Cockcroft Institute, Warrington, Cheshire
The University of Liverpool, Liverpool
For beam profile monitoring applications where low beam perturbation together with bi-dimensional imaging is required, ionization monitors based on neutral gas-jet targets shaped into a thin curtain are an interesting option. When integrated in ultra-high vacuum systems, such as in the Ultra-low energy Storage Ring (USR), where local vacuum preservation is of primary concern, such systems present severe difficulties linked to the creation and proper shaping of a high quality gas-jet curtain. In this contribution, investigations into the generation and evolution of the jet with the Gas Dynamics Tool (GDT) software and purpose-written C++ analysis modules are presented. By means of extensive numerical analysis, the advantages of a novel nozzle-skimmer system in terms of curtain quality are summarized as compared to traditional axisymmetric gas-jet creation and curtain shaping by means of scrapers. It is also shown that variable nozzle-skimmer geometries allow for modifying the gas-jet characteristics in a wide range, including jet splitting and local density modulation. Finally, the layout of a test stand that will be used for an experimental benchmark of these studies is shown.
Cockcroft Institute, Warrington, Cheshire
The University of Liverpool, Liverpool
The introduction of Silicon Photomultipliers (SiPMs) as single photon sensitive detectors represents a promising alternative to traditional photomultiplier tubes. This is especially true in applications in which it is compulsory to attain magnetic field insensitivity, low photon flux detection, quantum efficiency in the blue region that is comparable to standard photomultipliers, high timing resolution, dimensions comparable to the dimensions of an optical fiber diameters, and low costs. The structure of the SiPM is based on an array of independent avalanche photodiodes (APDs) working in Geiger-mode at a low bias voltage with a high gain. The output signal is proportional to the number of pixels "fired" by impacting photons. The detection efficiency for state-of-the-art devices is in the order of 20% at 500 nm. In this contribution, the measured dark count rates of different SiPMs are compared and the influence of this noise on the real signal is presented. These results are then used to correct the photon count and determine the optimized working parameters for a future beam loss monitor at CTF3/CLIC.