Dark Current and Radiation Shielding Studies For The ILC Main Linac

TL;DR

This study models dark current electrons in the ILC main linac, assessing radiation risks and shielding effectiveness, finding that a 2.3-meter concrete wall can reduce radiation to safe levels.

Contribution

It provides a detailed simulation of dark current effects and proposes effective shielding solutions for the ILC main linac.

Findings

A 2.3-m thick concrete wall reduces radiation to safe levels.

Dark current electrons can reach energies up to 19 GeV.

Shielding design can ensure dose levels stay below 25 μSv/hr.

Abstract

Electrons of dark current (DC), generated in high-gradient superconducting RF cavities (SRF) due to field emission, can be accelerated up to very high energies-19 GeV in the case of the International Linear Collider (ILC) main linac-before they are removed by focusing and steering magnets. Electromagnetic and hadron showers generated by such electrons can represent a significant radiation threat to the linac equipment and personnel. In our study, an operational scenario is analysed which is believed can be considered as the worst case scenario for the main linac regarding the DC contribution to the radiation environment in the main linac tunnel. A detailed modeling is performed for the DC electrons which are emitted from the surface of the SRF cavities and can be repeatedly accelerated in the high-gradient fields in many SRF cavities. Results of MARS15 Monte Carlo calculations, performed for the current main linac tunnel design, reveal that the prompt dose design level of 25 {\mu}Sv/hr in the service tunnel can be provided by a 2.3-m thick concrete wall between the main and service tunnels.