Observations of Photon-Induced Gas Desorption from Technological Materials Using Synchrotron Light
The advent of intense light beams from synchrotron sources provides a ready opportunity to redress the dearth of reliable data on the efficiency of the process of photon-induced gas desorption from solid surfaces. Paradoxically, the operation of vacuum within synchrotron machines is itself greatly influenced by the process, as was recognised in the pioneering work of Fischer, Hack and co-workers during the 1960’s /1/. With the widespread development of electron storage rings in recent years, there has been a great deal of interest in assessing the extent of self-cleaning within machines, and in examining the contributions of surface pre-treatments such as high temperature bakeout or plasma conditioning /2/. These considerations for the provision of vacuum walls with low desorption characteristics are equally relevant to the operation of controlled fusion machines, since the gaseous impurities can lead to serious plasma contamination. Indeed, the process can possibly lead to a runaway situation as successive waves of desorbed impurity act to stimulate further photon desorption. The present programme of experimental work is directed particularly towards elucidating the operation of the JET plasma experiment at Culham Laboratory where the radiation spectrum spans an energy range around 0.5 to 10 keV at a power level of a few watts per cm2 /3/. These conditions have been simulated using the Soft X-ray beam line at the Synchrotron Radiation Source (SRS), Daresbury Laboratory.
KeywordsStorage Ring Synchrotron Radiation Source Desorption Efficiency Electron Storage Ring Daresbury Laboratory
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