Design and development of radio frequency output window for circular electron–positron collider klystron

This paper presents the first phase of design, analysis, and simulation for the klystron coaxial radio frequency（RF）output window. This study is motivated by 800 kW continuous wave（CW）, 650 MHz klystrons for the future plan of circular electron–positron collider（CEPC） project. The RF window which is used in the klystron output section has a function to separate the klystron from the inner vacuum side to the outside, and high RF power propagates through the window with small power dissipation. Therefore, the window is a key component for the high power klystron. However, it is vulnerable to the high thermal stress and multipacting, so this paper presents the window design and analysis for these problems. The microwave design has been performed by using the computer simulation technology（CST） microwave studio and the return loss of the window has been established to be less than-90 d B. The multipacting simulation of the window has been carried out using MultiPac and CST particles studio. Through the multipacting analysis, it is shown that with thin coating of TiN, the multipacting effect has been suppressed effectively on the ceramic surface. The thermal analysis is carried out using ANSYS code and the temperature of alumina ceramic is lower than 310 K with water cooling.The design result successfully meets the requirement of the CEPC 650 MHz klystron. The manufacturing and high power test plan are also described in this paper.

CEPC positron source design

Purpose Circular Electron Positron Collider(CEPC)is a 100-km-ring e+e−collider for a Higgs factory.The injector is composed of a 10-GeV Linac and a 120-GeV Booster.The CEPC Linac is a normal conducting S-band Linac with frequency of 2860 MHz providing electron and positron beams at an energy up to 10 GeV with 100 Hz repetition frequency.The positron source is the most important part of the CEPC Linac,and the bunch charge of positron beam within some cut-off condition should be larger than 3 nC.Methods The positron source of CEPC is composed of a target,a flux concentrator,a capture section,a pre-accelerating section and a beam separation system.Higher positron yield and capture efficiency are the design goal.Based on simulation,the design will be presented and discussed in detail.Result The positron yield at the PSPAS exit is larger than 0.55,and the normalized rms emittance is 2370 mm-mrad with a strict cut-off condition.The detailed simulation results will be presented.Conclusions The design of the positron source including positron production and capture will be presented and can meet the requirements.