[Paper Review] Crystal collimation experiment on 70-GeV proton accelerator

A. G. Afonin, V.M. Biryukov+9 more|ArXiv.org|Nov 13, 2001

Crystallography and Radiation Phenomena8 references4 citations

TL;DR

This paper demonstrates the first experimental proof of crystal collimation in a 70-GeV proton accelerator, where a bent silicon crystal was used as a primary element to deflect beam halo particles into a secondary collimator. The technique reduced downstream radiation levels by a factor of two, confirming Monte Carlo predictions and validating crystal-based halo scraping for beam loss mitigation in high-energy accelerators.

ABSTRACT

The first proof-of-principle experiment on "crystal collimation" was performed with 70-GeV protons on IHEP accelerator. A bent crystal installed in the ring as a primary element upstream of a collimator has reduced the radiation levels downstream in the accelerator by a factor of two. The measurements agree with Monte Carlo predictions.

Motivation & Objective

• To demonstrate the feasibility of using bent crystals as primary elements in beam collimation systems to reduce beam loss and radiation background.
• To test the efficiency of crystal-assisted beam halo scraping in a real accelerator environment, specifically at the IHEP 70-GeV proton accelerator.
• To validate Monte Carlo simulations of multipass channeling and particle deflection in bent crystals under real operational conditions.
• To assess the performance and durability of silicon crystals under high-intensity proton beams without cooling or degradation over time.
• To explore the potential of crystal collimation for future applications in major accelerators like RHIC and the Tevatron.

Proposed method

• A bent silicon (111) crystal with a 3 mm bent section and 5 mm total length was installed upstream of a septum magnet in the accelerator ring.
• The crystal was oriented to deflect halo particles via channeling at a deflection angle of 0.65–1.7 mrad, based on critical angle theory for silicon.
• Beam extraction and halo scraping were studied using radiation monitors placed downstream of the beam stop (FEP), measuring relative radiation levels as a function of crystal alignment.
• The crystal's angular and horizontal position was adjusted with sub-micron precision (0.1 mm and 13.5 μrad) to optimize channeling efficiency.
• Beam profiles at the FEP entry face were measured using a kicker magnet and compared to those from the crystal to independently verify channeling efficiency.
• Radiation levels were monitored at three detector positions to assess the impact of crystal alignment, misalignment, and alternative scraping methods (e.g., amorphous targets).

Experimental results

Research questions

• RQ1 Can a bent crystal effectively deflect beam halo particles into a secondary collimator, reducing radiation levels in the accelerator ring?
• RQ2 To what extent does crystal channeling efficiency depend on angular alignment, and can it be experimentally verified?
• RQ3 How does the radiation background compare when using a crystal as a primary collimator versus direct scraping by a beam stop (FEP) or amorphous targets?
• RQ4 What is the maximum beam intensity that a crystal can handle without degradation, and does this match Monte Carlo predictions?
• RQ5 Can crystal collimation be reliably and reproducibly applied in high-intensity proton accelerators for long-term beam loss mitigation?

Key findings

• The crystal collimation system reduced downstream radiation levels by a factor of two when the crystal was optimally aligned, confirming its effectiveness in halo scraping.
• The measured extraction efficiency of the crystal was approximately 50%, consistent with both radiation monitoring and independent beam profile measurements.
• At optimal alignment, about 50% of the halo particles were channeled and deflected into the FEP beam stop, significantly reducing radiation background.
• The crystal demonstrated reliable performance over extended operation, with no observed degradation after 10 years of continuous use at 70 GeV proton intensity.
• Monte Carlo simulations were validated by experimental results, showing good agreement with predicted multipass channeling behavior and efficiency.
• Shorter crystals (down to 1 mm) are predicted to achieve 80–90% efficiency, motivating further development of ultra-short bent crystal systems.