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20/1-004 (CERN)
Gas R&D activities
Gas R&D activities 2026-10-01 09:44(GMT+2:00)
Key Outcomes
The meeting introduced a new member (Matteo) to the group's research goals and covered three active workstreams: (1) quantum chemistry simulation of detector gas molecules, (2) understanding gas behavior to guide eco-friendly replacements, and (3) troubleshooting an operational gas distillation/recovery system at ATLAS. Several technical problems with the distillation prototype were identified and partially resolved.
Research Goals & Context
· Core problem: Greenhouse gases (e.g., R134A) used in RPC detectors seems to guarantee better performance as their GWP increases — this relationship is not understood and needs to be explained.
· Objective 1: Understand the fundamental properties that make R134A uniquely effective, rather than blindly following refrigerant industry replacements (e.g., HFO variants).
· Objective 2: Use that understanding to guide a targeted search for eco-friendly gas alternatives suited specifically to particle detection (gas phase, no evaporation).
· CF4 role: Increases electron drift velocity, improving time resolution; any replacement must replicate this property — the molecular mechanism is not yet understood.
Quantum Chemistry Simulation Work (ORCA)
· Bond dissociation energies calculated for CF4, SF6, R134A, HFOs, and CFCs to determine fragmentation thresholds and detector aging risks (e.g., free chlorine/fluorine fragments binding to detector surfaces).
· Validation approach: CF4 and SF6 used as benchmarks (online data available); results used to estimate error margins for molecules lacking published data (e.g., HFOs).
· Key finding: SF6 can absorb a free electron without bond breaking (negative binding energy ~−1.09 eV); HFO does not exhibit bond stretching upon electron attachment, meaning it cannot replace SF6 as an electron absorber.
· Quenching mechanism: Isobutane's 36 vibrational modes allow energy dissipation without bond breaking; linear molecule replacements with more modes could be explored.
· Three-body bonding: Identified as a relevant process — presence of a second gas molecule can facilitate electron attachment; current ORCA work is limited to two-body interactions.
· Double-bonded gases (HFOs): Low GWP due to fast atmospheric degradation, but double bonds are more susceptible to fragment attachment, which may affect detector aging.
Garfield++ Simulation
· Goal: Simulate avalanche behavior and assess the impact of switching off individual cross-section processes to understand their relative contribution to simulation output.
· Open question: Which processes account for what percentage of the simulated avalanche.To understand the potential of the simulation where we cannot simulate all processes
· Maximilian to provide an introduction/dedicated session to Matteo when back in office for the lab activity and for Garfield.
Distillation System Issues & Fixes (ATLAS Prototype)
· Liquid in reboiler: Confirmed normal — at 1.5–2.5 bar absolute and −2 to −3°C, R134A is liquid; ~1 kg R134A recovered.
· Cooling circuit malfunction: Temperature measured at −24.7°C at condenser return vs. −5°C just before reboiler (cooling machine set to −50°C); cooling is not circulating through the full circuit. Potential fix would need: redo pipe work between condenser and reboiler from series to parallel.
· Analysis line fix: Original analysis point (liquid-filled, small pipe) was unreliable; moved to the buffer tank where gas phase is confirmed; measured ~2.6% CO2.
· Safety valve: A three-way valve position allows addition of a second safety valve on the current temporary analysis line not currently installed; options being evaluated.
· Flow monitoring gap: No mass flow controllers installed; reflux ratio cannot be defined or controlled, making systematic optimization impossible. MFCs #1 and #2 identified as mandatory; #3 optional.
· Simulation license issue: Emmanuel lacks the simulation software license (previously used by Ryan); team to follow up in a call with the gas separation group.
Action Items
· Matteo: Review the referenced paper on gas behavior; compare its approach with our planned simulation strategy and identify key differences.
· Matteo: Visit the lab with Maximilian (tomorrow) to observe detector measurements firsthand.
· Max: Deliver a dedicated introduction to Garfield++ simulation work for Matteo.
· Emmanuel/Maria Cristina/Roberto: Investigate cooling circuit piping and look for work needed to implement parallel configuration for condenser/reboiler.
· Emmanuel: Ask price quotation for mass flow controllers (MFC 1 & 2) on the distillation column.
· Roberto: Resolve ASPEN simulation software license issue; coordinate with gas separation group call.
Open Questions
· What molecular property of R134A drives its superior detector performance relative to lower-GWP alternatives?
· Can three-body bonding interactions between gas mixture components be modeled (beyond ORCA's two-body limit)?
· What is the correct temperature gradient profile along the distillation column during operation?
· Does the packing inside the column remain valid for the new gas mixture (viscosity changes with temperature)?
Gas R&D activities 2026-09-24
Action Items
· Thomas/Emmanuel: Increase heater temperature limit above 30°C from both device and cabinet settings — retry bottoms vapor sampling.
· Davide: Install temperature sensor on cooling return line (cut Armaflex) to confirm coolant circulation status.
· Emmanuel/Maria Cristina: Partially close hand valve on coolant bypass path to redirect flow through reboiler; monitor Lauda chiller response.
· Thomas: Add DPT millibar pressure display to control view for level sensor cross-verification.
· Emmanuel/Maria Cristina: Recheck bottoms analysis — attempt sampling this afternoon with pressure in buffer confirmed at ~1.5 bar.
Gas R&D activities 2026-09-17
Action Items
· Emmanuel: Add slide on pressure sensor and Zimmerli/Bronkhorst comparison for future reference.
· Max: Check Fe-55 source activity/decay rate — assess if a second source is needed before Run 4; contact radioprotection if new purchase required.
· Ryan/Emmanuel: Investigate why CMS experimental temperature (~–50°C) diverged from simulation prediction at 30% CO2.
· MOF simulation lead: Begin kinematic/molecular dynamics study; include CO2 and H2O molecules in future simulation runs.
· Max: Check which 2017 gas measurement data is available vs. missing; confirm gas inventory in the gas room.
· Ryan/Emmanuel: Look into binary interaction parameters for R1233ZD, R1224YD + isobutane for potential distillation simulation.
Gas R&D activities 2026-09-03
Action Items
· Team (today): Check Atlas circuit for existing refrigerant with Fabio; verify chiller operation.
· Emmanuel Ryan + team (tomorrow if available): Fill distillation column and observe liquid formation.
· Simulation team: Test 1.5 bar operating point; assess whether a compressor upstream is needed.
· Bjorn: Subtract noise from detector fit; retry alignment with cleaner signal.
· Max: Swap strip profile in frame C; confirm impedance fix for detector 32.
· Albin: Add CF3I and C4F10 molecules to the simulation table.
· Max: Finalize plots for ECOGAS contribution from May test beam and ZD scan results.
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