Scattering effects of residual gas and RMS emittance growth in DragonI LIA

In this paper, the multiple scattering effects of residual gas as isotropic disturbing forces, are introduced into the RMS envelope equation of cylindrically symmetric DC electron beams, so that the expression of emittance growth due to the scattering is obtained. Referring to the design parameters of beam transport system of DragonI LIA, the emittance growth is calculated. The result shows that the emittance growth due to gas scattering could be neglected if the pressure of vacuum tube is less than 3×１０－４Pa. And the measures to restrain the scattering effects are discussed．