Optimization of the collimation system for the Spallation Neutron Source accumulator ring

Abstract

The collimation system for the Spallation Neutron Source accumulator ring is designed for a capture efficiency close to 95% of the proton beam halo, dissipating about 2 kW of beam power. The collimation system consists of a two-stage collimation system (one scraper and two absorbers) cleaning the transverse halo and a beam-in-gap kicker system cleaning the gap residual and longitudinal halo. Preliminary studies indicate that a maximum level of uncontrolled loss of 0.01% of the total beam is achievable. On the other hand, the energy lost in the primary scraper may kick protons outside the rf bucket concentrating uncontrolled losses in areas of maximum dispersion. We use Monte Carlo simulations to clarify some beam dynamic issues that may compromise the high efficiency required. The material interacting with the beam and the shape of the scraper and absorbers have been carefully chosen to maximize the collimation efficiency and to minimize radioactivation. Furthermore, a realistic distribution of losses around the machine is used to identify potential hot areas. Finally, we determine the sensitivity of the collimation efficiency to misalignments and closed orbit errors. This paper describes the latest design of the collimation system and summarizes the results of these numerical studies.

Synchrotrons and accumulators for high-intensity proton beams

“…19 (ESS, 2002); (2) scraping at a high-dispersion lattice location (J-PARC) as shown in Fig. 20 (J-PARC, 2002); and, (3) using a beam-in-gap kicker (SNS) Catalan-Lasheras, Lee, et al, 2001;Cousineau et al, 2001). The latter method requires an adequate momentum clearance so that particles can reach the gap without loss.…”

SNS Beam-in-Gap Cleaning and Collimation

“…Much of the design work for the collimators was completed before installation of the ORBIT collimation package, and detailed descriptions of the system have been published [3]. The goal of our work was not to redesign the system but to fine-tune such parameters as primary scraper thickness and material, aperture shape, and collimator location.…”

“…The structure of the collimation routine is modeled after a standalone collimation code K2 [3], with routines adapted specifically for the SNS energy range. Physical processes included are multiple coulomb scattering, ionization energy loss, nuclear inelastic absorption and nuclear elastic scattering, rutherford scattering, and a detailed treatment of the collimator edge.…”

Collimation optimization in high intensity rings

“…A set of four movable scrapers made out of 0.5 cm platinum plates acts as primary collimator increasing the divergence of the halo protons. Two heavy absorbers presenting an equivalent mass close to 60 cm of stainless steel are located downstream as fixed aperture secondary collimators [8,11]. The first secondary collimator is located in the long straight section between doublets.…”