Material test chamber

For the study of material properties with respect to reachable impurity levels and outgassing rates, we constructed at PSI a bakeable high vacuum system equipped with a Baltzers dual-range gauge, operating from $10^{-9}$ mbar to 1 bar, and with a quadrupole mass spectrometer for analysis of any residual gas components. The test volume is a cylindrical steel tank slightly larger than the Aluminum pressure tank such that besides material samples also the final TPC and wire chamber components can be baked out up to 200$^o$C and high vacuum tested. Only metallic seals were used (except the large vacuum valve which has a viton seal required for frequent usage).

After week long baking out procedures, a high vacuum with metallic components (e.g. stainless steel or Covar frames) of 3$\cdot 10^{-9}$ mbar was reached, the residual gas component being mainly water. When closing the big vacuum valve to the turbo molecular pump, the vacuum pressure rose typically to 1-3$\cdot 10^{-6}$ mbar and remained stable without pumping for over a week. The residual gas components in the "closed valve" mode were mainly CO from the steel walls and related gases.

Similar results were also obtained after intense out-baking at 150$^o$C with teflon, teflon-glass and Kapton sheets, and also with resistor/capacitor components required for the TPC operation. We have hope that - if such residual pressures remain as partial pressures in the 10 bar protium - we can maintain gas purities below $10^{-8}$ over prolonged periods, sufficient for our $\mu p$ capture measurements. Nevertheless, we also foresee to install a continuously operating gas circulation and purifying system (see below). The effective purities during the runs will be continuously monitored by two methods, (i) by observing in the TPC muon capture reactions on impurities, (ii) by taking and analyzing gas samples in regular time intervals.