# Presentation: 096008

## Layer 0 Grounding

- Requirement in terms of noise performance
- Grounding/Shielding studies with L0 prototype
- Summary

- Kazu Hanagaki / Fermilab

## Best noise performance before installation

- capacitive load by sensor (0.7ADC~500e)

- capacitive load by cable (0.8ADC~600e)

- Total noise = 2.7ADC ~ 1900e. Differential noise = 2.5ADC ~ 1800e.

## Signal to Noise ratio

- A MIP creates 22000e.
- The best noise = 1800~1900e.
- Noise increase by 300~400e is expected after 15fb-1.
- The goal is to keep S/N better than 10.
- The current best noise performance before installing on the L0 support is already marginal.                                             Any additional noise must be avoided.

## L0 prototype module

- hybrid GND

- sensor GND

## Grounding Studies

- sensor

- SVX4/hybrid

- Metal box

- L0 support
- Kapton flex

- Analog cable GND(20)

- GND

- hybrid GND

- sensor GND

- Signal return

- Signal ground

## Noise level on the L0 support structure

- Hybrid only

- Sensor only

- Both hybrid and sensor

## Equivalent (?) circuit (cont’d)

- Connection important

- sensor

- SVX4/hybrid

- Metal box

- L0 support
- Kapton flex

- GND

- hybrid GND

- sensor GND

- Signal return

- Signal ground

- Smaller inductance (or smaller loop)

- Least impedance = least inductance  for high frequency (not resistance).

## After putting extra grounding plane

- Note! Still the hybrid grounding is not perfect in terms of getting low inductance... but the effect of the extra grounding by kapton flex is so clear!!!

- Single ground at hybrid

- Common ground at both hybrid and sensor

## Importance of low inductance connection

- 1 wire between hybrid and the extra grounding plane

- 3 wires

- 4 wires

## Low inductance connection (cont’d)

- 2 wires (~2cm)

- 2 wires (~4cm)

## Reducing the inductance

- Having lower inductance connection to GND seems crucial.
- L ~ (wire) length/radius:   M=l/2[log(2l/r)-1]
- L = /I
-   ~ area of the closed circuit
- People know these rules well, but sometimes forget to apply.
- But these rules are always critical for any grounding connections, both locally and generally.

- better

## How do we achieve????????????

- Sensor grounding.
- The sensor and hybrid need to be connected through rigid ground plane. This should work also as a shielding.          extension of kapton flex with copper mesh embedded.
- Hybrid side: proposal using the similar technique, but not yet decided.
- Need to decide; multi point ground vs single point ground.

## Summary

- No additional noise is allowed for L0.
- Low inductance ground connection is crucial, especially at the hybrid end.
- Grounding scheme at the hybrid must be fixed.
- Rigid grounding, or low inductance grounding path to the outside world must be maintained.

## Signal to Noise ratio

- S/N=10

- CSi

- Ccable

- Total noise estimates VS total capacitance

- Noise increase by 300~400e is expected after the irradiation.

## Irradiated sensor

- Irradiated sensor (not on the support structure)

- Non-rradiated sensor (on the support structure)

- Noise increase by ~200e.

- 1 ADC

- 0.7 ADC

## Radiation length

- (a) 16% of area occupancy is taken account.
- (b) 50% of volume occupancy assumed. May be possible to reduce.
- (c) heavy duty aluminum foil was measured to 20m thick.

| 100m Kapton | 0.04% | 600m Kapton | 0.21% |
| --- | --- | --- | --- |
| 3m Cu (a) | 0.02% | 16m Cu (a) | 0.11% |
| 300m (b) polypropylene | 0.07% | 1300m (b) polypropylene | 0.32% |
| 20m Al (c) | 0.02% | 20m Al (c) | 0.02% |
| Total | 0.15% | Total | 0.66% |

| Min (2 cables) | Max (12 cables) |
| --- | --- |

## Proximity to the grounding/shielding

- Only the difference is the weight on top of the cables.       Proximity to the shielding material.

- bottom cable

- top cable

- Noise due to capacitive coupling.

## Proximity to the Shielding (cont’d)

- The study is still on going...

- weight

| A:nothing     B: | top | bottom |
| --- | --- | --- |
| 75m Kapton (no weight) | 2.8 | 2.8 |
| 75m Kapton + 400m polypropylene mesh | 2.8 | 2.9 |
| 75m Kapton + 200m polypropylene mesh | 3.2 | 3.3 |
| 75m Kapton | 4.3 | 5.3 |

## Choice of spacer

- Dyconex has produced three different meshes with kapton sheet.
- hole radius: 60 m
- hole-distance: 190, 210 and 230 m
- corresponding to r ~1.95, 2.2 and 2.45
- Polypropylene mesh sheet