OPTIMIZATION OF FLUX CONCENTRATOR FOR SuperKEKB

For high luminosity electron-positron colliders, intense positron beam production is one of the key issues as well as electron. Flux Concentrator (FC) is a pulsed solenoid that can generate high magnetic field of several Tesla and is often used for focusing positrons emerged from a production target. It works as an optical matching device in a positron capture section. With this device, high capture efficiency is achieved. In this paper, we will discuss a design optimization of a FC for the SuperKEKB positron source. Geometrical parameters of the FC are optimized to achieve high peak field using the CST EM Studio [1]. Magnetic field distribution evaluated with the EM Studio is implemented into a particle tracking code to see a performance of the positron capture section. The tracking simulation includes a positron production at the target, focusing by the FC and subsequent solenoids and acceleration by RF structures till the end of the capture section. We report the results of a FC design optimized for higher positron yield with the tracking simulation.