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Simulation study on the emittance compensation of off-axis emitted beam in RF Photoinjector

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Chinese Physics C 2016年第11期40卷 184-190页

作者：黄瑞萱 Chad Mitchell 贾启卡 Christos Papadopoulos Fernando Sannibale [1NSRL University of Science and Technology of ChinaHefei 230029China ATAP Lawrence Berkeley National LaboratoryOne Cyclotron RoadBerkeleyCalifornia94720USA

To make full use of the photocathode material and improve its quantum efficiency lifetime, it can be necessary to operate the laser away from the cathode center in Photoinjectors. In RF guns, the off-axis emitted beam will see a time-dependent RF effect, which would generate a significant growth in transverse emittance. It has been demonstrated that such an emittance growth can be almost completely compensated by orienting the beam on a proper orbit in the downstream RF cavities along the injector [1]. In this paper we analyze in detail the simulation techniques used in reference [1] and the issues associated with them. The optimization of Photoinjector systems involving off-axis beams is a challenging problem. To solve this problem, one needs advanced simulation tools including both genetic algorithms and an efficient algorithm for 3D space charge. In this paper, we report on simulation studies where the two codes ASTRA and IMPACT-T are used jointly to overcome these challenges, in order to optimize a system designed to compensate for the emittance growth in a beam emitted off axis.

关键词： Photoinjector off-axis emission genetic algorithm ASTRA IMPACT-T RF effect emittance compen-sation

Drive laser system for the DC-SRF Photoinjector at Peking University

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Chinese Physics C 2016年第1期40卷 123-128页

作者：王志文黄森林林林赵刚全胜文刘克新陈佳洱 State Key Laboratory of Nuclear Physics and Technology Institute of Heavy Ion Physics Peking University

Photoinjectors are widely used for linear accelerators as electron sources to generate high-brightness electron beams. The drive laser, which determines the timing structure and quality of the electron beam, is a crucial component of a Photoinjector. A new drive laser system has been designed and constructed for the upgraded 3.5-cell DC-SRF Photoinjector at Peking University. The drive laser system consists of a 1064 nm laser oscillator, a four-stage amplifier, second and fourth harmonic generators, an optical system to transfer the UV pulses to the photocathode, and a synchronization system. The drive laser system has been successfully applied during stable operation of the DC-SRF Photoinjector and its performance meets requirements. A 266 nm laser with an average power close to 1 W can be delivered to illuminate the Cs2Te photocathode and the instability is less than 5% for long time operation. The design considerations for improving the UV laser quality, a detailed description of the laser system, and its performance are presented in this paper.

关键词： drive laser amplifier harmonic generation Photoinjector

Photoinjector beam quality improvementby shaping the wavefront of a drive laser with oblique incidence

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Chinese Physics C 2012年第6期36卷 561-565页

作者：何志刚王晓辉贾启卡 National Synchrotron Radiation Laboratory University of Science and Technology of China

To increase the quantum efficiency （QE） of a copper photocathode and reduce the thermal emit- tance of an electron beam, a drive laser with oblique incidence was adopted in a BNL type photocathode rf gun. The disadvantageous effects on the beam quality caused by oblique incidence were analyzed qualitatively. A simple way to solve the problems through wavefront shaping was introduced and the beam quality was improved.

关键词： Photoinjector drive laser oblique incidence wavefront shaping beam quality improvement

Design optimization and cold RF test of a 2.6-cell cryogenic RF gun

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Nuclear Science and Techniques 2021年第9期32卷 84-93页

作者： Cheng Wang Jian-Hao Tan Xiao-Xia Huang Yi-Xing Lu Lin Wang Wen-Cheng Fang Zhen-Tang Zhao Shanghai Institute of Applied Physics Chinese Academy of SciencesShanghai 201800China University of Chinese Academy of Sciences Beijing 100049China Shanghai Synchrotron Radiation Facility Chinese Academy of SciencesShanghai 201204China

To further improve the performance of acceler-ators,the first cryogenic normal-conducting RF gun in China was designed and manufactured.As a new and attractive trend,this optimized cryogenic RF gun can generate a low-emittance beam with a short-driven laser pulse because of its promising high gradient on the cath-ode.In this paper,optimization of the RF design and beam dynamics,including suppression of the peak RF field and elimination of the multipole mode,is presented.In addi-tion,the emittance growth caused by the alignment devi-ation and RF jitter is discussed.After the gun was manufactured,a cold test was conducted at both room temperature and cryogenic conditions.At room tempera-ture,the field distribution was obtained by the bead pull method.Under cryogenic conditions,the RF properties,such as the coupling coefficient and quality factor,varied with temperature.The test results agreed with the design.In the cryogenic test,vibration measurements were performed.Without vibration isolation,a maximum vibration of 50 lm was observed.These cold test results are the basis of the following high-power test.

关键词： Photoinjector Cryogenic structure C-band Cold test

Slice emittance and projected emittance

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Chinese Physics B 2008年第3期17卷 901-907页

作者：李正红 Science College South-Western University of Science and Technology

This paper presents an analytical description for the growth of the projected emittanee （here just referred to the transverse emittance） based on the concept of the slice emittance in an RF Photoinjector. In the RF Photoinjector, the slice emittance undergoes small changes, but the projected emittance changes significantly even in the drift space after the injector. Carefully adjusting the parameters of the RF Photoinjector, which usually means emittance compensation, the projected emittance can be minimized to the value of the slice emittance. The relation between slice emittance and projected emittance is explained in this paper. An emittance function, which shows such a relation, is also introduced. A model about the emittance growth in the RF Photoinjector is established, which accords with the particle simulation results by using the code ASTRA. The condition to minimize the emittance is also given by using the emittance function, which means the emittance compensation in the RF Photoinjector.

关键词： Photoinjector emittance slice emittance emittance compensation

Experimental Investigations of SRF at Peking University

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Experimental Investigations of SRF at Peking University