Status RF foil

1
Status RF foil

• Projects in progress
• Rectangular bellows
• Wakefieldsuppressors
• EMI measurements
• RF/vacuum foil
• Production methods used
• Coating
• Results and conclusions
• Interference Silicons

2
VELO Overview

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

3
Rectangular Bellow (1)
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Rectangular Bellow (2)
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Rectangular Bellow (3)

• Assembled last week
• Vacuum brazed this weekend
• Tests to be performed
• Vacuum tightness
• Mechanical behavior (10,000 movements)

6
Wake field suppressors
The Wake field suppressor is made of two 75 mm
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.
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Wakefield Suppressor test

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

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RF-test EMI effects (1)
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RF-tests EMI effects (2)
Study of RF pick-up in silicons and read-out
electronics
No signal observed for Al foil of 25 mm
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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
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VELO RF/vacuum box
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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

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RF and vacuum separation foil(2)

• 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
• lt 300 mm Al

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RF and vacuum separation foil(3)

• Production of the toblerone
• Machining from solid material
• In the sub-mm region for a
• 1200 mm long structure we
• expect
• Accuracy problems
• Stress (frequent annealing)
• Production from foil
• Requirements for
• Stiffness
• Welding
• Shape
• Choice of material
• Methods to be used

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RF foil box
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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

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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 material
• Buckling and folding

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Cold formation(2)

• April, 2001
• 0.25mm 99Al
• 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.

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Cold formation(3)

• May, 2001
• 0.28 mm 99Al
• Thickness of the deformed material
• Large thickness variations
• Minimal thickness 0.11 mm.
• Small cracks and pinholes.

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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

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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!

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Plastic deformations

• So-far we used plastic deformation
• For pure Al
• 30 at room temperature
• 60 at 200º C
• We need deformations of 400
• annealing steps required
• Principal mechanism
• Dislocation creep
• High dislocation density
• Grain elongation
• Cavity formation
• Induces multiplication and gathering of
  dislocations
• Cavitation is important cause of failure

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Superplastic Forming(2)

• September, 2001
• Aluminium 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
C Requirement small grain size (lt10mm) bubble or
cavity forming

• Al alloys for integral solutions with
• low weight
• high stiffness

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Superplasticity(1)

• Superplasticity
• Polycristalline solids which have the ability to
  undergo large uniform strains prior to failure
• Elongations 200 - 5500
• Fine grain size (lt 10 mm)
• Strain rate change 10-5 10-1 /s
• T gt 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

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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 size
• Strain enhanced grain growth is widespread
  problem in SPD!

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Superplasticity(6)

• What is the effect of the Magnesium addition?
• Atomistic models
• Embedded Atom Method Energy Functions
• Calculations of total internal energy of crystals
• Calculation of grain boundary energy and surface
  energy
• GBS more favorable than void formation
• Migration
• In pure Al 3 layers 9 Angstrom
• Al-Mg alloys 4 layers 13 Angstrom

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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 mm
• Black Magic sometimes conflicting advices

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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.

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SPD mold (1)
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SPD mold (2)
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Samples from the regions(1)
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Samples from the regions(2)
Neutral part no deformations
100 mm
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Samples from the regions(3)
Outer part Intermediate deformations
100 mm
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Samples from the regions(4)
Inner part Largest deformations
100 mm
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Elasticity tests RF foils(1)
Elastic behavior 300 mm foil Deformation 320
mm at 15 mbar 200 mm at -15 mbar Completely
elastic
N.B. Unfortunately, in the presentation there
was a factor 10 off in the quoted values for the
deflection.
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Elasticity tests RF foils(2)
April 16, 2002 Two more foils have been tested
AlMg3 Foil 0.2mm thick over
under pressure 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 pre
ssure 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
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Leak rate
1 forming step at 520º C 9.8 E-6 -gt 2.0 E-5
19 forming steps, 3 molds needed. 7.0 E-8 -gt 7.0
E-7 1 corner 8.0 E-5
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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

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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 detection With
Helium Before After 1.2e-3 3.2e-7 1.2e-5 7.2e-7 3
.6e-5 5.2e-7 3.8e-5 2.4e-6 1.2e-6 3.2e-7
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Explosive Formation(1)
Statement producer Uniform thickness after
deformation. Test have been performed.
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Explosive Formation(2)
The explosive sandwich method.
Pure aluminium
Aluminium 3 Mg
Pure aluminium
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Full size mold
Produced at VU by Frans Mul
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Summary Outlook

• Base solution for RF/vacuum foil obtained
• Material 200 mm 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

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RF foil and Silicons
Black Detector Red Rf foil Blue region
for detector, assuming 1 mm clearance
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RF foil and Silicons-detailed