Abstract
We have been exploring the development of multicomponent gas mixtures with optimal electron transport, gain, electrical and chemical properties of potential interest to the Superconducting Super Collider muon detectors focusing in particular on binary and ternary mixtures of Ar, N2, CO, CO2, CH4, CF4, NH3, and H2O. In this article, we report and discuss: (i) recent measurements of electron drift velocities as a function of the density-reduced electric field E N for CO2/CF4, CO2/CH4, CO2/N2, CO/Ar, Ar/Si(CH3)4, NH3/CF4/Ar, CO2/CF4/Ar, and H2O/CF4/Ar mixtures, (ii) calculated values of the mean electron energy as a function of E/N for a number of unitary gases and the gas mixtures CO2/CF4, CO2/CH4, and CF4/Ar, and (iii) effective ionization coefficients as a function of E/N for Ar/CF4, Ar/CO2, CO2/CH4, and mixtures of Ar/CF4 containing CO2 or H2O. Addition of CO2 or H2O or NH3 to CF4/Ar causes electron "cooling" and increases the electron yield; the addition of H2O (or NH3) may, also, improve the detector aging performance. Mixtures of Ar/CF4 with CO2 or H2O appear promising. All results reported are for the case of zero magnetic field.
| Original language | English |
|---|---|
| Pages (from-to) | 160-168 |
| Number of pages | 9 |
| Journal | Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment |
| Volume | 309 |
| Issue number | 1-2 |
| DOIs | |
| State | Published - Nov 1 1991 |
Funding
Efforts to identify appropriate gases for large particle detectors trace many decades, see refs. e.g., [1-4]. Recently, a number of such efforts, see e.g., refs. [5-8], have been directed toward the development of appropriate gaseous media for the Superconducting Super Collider (SSC) muon detectors. While much progress has been made, it seems that we still do not have a gaseous medium with optimum overall properties . For example, two of the most commonly considered gaseous media are mixtures of Ar/CO2 and Ar/C2He ofwhich the former suffer from decomposition, instability (aging) and low gain, and the latter from flammability problems [1,5]. Interestingly, addition of small amounts of a polar gas (e .g ., H 2 O, alcohols) to these detector-gas mixtures improves [1,5] the conditioning/ aging properties of the detector (e .g ., 1% isopropanol + 18% CO 2 + 81% Ar [7]) . Precision muon detectors for the SSC put stringent constraints on the gaseous medium used in such large devices [5,7]. Firstly, a muon * Research sponsored by the U.S. Department of Energy, under Contract no . DE-AC05-84OR21400 with Martin Ma-rietta Energy Systems, Inc., and under Contract no. DE-AS05-76ER03956 with the University of Tennessee, Knoxville, TN .