April 15, 2002 NIKHEF-1 Hans de Vries Status RF foil Projects in progress: Rectangular bellows...

April 15, 2002 NIKHEF-1 Hans de Vries

Status RF foil

Projects in progress:

Rectangular bellows

Wakefieldsuppressors

EMI measurements

• RF/vacuum foil Production methods used

Coating

Results and conclusions

Interference Silicons


VELO Overview

•Bellow•Wakefield suppressor•EMI pick –up•Cabling•RF foil box


Rectangular Bellow (1)





Assembled last week

Vacuum brazed this weekend

Tests to be performed:•Vacuum tightness•Mechanical behavior (10,000 movements)


Wake field suppressors

The Wake field suppressor is made of two 75 m thin CuBe foils,compressed with gear wheel and rack. CuBe is chosen for the good electrical and elastic properties. The foil can be hardened at 320º C to get better spring properties. Amount of material will be optimized.


Wakefield Suppressor test

•The CuBe2 Wake Field suppressor has been tested for 30.000 cycles.•No cracks or other damage was observed


RF-test: EMI effects (1)


RF-tests: EMI effects (2)

No signal observed for Al foil of 25 m

Study of RF pick-up in silicons and read-out electronics


Cabling

Cables inside vacuum:• Heat production• Signal shielding

Kapton with 3 Cu layers:• Outer layers for power and ground• Inner layer for signal

Very expensive!New design has been made to optimize nr. of kapton sheets required


VELO RF/vacuum box


RF and vacuum separation foil(1)

Why?• Separation extreme-high-vacuum of LHC from

Detector vacuum (outgassing electronics, cables,…!)• Stiffness

• Protect against RF effects• Wakefields in Vertex vessel• EMI in detectors

• Good conductivity

Physics requirement:• Restrict amount of material

– preferably low-Z (small radiation length)• Detectors should overlap

– Alignment– Stereo angle



Shape and material choice:• Physics

– Thin-walled “Roman pots” around detectors

•Wakefields–Small cylindrical aperture

•Compromise:–Corrogated structure–Toblerone shape

•Material:–Beryllium too expensive–Aluminum has been chosen

•Thickness:–Rigidity and conductance vs. low-material budget:

• < 300 m Al



Production of the toblerone:

Machining from solid material:In the sub-mm region for a1200 mm long structure weexpect:• Accuracy problems• Stress (frequent annealing)

Production from foil:Requirements for:• Stiffness• Welding• Shape

•Choice of material•Methods to be used


RF foil box


Production of RF foil

• Methods investigated:– Cold formation

• Press- anneal at 420°- cool- press …– More than 15 cycles, 2 – 100 bar– Two or more molds

– Superplastic deformation• Deform at 520°

– One cycle, p 10 bar

– Explosive formation– Cold formation

• Annealing at 320°


Cold formation(1)Oct, 2000

0.25 mm 99% Al- 12 steps - 9 to 40 bar

Between each step the plate is 20 min annealed at 420º C.

Surplus of materialBuckling and folding


Cold formation(2)April, 2001

0.25mm 99%Al :shaped in 2 steps.Step 1: formed the round shape, with 2 pressure steps from 15 to 20 bar. Step 2: 30 pressure steps from 10 to 32 bar.

- No more folds in the middle round shape.- Crystal structure.


Cold formation(3)

May, 2001

0.28 mm 99%Al Thickness of the deformed material:

Large thickness variations:Minimal thickness 0.11 mm.Small cracks and pinholes.


Cold formation(4)June 10, 2001

New material:0.3mm AlMg3

shaped in 2 molds. Final pressure: 95 bar without cracks. Between each pressure step the plate is a annealed at 520º Celsius. Radius less than 8 mm, but this shape is not reproducible


Cold formation(5)July 9, 2001

0.3 mm AlMg3

Shaped with 2 molds. The maximum pressure in step 2 is 60 bar. Between each pressure step the plate is a annealed at 520º C.The foil cracked at 65 bar on the 'sharp' edge.Radius = 13 mm.Strong crystal growth!


Plastic deformations

So-far we used plastic deformation

For pure Al:• 30% at room temperature• 60% at 200º CWe need deformations of 400%:

annealing steps required

Principal mechanism:• Dislocation creep• High dislocation density• Grain elongation• Cavity formationInduces multiplication and gathering of dislocationsCavitation is important cause of failure


Superplastic Forming(2)

September, 2001Aluminium Superplastic Forming (SPF)

Hot stretching process: sheet of superplastic grade aluminium alloy is forced onto or over a single surface tool by the application of air pressure. Typical temperatures T = 470 - 520° CRequirement: small grain size (<10m)bubble or cavity forming

Al alloys for integral solutions with:

• low weight

• high stiffness


Superplasticity(1)

Superplasticity:Polycristalline solids which have the ability to undergo

large uniform strains prior to failureElongations: 200% - 5500%

Fine grain size (< 10 m)Strain rate change 10-5 – 10-1 /sT > 0.5 Tm

Discovered in 1920 (Pb-Zn, Cd-Zn)not much interest in the West. 1947: sverhplastichnost

John Pillings and Norman Ridley• Superplasticity in crystalline solids


Superplasticity(5)

Mechanisms: Not quite well understood• Grain boundary sliding• Grain rotation• Partial melting• Uniform strains• Grain size effects• Presence of “dispersoids” like Mn, Zr, …

– Al6Mn and Al3Zr act as grain boundary pinning agents

Better performance for:• Increasing temperatures• Decreasing grain sizeStrain enhanced grain growth is widespread problem in

SPD!


