november 29, 2002 nikhef-1 hans de vries status rf foil rf/vacuum foil purpose production methods...

November 29, 2002 NIKHEF-1 Hans de Vries

Status RF foil

• RF/vacuum foil Purpose

Production methods used

Deformations: static - overpressure

Electrical properties

Coating

Cables

Interference Silicons


RF and vacuum separation foil(1)

• Protect against RF effectsWakefields in Vertex vesselEMI in detectors

• Good conductivity

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

Detector vacuum– (outgassing electronics, cables, NEG coating,…!)

• Stiffness

Physics requirement:• Restrict amount of material

– preferably low-Z (small radiation length)• Thin

• Detectors should overlap– Alignment– Stereo angle

• Complicated shape


RF and vacuum separation foil(2)

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

•Choice of material•Methods to be used


VELO Overview


Secondary vacuum box


Secondary vacuum box (detail)


Material data:

Material: AlMg3Young's modulus: 70.000 MPaPoisons ratio: 0.33Shear Modulus: 27.3 GPaYield Strength: 80-180 MPaUltimate Strength: 180-260 MPaElectrical conductivity: 1.9x107 ohm-1 m-1

(almost 50% of pure Al)Weldable!


Production of RF foil

– Hot gas forming• Deform at 350° Formation speed

– Superplastic deformation• Deform at 520°

– One cycle, p 10 bar Crystal growth, melting,Vacuum leaks

• Methods investigated:– Cold formation

• Press- anneal at 420° (or 350 °) - cool- press …– More than 15 cycles, 2 – 100 bar– Two or more molds Time consuming

– Explosive formation Uncontrolled


Full size foil

Full size rf foil with reinforcement ribs


3D measurement set-up

Mesh for 3D machine

-1000

-950

-900

-850

-800

-750

-700

-650

-600

-1600 -1400 -1200 -1000 -800 -600 -400 -200 0

Exploded view


Measurement of one slot

-900

-890

-880

-870

-860

-850

-840

-830

-820

-810

-702 -701 -700 -699 -698 -697 -696 -695 -694 -693

20 x 5 measurement points


3D result for one slot

-818

-830

-841

-852

-864

-875

-887

-694 -697 -701

-84

-83.5

-83

-82.5

-82

-81.5

-81

-81.5--81

-82--81.5

-82.5--82

-83--82.5

-83.5--83

-84--83.5


Projection for one slot

-84.2

-84

-83.8

-83.6

-83.4

-83.2

-83

-82.8

-82.6

-82.4

-82.2

-82

-702 -701 -700 -699 -698 -697 -696 -695 -694 -693

Variation in depth of one slot ± 0.1 mm


Minimum depth along foil

-85

-83

-81

-79

-77

-75

-73

-71

-69

-67

-65

-1600 -1400 -1200 -1000 -800 -600 -400 -200 0


Minima enlarged

-84.4

-84.2

-84

-83.8

-83.6

-83.4

-83.2

-83

-1400 -1200 -1000 -800 -600 -400 -200

Variation in depth for all slots: ± 0.2 mm


Close-up minima

-85

-83

-81

-79

-77

-75

-73

-1000 -950 -900 -850 -800

Position of slots along foil: 0.1 mm


Thickness measurements

Along central beam line: 0.28 0.29 0.27 mm

0.24 0.27 0.25 0.26 0.30 0.27 0.24 0.27 mm

Largest curvature point: 0.15 mm


FEM analysis: input

Input model for the FEMcalculations


FEM analysis: down

10 mbar over pressure in primary vacuum

Maximum deflection 0.88 mmin “floppy part” of foil


FEM analysis: up

10 mbar over pressure in secundary vacuum

Maximum deflection 1.04 mmin “floppy part” of foil


Deflection measurement


FEA for full box (1)


RF pick-up (1)

Foil thickness 30 m Al;Power level in the 50 ohm coaxial line:10 Watts at 40MHz. The Si detector was 5 mm from the foil outside conductor of the coax.

In this condition there was no influence on the noise background.


RF pick-up (2)

Cut a hole in the foil and put the silicon strip just 5 mm in front of this hole.

The power level in this coax line was still 10 watt at 40MHz.

The fieldlevels from this radiator are much higher then we can obtain with the beam through the RF foil.The result was that we do not see influence on the working of the silicon in combination with theelectronics of the test setup at NIKHEF in febr. 2002.


RF shielding

Frans Kroes has produced a note on

Attenuation of an EM field by AlMg4 screen of 0.2 mm

Conclusion:

Assuming a conductivity of 0.33 of pure Al:

At 1 mm distance to the rf screen:

1.415 x 10-3 V/m


Conductivity

Pure Al = 37 x 106 Ohm-1 m-1

• Measured (10%) conductivity of 1 m long 1 cm wide strips of AlMg3:

undeformed = 17 x 106 Ohm-1 m-1

deformed = 11 x 106 Ohm-1 m-1

• 45% for undeformed• 30% for deformed material


Coating

• The extreme deformation might result 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

• Outgassing properties have been studied


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


Cabling

Cables inside vacuum:• Heat production• Signal shielding

Kapton with 3 Cu layers:• = 25 micron kapton outside layer•--- 17 micron Cu (foil)•= 75 micron kapton•--- 17 micron lines (100 micron width)•= 75 micron kapton •---17 micron Cu (foil)•= 25 micron kapton outside layer


Outgassing (1)

Massspectra of outgassing after 48 hour

0.0E+00

5.0E-13

1.0E-12

1.5E-12

2.0E-12

0 5 10 15 20 25 30 35 40 45 50

Mass [amu]

Ion

Crr

ent

[A.l/

s.cm

^2]

Coated

Aluminum

Outgassing after 48 hour - Coated-Aluminum = 2.6E-09 mbar.l/s.cm 2̂ - Aluminum = 6.5E-10 mbar.l/s.cm 2̂

Outgassing poly-amide-imide coating


Outgassing (2)Contribution in the pressure of the secondary vacuum by out gassing

Seff=500l/s

1.E-08

1.E-07

1.E-06

1.E-05

1.E-04

1.E-03

0 1 2 3 4 5 6 7 8 9 10

time [day]

P [

mb

ar]

Coating

Flat Cable

Poly-amide-imide coating: 1.5 m2

Kapton cables: 20 m2


RF foil and Silicons


RF foil and Silicons-reinforcements


Summary

• Full size RF/vacuum foil has been obtained– Material: 300 m Al with 3% Mg– Minimal radius 8 mm – Deviations measured: ± 0.3 mm– FEM analysis has been performed– Variations measured for 10 mbar

overpressure– Electrical properties measured– Application of poly-amide-imide– Kapton cables with 3 Cu layers

november 29, 2002 nikhef-1 hans de vries status rf foil rf/vacuum foil purpose production methods...

Documents