High-Energy Molecular Beam Source Using a Non-diaphragm Type Small Shock Tube
The molecular beam technique  is one of the powerful tools to analyze gassurface interactions. Various methods have been developed to generate the molecular beams with the translational energy of 1-several eV, which corresponds to the typical activation energy of surface reactions. Although seeded beams combined with a heated nozzle are often used, the heatproof temperature of the nozzle limits the beam energy.Arc-heated beams  have the energy ofmore than 1 eV. The problem is, however, that the beams contain copper atoms due to electrode erosion and thus contaminate surfaces. Several researchers also investigated shock-heated beam sources . The replacement of a diaphragm and the long evacuation time between each shot, however, make the conventional shock-heated beam sources impractical for the scattering experiments of gas molecules on surfaces, since the scattering experiments require signal accumulation for a large number of beam pulses. In order to overcome these shortcomings, we have been developing a beam source using a nondiaphragm type small shock tube . Our objective is to develop a shock-heated beam source which can generate the beams with the translational energy of more than 1 eV with high operating frequency. It is noteworthy that the inner diameter of our shock tube is a few millimeters, far smaller than that of conventional shock tubes. The volume reduction leads to the shorter evacuation time, which enables generating molecular beams with high operating frequency. On the other hand, it should be noted that the boundary layer has significant effects on shock propagation in small diameter tubes . In addition, we developed a high-speed valve employing a current-loop mechanism  as a substitute for a diaphragm to reduce shock formation distance, which determines the tube length.
KeywordsMach Number Shock Tube Straight Tube Translational Energy Beam Source
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