Undulator-Based Positron Source at 250 GeV CM Energy with Different Optical Matching Devices: Pulsed Flux Concentrator and Quarter Wave Transformer

In the baseline design of the International Linear Collider (ILC) an undulator-based source is foreseen for the positron source. In this study the energy deposition in the pulsed flux concentrator (FC) of positron source is calculated for the ILC at 250 GeV center-of-mass energy. The peak energy of 33 J/g deposited by one beam pulse in the current design of the FC is above the limit for copper material. Several promising options were considered to solve the issue of overheating the FC: the quarter wave transformer (QWT) has a significantly bigger aperture and is considered as an valuable and safe alternative for the FC. Since the positron source with a QWT is expected to lead to a lower positron capture efficiency, also the expected positron yield was calculated in addition to the energy deposition in QWT