Dec. 4, 2001 CERN-1 Hans de Vries

• VELO Mechanics RF/vacuum foil Rectangular bellow Wake field suppressors Cabling

• Summary & Outlook

VELO mechanical aspects

Dec. 4, 2001 CERN-2 Hans de Vries

Global system design

• Decouple access to Si detectors from access to 1ary vacuum

• Use (ultra)pure neon venting

• NEGs need not be baked after access to Si detector

• Baking up to 150 oC is possible

• Mount two detector halves independently

• Note large-size, rectangular bellows and thin RF screen

2ary vacuum

1ary vacuum

air

Dec. 4, 2001 CERN-3 Hans de Vries

Dec. 4, 2001 CERN-4 Hans de Vries

RF and vacuum separation foil

Overlapping detectors• stereo angle• alignment

• Separate prim. and sec. Vacuum• Stiffness

• Protect against RF effects• Wakefields• EMC

• Restrict amount of material

Dec. 4, 2001 CERN-5 Hans de Vries

RF foil box – outside view

Dec. 4, 2001 CERN-6 Hans de Vries

RF foil box – inside view

Dec. 4, 2001 CERN-7 Hans de Vries

FEA on Al. 250 m

0.25 mm top plate0.5 mm side

plates

15 mbar

max. displacement

0.35 mmmax. stress [MPa]

58.8 MPa

Dec. 4, 2001 CERN-8 Hans de Vries

Aluminum (250 m thick):• FEA: max p 15 mbar irreversible deform., no safety factor • successfully welded 100 m on 300 m• press-shaping developed: superplastic forming of AlMg3• “cheap & readily” available (compared to Be)• Foil can be produced with radius of 6 mm • Sharp edges of detector have to be rounded off

Thin RF/vacuum foil

2000 2001

Dec. 4, 2001 CERN-9 Hans de Vries

Superplastic Forming

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.

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

http://www.superform-aluminium.comT = 470 - 520° Csmall grain sizebubble or cavity forming

Dec. 4, 2001 CERN-10 Hans de Vries

SPF mold (1)

Dec. 4, 2001 CERN-11 Hans de Vries

SPF mold (2)

Dec. 4, 2001 CERN-12 Hans de Vries

Latest RF foils

Deformation:32 m at +15 mbar 20 m at -15 mbarCompletely elastic

He leak tested

Concrete mold has been replaced by a brass one

Dec. 4, 2001 CERN-13 Hans de Vries

Explosive Formation

Statement producer:Uniform thickness after deformation.Test will be performed.

Dec. 4, 2001 CERN-14 Hans de Vries

Rectangular Bellow (1)

Dec. 4, 2001 CERN-15 Hans de Vries

Rectangular Bellow (2)

The diaphragms were cut out of a 0.15 mm stainless steel plate with a laser machine.Next the diaphragms have successfully been shaped in a forming mold.

Dec. 4, 2001 CERN-16 Hans de Vries

Rectangular bellow (3)

The forming mold with the pressure envelope.The pressure envelope is used to keep the system in place.

Dec. 4, 2001 CERN-17 Hans de Vries

Rectangular bellow (4)

With nitrogen at a pressure of 10 bar the diaphragm are deformed into the right shape.

Dec. 4, 2001 CERN-18 Hans de Vries

Rectangular bellow (5)

Dec. 4, 2001 CERN-19 Hans de Vries

Rectangular bellow (6)

7 stainless steel plates (0.15 mm) will be vacuum brazed together.

Before brazing, the 0.05 mm Ni-alloy solder is spot welded between the layers.

Dec. 4, 2001 CERN-20 Hans de Vries

• Install wake field suppressors after mounting 2ary vacuum container

• Upstream is “easy”: mounted with large flange off

• Downstream is more delicate: mount through top flanges

• 70 m CuBe, O/C, coated

Wake field suppressors (1)

Aim:Provide a continuous conducting wall throughout the VELO to guide the mirror charge

Dec. 4, 2001 CERN-21 Hans de Vries

Wake field suppressors (2)

The Wake field suppressor is made of two 0.075 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 320 degrees Celsius to get better spring properties.

Dec. 4, 2001 CERN-22 Hans de Vries

Wake field suppressors (3)

New design of the The Wake Field Suppressor, which follows better the contour of the beam pipe..

Dec. 4, 2001 CERN-23 Hans de Vries

Cabling (1)

Almost solidcable tree!

• Cables• Connectors

very expensive!

Dec. 4, 2001 CERN-24 Hans de Vries

Cabling (2)

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

Dec. 4, 2001 CERN-25 Hans de Vries

Cabling(3)

Dec. 4, 2001 CERN-26 Hans de Vries

Summary & Outlook

• Base solution for RF/vacuum foil– 300 m base material Al with 3% Mg– 170 m at inner region– Radius 6 mm

• Rectangular bellow– Diaphragms are ready– Will be assembled the coming months

• Wake field suppressors– The wake field suppressors work fine– A new design is in production

• Cabling solution available– Has to be discussed further