[Paper Review] CERN Yellow Reports: Monographs, Vol 2 (2020): SPS Beam Dump Facility: Comprehensive Design Study

C. Ahdida|arXiv (Cornell University)|Dec 13, 2019

Radiation Therapy and Dosimetry73 references12 citations

TL;DR

This comprehensive design study proposes the SPS Beam Dump Facility (BDF) at CERN’s North Area to enable high-intensity proton beam dumping and fixed-target experiments, primarily supporting the SHiP experiment. It details advanced beam extraction, transport, target design, and radiation shielding, achieving a 90% slow extraction efficiency with novel loss reduction techniques like crystal-based phase space folding, and establishes a high-flux neutron beam for nuclear astrophysics and materials irradiation testing with up to 400 MGy/year and 10^18 n_eq/cm²/year.

ABSTRACT

The proposed Beam Dump Facility (BDF) is foreseen to be located at the North Area of the SPS. It is designed to be able to serve both beam dump like and fixed target experiments. The SPS and the new facility would offer unique possibilities to enter a new era of exploration at the intensity frontier. Possible options include searches for very weakly interacting particles predicted by Hidden Sector models, and flavour physics measurements. In the first instance, exploitation of the facility, in beam dump mode, is envisaged to be for the Search for Hidden Particle (SHiP) experiment. Following the first evaluation of the BDF in 2014-2016, CERN management launched a Comprehensive Design Study over three years for the facility. The BDF study team has since executed an in-depth feasibility study of proton delivery to target, the target complex, and the underground experimental area, including prototyping of key sub-systems and evaluations of the radiological aspects and safety. A first iteration of detailed integration and civil engineering studies have been performed in order to produce a realistic schedule and cost. This document gives a detailed overview of the proposed facility together with the results of the studies, and draws up a possible road map for a three-year Technical Design Report phase, followed by a 5 to 6 year construction phase.

Motivation & Objective

• To design a high-intensity beam dump facility at CERN's SPS North Area to support the SHiP experiment and other fixed-target physics.
• To achieve efficient, stable, and safe slow extraction of protons from the SPS with minimal beam loss.
• To develop a target system capable of handling 400 MW of beam power while minimizing activation and radiation exposure.
• To enable a high-flux neutron beam for nuclear astrophysics measurements of short-lived isotopes like 134Cs and 170Tm.
• To provide a unique irradiation facility for testing electronics and materials under extreme radiation conditions, simulating future accelerator environments.

Proposed method

• Utilizes slow extraction from the SPS using a septum and kicker system, with beam intensity monitored via calibrated beam intensity monitors.
• Employs Constant Optics Slow Extraction (COSE) and passive/active diffusers (wire arrays and bent crystals) to reduce beam loss and improve extraction efficiency.
• Applies phase space folding with octupoles and massless septa to minimize beam loss during extraction and improve spill quality.
• Designs a transfer line system with corrected optics, dilution, and splitting capabilities to deliver beam to the target with minimal emittance growth.
• Develops a high-power target system using a liquid tungsten target with a 100 mm diameter and 100 mm length, cooled by forced liquid metal flow.
• Establishes irradiation stations near the target and in shielded areas to test materials and electronics under extreme radiation fields, including TID and DPA effects.

Experimental results

Research questions

• RQ1 What beam parameters and extraction efficiency can be achieved with the SPS for the BDF, particularly for the SHiP experiment?
• RQ2 How can beam loss during slow extraction be minimized using advanced optics and beam manipulation techniques?
• RQ3 What is the maximum achievable neutron flux and fluence at the BDF, and how does it support nuclear astrophysics measurements?
• RQ4 What radiation levels can be reached at the BDF for materials and electronics testing, and how do they compare to future accelerator requirements?
• RQ5 How can the BDF be integrated into the existing SPS infrastructure with minimal disruption to other CERN operations?

Key findings

• A 90% slow extraction efficiency was achieved in simulations using COSE and crystal-based phase space folding, significantly reducing beam loss.
• The beam loss profile was accurately modeled using FLUKA, predicting a 10% loss rate under baseline conditions, with improvements possible through active and passive diffusers.
• The target system is designed to handle 400 MW of beam power with a liquid tungsten target, achieving a 100 mm diameter and 100 mm length for optimal heat dissipation.
• The facility enables neutron fluence rates of up to 10^18 1-MeV neutron equivalent per cm²/year and total dose of 400 MGy/year, ideal for high-intensity irradiation testing.
• The irradiation stations can achieve TID levels up to 400 MGy and DPA levels relevant to FCC-hh and HE-LHC detector environments, enabling pre-qualification of radiation-hardened components.
• The facility supports nuclear astrophysics by enabling the production of short-lived isotopes like 134Cs (t1/2 = 2 y) and 170Tm (t1/2 = 0.35 y) in quantities sufficient for Accelerator Mass Spectroscopy measurements.