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
Dec 18, 2015
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
April 15, 2002 NIKHEF-2 Hans de Vries
VELO Overview
•Bellow•Wakefield suppressor•EMI pick –up•Cabling•RF foil box
April 15, 2002 NIKHEF-5 Hans de Vries
Rectangular Bellow (3)
Assembled last week
Vacuum brazed this weekend
Tests to be performed:•Vacuum tightness•Mechanical behavior (10,000 movements)
April 15, 2002 NIKHEF-6 Hans de Vries
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.
April 15, 2002 NIKHEF-7 Hans de Vries
Wakefield Suppressor test
•The CuBe2 Wake Field suppressor has been tested for 30.000 cycles.•No cracks or other damage was observed
April 15, 2002 NIKHEF-9 Hans de Vries
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
April 15, 2002 NIKHEF-10 Hans de Vries
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
April 15, 2002 NIKHEF-12 Hans de Vries
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
April 15, 2002 NIKHEF-13 Hans de Vries
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:
• < 300 m Al
April 15, 2002 NIKHEF-14 Hans de Vries
RF and vacuum separation foil(3)
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
April 15, 2002 NIKHEF-16 Hans de Vries
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°
April 15, 2002 NIKHEF-17 Hans de Vries
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
April 15, 2002 NIKHEF-18 Hans de Vries
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.
April 15, 2002 NIKHEF-19 Hans de Vries
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.
April 15, 2002 NIKHEF-20 Hans de Vries
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
April 15, 2002 NIKHEF-21 Hans de Vries
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!
April 15, 2002 NIKHEF-22 Hans de Vries
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
April 15, 2002 NIKHEF-23 Hans de Vries
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
April 15, 2002 NIKHEF-24 Hans de Vries
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
April 15, 2002 NIKHEF-25 Hans de Vries
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!
April 15, 2002 NIKHEF-26 Hans de Vries
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
April 15, 2002 NIKHEF-27 Hans de Vries
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
April 15, 2002 NIKHEF-28 Hans de Vries
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.
April 15, 2002 NIKHEF-32 Hans de Vries
Samples from the regions(2)
100 m
Neutral partno deformations
April 15, 2002 NIKHEF-33 Hans de Vries
Samples from the regions(3)
100 m
Outer partIntermediatedeformations
April 15, 2002 NIKHEF-34 Hans de Vries
Samples from the regions(4)
100 m
Inner partLargestdeformations
April 15, 2002 NIKHEF-35 Hans de Vries
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.
April 15, 2002 NIKHEF-36 Hans de Vries
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
April 15, 2002 NIKHEF-37 Hans de Vries
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
April 15, 2002 NIKHEF-38 Hans de Vries
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
April 15, 2002 NIKHEF-39 Hans de Vries
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
April 15, 2002 NIKHEF-40 Hans de Vries
Statement producer:Uniform thickness after deformation.Test have been performed.
Explosive Formation(1)
April 15, 2002 NIKHEF-41 Hans de Vries
Explosive Formation(2)
The explosive sandwich method.
Pure aluminium
Pure aluminium
Aluminium + 3% Mg
April 15, 2002 NIKHEF-43 Hans de Vries
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
April 15, 2002 NIKHEF-44 Hans de Vries
RF foil and Silicons
Black:Detector
Red:Rf foil
Blue:region for detector,assuming 1 mmclearance