Crystal Shadowing to Reduce Beam Losses

Why It Matters

By dramatically reducing beam losses, crystal shadowing protects critical SPS components and enables the higher proton intensities required for next‑generation fixed‑target experiments, improving overall accelerator reliability.

Key Takeaways

• Crystal shadowing cuts SPS beam losses by ~50%.
• New three‑crystal system installed for operational validation.
• Remote‑adjustable bent silicon crystals protect electrostatic septum.
• Supports upcoming high‑intensity experiments SHiP and HI‑ECN3.
• AI‑based control ensures reliable crystal alignment during extraction.

Pulse Analysis

Slow extraction in the SPS is essential for delivering long, uniform proton pulses to fixed‑target experiments, but it also generates a halo of stray particles that strike sensitive hardware. The electrostatic septum, which separates the circulating beam from the extracted stream, historically suffers from high radiation damage, limiting maintenance access and long‑term operation. Crystal shadowing leverages thin, bent silicon crystals positioned downstream of the beam to act like a shield, steering halo particles away and creating a ‘shadow’ of reduced loss similar to a rock sheltering water flow.

The upgraded system comprises three precisely aligned crystals whose angles can be tuned remotely to match real‑time beam conditions. Detailed beam‑dynamics simulations guided the design, while an AI‑driven feedback loop continuously optimises crystal positioning, replicating the 50% loss reduction observed with the single‑crystal prototype in 2021. This performance has been validated both in dedicated test campaigns and during routine SPS operation, confirming that the crystal‑shadowing concept scales effectively and can be integrated without disrupting existing extraction procedures.

Looking ahead, the reduced loss environment is a critical enabler for ambitious projects like the Search for Hidden Particles (SHiP) and the High‑Intensity ECN3 (HI‑ECN3) experiment, which demand significantly higher proton intensities. By safeguarding the septum and other downstream components, crystal shadowing extends component lifetimes, lowers maintenance costs, and supports more aggressive beam parameters. The success at CERN also showcases a transferable technology for other high‑power accelerators seeking to balance beam performance with equipment protection, marking a notable advance in accelerator collimation strategies.