| Irfu-08-86
|
|---|
| Final Surface Preparation for Superconducting Cavities |
| G. Ciovati ,T. Higo ,P. Kneisel ,
J. Mammosser ,A. Matheisen , P. Michelato , H. Padamsee ,D. Reschke , T. Rothgeb , T. Saeki , K. Saito , B. Visentin ,H. Weise , Chr. Oevermann |
| This report attempts to describe the “final preparation” procedures known to yield the
highest gradients for 9-cell cavities. These final steps include degreasing, light
electropolishing (EP), high pressure rinsing (HPR) with ultra-pure water (UPW), drying,
evacuation, and mild baking. A core set of final treatment parameters is followed by all the
laboratories working towards high gradient 9-cell cavities. These laboratories are (in
alphabetical order) Cornell, DESY, KEK and JLAB. The bulk of the 9-cell high gradient data
is coming from DESY. Work on single cell cavities at these and other labs (e.g. Saclay,
INFN) has also contributed to defining and understanding the procedures.
The procedures are yielding similar results and similar gradient spreads across the
laboratories. Therefore it is reasonable to conclude that the essential steps needed for high
gradient results are known and are being followed. However there is a substantial variation in
many details, as for example the voltage selected for EP or the temperature for mild baking.
Tables are given for some of these parameter ranges. It is possible that the gradient spread
observed at all laboratories is partly due to the variation in some of the key parameters, but
this is far from certain.
Specific experience at individual laboratories have also suggested that certain key
parameters are critical to good performance, such as the HF content during EP, or the impact
of the HPR pressure jet during rinsing. Studies are underway to identify the best method of
measuring and controlling such parameters. This report also tries to list some of these key
parameters and methods under development.
The sequence of pre-treatment steps in cavity preparation is not covered here. But the
general principles for the common items in the final preparation treatment cycle are also
applicable to pre-treatment steps. |
