Effects of rf breakdown on the beam in the Compact Linear Collider prototype accelerator structure

TL;DR

This paper investigates how RF breakdowns in high-gradient accelerator structures impact the beam in the CLIC prototype, providing measurements and analysis of beam trajectory changes correlated with breakdown events.

Contribution

It offers new measurements of beam orbit changes during RF breakdowns and analyzes their correlation with RF power and breakdown location in the accelerator structure.

Findings

Fast beam trajectory changes occur during RF breakdowns.

Breakdown scenarios are identified and explained based on power measurements.

Distribution of orbit change magnitudes correlates with breakdown location.

Abstract

Understanding the effects of RF breakdown in high-gradient accelerator structures on the accelerated beam is an extremely relevant aspect in the development of the Compact Linear Collider (CLIC) and is one of the main issues addressed at the Two-beam Test Stand at the CLIC Test Facility 3 at CERN. During a RF breakdown large electro-magnetic fields are generated and produce parasitic magnetic fields which interact with the accelerated beam affecting its orbit and energy. We discuss here measurements of such effects observed on an electron beam accelerated in a CLIC prototype structure. Measurements of the trajectory of bunch-trains on a nanosecond time-scale showed fast changes in correspondence of breakdown which we compare with measurements of the relative beam spots on a scintillating screen. We identify different breakdown scenarios for which we offer an explanation based also on measurements of the power at the input and output ports of the accelerator structure. Finally we present the distribution of the magnitude of the observed changes in the beam orbit and we discuss its correlation with RF power and breakdown location in the accelerator structure.