  Protons that are trapped in the Earth's magnetic field are one of the main
threats to astronomical X-ray observatories. Soft protons, in the range from
tens of keV up to a few MeV, impinging on silicon X-ray detectors can lead to a
significant degradation of the detector performance. Especially in low earth
orbits an enhancement of the soft proton flux has been found. A setup to
irradiate detectors with soft protons has been constructed at the Van-de-Graaff
accelerator of the Physikalisches Institut of the University of T\"ubingen. Key
advantages are a high flux uniformity over a large area, to enable irradiations
of large detectors, and a monitoring system for the applied fluence, the beam
uniformity, and the spectrum, that allows testing of detector prototypes in
early development phases, when readout electronics are not yet available. Two
irradiation campaigns have been performed so far with this setup. The
irradiated detectors are silicon drift detectors, designated for the use
on-board the LOFT space mission. This paper gives a description of the
experimental setup and the associated monitoring system.
