Qin Bin

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.

Central region design for a 10 MeV internal ion source cyclotron

Internal ion sources are widely adopted in commercial cyclotrons used for short-life isotopes production. Without beam manipulation provided by the external beam injection line, the central region of this type of cyclotron is more sensitive and should be carefully designed. A design study and beam dynamics simulation for the central region of a 10 MeV compact cyclotron is presented. The OPERA3D/TOSCA code was used to calculate the electric field from a parameterized three dimensional (3D) central region model. With iterative structure optimizations of the central region, the beam centering and vertical focusing is well controlled, and the RF phase acceptance is around 25°. A c++ code for beam simulation in the central region was developed and tested.

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.