Investigation of sputtering of thin diamond-like carbon (DLC) target foils by low energy light ions

Abstract

Along with use for stripping and timing of high energy ions in accelerator experiments, ultra-thin DLC foils are being successfully applied to the instrumentation for fusion and space plasma research. In the latter case, the foils are exposed to light ions and neutral atoms in the keV energy range. Unlike high energy ion irradiations, the foil lifetime is determined by thinning of the foil due to sputtering by particles that transit the foil. In this work, sputtering of thin (1–3 μg/cm 2) DLC foils produced by two different techniques such as modified glow discharge deposition and laser plasma ablation has been investigated using high intensity He + beams at 4 keV. A loss of foil material under ion impact was estimated from on-line measurements of energy loss of transmitting ions by means of an electrostatic analyzer. For comparison, samples of arc-deposited carbon foils were also evaluated. To avoid any carbon build up on the foils under ion irradiation, the measurements were carried out in an oil-free vacuum environment. Calculated from the measurements, results on both threshold fluence and total sputtering yield of the foils for the incident He + ions are presented together with some extrapolations to other low energy projectiles of fusion plasma interest. This enables an estimate for operational lifetime of the DLC foils determined by sputtering.