High sensitivity He desorption leak detection method

A new high sensitivity leak detection method has been developed for the superconducting radio-frequency (SRF) acceleration cavities for the CEBAF linacs. The vacuum integrity of the SRF cavity pairs and the associated indium-sealed vacuum flanges is essential for the successful operation of the accelerator. These SRF cavity pairs are immersed in superfluid helium to minimize rf heat load to the cryogenic system. Conventional leak detection techniques are not appropriate to leak check these cavity pairs at superfluid helium temperature (2 K), since He will be adsorbed onto the cavity surfaces. Further, the sensitivity of the conventional leak detectors is limited to 10-11 atm cm3 s-1 at 293 K. In this article, the details of the He desorption leak detection procedure and the results with production cavity pairs are presented