Zhentang Zhao

Phase-merging enhanced harmonic generation free-electron laser

Together with one of its variants, the recently proposed phase-merging enhanced harmonic generation (PEHG) free-electron laser (FEL) is systematically studied in this paper. Different from a standard high-gain harmonic generation scheme, a transverse gradient undulator is employed to introduce a phase-merging effect into the transversely dispersed electron beam in PEHG. The analytical theory of the phase-merging effect and the physical mechanism behind the phenomenon are presented. Using a representative set of beam parameters, intensive start-to-end simulations for soft x-ray FEL generation are given to illustrate the performance of PEHG. Moreover, some practical issues that may affect the performance of PEHG are also discussed.

Status of the Shanghai Synchrotron Radiation Facility

The Shanghai Synchrotron Radiation Facility (SSRF) made its ground breaking at Zhang-Jiang High Tech Park on Dec. 25, 2004 and moved into its construction phase with the plan of commencing user’s operation from April 2009. The SSRF complex is based on a 3.5GeV storage ring optimized to operate with top-up injection, mini-gap undulators and superconducting RF system, the 432m circumference storage ring provides 18 ID straight sections (4×12.0m and 16×6.5m), and four of them will be used for the first SSRF beam lines. The SSRF project was proposed in 1995, and since then it has experienced the conceptual design stage, the R&D program and the design optimization phase. This paper presents the updated design specifications and the construction status of the SSRF project.

Storage Ring Light Sources

This article outlines the development and evolution of storage ring light sources, focusing on the latest, third generation light sources. After making brief historical remarks, it describes the current status, the performance, and the technological advancements of third generation light sources. The future developments of the ultimate storage ring as the next generation light source are envisioned.

Compensating the electron beam energy spread by the natural transverse gradient of laser undulator in all-optical x-ray light sources

All-optical ideas provide a potential to dramatically cut off the size and cost of x-ray light sources to the university-laboratory scale, with the combination of the laser-plasma accelerator and the laser undulator. However, the large longitudinal energy spread of the electron beam from laser-plasma accelerator may hinder the way to high brightness of these all-optical light sources. In this paper, the beam energy spread effect is proposed to be significantly compensated by the natural transverse gradient of a laser undulator when properly transverse-dispersing the electron beam. Theoretical analysis and numerical simulations on conventional laser-Compton scattering sources and high-gain all-optical x-ray free-electron lasers with the electron beams from laser-plasma accelerators are presented.

Generating isolated terawatt-attosecond x-ray pulses via a chirped-laser-enhanced high-gain free-electron laser

A feasible method is proposed to generate isolated attosecond terawatt x-ray radiation pulses in high-gain free-electron lasers. In the proposed scheme, a frequency chirped laser pulse is employed to generate a gradually-varied spacing current enhancement of the electron beam and a series of spatiotemporal shifters are applied between the undulator sections to amplify a chosen ultra-short radiation pulse from self-amplified spontaneous emission. Three-dimensional start-to-end simulations have been carried out and the calculation results demonstrated that 0.15 nm x-ray pulses with peak power over 1TW and duration of several tens of attoseconds could be achieved by using the proposed technique.

Current status of the SSRF project

The Shanghai Synchrotron Radiation Facility (SSRF) is an intermediate energy light source under design and R&D at Shanghai National Synchrotron Radiation Center (SSRC). It is based on a 3.5 GeV electron storage ring with a circumference of 396 m, a beam current of 200-300 mA and a beam emittance of 5-12 nm/spl middot/rad. Since its R&D began in 1999, the design of the SSRF has been evolved smoothly towards a cost-effective machine required by its future users, and the prototypes of its key components have been manufactured and tested up to the design specifications. This paper reviews the design and R&D progress of the SSRF project and presents its current status.

Studies of bunch lengthening at the BEPC

The Beijing Electron-Positron Collider (BEPC) has been operating for more than ten years. In addition to providing colliding beams for high energy physics and a single beam for synchrotron radiation study, we carried out many machine related beam experiments for understanding better the beam physics and for improving performance. Among them, measurements of bunch length and its lengthening, and the impedance implied thereby, play crucial roles in the future plans for luminosity upgrades. This paper reviews the measurement of the bunch length in the BEPC storage ring, concluding with the scaling law for the bunch lengthening above the microwave instability threshold. The low frequency impedance of the storage ring is also obtained from the bunch lengthening due to the potential well distortion in low bunch current

Storage Ring based PEHG FEL for EUV Lithography Storage Ring based PEHG FEL for EUV Lithography

In this paper we consider a storage ring based phase-merging enhanced harmonic generation FEL for producing intense EUV radiation pulses, which may be useful for the EUV lithography.

R&D OF C-BAND ACCELERATING STRUCTURE AT SINAP*

Research and design of a C-band (5712 MHz) high-gradient travelling-wave accelerating structure is being carried out at Shanghai Institute of Applied Physics. The structure consists of 53 regular disk-loaded cells and two waveguide couplers, and its length is about 1 m. This paper presents a design of the accelerating structure, the experimental model, and the preliminary results of an RF cold test of the model structure.

First Group of Insertion Devices for SSRF

Shanghai Synchrotron Radiation Facility (SSRF) is an intermediate energy (3.5GeV) light source under construction. Seven beamlines have been chosen and five IDs will be built in the first stage. Two wigglers used for X‐ray absorption fine structure (XAFS) and X‐ray imaging (XI), two in‐vacuums undulators used for macromolecular crystallography (MC) and hard X‐ray microfocus (HXM) and one EPU used for scanning transmission X‐ray microscopy (STXM) are under design. This paper describes the characteristics and the design parameters of these five IDs in detail.