Beam monitors based on residual gas ionization

At GANIL we have developed two beam monitors based on ionization of the residual gas of the beam transport lines under the impact of the high-energy heavy ion beams. One provides the beam profile, i.e., its spatial distribution, and the second one measures its time structure, i.e., the length of the beam bunches delivered by the 10-MHz cyclotron. They are operated for beam intensities between a few nanoamperes and some microamperes and in a beamline vacuum better than 10−6 mbar. The charged ions or the electrons produced in the residual gas drift by means of an electrostatic field onto a microchannel plate (MCP) which amplifies the primary current. The MCP output signal is collected on a multistrip anode to get the beam profile, whereas the fast time structure of the beam is measured by means of a 50-Ω anode. Calculations and results are presented as well as discussions about the different parameters of both devices.