Sensitive Beam Profile Monitor for Emittance Measurements

摘要

A beam profile monitor based on secondary emission phenomenon in porous dielectric layers is described. A Cs I layer with a thickness of 125 microns and a relative density 4% of the bulk density is obtained on a 4 cm diameter aluminium disk by evaportion of about one gram at 4 Torr Argon pressure. Observations on density dependence on pressure, hygroscopy and velocity of deposition are reported. Integrated currents measured on 1 mm collector strips equally spaced 1 mm apart allow profile determination. A secondary emission coeffficient greater than 4 has been measured for a 25 MeV electron beam of 5x10 exp -9 A mean current. Dependences of secondary yield on beam intensity and polarization voltage have been measured, as well as transient response for an uncharged layer. Transverse beam profiles have been measured and compared with other profile determinations. Good homogeneity and sensitivity make that type of a monitor interesting for low intensity beams, like positron linac beams, making it available for emittance measurements. (ERA citation 09:012594)