Small-angle multiple scattering of charged particle beams

The scattering of self-pinched particle beams propagating in gas is investigated using Moliere’s treatment of multiple scattering. Nordsieck lengths significantly longer than those predicted on the basis of less accurate scattering formalisms are obtained numerically. An improved analytic expression for the Nordsieck length is derived and agrees well with the numerical results. Experimental data on beam expansion from the ASTRON experiment show good agreement with numerical simulations and analytic results. The evolution of a thin annular beam due to scattering is studied, and the beam is found to acquire a Bennett profile in a distance on the order of one Nordsieck length.