Carbon ion beam focusing using laser irradiated, heated diamond hemispherical shells

Experiments preformed at the Los Alamos National Laboratory's Trident Laser Facility were conducted to observe the acceleration and focusing of carbon ions via the Target Normal Sheath Acceleration (TNSA) mechanism using hemispherical diamond targets. Trident is a 200 TW class laser system with 80 J of 1μm, short-pulse light delivered in 0.5ps, with a peak intensity of 2 × 10²⁰ W/cm². Targets where Chemical Vapor Deposition (CVD) diamonds formed into hemispheres with a radius of curvature of 400μm and a thickness of 5μm. The accelerated ions from a hemisphere were diagnosed by imaging the shadow of a witness copper mesh, located 2.4mm behind the target, onto a film pack located 5 cm behind the target. Ray tracing was used to determine the location of the ion focal spot. The TNSA mechanism favorably accelerates hydrogen found on the targets. To make the carbon beam detectable, targets were first heated to several hundred degrees Celsius using a CW, 532nm, 8W laser. Imaging of the carbon beam was accomplished via an auto-radiograph of a nuclear activated lithium fluoride window in the first layer of the film pack. The focus of the carbon ion beam was determined to be located 630 ± 110μm from the vertex of the hemisphere. LA-UR 09–06918