RIKEN/SPring-8, Hyogo
To realize a compact FEL facility, a high frequency accelerator is indispensable to shorten the accelerator length. Then, a high-harmonic cavity used for nonlinear correction of a beam energy chirp encounters a technological difficulty of extremely high frequency RF system. In order to overcome this difficulty, a method of over-correction is proposed. In this method, a correction cavity is installed before any bunch compressors. Since the effective frequency of the correction cavity is increased as the electron bunch length compressed, the same RF frequency as main accelerators can be used for the correction cavity.
SOLEIL, Gif-sur-Yvette
Imagine Optic, Orsay
BNL, Upton, Long Island, New York
LOA, Palaiseau
RIKEN/SPring-8, Hyogo
JASRI/SPring-8, Hyogo-ken
The VUV Self-Amplified Spontaneous Emission of the SPring-8 Compact SASE Source (SCSS) Test Accelerator is characterized at different stages of amplification up to saturation [1]. Experimental measurements are performed by use of a VUV Hartmann wavefront sensor. This kind of sensor gives access to both intensity and phase profiles of the incoming beam. We characterize the mode selection when approaching the saturation regime of the FEL. Optical quality of the saturated SASE radiation is measured to be better than Lambda/5 PV and Lambda/22 rms (Lambda = 61.5 nm) depending on the machine optimization. Moreover, pointing of the beam as well as spatial structure, size and position of the source are retrieved and their shot-to-shot fluctuations investigated. Analytical [2] and numerical calculations [3], using SRW and GENESIS codes, show good agreement with the experimental measurements. All these elements are of crucial importance for a better understanding and optimization of the FEL and of course for user applications requiring a stable focused beam on their samples. We are grateful to the SCSS Test Accelerator Operation Group at RIKEN for continuous support in the course of the studies
[1] R. Bachelard et al., "Wavefront and Transverse Structure of the FEL Self-Amplified Spontaneous Emission", to be submitted
[2] M. Xie, NIMA 445, 59(2000)
[3] O. Chubar et al., Proc. EPAC-98, 1177(1998)
RIKEN/SPring-8, Hyogo
JASRI/SPring-8, Hyogo-ken
Stable SASE FEL has been routinely used for user experiments since May 2008 at the SCSS test accelerator, which was constructed to perform a proof-of-principle experiment towards realization of a compact and high performance XFEL facility. In FY2008, a beam time of 840 hr (95 days) was provided to 11 research groups with a downtime rate of ~4%, a pulse energy of ~30μJ and an intensity fluctuation of ~10% in STD. A feature of our stable operation is power-saturated SASE FEL kept over a full operation period
- in spite of a day-by-day operation,
- without a complicated beam feedback control, and
- without hard maintenance.