Superplasticity(6)

What is the effect of the Magnesium addition?

Atomistic models:

Embedded Atom Method Energy FunctionsCalculations of total internal energy of crystalsCalculation of grain boundary energy and surface energy

GBS more favorable than void formation

Migration:In pure Al3 layers 9 AngstromAl-Mg alloys 4 layers 13 Angstrom


Superplasticity(7)

Laboratory research:• Small scale, small samples• Mainly 2D-elongations

Commercial firms:• Al-Cu-Zn alloys not weldable!• Special patents• Expensive tools! Control of many variables

– Special additions like Zr – Equal Angle Channel Extrusion for homogeneous material– Special heat treatment during rolling process

• Thickness used is normally 2 – 3 mm no experience 100 m

• Black Magic: sometimes conflicting advices


Superplasticity(8)

Deformations:•No sharp corners:Superplasticity, while capable of reproducing fine details, cannot produce very sharp corners. Careful considerations needs to be given to determining the minimum radii of curvature that can be sustained without excessive thinning or wrinkling of the sheet.

Other problems: Cavitation and fracture

We have 3D deformations. At strongest radii small leaks and/or pin holes were found.


SPD mold (1)


SPD mold (2)


Samples from the regions(1)



100 m

Neutral partno deformations



100 m

Outer partIntermediatedeformations



100 m

Inner partLargestdeformations


Elasticity tests RF foils(1)

Elastic behavior:300 m foil

Deformation:320 m at +15 mbar 200 m at -15 mbar

Completely elastic

N.B.: Unfortunately, in the presentation there was a factor 10 off in the quoted values for the deflection.


Elasticity tests RF foils(2) April 16, 2002 Two more foils have been tested:

AlMg3 Foil 0.2mm thick over underpressure [mbar] deflection [mm] pressure [mbar] deflection [mm]

3 0.2 2.4 0.2 5 0.3 3 0.3 7 0.4 4,5 0.4 9 0.5 5 0.5 10 0.55 6 0.6

AlMg3 Foil 0.28mm thick (CERN material)over under

pressure [mbar] deflection [mm]under pressure [mbar]deflection [mm] 3 0.1 3 0.1 6 0.2 5 0.2 9 0.3 6.5 0.3 10 0.33 8 0.4 10 0.5


Leak rate

19 forming steps,3 molds needed.

7.0 E-8 -> 7.0 E-71 corner= 8.0 E-5

1 forming step at 520º C

9.8 E-6 -> 2.0 E-5


Coating

• The extreme deformation results in tiny leaks in the material.

• Also a protective layer might be used at the inside of the detector box.

• Apply poly-amide-imide coating– Solution in N-Methyl-2-Pyrrolidone (NMP)– Drying and polymerization at 60º, 150º, 260º and

315º C– Properties like Kapton and Torlon – Good electric insulation– Radiation resistant 30 MGy, strength not changed


Final solution(?)

A thin layer of poly-amide-imide is air brushed on the inside of the foil for electrical protection and to increase vacuum tightness

Effect of the layer:

Leak detectionWith Helium

Before After1.2e-3 3.2e-71.2e-5 7.2e-73.6e-5 5.2e-73.8e-5 2.4e-61.2e-6 3.2e-7


Statement producer:Uniform thickness after deformation.Test have been performed.

Explosive Formation(1)


Explosive Formation(2)

The explosive sandwich method.

Pure aluminium

Pure aluminium

Aluminium + 3% Mg


Full size mold

Produced at VU by Frans Mul


Summary & Outlook

• Base solution for RF/vacuum foil obtained– Material: 200 m Al with 3% Mg– Minimal radius 8 mm (cold formation and

SPD)– Tolerances estimated to be 1 mm– Application of poly-amide-imide:

• Vacuum tight• Intrinsically baked out • Only applied inside the secondary vacuum• Good electric insulation• Radiation resistant• More layers can be applied• Can be used as glue

– Full scale box will be produced before summer


RF foil and Silicons

Black:Detector

Red:Rf foil

Blue:region for detector,assuming 1 mmclearance


RF foil and Silicons-detailed

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April 15, 2002 NIKHEF-1 Hans de Vries Status RF foil Projects in progress: Rectangular bellows...

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