A TM01 mode launcher with quadrupole field components cancellation for high brightness applications

G Castorina,J Rosenzweig,V A Dolgashev,G Franzini,L Celona,B Spataro,L Palumbo,S Gammino,G Sorbello,G Torrisi,M Migliorati,A Mostacci,A Cahill,F Cardelli,L Ficcadenti,A Marcelli

doi:10.1088/1742-6596/1067/8/082025

Abstract

The R&D of high gradient radiofrequency (RF) devices is aimed to develop innovative accelerating structures based on new manufacturing techniques and materials in order to construct devices operating with the highest accelerating gradient. Recent studies have shown a large increase in the maximum sustained RF surface electric fields in copper structures operating at cryogenic temperatures. These novel approaches allow significant performance improvements of RF photoinjectors. Indeed the operation at high surface fields results in considerable increase of electron beam brilliance. This increased brilliance requires high field quality in the RF photoinjector and specifically in its power coupler. In this work we present a novel power coupler for the RF photoinjector. The coupler is a compact X-band TM01 mode launcher with a fourfold symmetry which minimized both the dipole and the quadrupole RF components.

Highlights

Nowadays, the attainment of higher accelerating gradients and the construction of the so called 5th generation light sources, i.e. hard X-ray Free Electron Lasers (FEL), are two of the hot topics in the modern accelerator technology
The TM01 mode launcher can be fed by a standard branched power network with three 3-dB power splitters and symmetric waveguide lines
A novel RF power coupler for RF photoinjector designed for high brightness applications has been presented

Summary

INTRODUCTION

The attainment of higher accelerating gradients and the construction of the so called 5th generation light sources, i.e. hard X-ray Free Electron Lasers (FEL), are two of the hot topics in the modern accelerator technology. Among the most promising techniques to reduce the breakdown probability in a RF gun is coupling the power from the axis, removing the coupler from the main cell where the probability of the RF breakdown is higher [3] This coupling layout is possible by going from the rectangular TE10 mode to the circular TM01 mode. This modified version, based on a four fold symmetry, allows the on-axis power coupling and removing at the same time dipole and quadrupole components This original and compact layout keeps the maximum surface electric and magnetic fields sufficiently low to guarantee multi-MW delivery (up to 200 MW) to a device of this structure

SYMMETRY MODE LAUNCHER

POWER DELIVERY NETWORK

HARMONIC ANALYSIS OF THE FIELDS

CONCLUSION