中国工程物理研究院FEL-THz束线从头至尾模拟设计(英文)

中国工程物理研究院正在开展自由电子激光太赫兹源(FEL-THz)的研究。介绍了中物院FEL-THz束线的设计,通过PARMELA和TRANSPORT等程序优化了束线参数,并通过IMPACT-T和ELEGANT程序核对了模拟结果。优化结果表明,电子束在摇摆器入口处能量7～8MeV、平均电流5mA、横向归一化发射度小于10mm·mrad,满足设计要求。     

BBU effect in an ERL-FEL two-purpose test facility

Both the energy recovery linac (ERL) and the free electron laser (FEL) are considered to be candidate fourth generation light sources. It is proposed to combine an FEL into an ERL facility to integrate the advantages of both, and to realize a compact two-purpose light source. A test facility to verify this principle is being designed at the Institute of High Energy Physics, Beijing. One main concern is the beam breakup (BBU) instability which limits the available beam current. To this end, we developed a numerical simulation code to calculate the BBU threshold, which is found to have only a small reduction even in a high-FEL-bunch-charge operation mode, compared with that in the case with ERL bunches only. However, even with the ERL beam current far below the BBU threshold, we observed a fluctuation of the central orbit of the ERL bunches in the presence of an FEL beam. We then present a physical model of BBU and understand the mechanism of the orbit-fluctuation in an ERL-FEL two-purpose machine. We found that by choosing an appropriate FEL bunch repetition rate, the central orbit fluctuation amplitude can be well controlled.     

Suppression of the emittance growth induced by coherent synchrotron radiation in triple-bend achromats

The coherent synchrotron radiation (CSR) effect in a bending path plays an important role in transverse emittance dilution in high-brightness light sources and linear colliders, where the electron beams are of short bunch length and high peak current. Suppression of the emittance growth induced by CSR is critical to preserve the beam quality and help improve the machine performance. It has been shown that the CSR effect in a double-bend achromat (DBA) can be analyzed with the two-dimensional point-kick analysis method. In this paper, this method is applied to analyze the CSR effect in a triple-bend achromat (TBA) with symmetric layout, which is commonly used in the optics designs of energy recovery linacs (ERLs). A condition of cancelling the CSR linear effect in such a TBA is obtained, and is verified through numerical simulations. It is demonstrated that emittance preservation can be achieved with this condition, and to a large extent, has a high tolerance to the fluctuation of the initial transverse phase space distribution of the beam.     

Design studies on the ERL-FEL test facility at IHEP, Beijing

A proposed compact ERL test facility at IHEP, Beijing, is presented in this paper, and includes the design parameters, the essential lattice, and the key components features, such as the photocathode DC gun and the CW superconducting accelerating structures. Some important beam physics issues such as the space charge effect, the coherent synchrotron radiation (CSR) effect and the beam break-up (BBU) effect are briefly described with the simulation results.     

Suppression of the emittance growth induced by CSR in a DBA cell

The emittance growth induced by Coherent Synchrotron Radiation (CSR) is an important issue when electron bunches with short bunch length and high peak current are transported in a bending magnet. In this paper, a single kick method is introduced that could give the same result as the R-matrix method, but is much easier to use. Then, with this method, an optics design technique is introduced that could minimize the emittance dilution within a single achromatic cell.