Parasitic crossing at an asymmetric B factory, APIARY

Effects of parasitic crossings (''near miss'' collisions of two counter-rotating beams at unwanted positions near the IP) are studied in terms of computer simulations for an asymmetric B Factory, APIARY- 6.3d. Beams are separated horizontally at the first parasitic crossing points by about 7.6 times the horizontal rms size of the low energy beam (the larger in size of the two beams), σ0x,+. Simulations, including both the beam collision at the IP and parasitic crossings, have been performed for different separation distances, d. It is found that the ratio d/σ0x,+ is a good scaling parameter of beam blowup behavior. The results show that beam blowup due to the parasitic crossings is diminished for d ≥ 7σ0x,+, in agreement with the bunch separation experiment at CESR. Thus, the nominal separation 7.6 σ0x,+ turns out to be acceptable, but with only a small margin. Some methods to mitigate the effects of the parasitic crossings are discussed. 3 refs. , 5 figs., 2 tabs