QUANTITATIVE CLEANING CHARACTERIZATION OF A LITHIUM-FLUORIDE ION DIODE

An ion source cleaning testbed was created to test plasma-cleaning tec hniques, and to provide quantitative data on plasma-cleaning protocols prior to implementation on the SABRE accelerator, The testbed was des igned to resolve issues regarding the quantity of contaminants absorbe d by the anode source (LiF), and the best cleaning methodology, A test chamber was devised containing a duplicate of the SABRE diode. Radio- frequency (RF) power was fed to the anode, which was isolated from gro und and thus served as the plasma discharge electrode. RF plasma disch arges in 1-3 mtorr of Ar with 10% O-2 were found to provide the best c leaning of the LiF surface, X-ray photoelectron spectroscopy (XPS) sho wed that the LIF could accrue dozens of monolayers of carbon just by s itting in a 2 x 10(-5) vacuum for 24 h. Tests of various discharge cle aning protocols indicated that 15 min of an Ar/O-2 discharge was suffi cient to reduce this initial 13-45 monolayers of carbon impurities to 2-4 monolayers, Rapid recontamination of the LiF was also observed, Up to ten monolayers of carbon returned in 2 min after termination of th e plasma discharge and subsequent pumping back to the 10(-5) torr rang e, Heating of the LiF also was found to provide anode cleaning. Applic ation of heating combined with plasma cleaning provided the highest cl eaning rates.