Simulation of angular distribution of molecular flux at the exit of narrow tubes and slits

Ogiwara, Norio; Kamiya, Junichiro   

In order to develop the gas sheet target, angular distribution of molecular flux at the exit of narrow tubes and slits was simulated with Monte Carlo method. For the tubes, the greater part of the flux is collimated near the polar angle. However, for the length-diameter ratio / (: length, : diameter) greater than 10, angular distribution is almost independent of the value of /. Even at the / of 100, the fraction of outgoing molecules with the polar angle less than 0.01 rad is limited to be less 0.5%. On the other hand, the emitted molecules from the slit can be shaped into the sheet. To do so, the following 2 conditions are required; and . Where, the marks , and refer to the long and short sides, and the depth of the slit, respectively. With the parameter set of : : = 100 : 50 : 0.1, the fraction of outgoing molecules collimated within the azimuth of 0.01 rad becomes to be 25% of all the molecules.