1. The Mechanical Structure for the SVD Upgrade
Immanuel Gfall (HEPHY Vienna)

2. Immanuel Gfall (HEPHY Vienna)
Design Goals
Lowest possible material budget
Gravitational sag equal or lower than 100µm
Minimum coefficient of thermal expansion
Low moisture susceptibility
Radiation hardness up to 10 Mrad
Compliant with the Origami concept
Immanuel Gfall (HEPHY Vienna)

3. Origami Module Readout Side
High component density
Sensitive wirebonds
Flexible structure
Thermal expansion
Bad attributes for mounting the structure on top side
Immanuel Gfall (HEPHY Vienna)

4. Immanuel Gfall (HEPHY Vienna)
Origami Rohacell Core
Rohacell core is an already existing volume
Electrical and thermal separation from sensor
Evenly distributed material
Small modifications of the core can lead to good structural strength
Immanuel Gfall (HEPHY Vienna)

5. Origami Module Sensor Side
Rigid contact surface
Conventional rib design is possible
Wire bonds and fanouts limit the contact area
Immanuel Gfall (HEPHY Vienna)

6. Immanuel Gfall (HEPHY Vienna)
Two Design Options
Option 1: Sandwich
Option 2: Ribs
Immanuel Gfall (HEPHY Vienna)

7. Option 1- Sandwich Design
Carbon Fiber Reinforced Plastic (CFRP) layers cover Rohacell core
Separating Sensor from CFRP using a thin isolating film (eg. Sil-Pad strips)
Origami hybrid sits on top of Sandwich (not drawn in this sketch)
CFRP Sandwich
Sensor
Immanuel Gfall (HEPHY Vienna) 7

8. Option 1 – Simulation Boundary Conditions
Rohacell: 2 mm thickness
CFRP: 2 x 0.14 mm plies
40 mm wide, 2.28 mm thick, 698 mm long
Sensor weight: g
Structure weight: 15 g
Fixed support at both ends
Average radiation length: 0.629% X0
Immanuel Gfall (HEPHY Vienna)

9. Immanuel Gfall (HEPHY Vienna)
Option 1 - Simulation
Max. sag: mm
Avg. sag: 0.05 mm
Immanuel Gfall (HEPHY Vienna)

10. Immanuel Gfall (HEPHY Vienna)
Option 2 – Rib Design
Sandwich composite ribs
CFRP ribs support horizontally arranged sensors
Sandwich rib structure supports vertically arranged sensors
Immanuel Gfall (HEPHY Vienna)

11. Option 2 – Mounting Points
Elevated Rohacell mounting points
Serve as contact area and isolation for the sensors
Immanuel Gfall (HEPHY Vienna)

12. Option 2 – Simulation Boundary Conditions
Rohacell: 1.2 mm thickness
CFRP: 2 x 0.14 mm plies per rib
6.5 mm high, 1.48 mm wide, 698 mm long
Structure weight: 4.8 g (both ribs)
Fixed support at both ends
Average radiation length: % X0
Immanuel Gfall (HEPHY Vienna)

13. Immanuel Gfall (HEPHY Vienna)
Option 2 – Simulation
Horizontal Sensors
Max sag: mm
Avg sag: mm
Immanuel Gfall (HEPHY Vienna)

14. Immanuel Gfall (HEPHY Vienna)
Option 2 – Simulation
Vertical Sensors
Max sag: mm
Avg sag: mm
Immanuel Gfall (HEPHY Vienna)

15. Radiation Length Option 1
“Batman” distribution of pipe and coolant
Pipe
Coolant
APV
Kapton
Sensor
CFRP
Rohacell
Immanuel Gfall (HEPHY Vienna)

16. Radiation Length Option 2
APV
Kapton
Pipe
Coolant
Sensor
CFRP
Rohacell
Immanuel Gfall (HEPHY Vienna)

17. Pros & Cons of Option 1 (Sandwich Design)
+ Even distribution of material budget
– High fabrication effort & cost
– Connector issues with bent kapton
– Additional capacitance decreases signal to noise by ~ 2.5%
– Bonding potentially more complicated
Immanuel Gfall (HEPHY Vienna)

18. Pros & Cons of Option 2 (Rib Design)
+ Significantly easier to build + High assembly precision + Gravitational sag constant in φ – Particles could hit the structure before they hit the sensor (although unlikely) – Uneven material distribution
Immanuel Gfall (HEPHY Vienna)

19. Immanuel Gfall (HEPHY Vienna)
Discussion
Homogeneous design vs. lower average radiation length
Construction effort of sandwich vs. rib design
Higher costs of sandwich design
Problem of twist resulting from slanted sensors
Immanuel Gfall (HEPHY Vienna)

20. Immanuel Gfall (HEPHY Vienna)
Outlook
Construction of mechanical mockup
Thermal simulation / measurements
Integration of cooling
Construction of outermost ladder
Endring design
Immanuel Gfall (HEPHY Vienna)