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Bi-monthly meeting of MIT-BNL He3-ABS Collaboration
Meeting Minutes
Date/Time: Sep 11, 2025 - 10:03–10:27]
Location: Zoom Meeting
Attendees:
- Prajwal MohanMurthy
- Maggie Kerr
- Frank Rathmann
- Deepak Raparia
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1. Opening Remarks
- Prajwal initiated the meeting, noting the use of AI-generated minutes to save time.
- The purpose was to review technical progress on the helium cryogenic system and related components over the past few weeks.
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2. Technical Updates
1K and 4K Cryogenic Components
- Helium is cooled to ~1.3 K from 4 K through evaporative pumping.
- Reliable liquid helium formation confirmed via pressure response.
- Assembly requires brazing the top cap to ensure vacuum-tightness.
Brazing & Machining
- Prajwal, Joe, and Jim consulted two brazing outfits (Ipswich, MA and New Hampshire).
- Both recommended refinishing component edges to a slanted design for better braising with more material is in contact.
- MIT Central Machine Shop is completing the machining refinements.
- Bright-dipping is arranged to remove copper oxides prior to brazing.
Materials & Coatings
- Issue: copper does not bond reliably with stainless steel during brazing.
- Solution: nickel sulfamate coating on steel and copper components to ensure adhesion.
- Aotco (local vendor near Bates Lab) will provide coating services within a week.
- Cheaper and faster than replacing parts with full copper.
Nozzle & Sensors
- The nozzle, housing the multi-channel plate (MCP), is thermally anchored to the 1K pot.
- Two temperature sensors will be installed on the nozzle (primary + backup).
- Additional sensors allocated: one on the 4K part, one on the 1K part, and one on the copper heat shield.
- High-precision calibrated resistive sensors reserved for the nozzle and 1K region.
- Wiring setup with quad cables to the feedthrough (~20 leads) for up to 5 sensors.
Multi-Channel Plate & Skimmers
- Two spare MCPs available; one previously broke.
- MCP inside nozzle; followed by two skimmers for angular selection (~0.5° dispersion).
- Beamline sequence: He-3 thermalizes at 4K → 1K → nozzle → MCP → skimmers → magnet.
Thermal Braiding
- Thermal braids between the 1K pot and nozzle improve conductivity.
- Copper tubing tensioned to final geometry using a custom-built wrench before brazing.
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3. Timeline & Next Steps
- Finishing and coating to be completed in coming weeks.
- Brazed assembly expected before Prajwal’s upcoming visit to BNL.
- Cryo-head assembly: late October–November.
- Vacuum testing: January.
- Polarization and temperature measurements: February–March.
- Preliminary results to be presented at APS April meeting.
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4. Questions & Clarifications
- Frank inquired about sealing and leak-tightness.
- Prajwal explained cryo-soldering at ~500°C in vacuum ensures full sealing.
- Discussion about coating steel vs. replacing with copper resolved in favor of nickel sulfamate coating.
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5. Closing
- General agreement that the project is on schedule.
- Meeting adjourned with thanks to participants.