Study of wire cutting effects on surfaces of diamond turned copper structures S. Heikkinen CERN TS/MME/MM Team meeting Motivation: Why structures after CTF-3 high power test (and wire cutting) do look like this? Surfaces full of pits

A test was performed Specimen: Output coupler of high power tested 30GHz Mo iris structure Slice cut for reference before wire cutting The rest went through a similar wire cutting process as the structures. Reference slice “Before wire cut” Reference slice “Before wire cut” Test piece “After wire cut” Test piece “After wire cut” 1. Mechanical cut 2. Wire cut

Specimens on a SEM stage After wire cut Before wire cut

SEM images of the diamond turned surfaces Before wire cutAfter wire cut

SEM images of the diamond turned surfaces Before wire cutAfter wire cut

SEM images of the diamond turned surfaces Before wire cutAfter wire cut

SEM images of the diamond turned surface Region close to wire cut Wire cut Diamond turning

SEM image of the rough machined surface far away from the wire cut

Some related structures tested and inspected earlier: 30CNSD1P2.Cu, 30 GHz disc structure brazed diamond turned discs, fabricated high power tested in CTF-3, 2007 wire cut for the post mortem inspections,

Some related structures tested and inspected earlier: 30CNS2P3.Cu, 30 GHz disc structure brazed diamond turned discs, fabricated high power tested in CTF-3, 2007 wire cut for the post mortem inspections,

Some related structures tested and inspected earlier: 30 GHz disc structure brazed diamond turned discs, fabricated <2003 high power tested in CTF-2, <2003 wire cut for the post mortem inspections, 2003

Known phenomena Due to: contaminations inadequate flushing and penetration of the EDM dielectric fluid

Conclusion: Wire cutting causes pitting to the cut and adjacent surfaces Poor flushing due to cavity geometry Flushing difficult to be improved Recommended: Use other cutting techniques