A bench set-up for low-beta beam-current test measurements with COSY

Beam current bench tests and simulations, e.g. with beam monitors, are of interest for diagnostic purposes. For highly-relativistic tests, the common coaxial wire method may be used. In contrast, a configuration for non-relativistic beams was devised for transverse impedance measurements. We have combined the two approaches to permit both frequency and time domain low-beta bench tests of the line charge, and of the longitudinal beam impedance. The basic structure is of coaxial 50 Ω geometry, where the outer diameter matches the beam-pipe diameter of COSY, while the inner conductor carries, both around the azimuth and along the axis, suitable pin-and-loop arrays for imposing electric and magnetic fields, respectively. The arrays ensure nearly azimuthal (coaxial) symmetry, and are wired via delay lines such that axially varying field patterns may be generated, permitting the simulation of a broad beta range. We use standard measurement techniques with a network analyzer at a frequency range from 500 kHz up to 100 MHz. A calibration procedure, measuring field pick-up via coupling loops and pins installed in the outer beam pipe wall, ensures the correct |E|/|B| ratio