On the outgassing rate versus time characteristics in the pump-down of an unbaked vacuum system

In order to derive theoretically the outgassing rate versus time characteristics(Q vs t) in the pump-down of an unbaked vacuum system, a thermal desorption model in the light of adsorption-desorption of gas molecules on surface has been proposed. In this model the outgassing rate is described as a function of time using the conservation of mass equation for gas molecules in the vacuum system. In order to solve this equation, it is essential to introduce an auxiliary equation which enables to determine the surface covarage as a function of the heat of adsorption. When this auxiliary function is expressed with the variation of heat of adsorption in the Temkin isotherm and the Freundlich isotherm, the solution for the outgassing rate gives a power law Q = const.(1/t)X where x is a constant as much as 1, which is usually familiar in the pump-down of a vacuum system. (author)