Parameter of MDT Ageing and Reanimation

We present results of ageing tests performed in Ar-CH4-N2-CO2 (94-3-2-1) and Ar-CO2 (93-7). In the latter gas no sign of ageing has been observed under different different operating parameters with the final design end plug. In Ar-CH4-N2-CO2 (94-3-2-1) a strong dependence of the lifetime on the anode voltage, the counting rate, the irradiation length and the gas flow has been observed. This dependences imply that the lifetime of a drift tube can not be described solely by the charge per unit length (as has been assumed by many for a long time). The potential of sputtering as a backup technique in case of unforeseen effects that lead to ageing of drift tubes has been investigated. The problem of cracks as a byproduct of this technique could be solved. Reanimation up to a level of about 90% could be achieved in Ar-O2 (99-1) and Ar-CO2 (93-7) each at atmospheric pressure and a current with reversed polarity of 1 micro A/cm.