In-Beam Diamond Start Detectors

This paper describes operation principles and the in-beam performance of Start Detector (SD) assemblies consisting of Diamond Detectors (DDs) grown by Chemical Vapour Deposition (CVD) and Front End Electronics (FEE) which have been designed for and used in various nuclear physics experiments at GSI Helmholtz Center for Heavy Ion Research in Darmstadt. In parallel to the FEE design we have performed extensive calculations to model the dependence of the signal-to-noise ratio (S/N) and the time resolution sigma(t) on various quantities such as the collected charge Q(col), the detector capacitance C(D), the temperature T, and finally the noise contribution and bandwidth of the amplifier. In combination with the new FEEs (including an application-specific integrated circuit, ASIC) we have tested both polycrystalline and single-crystal diamonds of various sizes and thicknesses with relativistic ion beams ranging from protons to heaviest ions. For heavy ions all setups deliver time resolutions sigma(t) < 60 ps. In case of protons the small primary detector signals require single-crystals as material and more elaborated designs like segmentation of the detector area and the increase of the amplifier input impedance. The best time resolution obtained for relativistic protons was sigma(t) = 117 ps.