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865/1-B03 (CERN)
BGI Regular Meeting
Minutes – BI BGI Bi-weekly Meeting
Participants: Chiara, Hampus, James, Juri, Justus, Lauren, Lukas
Apologies: William, Mark, Wilfried
1. PS & SPS BGI
Deliverables
The first deliverable for the PS/SPS BGI DAQ system is the production of a single profile in a cycle, currently scheduled for 2nd April. The team noted that this milestone may slip by approximately one week, depending on the status of ongoing testing. A decision will be taken later this week after reviewing progress.
It was emphasized that any delay should be communicated clearly to OP, given the importance of the BGI measurements for high-intensity beams.
System Status
- Hardware installation in the SPS is complete.
- Ongoing testing is being carried out on both the PS and SPS systems.
SPS Shielding
Operation with the new RF shielding configuration appears stable in the presence of multi-bunch beams. At present, there is no strong indication of an EMI issue that would require replacing the horizontal SPS shield.
The team agreed to:
- Compare horizontal and vertical BGI performance once data becomes available.
- Decide afterwards whether the horizontal shield should be upgraded.
If required, an intervention could potentially be performed during the injector technical stop in June.
EMI Measurement Campaign
To better understand the SPS EMI mitigation mechanisms, a dedicated measurement campaign was proposed using the stretched-wire method.
The aim is to measure induced common-mode voltages on the Timepix electronics for different RF shielding configurations:
- Original configuration (diamond shield, no bottom plate)
- Working configuration (hex-packed shield + bottom plate)
- Bottom plate only
- Shield only
Available hardware includes a spare SPS BGI instrument and bottom plate.
A small air-side breakout PCB will be required to probe signals.
Possible collaboration was discussed with the ABP metamaterial study, which also intends to test on the SPS BGI instrument.
2. HL-LHC BGI
Magnet Design Report
The magnet design report from TE-MSC has been circulated for comments. The magnet is designed to operate with the existing BBLR power converter, which is limited to 40 V.
Voltage margin is limited, and most of the voltage budget is consumed by:
- DC resistance of the magnet
- Resistance of the supply cable
The team will verify that the power cable ordered by BI matches the assumptions used in the magnet design, since any increase in resistance could prevent the magnet from reaching the required current.
Mechanical Integration
The latest integration drawing shows the removal of a third flange, slightly relaxing spatial constraints.
The design remains compatible with the SPS integration envelope, although space for services (HV connections, electronics, heating jackets) remains limited.
Vacuum and Bake-out
Questions were raised regarding the feasibility of installing heating jackets around the flanges, given the currently assumed clearance (~5 mm).
It was agreed that the vacuum team should review the design to confirm whether:
- Heating collars can be installed
- Bake-out can be performed without permanent heating equipment installed.
Bake-out temperatures around 150 °C are currently expected due to adhesive limitations.
HL-LHC BGI – Detector Assembly
The assembly of the pixel detector and cooling stack remains one of the final open design items.
Recent progress:
- Visit to EP-DT to discuss sensor handling and bonding procedures.
- Adhesive bonding was recommended as the most robust approach, compared with soldering/brazing options.
Concerns discussed:
- Replacing a failed chip after assembly could be difficult.
- A possible solution would be an intermediate copper plate, allowing replacement of the chip module without disassembling the full cooling structure.
Planned activities:
- Outgassing tests of candidate adhesives (results expected mid-April)
- Thermal performance tests of the cooling stack during summer
The aim remains to complete the mechanical design by end-September, allowing production drawings to start before the end of the year.
HL-LHC BGI – Impedance Matching
The impedance working group requires that the BGI detector is impedance-matched before installation.
Conceptual scheme:
- High-voltage cable
- Decoupling capacitor
- Matching resistor
- Grounded filter box
Open technical questions remain regarding:
- The feedthrough connector
- The transition between feedthrough and coaxial cable
- Mechanical implementation of the filter box
The high-voltage cable already ordered happens to have 45 Ω impedance, matching the intended design.
Further discussions are required with Mark McLean and Wilfried to finalize the implementation.
Electrical Safety Procedure
A new CERN procedure for custom electrical equipment is being prepared in the framework of the ESP.
Key points:
- A risk analysis and documentation must be produced for all equipment.
- Before installation, the equipment must receive a Certificate of Conformity signed by the group leader.
This requirement will apply to the BGI high-voltage system.
Wilfried has already begun incorporating appropriate safety measures in the design (discharge procedures, verification tests).
A BI-specific session on the new procedure is planned for 25 June.
HL-LHC BGI – Budget
The updated magnet cost estimate is approximately 700 kCHF, higher than earlier estimates.
The magnet group has confirmed this figure in writing.
The BI team will forward this information to the HL-LHC project, noting that the increase should not currently be absorbed within the BGI budget.
Production Readiness Review
The BGI instrument will be presented at the HL-LHC Project Board on 22 April.
The review will focus on:
- Overall schedule
- Remaining technical risks
- Timeline for finalizing the design.
3. Telescope
April Test Beam
A telescope test beam is planned mid-April. Setup will begin during the week preceding Easter.
Current preparation activities include:
- Improvements to the telescope control software
- Integration of motion stages and monitoring tools
- Documentation on Confluence and EDMS
Wilfried is available to assist with mechanical or electrical setup if required.
Detector Assemblies
New hybrid pixel detector assemblies are planned. These would be fully assembled HPDs, which could then be thinned on the ASIC backside to approximately 150 µm.
Initial cost estimates:
- ~20 kCHF for assembly
- Additional cost for thinning.
Telescope Software
Migration from BIPXL v4 to v5 was discussed.
Advantages:
- Avoid long-term maintenance of legacy (v4) software
- Enable improved data acquisition features
The upgrade effort is expected to be small.
The team will consider performing the upgrade before the July test beam campaign.
Action List
| Action | Responsible |
|---|---|
| Decide whether to shift PS/SPS BGI deliverable by one week | Hampus |
| Inform Operations if schedule changes | Hampus |
| Coordinate stretched-wire measurements with ABP/RF | James |
| Verify resistance assumptions for magnet power cable | Gunn |
| Define timeline for remaining HL-LHC BGI design decisions | James / Chiara |
| Clarify impedance-matching implementation | Mark / James |
| Prepare material for HL-LHC project board | James |
| Continue telescope preparation for April test beam | Justus |
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