[Paper Review] A study of HFO-1234ze (1,3,3,3-Tetrafluoropropene) as an eco-friendly replacement in RPC detectors

L. Benussi, S. Bianco+6 more|arXiv (Cornell University)|May 7, 2015

Particle Detector Development and Performance5 references17 citations

TL;DR

This study evaluates HFO-1234ze (1,3,3,3-tetrafluoropropene) as an eco-friendly alternative to high-GWP fluorinated gases in Resistive Plate Chamber (RPC) detectors. It demonstrates that HFO-1234ze enables stable RPC operation with low streamer probability and high detection efficiency when combined with SF6 or argon, though full replacement of C2H2F4 requires voltage adjustments beyond current system limits, highlighting its potential for sustainable LHC detector operation.

ABSTRACT

The operations of Resistive Plate Chambers in LHC experiments require F-based gases for optimal performance. Recent regulations demand the use of environmentally unfriendly F-based gases to be limited or banned. This report shows results of studies on performance of RPCs operated with a potential eco-friendly gas candidate 1,3,3,3-Tetrafluoropropene, commercially known as HFO-1234ze.

Motivation & Objective

• To identify and test environmentally sustainable fluorinated gas alternatives for RPC detectors used in high-energy physics experiments.
• To address the regulatory phase-out of high-global-warming-potential (GWP) gases like C2H2F4 (GWP=1430) and SF6 (GWP=23900) in LHC experiments.
• To evaluate HFO-1234ze as a viable replacement candidate in RPC gas mixtures with respect to detection efficiency, streamer suppression, and timing resolution.
• To assess the performance of HFO-1234ze-based mixtures in both streamer and avalanche modes, particularly under realistic LHC background conditions.

Proposed method

• A 12-element RPC hodoscope system at INFN Frascati, modeled after the CMS GGM system, was used to test gas mixtures under controlled T and RH conditions.
• Gas mixtures were flushed into the system with humidity stabilized at ~40%, and performance was measured using a 5 GSa/s digital oscilloscope triggered by scintillator layers.
• Effective high voltage (HV_eff) was calculated using the standard formula: HV_eff = HV × P₀/P × T/T₀, with P₀ = 990 mbar and T₀ = 290 K.
• Signal analysis used four time windows: baseline (10 ns before signal), signal window (150 ns around trigger), control region (150 ns before baseline), and delayed region (150 ns after signal) for noise and timing evaluation.
• Offline analysis was performed using ROOT software, with baseline subtraction and threshold-based signal identification to extract charge, time resolution, and efficiency metrics.
• Multiple gas mixtures were tested: varying HFO-1234ze fractions replacing C2H2F4, with and without SF6 or argon additions, at fixed isobutane (4.5%) content.

Experimental results

Research questions

• RQ1 Can HFO-1234ze replace C2H2F4 in RPC gas mixtures while maintaining detection efficiency above 90%?
• RQ2 What is the impact of HFO-1234ze on streamer probability and quenching efficiency compared to R134a and C2H2F4?
• RQ3 How does adding argon to HFO-1234ze-based mixtures affect the working point and RPC performance?
• RQ4 Can HFO-1234ze-based mixtures achieve acceptable time resolution and signal charge with low electronic thresholds?
• RQ5 What is the maximum fraction of HFO-1234ze that can be used before voltage requirements exceed safe operational limits?

Key findings

• HFO-1234ze exhibits strong quenching characteristics, significantly reducing streamer probability compared to R134a, making it a promising candidate for eco-friendly RPC operation.
• Replacing 23% of C2H2F4 with HFO-1234ze shifts the working point by approximately 1500 V, but this shift is manageable with SF6 addition to maintain low streamer fractions.
• Mixtures with 45% HFO-1234ze replacement of C2H2F4 required excessively high voltages, limiting full replacement within current HV system constraints.
• Adding argon to HFO-1234ze-based mixtures reduces the required working voltage and improves performance, but full detection efficiency (>90%) was not achieved at low streamer fractions with the tested electronic thresholds.
• Time resolution, measured as the difference in time-over-threshold between two RPCs, remained within acceptable limits (divided by √2 for real resolution), indicating good timing performance.
• The study confirms that HFO-1234ze is a viable alternative for RPCs, but full C2H2F4 replacement is not feasible without system upgrades due to voltage constraints.