Measurements of dynamic surface changes by digital holography for in situ plasma erosion applications

There are currently few viable diagnostic techniques for in situ measurement of plasma facing component erosion. Digital holography is intended to fill this gap. Progress on the development of single and dual CO2 laser digital holography diagnostics for in situ plasma facing component erosion is discussed. The dual laser mode's synthetic wavelength allows the measurable range to be expanded by a factor of similar to 400 compared to single laser digital holography. This allows the diagnostic to measure surface height changes of up to 4.5 mu m in single laser mode and up to 2 mm in dual laser mode. Results include ex situ measurements of plasma eroded targets and also dynamic measurements of nm and mu m scale motion of a target mounted on a precision translation stage. Dynamic measurements have successfully been made with the system operating in both single and dual laser modes, from similar to 50 nm to similar to 4 mu m in single laser mode and up to similar to 400 mu m in dual laser mode (limited only by the stage speed and camera acquisition duration). These results demonstrate the feasibility of using digital holography to characterize plasma facing component erosion dynamically, i.e., during plasma exposure. Results of proof-of-principle in situ digital holographic measurements of targets exposed to an electrothermal arc plasma source are presented.

Automated summary

Digital holography is used for in situ measurement of plasma facing component erosion, with development of single and dual CO2 laser digital holography diagnostics. The synthetic wavelength in dual laser mode expands the measurable range, successfully achieving dynamic measurements and demonstrating the feasibility of digital holography in characterizing plasma facing component erosion dynamically.