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Beam Line Design at the Caep Thz Free Electron Laser
| Content Provider | Semantic Scholar |
|---|---|
| Author | Bai, Weichen Wang, Hao |
| Copyright Year | 2013 |
| Abstract | China Academy of Engineering Physics (CAEP) is currently building a THz Free Electron Laser (FEL-THz) source which serves as a radiation light source used for research in a variety of experimental fields. In this paper, we present the design of the beam line, which was accomplished using PARMELA and TRANSPORT computer simulations. The accelerator consists of a 350 kV photocathode DC gun providing a pulsed electron beam, in conjunction with one cryomodule containing two 4-cell superconducting RF cavities. The energy of the electron beam is 7~8 MeV, and the maximum of the average beam current is 5 mA. A emittance typically below 10 pi mm.mrad can be achieved. INTRODUCTION Electromagnetic radiation in the frequency range from about 0.1 to 10 THz is known as the ‘THz gap’, which corresponds to wavelengths between 3mm and 30μm, photon energies between 0.4 and 40 meV. It can be used in many regions, such as in pharmacy [1], in medicine and biology [2] and in security [3]. But there is lack of efficient sources and of sensitive detectors. Free electron laser can provide high power radiation and is monochromatic and tunable. Due to its excellent properties above, FEL-THz source is one of most perfect choices to generate THz radiation. China Academy of Engineering Physics (CAEP) is currently building a THz Free Electron Laser source which serves as a radiation light source used for research in a variety of experimental fields. The performance of a free electron laser depends crucially on the electron beam parameters. Requirements at the undulator for our high power cw FEL are as follow: The electronic energy is 6-8 MeV, transverse emittance is less 10π mm·mrad, energy spread less 0.75%, beam length less 10 ps and the facility will radiate with a average power about 10 watt between the wavelength range of 100-300 m. A block diagram of the facility is shown in Figure 1. Its injector consists of a high DC voltage GaAs photocathode Gun drived by a frequency-doubled, mode-locked Nd:YLF laser, two solenoidal lens, a room temperature 1.3 GHz buncher cavity, a cryounit with two 4-cell superconducting cavities. And its transport line is antisymmetric to cancel chromatic aberration with four quadrupoles lens and two bend magnets. Undulator with resonance cavity is used to radiate THz laser from electron beam. Not only analytical calculations are needed to give an estimate of the expected performance, but also numerical start-to-end simulations are required to account for various aspects of beam dynamics and to match the demands of wiggle [4]. In this paper, we present the optimize simulation results and give some parameters analysis. To account for space charge effects, beam dynamics code PARMELA [5] was used to simulate the module from cathode to wiggle without including electron-photon interaction. Dispersion section was simulated first by TRANSPORT [6], then by PARMELA. INJECTOR PROPERTIES Design study of CAEP FEL-THz injector has been carried out by PARMELA supplemented by POISSON. Initial electron bunch produced at cathode by laser. Electron bunch is uniformly distributed with 6 mm in diameter transversely. Longitudinally, the bunch is 50 ps long with a Gaussian distribution whose FWHM value is taken to be 18 ps due to the rather long response time of GaAs. The gun operates at a nominal accelerating voltage of 320 kV and bunch charge of 90 pC. The average beam current is 5 mA with laser laser frequency 54.167 MHz. The total beam line of injector is 396.28 cm long, and the design machine parameters of injector are listed in Table 1. The accelerating field gradient in the DC gun is not high, limited by the field emission and the punch through the ceramic insulator. The maximum field gradient is 4.12 MV/m on the cathode surface. The length of gun is 14.7 cm, and there is a nose at 9.8 cm to focus the beam slightly. Table 1: 90 pC Elements Parameters |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | http://accelconf.web.cern.ch/accelconf/IPAC2013/papers/tupwo029.pdf |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
