| Popis: |
The characteristics of a particle beam produced by expanding monodisperse aerosols through a capillary nozzle into a vacuum were studied. The particle beam generator consists of a capillary, 100 μm diameter × 5 mm length, which produced the particle beam, and a skimmer with a 350-μ aperture. The vacuum chambers upstream and downstream of the skimmer were at 0.5 Torr (67 Pa) and 0.2 Torr (27 Pa), respectively. The efficiency of particle transmission through the capillary-skimmer system, defined as the ratio of number of particles collected downstream of the skimmer to the number of particles that enter the capillary during times of collection, was measured at variable capillary-skimmer separations, ranging from 2.0 to 14.7 mm. The angular spread of the particle beam was also measured at these same capillary-skimmer separations. At the minimum separation, transmission efficiencies were greater than 90% for particles 1.52 μm or smaller. For larger particles, the efficiency decreased with increasing particle size and was 71% for 5.48-μm particles. As the capillary-skimmer distance increased, the transmission efficiency decreased primarily because the skimmer acted as a limiting aperture. The solid angle of the particle beam deposit also showed a dependence on particle size. A minimum in the solid angle was observed for particles of 0.5 μm diameter. This focusing effect is explained by the variation of particle trajectories with aerodynamic particle diameter at the entrance to the capillary. |
