Long term experience with perfluorobutane in COMPASS RICH

TL;DR

This paper reviews the 20-year operational experience with perfluorobutane as a radiator gas in the COMPASS RICH detector, highlighting improvements in gas handling, refractive index measurement, and environmental considerations.

Contribution

It provides a detailed account of the long-term use, measurement techniques, and environmental management of perfluorobutane in a high-energy physics detector.

Findings

Refractive index measurement accuracy reached 1 ppm.

Material waste in filtering was reduced from 30% to 5%.

Potential alternative radiators are discussed.

Abstract

COMPASS RICH-1 has used high-purity perfluorobutane as radiator gas since 2001. The operation and control of the radiator gas has evolved over years with continuous improvements. We report on the experience gained in the 20 year-long operation of perfluorobutane as COMPASS RICH radiator. Very accurate values for the radiator gas refractive index are needed for high-performance particle identification. The procedure has evolved over years and the one presently in use, which provides refractive index estimate at the 1 ppm level, is discussed. Perfluorobutane procurement is becoming challenging, and the minimization of material waste is now a priority for the protection of the environment. Commercially available perfluorobutane needs dedicated filtering before usage and typical material losses in the filtering procedure were around 30%. Recent efforts allowed us to reduce them to about 5%. A potential alternative to fluorocarbon radiators in gaseous RICHes is also presented.