Pei Yuanji

Physical design of FEL injector based on the performance-enhanced EC-ITC RF gun

To meet requirements of high performance THz-FEL (Free Electron Laser), a compact scheme of FEL injector was proposed. Thermionic cathode was chosen to emit electrons instead of photo-cathode with complex structure and high cost. The effective bunch charge was improved to ~200pC by adopting enhanced EC-ITC (External Cathode Independently Tunable Cells) RF gun to extract micro-bunches, and back bombardment effects were almost eliminated as well. Constant gradient accelerator structures were designed to improve energy to ~14MeV, while focusing system was applied for emittance suppressing and bunch state maintenance. Physical design and beam dynamics of key components for FEL injector were analyzed. Furthermore, start-to-end simulations with multi-pulses were performed by using homemade MATLAB and Parmela. The results show that continual high brightness electron bunches with low energy spread and emittance could be obtained stably.

A Novel Method for Rigorously Analyzing Beam Loading Effect Based on the Macro-Particle Model

The beam loading effect is a considerable issue for a high average current beam. We apply a novel method without utilizing the specious beam current value to rigorously analyze the beam loading effect in S-band linacs. By tracking every macro-particles state and using the energy conservation law, power dissipated from the beam is calculated in each cell. In the new particle-based algorithm, the concept of equivalent beam current is proposed. Its value is not constant and it has a small variation through the accelerating structure. Also, we introduce the iteration algorithm as comparison and we find that the two algorithms coincide with each other very well.

Physical design of a 10 MeV LINAC for polymer radiation processing

In China, polymer radiation processing has become one of the most important processing industries. The radiation processing source may be an electron beam accelerator or a radioactive source. Physical design of an electron beam facility applied for radiation crosslinking is introduced in this paper because of its much higher dose rate and efficiency. Main part of this facility is a 10 MeV travelling wave electron linac with constant impedance accelerating structure. A start to end simulation concerning the linac is reported in this paper. The codes Opera-3d, Poisson-superfish and Parmela are used to describe electromagnetic elements of the accelerator and track particle distribution from the cathode to the end of the linac. After beam dynamic optimization, wave phase velocities in the structure have been chosen to be 0.56, 0.9 and 0.999 respectively. Physical parameters about the main elements such as DC electron gun, iris-loaded periodic structure, solenoids, etc, are presented. Simulation results proves that it can satisfy the industrial requirement. The linac is under construction. Some components have been finished. Measurements proved that they are in a good agreement with the design values.

Design of an electron gun for terahertz radiation source

An EC-ITC (External-Cathode Independently Tunable Cells) RF gun was employed with the aim of obtaining short-pulse bunches with high peak current for a terahertz radiation source. A gridded DC gun plays a key role as the external injecting electron source of the ITC RF gun, the performance of which determines the beam quality in the injector and transport line. In order to make the beam well compressed in the ITC RF gun, the energy of the electrons acquired from the gridded DC gun should be 15 keV at most. A proper structure of the gridded gun with double-anode is shown to overcome the strong space- charge force on the cathode, which is able to generate 6 μs beam with 4.5 A current successfully.

Physical calculation for anX-band hybrid dielectric-iris-loaded accelerator

A small, high performance X-band hybrid dielectric-iris-loaded travelling-wave linac with the length of 1.47 m and the maximum accelerating gradient of 45 MV/m has been designed. The beam energy of 33 MeV, the energy spread of 0.5%, the beam emittance of about 5.7 πmm mrad and the capture efficiency of 40% are reached by adjusting the sizes of the accelerating cavities and the phase velocity. The attenuation per unit length of structure, the shunt impedance Rs, the quality factor Q, the group velocity and the phase velocity are also presented.

Design of a 200keV high pulse current electron beam facility

In the paper, design of a 200 keV high pulse current electron beam facility is introduced. Physical parameters of the beam have been selected to satisfy the plasma experiments need. LaB6 has been used as cathode material for its desirable qualities. Temperature distribution simulation in vacuum chamber has been finished. Because the maximum working temperature in the system is about 2400deg C, grid is made of Molybdenum which is heat-resistant. In order to get high pulse current and line shaping electron beam, shape of electrodes has been optimized. Electric field distribution and process of electron beam emission have been simulated with considering space charge effects. Ceramic flanges electrics and mechanics properties have also been analyzed. Exit window is made of titanium with 40 mum thickness. During passing through the window, relationship between initial energy and energy loss of the electron beam has been obtained by MC simulation. Assembling of the facility has been finished and some parameters have been measured in testing experiments.