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In a standard molecular beam source the maximum attainable intensity in the collimated beam is limited first by the effusion rate through the oven slit, which must be made sufficiently narrow to attain free molecule flow, and second by unfavorable geometrical factors encountered in selecting a collimated beam from random initial velocities. This paper will propose that the first slit be placed in the flow from a miniature high velocity nozzle coaxial with the final beam. The nozzle converts part (∼¾ for a Mach number of 4 in the design for air to be presented) of the random translational and internal energy of the oven gas into directed mass motion. The mass motion provides an initial rough collimation, which improves both the effusion rate and the geometrical factors, indicating a considerable possible beam intensification (by a factor of ∼75 in the sample design). The velocities of the molecules in the final beam are grouped about the initial mass velocity which provides a partial velocity selection. In this paper a theoretical design study and estimates of performance of this type of source are given.
Kantrowitz et al. (Tue,) studied this question.