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The progress of the Beijing IR-FEL project carried out at IHEP is reported. Some specific developments of software and hardware are described, rather than striving for general coverage. First, computational studies of the effects of emittance and pulse length on the small-signal gain are presented. Then some experimental results for the microwave electron gun injector are given. Modifications of the beam transport system and the optimization and measurements of the NdFeB undulator are described. Finally, some aspects of the beam diagnostics and a spontaneous-emission experiment are discussed.

The design of a 1.5 m long NdFeB permanent magnet undulator is described. The characteristics are presented. It consists of 400 blocks of permanent magnets (7.5 × 7.5 × 40 mm3) arranged in a Halbach configuration and provides a periodic magnetic field with a peak field of 0.45 T for a gap of 1 cm.

We used transition radiation techniques instead of the original phosphor targets to improve the electronic beam diagnostic system at Beijing Free Electron Laser. The beam profile, sie (3.3 x 2.4 mm), position and divergence angle (sigma (rms) = 2.5 mrad) in transverse have been obtained from optical transition radiation. We also present the experimental set-up and some preliminary results.

This paper first mentions the rationale to start a Compton regime, rf linac-based FEL research project in IHEP. Then the physical design parameters are given based on both the analytical formulae and a one-dimensional numerical computation. Considerations are given in sequence regarding the expected tuning range, the microwave gun performance, the longitudinal phase space, factors affecting the accelerated beam energy spread, beam transport system, optical resonator, and undulator design.

The detection of nuclear particles with superconducting tunnel junctions using D. C. Josephson effect is expected to have the merits of good energy resolution and fast time response. It was the first time to perform such an experiment to detect Sr90-Y90 β-particles by the Nb-NbOx-Pb superconducting tunnel junctions. The results showed that, under the β-particle irradiation, not only the critical current and energy gap voltage of the superconducting tunuel junctions decreased, but also voltage pulse signals at both ends of the superconducting tunnel junction were produced. In this paper we report some phenomena observed about β-particle detection with superconducting tunnel junctions using D. C. Josephson effect.

The phase-adjusted focusing laser accelerator requires a laser field with special polarized distribution—a radial polarization. The theoretical work shows, by properlytransforming the TEM00 mode, such a laser field can be obtained and propagate stably in the free space. The experimental result agrees with the theoretical analysis.

A method of measuring micro-vibration amplitude with laser is presented. By using the optical resonant characteristic of Fabry-Perot etalon and intensity-comparison lock-in technique of laser, we have completed a measurement with the minimum amplitude of vibration at the order of 10-12 cm under the condition of an ordinary laboratory.