vrije universiteit amsterdam cern, november 27, 2000 velo system j.f.j. van den brand lhcb vertex...

vrije Universiteit amsterdam CERN, November 27, 2000 VELO System J.F.J. van den Brand

LHCb Vertex Detector System:Status Report

J.F.J. van den BrandSubatomic Physics Group, VUA - NIKHEF

• Milan design

• Optimized design • mechanics

• vacuum system

• cooling system

• Summary


Mechanics: “TP” design

Side flange

Bending hinges

Detector support and cooling

Bellows (22000signal wires)

Support frame

Si detector

moves by 30 mmonly two positions:open or closed !!

See LHCb 99-042/VELO

top half = bottom half


Milan design

VELO Design:

• Single flange • XY table• CO2 cooling• WF suppressors• Second. vacuum• Studied

• assembly• alignment

• To do• further design• FEA


Detector and support frame

• both halves on same side• VD easier to mount and position in the tank• install complete VD at once• the two halves are no longer interchangeable


Vacuum vessel

• Employ top flange

• Easier installation• Shorter cables• Length 2000 mm• Width 1200 mm


Top flange

770 19

00

Lif

t 60

0

• Length 1500 mm• Distance from

ceiling 1900 mm• Install using wires• Baking to 60o C?• Regenerate NEGs

after every access to Si detectors


Optimized System

1250

1820

2150

1450

Total length: 1750

• Two detector boxes

• Baking up to 150o C

• Decouple access to Si detectors


Support system

bellows

chain/beltcooling/bake out

gearbox 1:40

ball spindle 16x25 mm

linearbearing 2x

30 +5

motor

• Microswitches at out position

• LVDTs• Steel frame• Alignment:

– 2 planes

– 3 points each

– define IP


Support system

• Alignment pins for reproducible coupling

• reproducible positioning


Vessel Installation• Move bellows to

in-position• Install vessel

from top• Align vessel• Mount vessel to

frame• Mount bellows• Pump-outs visible


Install 2nd-Vacuum Vessel• Remove upstream

flange• Need 2 m access• Rectangular bellows

– 60 mm stroke– normal 35 mm– lateral 6 mm

• Fabrication– Palatine, Bird– Calorstat, MB– cost


Vacuum vessel / Positioning system

• Moving parts not in vacuum

• Thin vacuum container

• Special bellows construction

Secundaryvacuum

Primaryvacuum


After installation• Detector system

separated from vacuum system functionality

• Mount positioning system to detector housing

• Install– pump-out, valves

– turbos, damping


Connect inner system to motion drives

• Mount M8 through side flanges


Detector Installation

• Install detector halfs from sides

• Decouple detectors from box

• Tooling needed


VELO Assembly

• Detectors mounted


Wakefield suppressors• Mount screens

after mounting 2nd vacuum container

• Mount through top flanges– seal with view

ports?

• Upstream: mount with large flange off WF screens

420

910

IP


Wakefield suppressor: downstream• Up/downstream

suppressors are identical

• Material: CuBe• Length: 179 mm• Thickness: 100

m• 16 segments• Mounting to box

non-trivial


Wakefield suppressors• Segments deform

differently during movement

• Coating needed on suppressors

• Press-fit to beam pipe structure

• Anneal CuBe, deform, harden at 400o C


Detector Mounting

Install Modules

3D alignment

Mount References


Thin Vacuum foil

• Beryllium expensive: k$ 500 per container

• Aluminum– welding 250 m Al

is possible– press-shaping

being developed

• FEA ongoing


Thin Vacuum foil

• Labour intensive: press, anneal, etc.• welding 250 m Al is possible• Extensive prototyping program

Chiel Bron

CP?!


Thin Vacuum foil• Increase radius: 10 20 mm to avoid

folding• Crystal structure is affected• Employ Al with magnesium alloy• Deform at higher temperature: 150 - 200o

C


Foil design ongoing (continued)


Foil design ongoing


Control of Vacuum System

• Group active with experience at former NIKHEF accelerator

• Propose meeting in Q1 2001


Vacuum Tests

• Self-regulating valve behaves as advertized

• Various gas flows have been characterized


Vacuum constraints

LHC:• beam life time: static density of 10-7 mbar 2 m (H2 300K) 0.01 % of LHC limit for integrated density ( 2.7 106 cm 1.6 109 molecules/cm3 )

• beam stability: dynamic effects must be taken into account

LHCb:• 10-7 mbar 1.2 m (H2 300K) 1.5 % of LHCb nominal luminosity

Difficult to achieve with silicon detectors, electronics and signal wires directly in LHC vacuum ! differential pumping.

