LI THIN FILM THICKNESS MEASUREMENTS USING LOWENERGY ELECTRON BEAM

摘要

For a heavy ion linac, employing chargernstrippers is often necessary to improve the performance.rnThe most promising approach, especially for a high-powerrnlinac, is to use a liquid metal, thin film as arnstripper. Some liquid metals have low vapor pressure andrngood thermal properties, allowing such a stripper tornwithstand extreme heat load from ion bombardments.rnBased on fluid-dynamic, thermal, and nuclear physicsrnconsiderations, a liquid lithium thin film with thernthickness of ~8 μm (0.4 mg/cm 2 ), flowing at >50 m/s mayrnact as the best stripper for a uranium beam at 34+, 12rnMeV/u. As the next-stage development, formation of suchrnfilms is demonstrated at Argonne National Laboratoryrn(ANL). From simple fluid-dynamic considerations, thernfilm thickness and the velocity are estimated to be <～13rn?m and ～58 m/s, respectively. This paper describes howrnto measure the Li film thickness using low energy electronrnbeams (LEEB). When applied to the Li film, LEEB isrnabsorbed and scattered in the film. Changing the filmrnthickness affects characteristics of the transmittedrnelectrons, from which the film thickness may be back-calculated.rnPreliminary calculations show that thernelectron energy of <～30 keV provides the best sensitivityrnfor Li film thicknesses up to 20 μm.