RF deflecting cavity design for bunch length measurement of photoinjector at Tsinghua University

RF deflecting cavity can be used for bunch length measurement and is designed to diagnose the beam produced by the photocathode electron gun which was built at Tsinghua University for the Thomson scattering experiment. Detailed discussion and calculation for measuring the 3.5 MeV bunch and another with further acceleration to 50 MeV, which is under development, are presented. A standing-wave deflecting cavity working at 2856 MHz is designed and the power feeding system has been planned.

Streak camera calibration for bunch length measurement at BEPC II

Purpose Streak camera is an important device for bunch length measurement.The errors introduced by streak camera should be considered in measurement.In order to accurately measure bunch length,some streak camera calibrations are studied at BEPC II.Methods In this context,the point spread function,caused by the optical system,is measured at focus mode with both deflec-tions disabled.In the same conditions,the influence of camera gain on measurement is studied.For the dual sweep mode of streak camera,a calibration method using electrical delays is applied to calibrate the beam size result.Results Firstly,a point spread function calibration 1.78 ps of streak camera optical system is obtained with focus mode.Secondly,studying the effect of camera gain on measurement,an optimal camera gain range from 506 to 662 is selected,in which the bunch length measurement error is within 0.5 ps.Thirdly,a dual sweep calibration factor 1.02 is obtained.Conclusions For BEPCII bunch length,there is a little difference before and after the streak camera calibrations.However,for the accurate measurement of ultra-short bunch length,the calibrations are of great significance.

Bunch length measurement at Tsinghua Thomson scattering X-ray source

The length of electron beam from a photocathode RF gun is determined by a spectrometer, according to the relative energy spread induced by the bunch length during the acceleration in a linac. For a photocathode RF gun, different laser injected phase and beam charge are studied. The compression is changed for the different laser phases, as from 10 ° to 30 ° , and the bunch length is lengthened due to the strong longitudinal space charge force, caused by the increased charge.

RF deffecting cavity for bunch length measurement in Tsinghua Thomson scattering X-ray source

An RF deffecting cavity used for bunch length measurement has been designed and fabricated at Tsinghua University for the Thomson Scattering X-Ray Source. The cavity is a 2856 MHz, π-mode, 3-cell standing-wave cavity, to diagnose the 3.5 MeV beam produced by photocathode electron gun. With a larger power source, the same cavity will again be used to measure the accelerated beam with energy of 50 MeV before colliding with the laser pulse. The RF design using MAFIA for both the cavity shape and the power coupler is reviewed, followed by presenting the fabrication procedure and bench measurement results of two cavities.

Simulation and Error Analysis of Electro-optic Sampling Measurement of Ultrashort Electron Beam Bunch Length

For the development of high energy physics,it is needed to improve the performance of the relativistic electron bunch.The measurement of the ultrashort relativistic electron pulse becomes one of the key technologies.The electro-optic sampling measurement of relativistic electron pulses is a promising method.This method is nondestructive, non-intrusive,and real-time monitoring.Distance and angles of the reference frames will cause system deviations.In this paper these system deviations are analyzed by simulation.It provides a reference for the experiment.

Electro-optical sampling non-synchronous delay scanning measurement of electron beam bunch length at BFEL

The Electro-optical sampling delay scanning technique can be used for electron beam bunch length measurement. A novel non-synchronous delay scanning technique based on the electro-optical sampling measurements is presented. Based on Beijing Free Electron Laser （BFEL）, the electron beam bunch length was measured with the electro-optical sampling technique for the first time in China. The result shows that the electron beam bunch length at BFEL is about 5.6±1.2 ps.

Generation and measurement of sub-picosecond electron bunch in photocathode rf gun

We consider a scheme to generate a sub-picosecond electron bunch in the photocathode rf gun by im-proving the acceleration gradient in the gun, suitably tuning the bunch charge, the laser spot size and the acceleration phase, and reducing the growth of transverse emittance by laser shaping. A nondestructive technique is also reported to measure the electron bunch length, by measuring the high-frequency spectrum of wakefield radiation which is caused by the passage of a relativistic electron bunch through a channel surrounded by a dielectric.

First experimental research of the bunch compressor at CAEP

Magnetic bunch compressor is one of the key technologies on the path to next generation accelerator driven facilities. In this paper we report the design principles and the first experimental research of the bunch compressor developed at Chinese Academy of Engineering Physics （CAEP）. The length of the bunch after compressor is found to be about 0.7 ps （rms） and the peak current exceeds 500 A when operated in the optimized condition. The sensitivity of the bunch length on the phase of the acceleration field and magnetic field of the bunch compressor was also measured and analyzed.