The CPS Gas-Ionization Beam Scanner

A non-destructive beam scanner was installed in the CPS ring early in 1968. Deriving a signal from the electrons liberated by the proton beam from the residual gas in the vacuum chamber and using a crossed electric and magnetic fields system of electron collection, the scanner gives the projected proton density distributions in the horizontal and vertical planes. Spatial resolution is better than 1 mm. An important feature is the use of a single collector which receives electrons from a slice of the beam close to the zero equipotential surface. The electric equipotential surfaces are arranged to be parallel to the beam and scanning is achieved by displacing these equipotentials laterally in the region of the beam. In particular, the zero equipotential, which always passes through the detector, is scanned right through the beam. Trials at scanning times down to 1 ??S and normal CPS vacuum have yielded some interesting results. A double beam has been seen under certain conditions on the ´flat top´ at 19 GeV/c, and other applications have been the study of beam dimensions during the first few ms after injection as well as debunching and slow ejection studies.