上海硬X射线自由电子激光装置正式开工建设

4月27日，我国迄今为止投资最大、建设周期最长的国家重大科技基础设施项目——硬X射线自由电子激光装置在上海张江综合性国家科学中心开工建设。这一总投资近100亿元的“大围重器”计划于2025年竣工并投入使用，为科研用户提供高分辨成像、先进结构解析、超快过程探索等尖端研究手段。

Two-stage EEHG for coherent hard X-ray generation based on a superconducting linac

A two-stage echo-enabled harmonic generation(EEHG)scheme is proposed for a superconducting linacdriven FEL to produce coherent hard X-rays.Electron beams of quite different bunch lengths are separately used in each stage of EEHG,and a monochromator is designed to purify the radiation from the first stage for seeding the second stage.Theoretical analysis and 3D simulations indicate that the proposed scheme can generate high-repetition-rate coherent hard X-ray pulses directly from a conventional UV seed laser.

Hard X-ray free-electron laser based on echo-enabled staged harmonic generation scheme

A novel approach to producing coherent hard X-ray based on the echo-enabled staged harmonic generation (EESHG) free-electron laser scheme is proposed. This scheme is not a simple cascaded echo-enabled harmonic generation (EEHG) but consists of an EEHG and a conventional high-gain harmonic generation (HGHG) like configuration, which also works in the EEHG principle. It is shown that fully coherent hard X-ray radiation can be obtained directly from a conventional VUV seed laser with reduced size and cost in comparison with the self-amplified spontaneous emission (SASE) based hard X-ray facilities.

1.3 GHz连续波超导射频腔的数字低电平系统和模拟腔研究

上海高重复频率硬X射线自由电子激光装置的超导射频(Radio Frequency,RF)腔需要高精度射频低电平(Low Level Radio Frequency,LLRF)系统,以稳定腔场的幅度和相位。但是,由于1.3 GHz连续波超导射频腔的高负载品质因数,腔体在电磁频域中的带宽较小。在加速器老练或重启过程中,超导腔相对较小的失谐就会有较大的反射电压,触发联锁保护系统,导致腔体难以馈入功率。为此将自激励(Self-Excited Loop,SEL)控制系统被引入到低电平控制系统中,以防止这种情况的发生;同时把发生器驱动系统(Generator Driven Resonator,GDR)低电平控制系统加载到加速器正常工作状态。此外,开发了数字模拟腔用来验证LLRF系统的设计算法,减少了在真实腔体中测试损害腔体的风险,节省机器时间和调试成本。研究结果表明:即使腔体失谐,SEL控制系统依然可以使腔场幅度稳定到设定值,且反射电压较小。经过比较和验证,数字模拟腔被证明是测试新的低电平算法的可靠平台。