Abstract
Collimators are commonly used in particle accelerators to prevent particles traveling at large amplitudes from hitting the vacuum chamber. We derive here, for a single-pass linac, a one-dimensional analytical expression for the efficiency of a two-stage fully absorbing collimation system (CS), based on the CS geometrical and optical properties only. We show that, in the presence of physical space or optics constraints, the best betatron phase advance in between the first and the second collimation stage may differ from the usually prescribed $\ensuremath{\pi}/2$. The analytically computed collimation efficiency is then compared to particle tracking results.
Highlights
Control of beam losses in particle accelerators is often mandatory to protect equipment. This includes preventing halo particles traveling at large amplitudes and eventually hitting the vacuum chamber creating secondary showers
A collimation system (CS) design usually includes a spoiler and an absorber; the purpose of the spoiler is to increase the transverse footprint of any unwanted particles before they are stopped in the absorber
The quasiperiodic motion carries the requirement of a secondary collimator with a larger aperture than that of the first, because particles that do not interact with the primary collimator must not be affected by the secondary one
Summary
Control of beam losses in particle accelerators is often mandatory to protect equipment. This includes preventing halo particles traveling at large amplitudes and eventually hitting the vacuum chamber creating secondary showers. The halo is usually intercepted by absorbing metal blocks called collimators; they locally restrict the vacuum chamber physical aperture without affecting the main beam. The halo paprffitffiifficffiffiffilffieffiffisffiffi have betatron oscillation amplitudes larger than "u u, u being the betatron function. To intercept both large amplitude and large angle particles both a primary and a secondary collimator are needed. The present scheme relies instead on a CS consisting of two fully absorbing apertures in the beam path, such as, e.g., a 20 cm long Cu block whose stopping power for proton beams up to the MeV range and electron beams up to the GeV range is high [1]
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