Numerous applications of CO2 snow cleaning for vacuum technologies were developed including cleaning stainless steel vacuum components, electron, ion and x-ray optics, residual gas analyzers (RGA), UHV and HV parts, and many others. Hydrocarbon removal from electropolished stainless steel parts is as effective as high purity reagent grade solvents such as acetone and methanol. For small complex structures CO2 snow cleaning is better than air blowing or ultrasonics, as discussed below. Snow cleaning can remove the machining oils, particle residues, and other debris from the stainless steel surfaces and even weld rods, tips, and surfaces before welding.
Cleaning vacuum assemblies also works well to remove contamination left from assembly or repair. An early example was given by Layden and Wadlow comparing CO2 snow cleaning to solvent cleaning on an RGA. Initial pump down times were slow after solvent cleaning, which involved disassembly and ultrasonically cleaning. Repeated solvent cleaning led to an improved pump down time but still not as fast as needed. For CO2 cleaning, just the filament, grids, and aperture were removed. The remaining assembly was cleaned as one piece. Analysis of outgassing elements after solvent cleaning showed hydrocarbons and alkaline based contamination; and after CO2 snow cleaning, these peaks were reduced or eliminated. This demonstrates the ability to clean complex vacuum equipment with CO2 snow. The same concepts here can be applied to other electron and ion sources, and many other vacuum parts. Another set of comparable results have been shown by Vondrasek in several papers related to an ECR for a breeder reactor. Work done by many high energy physics labs mirror these results.
One user in 1993 has remarked that CO2 Snow Cleaning a SIMS source after rebuilding led to reduced high voltage arcing when energized. This was attributed to reduced particle populations that can be sources of high voltage discharge. A similar result has been mentioned for high voltage equipment at William and Mary (unpublished) for vacuum equipment. These later results were taken and expanded for RF cavities at Jefferson Lab. In fact, this has been used when cleaning similar synchrotron RF cavities in Europe. This application was documented by Dangwal and included data on removing field emitter spikes. Other high energy physics sites have incorporated these cleaning procedures. Similar work has been done on other instruments and parts related to high energy physics and other areas. CO2 snow has also been used to clean large vacuum chambers using both the standard and LASU nozzles.
Jantzen et al. studied CO2 snow cleaning of cast, small, and complex machined parts. They compared particle removal efficiencies of blowing air, ultrasonics, and CO2 now cleaning on these small parts. Overall, CO2 snow cleaning outperformed the other methods for particle removal regardless of material or geometry. This implies that CO2 snow cleaning can assist in cleaning many different HV and UHV parts.
A customer involved in vacuum system fabrication relayed information that CO2 cleaning as a prep step before welding led to less staining near the weld zones and less weld defects during fabrication. There are patents on cleaning welding equipment.
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