Corrugated Thin Diamond Foils for SNS H-Injection Stripping

We have prepared and tested corrugated, thin diamond foils for use in stripping the SNS H-Linac beam. Diamond has shown promise for providing ca. 10X increased lifetime over traditional carbon foils. The preferred foil geometry is 10 to 12 mm by 20 mm at 350 microgram/cm², mechanically supported on preferably one, but no more than two, edges. The foils are prepared by chemical vapor deposition (CVD) on a patterned silicon substrate, followed by chemical removal of the silicon. This yields a foil with trapezoidal corrugations to enhance mechanical strength and foil flatness. Both micro- and nano-crystalline diamond foils have been grown. Microwave plasma CVD methods that incorporate high argon gas content were used to produce the latter. Sixteen foils of a variety of characteristics have been tested using the BNL 750 keV RFQ H-beam at a current scaled to simulate the energy deposition in the SNS foil. Long foil lifetimes, up to more than 130 hours, have been demonstrated. Characterization of the foils after beam testing indicates creation of sp2 defects within the ion beam spot. Current efforts are centered on development of corrugation patterns that will enhance flatness of single-edge supported foils.