Direct measurements and spectroscopic analysis of secondary electron emission from carbon foams*

Secondary electron emission (SEE) from plasma-facing components can significantly impact the performance of many devices such as electric propulsion thrusters, plasma gun components, fusion device first walls, divertors, and bias electrodes. To this end, materials with geometrically complex morphologies have been found to be effective at suppressing SEE yield compared with flat surfaces. SEE measurements of carbon foams and flat graphite are presented and agree with recent experimental and analytical findings. An optimal geometric configuration for reticulated carbon foams showing up to to 45% reduction of SEE yield compared with flat graphite was also determined. SEE angular measurements also revealed a loss of angular dependence for carbon foams with < 100 geometric features, as has been shown in previous studies of tungsten nano-fuzzes. A double-pass cylindrical mirror analyzer (CMA) typically used for Auger electron spectroscopy was also used to study the SEE spectra from foams compared to flat graphite surfaces. This analysis revealed that generation of true (0 – 50 eV) SEs may be enhanced by up to 5% from foam surfaces compared to flat graphite surfaces, and that foams may suppress backscattered secondary electrons by > 80%. These results can inform the basic SEE physics and design space of plasma-facing components, particle accelerator walls, electron microscopy, and RF components for multipactor effect mitigation.