ABSTRACT
The space charge effect stands for the deflection by the total, averaged charge of all other particles in the beam. This chapter describes the manifestation of coulomb effects, an appreciation for the difficulties in the theoretical description, and the knowledge necessary to estimate and then minimize the effects in a microbeam instrument. For microbeam columns the importance of the Boersch effect is found in the possible increase of the chromatic aberration disk. The chapter shows that current density distribution in the beam is only slightly disturbed, and calculates the trajectory of a test particle in first-order perturbation theory. The extended two-particle approximation breaks down when the test particle is involved in two or more strong collisions simultaneously or successively in the same beam segment. In an extended beam, the displacement of a weak complete collision behind the crossover compensates the displacement before the crossover.
