DESY Experiences on Use of Gas overlay during Assemblies Choice of gas Benefit and Drawback of gas overlay Conclusion for application at DESY A.Matheisen DESY TTC Topical Workshop on SRF Cryomodule Clean Room Assembly CEA Saclay, 12th november 2014

DESY Experiences on Use of Gas overlay during Assemblies Choice of gas Benfit: low cost Available in high cleanliness 99.999999 standard particle counters can be applied Low Hydro carbon when extracted from pure N2 liquid Draw back: At higher temperatures reaction with Nb and N2 possible (Problem during helium vessel welding)

DESY Experiences on Use of Gas overlay during Assemblies DESY Experiences on Use of Gas overlay during Assemblies Choice of gas (cont.) Ar gas Draw back: Cost Special calibration of gas particle counters needed Special equipment for slow pumping slow venting vacuum stands Benefit Available in high cleanliness 99.999999 Low Hydrocarbon when extracted from pure liquid. At higher temperatures no reaction with Nb and Ar (during helium vessel welding) Easy to detect with RGA in case of leaking valves in venting / flushing line

DESY Experiences on Use of Gas overlay during Assemblies DESY Experiences on Use of Gas overlay during Assemblies Choice of gas (cont.) At DESY Cleanroom Argon is in use for cavity preparation preparation of CAV for tank welding and module assembly During tank welding locally higher temperatures can not be exclude DESY Cleanroom is equipped with Argon for venting and flushing To prevent errors during cavity processing and for economical reasons only one ultra pure gas line is in use  Argon In General both gases work well for venting (Fast and Slow venting) Gas overlay Only when Nb is exposed to higher temperatures Argon is beneficial

DESY Experiences on Use of Gas overlay during Assemblies Benefit and drawback of gas overlay Why we should use gas overlay (flushing) during module assembly? Costs money needs more infrastructure We are in ISO 4 cleanroom  But Film 1 2 3

DESY Experiences on Use of Gas overlay during Assemblies Benefit and drawback of gas overlay Conclusion Benefit Stable and defined condition at ports in resp. to laminar flow conditions Over pressure inside cavity blows off remaining residues during start of dismounting of flanges Beneficial if particle are remaining on the flanges or bore holes Very flexible and adjustable air flow to different geometries Draw back Needs extreme clean piping (contradiction to Slow pumping slow venting) Connecting valves have to be clean before connecting to flushing line QC needs to be done with great care before connecting to flushing line High gas consumption Point of use filters are mandatory in the flushing line In case of particle in the lines “heavier” once may rest at areas with min flow speed CAV Iris and beam tube 78 mm ID Equator 110 mm ID

DESY Experiences on Use of Gas overlay during Assemblies Conclusion for application at DESY At DESY ISO 4 cleanroom Argon overlay gas is requested due Tank welding procedure on CAV in Cavity preparation cycle For module assemblies N2 gas is adequate At DESY cleanroom vacuum lines und cavity accessories underlay a strong quality control, even if slow pumping and slow venting is in use Investigation by flow visualization shows a benefit on gas At DESY Argon gas overlay is in use sine years for power coupler assembly during string assembly and “special” repairs