Design and preliminary test of the LLRF in C band high-gradient test facility for SXFEL
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Design and preliminary test of the LLRF in C band high-gradient test facility for SXFEL Cheng-Cheng Xiao1
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Jun-Qiang Zhang1
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Jian-Hao Tan1 • Wen-Cheng Fang1
Received: 14 July 2020 / Revised: 8 September 2020 / Accepted: 9 September 2020 / Published online: 10 October 2020 China Science Publishing & Media Ltd. (Science Press), Shanghai Institute of Applied Physics, the Chinese Academy of Sciences, Chinese Nuclear Society and Springer Nature Singapore Pte Ltd. 2020
Abstract This paper describes the design and preliminary test of the low-level radio frequency (LLRF) part of the C band high-gradient test facility for the Shanghai Soft X-ray Free-Electron Laser (SXFEL)-Linear Accelerator (LINAC). Before installation, the accelerating structures should be tested and conditioned. During the conditioning process, breakdown detection is needed to protect the accelerating structures and klystron from damage. The PCI extensions for instrumentation-based LLRF system and auto-conditioning algorithm are designed and applied in the LLRF part of the C band high-gradient test facility. Three C band accelerating structures and 1 pulse compressor have completed conditioning and were installed in the SXFEL-LINAC. Keywords Accelerating structure High gradient C band Breakdown LLRF Conditioning
1 Introduction A revolutionary advance in light sources has been realized with the recent advent of the free-electron laser (FEL) [1]. The FEL is regarded as a fourth-generation light source [2] and has a series of advantages that cannot be replicated by existing laser sources. These advantages This work was supported by the National Key R&D Program of China (No. 2018YFF0109203). & Wen-Cheng Fang [email protected] 1
Shanghai Advanced Research Institute, Chinese Academy of Sciences, Shanghai 201210, China
include a continuously adjustable frequency, a wide spectrum range, high and adjustable peak and average powers, excellent coherence, strong polarization, and controllable temporal structure [3]. The Shanghai Soft X-ray Free-Electron Laser (SXFEL) facility is the first coherent X-ray light source in China [4]. It is being developed in two steps, namely the SXFEL test facility (SXFEL-TF) and the SXFEL user facility (SXFELUF) [5]. The SXFEL-TF is a critical development step toward the construction of a soft X-ray FEL user facility in China and is currently undergoing commissioning at the Shanghai Synchrotron Radiation Facility (SSRF) campus. The test facility will generate 8.8 nm FEL radiation using a 840 meV electron LINAC with a two-stage cascaded HGHG-HGHG or EEHG-HGHG (high-gain harmonic generation, echo-enabled harmonic generation) scheme [6, 7]. The LINAC in SXFEL-TF is designed to increase the beam energy from 150 to 840 meV. C band accelerating structures are applied here to guarantee a high gradient. The entire LINAC is built with 12 C band accelerating structures working at 40 MV/m. The RF field stabilization is controlled by a low-level radio frequency (LLRF) system based on accurate RF field measurements a
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