“The Even-Lavie valve as a source for high intensity supersonic beam”

Introduction The art of supersonic beams has advanced since its early years [1–6], when simple cw sources were used. The main limitation on achieved beam intensity was set by the pumping capacity of the source chambermainly large diffusion pumps and Roots pumps (with capacities of 3.000-10.000 liter/second). It was realized that when the background pressure was too high in the source chamber, beam propagation was diminished, and careful adjustment in the skimmer design was required to avoid the generated barrel shock wave and Mach disk structure [7–9] (Fig. 1). These limitations were overcome when pulsed gas sources became available [10–16]. If the gas pulse is short enough (shorter than a typical molecular reflection time from the walls of the vacuum chamber), and if the repetition rate is low enough to so that the mean gas pressure is less than 10 mbars in the source chamber, then the gas expands without hindrance, and no structured shock waves interfere with the jet propagation. Much smaller turbo-molecular pumps (300–500 l/sec) can now be used for low repetition rate experiments (10-50Hz), while bigger pumps (3000 l/sec) are still required for higher repetition rates (1–5 KHz) pulsed valve systems. The following parts will summarize our experience with one type of a pulsed valve that we developed, and is still the only one that can be used over a very wide temperature scale (4-550 K). The valve is an electromagnetic actuated device. Readily available computer simulation programs can now be used to optimize the electromagnetic structure, the mechanical movement dynamics, the nozzle shape and the interaction of the high density resulting jet with skimmers. These processes will be explained and experimental results will be shown. These valves, known as the “Even-Lavie” valves are now widely used in more than 100 labs. Some details have been published before [17].