FRIB Lithium Stripper Thickness and Stability Measurements
Claude B. Reed, J. A. Nolen, Yoichi Momozaki, James R. Specht, David Chojnowski, Ronald Lanham · 2011
This report documents the results of a number of tests of the prototype liquid lithium thin film stripper for FRIB, in which 1) the thickness of a flowing film of liquid lithium was measured in real time, 2) the thickness distribution of the film was measured in real time, and 3) the stability of the films was determined based on both digital video recordings and digital signal recordings of Faraday cup current. The high-pressure liquid lithium system, capable of driving liquid lithium at up to 13.9 MPa (2000 psia) through a nozzle opening as large as 1 mm (40 mil) in diameter, is described. As part of the work reported here, the system was modified to facilitate convenient and efficient testing of design variations in nozzle and deflector geometry so that their effect on film thickness and film stability improvement could be determined. A previously developed electron beam based thickness measuring system was recalibrated for this specific geometry and used to measure the film thickness under a number of different flow conditions and deflector designs. A thin film ~9 mm in width flowing at a velocity of ~60 m/s was formed under several flow conditions and with several deflector designs. A deflector design was found that practically eliminates the puddle issue. The film stability is judged to be excellent; based upon a ~25 minute stable flow run during which time only a single breakup of the film occurred. That breakup event, which lasted only about 0.6 second, was most likely caused by an Ar gas bubble that became trapped in the high-pressure lithium line, during lithium transfer operations. The trapped gas issue will not be a problem for the FRIB stripper system because a pumped, closed loop system will be used, eliminating the need for lithium transfer operations. Based on thickness distribution measurements from the electron beam system, the expected central thickness (at halfway between center spot and bottom spot) is 632 ± 35 μg/cm2 (± 5.5% for 1 mm spot diameter). This corresponds to a physical thickness of the flowing lithium film of 12.3 ± 0.7 μm.