SNS foil after 300 Coulomb of injected charge.

Corrugated Thin Diamond Foils for SNS H- Injection Stripping 

Robert Shaw, Leslie Wilson (ORNL), and Charles Feigerle (University of Tennessee/Knoxville) 

Diamond stripping foils are under development for the Spallation Neutron Source (SNS) accelerator. These foils convert accelerated H- particles into protons for merging with the accumulator ring circulating beam. They must survive the intense ion beam irradiation for at least a few 100 beam hours to maintain efficient user facility operation at the SNS.

Free-standing, flat 350 microgram/cm² (i.e., 1 micrometer thick) foils as large as 17 x 5 mm 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; typical fine foil supporting wires are not required for diamond foils.

Diamond foils have been mounted at the SNS since early 2006 and have performed well up to 1 MW SNS power. The foils are in routine neutron production up to the current 800 kW nominal beam power (of the 1.4 MW design value). Foil curling and graphitization is observed at high operating temperatures. A few diamond foils have been tested at LANSCE/PSR, where one foil was in service for a period of five months (820 Coulombs of integrated injected charge) before it was replaced. Diamond foils have also been tested in Japan at KEK (650 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.

We are currently boron-doping diamond foils for improved electrical conductivity and testing foil lifetimes using a 30 keV electron beam test stand.

     Sketch depicting the corrugation pattern for a foil at 50 lines/inch pitch.
The vertical dimension is not to scale.