The Belle II Silicon Vertex Detector Florian Buchsteiner (HEPHY Vienna)

The Belle II Silicon Vertex DetectorFlorian Buchsteiner (HEPHY Vienna)

IntroductionLadderSupport

StructureCoolingSummary

01 July 2014F. Buchsteiner: The Belle II Silicon Vertex Detector 2




Overview


Layer

Radius [mm]

Ladders

Sensors /

Ladder

Slanted?

Windmill angle

[°]

Overlap [%]

6 135 16 5 9 9.0

5 104 12 4 5 3.8

4 80 10 3 6 15.4

3 38 7 2 x 6 7.1

Rect (122.8 x 38.4 mm , 160 / 50 um pitch)2

Rect (122.8 x 57.6 mm , 240 / 75 um pitch)2

W edge (122.8 x 57 .6-3 8.4 m m , 240 / 75..50 um pitch)2

0

0

10

3

45

6[cm] layers

[cm]

20

-10-20-30 10 20 30 40

6

z APVs

z APVs

z APVs

64

4

4 4

46

6

6

rphi APVs

rphi APVs

rphi APVs

6

64

4

4 4

4

4

46

6

66 6

6 6 6

6

Components

Not shown: Outer shell (CF)


Ladders

End rings(SUS)

Carbon fiber(CF) cone

End flange(aluminum)

Requirements & Features

Support for detectors with readout and cooling Light-weight (minimal radiation length) Stable in time (no vibrations except during

earthquake) Absorb thermal gradients

Fully assembled SVD can be split into halves Important for quick assembly/disassembly around

beam pipe and pixel detector (PXD)

PXD + SVD = VXD (Vertex Detector) Also includes beam pipe and heavy metal masks

(enclosed)





The basic element (“atom”) of the SVD Consists of

Double-sided silicon detectors Readout electronics Support structure Cooling infrastructure

One distinct type for each layer

Ladder


Longest ladder type (L6) shown here

Exploded Ladder


Origami flexesAPV25 chips

Airex spacer

Silicon Sensors

PCB Hybrid

PCB Hybrid

Pitch adaptersRibs

FWD End Mount

BWD End Mount


Origami prototype module

Silicon sensor

Flex hybrid

Pitch adapter for top side of sensor

Pitch adapter for bottom side of sensor

APV25 readout chip

Ladders and Layers

Ladders of L4,5,6 are similar Different number of rectangular sensors with

Origami readout 1 slanted sensor (different angles)

Ladders of L3 are more conventional Straight design (no slanted part) Just PCB hybrids on sides (no Origami readout)


L3 ladder

L3 bridges

Ladder Support Structure

2 Ribs + End Mount (aluminum) on each side Rib structure: 3mm Airex core with laminated

0.15mm CF sheets End mounts serve as

Mounting points to end ring Heat sinks for readout electronics on PCB hybrids


Mounting a Ladder

Ladders are positioned by two precision pins Fixed on backward side Sliding on forward side to allow thermal

movement


Slide Lock Mechanism (SLM)

SLM is used in layers 4,5,6 No screw driver access from

top Pin fits into precision hole in

end ring Locked by set screw Also provides cooling contact


BWD FWD

APV25 cover

End mountKokeshi pin

= origin of ladder

Swallow tailSpring

Precision hole

Set screw hole

Ladder Mount of Layer 3

L3 uses a different approach Very limited space Screwdriver access from top possible

(unlike L4,5,6) Oblong holes for precision pin and

washer + screw (forward side) Precision pin defines position Washer + screw push bridge against end ring

Simple holes for fixed mounting (backward side)


Precision pin

Washer + screw

L3 forward side

Issues Addressed


Rev. 0.12: Screwed connection between ribs and end mounts Torque to tighten screws caused

deformations of rib Rev. 1.0: new joint without screws Re-design of ribs and end mounts

Rev. 0.12: Individual end mount design in each layer Complex shape Difficult (& expensive) to manufacture Rev. 1.0: unified end mount design for L4-L6 General improvement (simplification) of all parts

Modified End Mounts


Glued joint between ribs and end mounts Secured by pin with 1 mm Tested with simple mockup Assembly done with gluing jig No distortion during assembly Slimmer ribs at joint More space to route pitch adapters

New design is easier (& cheaper) to manufacture

FWD Sliding Mechanism Rev. 0.12

Tricky task: provide thermal contact and allow linear motion

Design with undulated spring was too loose Improved the design


Swallow tailSpring

New Sliding Mechanism Version 1

Components End mount with swallow tail Prism rail (brass) Adjustment insert (brass) Ball plungers

Various spring forces Mockup exists Works very well Good thermal contact


New Sliding Mechanism Version 2 (Final) Components

End mount with swallow tail Prism rail (brass) Coil spring (various forces) 1.5mm stainless steel ball Grub screw Easier to machine Preferred solution Mockup exists Works even better! Good thermal contact Cheaper than Version 1


Ribs Rev. 0.12


Rib Displacement Volume [cm3]

Dmax [mm]

L6 13.80 7.44

L5 11.18 4.19

L4 8.61 2.29

Dmax under (non-realistic) conditions – only for comparison between variants

Stiffness Improved Ribs (Final)

