Room temp

- 1

- Test for buckling (external)

- Design Pressure = 24 psid            MAWP FNAL = 25 psid  -
- Effectively, the same for MICE and MuCool

## FEA results on current bellows window design

- The current window design has a double curvature to ensure that the thinnest part is membrane stress dominate

- 30 cm diam.

| 
Window Type` | MICE Req.
Burst Pressure | FEA calc.
Burst Pressure | MICE Req.
Buckling Pressure | FEA calc.
Buckling Pressure |
| --- | --- | --- | --- | --- |
| Absorber
(30 cm diam) | 
96 psid | 
105 psid | 
25 psid | 
26 psid |
| Safety
(32 cm diam) | 
96 psid | 
105 psid | 
25 psid | 
26 psid |

- The current window FEA analyses show that the shape scales can use same analysis for different diameters of same profile!

- Step loading the window with internal pressure until ultimate tensile stress is reached – numerical definition of rupture

## MICE window FEA  

- Behavior of Window under incremental **external** load...

- The same FEA was applied to all the window shapes that were developed subsequently...

- MICE window FEA**  **

## Window manufacture (U Miss)

- Backplane for window
- pressure tests

- Backplane with connections,
- and with window attached

- Flange/window unit machined
- from aluminum piece (torispherical 30 cm diam)

## Photogrammetry 

- Photogrammetry
- set-up

- Photogrammetry

- Contact vs. non-contact measurements (projected light dots)
- “Several” vs. ~ thousand point measurements (using parallax)
- Serial vs. parallel measurements (processor inside camera)
- Can do measurements and performance tests
- Better fit to spherical cap.
- Precision measurement of real space points
- Photogrammetry is the choice for shape
- and pressure measurements

- Photogrammetry
-   ~1000 points

- Strain gages
-  ~ 20 “points”

- CMM ~
- 30 “points”

## Rupture tests

- Leaking appeared at 31 psi ..outright rupture at **44 psi!**

-  photogrammetry measurements

- 1.

- 3.

- Burst  at ~ **120 psi**

- 4.

- Burst  at ~ **152 psi**

- Cryo test

- 2.

- “350” windows

- Burst at ~ **120 psi**

- 1.

- 130 window

## FNAL Absorber window test status

-  Performance measurement on **torispherical **windows
- Discrepancies between photogrammetry and FEA predictions  are < 5%
- Room temperature and crygogenic tests validated design

-  Performance measurement on the 21 cm **“bellows”** window

- Tests:
- Measured at 190 m .. Designed for 132 m
- Leaked at seal in first pressure test (design improved)
- Burst at 144 psid.. (predicted burst at 104 psid)
- Corrections:
- Revised FEA calculations ... and ~144 is predicted
- Optical coatings determined to be major source of measurement error

## Optical coating

- Vapor deposition:
- Set-up and experts at FNAL
- Safety review completed
- Working to achieve proper TiO2  uniform coating < 2 m
- Alternatives:
- Chemical process for deposition
- Simpler technology
- Need to demonstrate on aluminum
- No coatings:
- Test photogrammetry, other CMM methods can give sufficient results

- Broken window in deposition test

- Cryostat for deposition test

## Further R & D questions

** **So far, we have looked at the window safety from a single source of loading only, i.e. the pressure load.
-  Other possible loads considered, but not rigorously analysed. These include:
- Thermal load caused, possibly, by the uneven temperature  distribution of the liquid hydrogen during operation
- Stress from beam deposition – (pizeo-electric instrumentation)
- Thermal cycling – fatigue tests
- Still need to study the high stresses at the edge of the new window
- Other alloys are still under consideration (i.e., Al Li alloys, Albemet)
- Window instrumentation is still planned

## Optical Occlusion

- Can be used as a threshold for occlusion or clearance
- Baumer electronics laser distance sensor is one candidate
- Test set-up at NIU:

## Progress since last MUTAC review 

- New manufacturing of bellows windows (just started)
- Optical coating (thickness control)
- Vapor deposition
- Chemical deposition
- Tests for uncoated
- Upgrades to projector and new camera. Optical table obtained for dedicated destructive tests.
- Plans are maturing for vacuum tests

## Concluding Remarks

- ICAR funding loss has hurt this program
- Do not want “institutional” knowledge to disappear.
- Absolutely need to go through a complete testing cycle for the new window, to continue progress.
- Have a dedicated window test area at FNAL, and can accommodate all Mucool and MICE window tests.
- Takes good advantage of expertise at FNAL
- If new window source is established, will expedite tests and certifications.
- Can have possible beam test of thin window on LH2
- Good program for students

## Safety Strength requirements

-     Pb = 5 x P x St/Sw   where **P** is the **maximum working pressure** and St is the minimum tensile stress at test temp and Sw is the minimum tensile stress at working temperature
-                                   The S value for 6061 T6 material is 310 MPa at room temperature and 415 MPa at working temp.
-  Pb = 5 x 310 / 415 x P  = 5 x 0.76 P  = 4xP
- Hence a burst pressure of **4 times the working pressure when** tested at room temperature will meet the requirement of section UG -101 in Div. 1 of ASME VIII

- The ASME design code stipulates the following stress limits:
- Primary membrane stress, the lower of Sm  < 2/3 of yield or 1⁄4 UTS
- Primary bending stress Sb = 1.5 Sm
- The MAWP exceeds these limits, but because of the the non-standard design,  ASME allows certification based on **burst tests:**