A Collimation System Baseline Design for the Electron Storage Ring at the Electron-Ion Collider

TL;DR

The paper addresses beam-loss management for the Electron Storage Ring of the EIC by proposing a baseline collimation system embedded in the IR4 region. It leverages high-energy, multi-energy optics and a dedicated betatron-collimation insertion, validated through high-statistics multi-turn tracking with the Xsuite/BDSIM framework and custom models for Touschek and beam-gas scattering. The results show that a minimal configuration with one primary collimator per plane can localize halo and suppress IR6 losses by about one to two orders of magnitude, while preserving momentum acceptance of about $8-10\sigma_p$ and multi-hour lifetimes, with heat loads below the 3 mW/cm threshold in the cryogenic regions. This baseline enables ongoing lattice optimization and sets the stage for incorporating crab cavities, detector solenoids, refined vacuum models, and realistic machine-error effects in a path toward operation.

Abstract

We present the baseline design of the electron ring collimation system for the Electron-Ion Collider (EIC) at Brookhaven National Laboratory (BNL). The system addresses beam losses in a high-current electron storage ring with superconducting (SC) final-focus magnets and sensitive detectors, where uncontrolled losses can generate heat loads, radiation, and detector backgrounds and damage. The proposed collimation insertion localizes halo particle losses through reducing interaction region beam losses from beam-gas and Touschek scattering by several orders of magnitude while keeping detector backgrounds and cryostat heat loads within acceptable limits. Multi-turn particle tracking simulations show that the collimators do not significantly impact machine acceptance or beam lifetime, and their positions and apertures can be re-optimized for future lattice configurations. Ongoing work includes incorporating crab cavities and solenoid fields into simulations, refining vacuum conditions, and optimizing collimator geometry and materials. This design establishes a robust baseline for the EIC electron ring collimation system and supports continued lattice optimization for machine operations.

Figures (9)

• Figure 1: Schematic drawing of the EIC. The numbers from 2 through 12 indicate six insertion regions around the rings.
• Figure 2: Schematic drawing of the ePIC detector (top) and 6 o'clock interaction region (bottom), where $\theta$ and $\eta$ are polar angle and pseudorapidity, respectively.
• Figure 3: Schematic layout of IR4 with emphasis on the drift regions reserved for collimator placement.
• Figure 4: Optics functions of the ESR IR4 section in the collimation insertion. The beam direction is from right to left. Solid blue and red lines with markers represent the horizontal and vertical planes, respectively. Vertical dashed lines indicate the positions of the collimators relative to IP6, which is at $S = 0m$. The rows, from top to bottom, show the betatron functions, dispersion, and fractional part of the betatron phase advance (with respect to the IP6 phase), while the columns, from left to right, correspond to 5, 10, and 18GeV beam energies. Collimator names such as "D04H1" or "D04V1" indicate the first ("1") horizontal ("H") or vertical ("V") collimator located in interaction region "04".
• Figure 5: Estimated residual $H_{2}$ gas pressure in ESR IR6 for delivered beam doses of 100Ah (black solid line) and 10kAh (blue dashed line). The beam direction is from right to left. The corresponding average pressures are 15.4 Pa (115.2nTorr) and 1.3 Pa (9.4nTorr), respectively.