Significant Dmax improvement in all cases

L5: very limited space towards L4 <1mm clearance to PA1/PA2 in some cases


Rib Displacement Volume [cm3]

Dmax [mm]

L6 16.17 1.79

L5 12.37 1.89

L4 8.21 0.63




End Rings

Supporting Ladders Cooling for PCB hybrids


Individual rings for L5, L6 Combined L3+4 end rings

Integrated Cooling Channel

Made from two halves (SUS) with diffusion welding


Carbon Fiber Cones

End Rings are glued onto Carbon Fiber Cones Separation between PXD and SVD regimes

Made from CF because its CTE~0


End Flanges Supports SVD

End flanges are screwed to CDC Feed-through openings for cables &

pipes


Material Aluminum

Outer Shell Only mechanical connection between

forward & backward sides (total VXD ~80kg + part of cable weight)


Has to tightly seal the VXD volume (temperature, dew point)




SVD Cooling

Total dissipated power 1748 APV25 chips ~ 0.4W / chip ~ 700W in total

Cooling of APV25 chips required Common CO2 (IBBelle) system with PXD

Operated at -20°C Dry volume with due point of -30°C Ambient temperature inside dry volume: ~20°C

Thermal mockup of VXD Under construction at DESY to study thermal

behavior01 July 2014

F. Buchsteiner: The Belle II Silicon Vertex Detector 30

MARCO used @ DESY

Overview of Heat Transfer Points


Origami CoolingBackward PCB Hybrid

Forward (Sliding) SLM

L3 Bridge

Sufficient heat transfer measured with mockups ΔT~10°C for Origami ΔT~20°C for edge hybrids

Cooling of APV25 Chips

Edge hybrids APV25 chips cooled by

end rings End mount / L3 bridges

used as heat sink Origami flexes

100µm thin pre-bent SUS pipe

1.6mm Directly attached to

APV25 chips


APV25 chips

End mountEnd ring

APV cover

Setup (1/2)

Dummy end ring with big metal block in water bath

Final SLM with weak or strong springs Heater wires simulating APV25 power (4W total)


Setup (2/2)

SLM must also work in upside-down position loaded with the weight of a ladder

Adding 100 g to simulate this condition


Result With Weak Spring

Larger T with 100 g load spring too weak


1000 1500 2000 2500 3000 3500 4000 4500 5000 55000

5

10

15

20

25

30

35

40

45

50Sliding SLM Thermal Mockup Test (weak spring)

3 APV

2 APV guard

1 end ring

0 water bath

Time [s]

Tem

pera

ture

[°C

]

No weight

With 100 g

0 2000 4000 6000 8000 10000 1200010

15

20

25

30

35

40

45Sliding SLM Thermal Mockup Test (strong spring)

3 APV

2 APV guard

1 end ring

0 water bath

Time [s]

Tem

pera

ture

[°C

]

Result With Strong Spring

T always around 15°C spring is strong enough


No weight

With 100 g

L3 Bridge (1/3)

Thermal simulation End ring contact surface of bridge is held at -20°C APV25 bar sinks 4.8W of heat (=12 APV25 chips)

Result of long bridge (backward side)


-4.6°C

-20°C

ΔT~15°C

L3 Bridge (2/3)

Thermocouples:


0 water bath

1 heat sink

2 bar back3 bar front

4 APV center

5 APV end

4.8W(dummy APVs)

L3 Bridge (3/3)


600 800 1000 1200 1400 160015

20

25

30

35

40L3 Bar Thermal Mockup Test

5 APV end

4 APV cen-ter

3 bar front

2 bar back

1 heat sink

0 water bath

Time [s]

Tem

pera

ture

[°C

]

ΔT~17°CConsistent with simulation

Origami Cooling (1/3)

Simulation


CO2 cooling pipe

APV25 chip

“GapPad”: 1mmKeratherm Softtherm 86/125

ΔT~10°C (@ pre-amp)


Thermal test using 2-sensor-Origami module (20 APV25 chips)

Tested in a dry box with blow CO2 system

Placed a few thermocouples Watched by infrared camera

Unfortunately, no absolute readings



Pipe @ room temperature APV chips much hotter


APVs on without cooling APVs on with cooling

Pipe has -16°C (thermocouple)APV chips have similar temp.

Camera does not providecorrect absolute values!

DESY Beam Test – SVD Cooling

Installed 4 SVD modules Layer 3 module with conventional hybrids 3 Origami modules with 1.6 mm cooling pipe

Cooling pipe tested up to 150 bar SVD modules operated

Without cooling at 0°C at -10°C (humidity minimum)

Sensor bias current followed CO2 temperature Indicates proper cooling contact





Summary Mechanics

Revised ladder design Ribs and end mounts FWD sliding mechanism

Fine tuning of end ring design Cooling

Common CO2 cooling with PXD Overall performance will be verified with thermal VXD

mockup DESY test beam: SVD modules cooled down to -10°C

(humidity minimum) Significant decrease of sensor bias current indicates proper

heat transfer Air temperature in box close to that of ambient air


Documents

The Belle II Silicon Vertex Detector Florian Buchsteiner (HEPHY Vienna)