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A high average power THz radiation facility has been developed by the China Academy of Engineering Physics. It is the first CW THz user facility based on superconducting accelerator technology in China. The superconducting linac module, which contains two 4-cell 1.3 GHz TESLA-like superconducting radio frequency cavities, is a major component of this facility. The expected electron energy gain is 6–8 MeV with a field gradient of 8–10 MV/m. The design and fabrication of the linac module is complete. This paper discusses its assembly and results from cyromodule tests and beam commissioning. At 2 K, the cryomodule works smoothly and stably. Both cavities have achieved effective field gradients of 10 MV/m. In beam loading experiments, 8 MeV, 5 mA electron beams with an energy spread less than 0.2% have been produced, which satisfies our requirements.

China Academy of Engineering Physics terahertz free electron laser (CAEP THz FEL, CTFEL) is the first THz FEL oscillator in China. CTFEL spectrum covers from 0.7 THz to 4.2 THz. However, there are still many applications requiring lower frequency. The super-radiation of the ultra-short electron beam bunches could generate ultra-fast, carrier-envelope-phase-stable, and high-field terahertz. The coherent diffraction/transition radiation (CDR/CTR) and coherent undulator radiation (CUR) can be also synchronized naturally. In this paper, the dynamic and the design of the super-radiation are introduced. The main parameters of the CDR/CTR and CUR are also discussed. A multi-color pump-probe system based on super-radiation is also proposed., Proceedings of the 39th Free Electron Laser Conference, FEL2019, Hamburg, Germany

The higher order modes (HOMs) of the 1.3GHz 4-cell cavity on CTFEL facility is analyzed in this paper. The passbands of the HOMs in the 4-cell cavity were simulat-ed, and the most harmful modes were determined. The power of the wakefields was estimated. By microwave test at room temperature, the frequencies of the HOMs were measured, as well as the external Q’s of the HOM cou-plers. Besides, a frequency distribution measurement system was built. The HOM signal excited by beam at 2 K temperature is measured, and some preliminary results are obtained. The measurement techniques and results of the HOM damping performance are presented in this paper., Proceedings of the 10th Int. Particle Accelerator Conf., IPAC2019, Melbourne, Australia

The THz Free Electron Laser facility (CAEP THz FEL, CTFEL) of the China Academy of Engineering Physics uses high quality electron beams to generate high average power terahertz radiations. A 1.3 GHz RF buncher is used in front of the superconducting linear accelerator of the CTFEL facility to improve the electron beams quality. The RF buncher is driven by a solid state power amplifier (SSPA), and the SSPA is feedback controlled by a low level RF (LLRF) control system to ensure the high stability of the amplitude and phase of the bunching field in the buncher cavity. The SSPA operates at 1.3 GHz and outputs 0 to 5 kW of continuous wave power. This paper mainly introduces the principle and composition of the SSPA, and presents some experiments on the RF buncher driven by the SSPA., Proceedings of the 39th Free Electron Laser Conference, FEL2019, Hamburg, Germany

Coherent radiation can be used to measure the longitudinal distribution of the electron beam bunch of any length, as long as the coherent radiation spectrum can be measured. In many cases, the Kramers-Krönig relationship is used to reconstruct the temporal distribution of the beam from the coherent radiation spectrum. However, the extrapolation of the low frequency will introduce the uncertainty of the reconstruction. In this paper, GrEedy Sparse PhAse Retrieval (GESPAR) method was used to reconstruct the beam longitudinal distribution measured by coherent transition radiation on the THz FEL facility of China Academy of Engineering Physics. The results indicate that the GESPAR method works well for the complex and ultrashort distribution. It will be an effective tool to accurately measure the femtosecond bunch temporal structure., Proceedings of the 10th Int. Particle Accelerator Conf., IPAC2019, Melbourne, Australia

China Academy of Engineering Physics terahertz free electron laser (CAEP THz FEL, CTFEL) is the first THz FEL user facility in China, which was an oscillator type FEL. This THz FEL facility consists of a GaAs photocathode high-voltage DC gun, a superconducting RF linac, a planar undulator and a quasi-concentric optical resonator. The terahertz laser’s frequency is continuous adjustable from 0.7 THz to 4.2 THz. The average power is more than 10 W and the micro-pulse power is more than 0.3 MW. In this paper, the specific parameters and operation status of CTFEL are presented. Finally, some user experiments are introduced briefly., Proceedings of the 39th Free Electron Laser Conference, FEL2019, Hamburg, Germany

A 2×4-cell superconducting linac module for the THz-FEL facility has been developed at the China Academy of Engineering Physics, which is expected to provide 6~8 MeV quasi-CW electron beams with an average current of 1~5 mA. The module consists of two 4-cell cavities, two power couplers, two tuners and the cyromodule. The main components are tested before the module assembly. The cavity test includes microwave measurement at room temperature and vertical test at 2 K. The conditioning and test of the couplers are also finished. The performances of the main components and the whole module are present-ed in this paper. The horizontal test indicated that the effective field gradients of both cavities have reached 10 MV/m, which have satisfied our designed goal., Proceedings of the 13th Symposium on Accelerator Physics, SAP2017, Jishou, China

China Academy of Engineering Physics tera-hertz free electron laser (CAEP THz FEL, CTFEL) is the first THz FEL oscillator in China, which was jointly built by CAEP, Peking university and Tsinghua university. The stimulated saturation of the CTFEL was reached in August, 2017. This THz FEL facility consists of a GaAs photocathode high-voltage DC gun, a superconducting RF linac, a planar undulator and a quasi-concentric optical resonator. The terahertz laser's frequency is continuous adjustable from 2 THz to 3 THz. The average power is more than 10 W and the micro-pulse power is more than 0.1 MW., Proceedings of the 60th ICFA Advanced Beam Dynamics Workshop on Future Light Sources, FLS2018, Shanghai, China

The CAEP THz-FEL facility is the first high average power THz radiation user facility in China. The superconducting accelerator including double 4-cell superconducting radio frequency (SRF) cavities is one of the most important components for this facility. The construction and horizontal test of the superconducting accelerator have been finished. At 2K state, the effective gradients of both cavities have reached our designed goal, 10 MV/m. This paper mainly presents the commissioning results of the superconducting accelerator. In the commissioning experiments, the kinetic energy of 5mA electron beams can be accelerated to 8 MeV successfully, with the energy spread less than 0.2%, much better than our design goal. Further beam loading experiments are in progress., Proceedings of the 13th Symposium on Accelerator Physics, SAP2017, Jishou, China