(rough!)

See LHCb 99-045/VELO


Static pressure in VDConsider outgassing by: assuming outgassing rates of:

(mbar • l • s-1 • cm-2)

11 m2 Kapton (signal wires, pumped 40 hours) 10-7 H2O 2.3 m2 Al housing (per half) 10-10 H2

1.5 m2 bellows (per half) 10-9 H2

8 m2 SS vessel 10-10 H2

Pumps in detector volume: 140 l/s (per half) H2OPumps in tank: 4000 l/s H2

Bypass tube: 200 mm 4 mm pumped in the middle.

Calculate using a static flow model.Result: 1•10-4 mbar in detector volume

1•10-8 mbar in VD tank2•10-8 mbar • l • s-1 from det. vol. to VD tank


Summary table:(Data are approximate. QLHCb_total = estimate for the full vertex detector, i.e. both halves.)

Item Outgassing rate of item QLHCb_total

[mbar l s -1] Kapton foil, after 40 hrs pumping 1 E-7 mbar l s -1 cm-2 n/a sample Kapton flat cable QPI 3 E-5 mbar l s -1 130 E-4 male/female pair of PEEK D-type 25-pin connectors 6 E-6 mbar l s -1 / pair 50 E-4 male/female pair of stand. D-type 25-pin connectors 1 E-5 mbar l s -1 / pair 100 E-4 Liverpool carbon-fiber Si support 1 E-8 mbar l s -1 cm-2 ~ 1 E-4

Outgassing measurements

Continue: measure all unknown outgassing rates of components in a detector station


Dynamic Vacuum

Beam-induced particle bombardment desorption, emission

Ions, photons, electronsenergies up to keV

• Local pressure runaway (ion/electron-induced desorption)• Local static charge increase (electron multipacting)

LHC beam instability

See Adriana Rossi’s presentation


Dynamic Vacuum (continued)

Perhaps a solution:

use coating of surfaces by Tiadvantages: low SEY , low , local pumping

Design issues: • better surfaces ? (NEG ?)• in-situ coating required or not ? • thickness of layer needed ?• what re-coating rate ?• affordable cathode temperature in-situ ? • wake field / RF properties ?• side effects ? (peeling, ...)

We need , for:• different materials • surface conditions (un)baked, saturated, activated, etc. • different impact energy spectra

Data available only in a few months ! (Mahner et al.)


Cooling system with mixed-phase CO2

Phase diagram CO2

1

10

100

-80 -70 -60 -50 -40 -30 -20 -10 0 10 20 30 40 50

Temperature [°C]

Pre

ssur

e [b

ar]

vapor

liquidsolidgas

critical point

triple point

*


CO2 Cooling Tests

Cooling system

-30o C

40 W/module


CO2 gas-liquid storage tank57.3 bar at 20 C

CO2 supply line

compresssor

P [W]

P [W]

P [W]

flow restrictions

cooling lines

gas only

pressure (temperature)regulating valve

heat to 20 C

Mixed-phase CO2 Cooling systemSee LHCb 99-046/VELO

cool to 20 C

supply lineexpansion valve


CO2 Cooling Tubes

Cooling tubes

1.1 (0.9) mm S.St.

Welding and brazing


FEA ongoing


Tests ongoing


RF tests at NIKHEF

Simulation with MAFIA

First 3 measured eigenmodes:•220 MHz•270 MHz•380 MHz

Outlook:•Eigenmodes•Short range effects; Z/n•Electric field inside secondary vacuum

Picture 1 of tank removed

Picture 2 of tank removed


Wake field Suppressor

Central cooling line

Temperature sensors (2 per station, 4 wires per measurement


Detector Modules

Number of planes: 25

Discuss

Liverpool delivers modules

40 W, 1 m cable, 50 % isolation thickness, 10 - 15 K T, radiative cooling

44 pins,440 / module


Summary• Design is based on secondary vacuum system

– Beryllium option: costly and uncertain

– needs approval for TDR

• Current design – allows baking up to 150o C

– decouples Si detectors from primary vacuum system

– employs venting with Argon

– cooling based on CO2 in gas-liquid phase

• Self-regulating valves behave as advertised

• Wakefield excitation under study

• Need information on dynamic vacuum effects

• Propose meeting on control issues (e.g. NIKHEF)

vrije universiteit amsterdam cern, november 27, 2000 velo system j.f.j. van den brand lhcb vertex...

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