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In recent years several low cost computer controlled residual gas analyzers (RGAs) have been introduced into the market place. It would be very useful to know the performance character- istics of these RGAs in order to make an informed selection for UHV applications. The UHV applications include extreme sensitivity helium leak detection and monitoring of the residual gas spectra in UHV systems. In this article, the sensitivity and linearity data for nitrogen, hydro-gen, and helium are presented in the pressure range 10−8–10−1 Pa. Further, the relationships between focus voltage and ion currents, relative sensitivity, and fragmentation factor are also included. A direct comparison method is used in obtaining this data. Spinning rotor and extractor gauges are the transfer standard gauges used in Jefferson Lab’s vacuum calibration facility, with which all the reported measurements here were carried out.

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The useful performance range of the superconducting rf (SRF) cavities in the CEBAF accelerator at Jefferson Lab is frequently limited by electron field emission and derived phenomena. Improvements are required to support future operation of the accelerator at higher than 5 GeV. Twelve operational cryomodules have been successfully processed to higher useful operating gradients via rf-helium processing. Progress against field emission was evidenced by improved high-field Q, reduced x-ray production and greatly reduced incidence of arcing at the cold ceramic window. There was no difficulty reestablishing beamline vacuum following the processing. Cavities previously limited to 4-6 MV/m are now operating stably at 6-9 MWm. By applying a pulsed-rf processing technique, we have also improved the pressure stability of the thermal transition region of the input waveguide for several cavities.

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.