BaBar drift chamber aging study

In order to obtain a reliable estimate of the lifetime of the BaBar drift chamber, a dedicated aging test chamber has been constructed. The working gas mixture is Helium/Isobutane (80/20). After accumulating up to 0.11 C/cm charge dose the anode wire showed no appreciable signs of aging, but the field wires showed a small Malter effect. At 0.2 C/cm the gas gain dropped ∼6–9% and the Malter effect reaches a more serious level. By adding ∼4000 ppm of water vapor into the gas mixture the Malter effect was virtually eliminated. Thereafter up to 0.31 C/cm the anode wire aging showed no further degradation.