Beam interaction with rest gas is important mainly because of activation of the accelerator elements and background to experiments (in colliders). The research collected here is concentrated on different processes: beam gas ionization and interaction of the electrons/ions with beam space charge.

The useful theoretical description of the ionization process was first given by Hans Bethe in his famous paper "Zur Theorie des Durchgangs schneller Korpuskularstrahlen durch Materie" (1930, Annalen der Physik, vol. 397, Issue 3, pp.325-400). In this paper Bethe obtained a differential cross-section for nonrelativistic ion-atom collisions. In 1932 he published relativistic extension to his calculations introducing the "Bethe rise" for high-gamma projectiles.

For relativistic case a paradygmatic approach is Weizsacker-Williams method of equivalent photons is used. In the paper of A.B.Voitkiv and J.Ullrich On the relation between ionization of light atoms by virtual and real photons an application of this method to ultra-high relativistic projectiles is discussed. It is shown that for gamma>1000 the ionization process is trurly photo-like mechanism and the Weizsacker-Williams approximation is valid.

Selection of papers: