Spallation neutron source (SNS) diamond stripper foil development

Diamond stripping foils are under development for the SNS. Freestanding, flat 300 to 500 mug/cm² foils as large as 17 x 25 mm² have been prepared. These nano-textured polycrystalline foils are grown by microwave plasma- assisted chemical vapor deposition in a corrugated format to maintain their flatness. They are mechanically supported on a single edge by a residual portion of their silicon growth substrate; fine foil supporting wires are not required for diamond foils. Six foils were mounted on the SNS foil changer in early 2006 and have performed well in commissioning experiments at reduced operating power. A diamond foil was used during a recent experiment where 15 muC of protons, approximately 64% of the design value, were stored in the ring. A few diamond foils have been tested at LANSCE/PSR, where one foil was in service for a period of five months (820 C of integrated injected charge) before it was replaced. Diamond foils have also been tested in Japan at KEK (640 keV H) where their lifetimes slightly surpassed those of evaporated carbon foils, but fell short of those for Sugai´s new hybrid boron carbon (HBC) foils.