Molecular-Beam Sources Fabricated from Multichannel Arrays. I. Angular Distributions and Peaking Factors

Abstract

An apparatus for measuring the leak rates and angular distributions of the molecular flux from multichannel sources was constructed. Four types of beam sources were tested: A single capillary, a crinkly foil stack, an electron-beam milled quartz membrane, and two sources constructed by fiber optics techniques. The leak rates of the sources were compared to the predictions of Knudsen flow. The angular distributions were characterized by a ``peaking factor,'' defined as the ratio of the center-line beam intensity from the source to that from a cosine emitter of the same total flow rate. The measured peaking factors agreed with the theoretical predictions of free molecule flow at low source pressures and approached the limit for isentropic flow at high source pressures.

Angular profiles of molecular beams from effusive tube sources: I. Experiment

“…Some of the past experimental investigations of this type were performed by Giordmaine and Wang (1960), Hanes (1960), Jones et al (1969), Steinruck and Redulic (1986), McGilp (1986, 1988), and, more recently, Buckman et al (1993). Most of these measurements have used large separations between the source and the detector (40 cm or greater); however, the most recent of these, by Jones et al (1969), , and Buckman et al (1993), obtained distributions for single capillary and multi-capillary arrays at separations of as little as 1.5 mm from the source tube. A summary of these experiments is given in table 1.…”

“…In their work they noted the smallest source-detector distance used and also took measurements over a wide range of source driving pressures, P s . McGilp (1986, 1988) (also using method B) focused on the comparison between experimental profiles and theoretical analytical profiles of Zugenmaier (1965), Jones et al (1969) andClausing (1930). They found significant discrepancies at moderate pressures between the various theories and their experimental data.…”

Development of an (e,2e) electron momentum spectroscopy apparatus using an ultrashort pulsed electron gun

“…17,18 Since a multi-capillary beam source can improve the directivity of the target gas beam, compared with a single tube gas nozzle, it is employed when more uniform target density distributions at around the ionization point are needed rather than more intense target density.…”