Direct simulation Monte Carlo method for gas cluster ion beam technology

A direct simulation Monte Carlo method has been developed and applied for the simulation of a supersonic Ar gas expansion through a converging-diverging nozzle, with the stagnation pressures of P0=0.1-10 atm, at various temperatures. A body-fitted coordinate system has been developed that allows modeling nozzles of arbitrary shape. A wide selection of nozzle sizes, apex angles, with diffuse and specular atomic reflection laws from the nozzle walls, has been studied. The results of nozzle simulation were used to obtain a scaling law P0T019/8dαLnβ=const. for the constant mean cluster sizes that are formed in conical nozzles. The Hagena's formula, valid for the conical nozzles with a constant length, has further been extended to the conical nozzles with variable lengths, based on our simulation results