Performance of TMS ionisation chambers in a calorimeter for cosmic ray particles

At the Karlsruhe Research Centre a large calorimeter for high energy cosmic ray particles has come into operation. As active detectors within the iron absorber liquid ionisation chambers using 8 m³ of purified tetramethylsilane (TMS) are used. The method of chamber cleaning and the purification procedure for the liquid are described. The chamber cleaning consists of a chemical process followed by a physical cleaning by glow discharge in an argon atmosphere. The liquid is purified by passage of its vapour over molecular sieves and Oxysorb. All details of the purification system have been optimized for mass production