91 research outputs found
A simple method for the determination of the structure of ultrashort relativistic electron bunches
In this paper we propose a new method for measurements of the longitudinal
profile of 100 femtosecond electron bunches for X-ray Free Electron Lasers
(XFELs). The method is simply the combination of two well-known techniques,
which where not previously combined to our knowledge. We use seed 10-ps 1047 nm
quantum laser to produce exact optical replica of ultrafast electron bunches.
The replica is generated in apparatus which consists of an input undulator
(energy modulator), and the short output undulator (radiator) separated by a
dispersion section. The radiation in the output undulator is excited by the
electron bunch modulated at the optical wavelength and rapidly reaches 100
MW-level peak power. We then use the now-standard method of ultrashort laser
pulse-shape measurement, a tandem combination of autocorrelator and spectrum
(FROG -- frequency resolved optical gating). The FROG trace of the optical
replica of electron bunch gives accurate and rapid electron bunch shape
measurements in a way similar to a femtosecond oscilloscope. Real-time
single-shot measurements of the electron bunch structure could provide
significant information about physical mechanisms responsible for generation
ultrashort electron bunches in bunch compressors. The big advantage of proposed
technique is that it can be used to determine the slice energy spread and
emittance in multishot measurements. It is possible to measure bunch structure
completely, that is to measure peak current, energy spread and transverse
emittance as a function of time. We illustrate with numerical examples the
potential of the proposed method for electron beam diagnostics at the European
X-ray FEL.Comment: 41 pages, 18 figure
Perceived responder legitimacy and group identification predict cooperation and compliance in a mass decontamination field exercise
Emergency responders’ failure to communicate effectively during decontamination following a chemical or biological incident has been associated with increased public anxiety and reduced public compliance. In this study we applied the social identity approach to evaluating a field exercise that involved mass decontamination. Questionnaires were collected from 115 volunteers, who participated in the exercise as simulated casualties. Volunteers’ perceptions of effective responder communication predicted increased self-reported compliance with decontamination, mediated by perceived responder legitimacy and identification with other group members. Developing effective communication strategies using a social psychology perspective could improve the way in which incidents are managed
Design considerations of a MW-scale, high-efficiency, industrial-use, ultraviolet FEL amplifier
First Observation of Self-Amplified Spontaneous Emission in a Free-Electron Laser at 109 nm Wavelength
We present the first observation of Self-Amplified Spontaneous Emission
(SASE) in a free-electron laser (FEL) in the Vacuum Ultraviolet regime at 109
nm wavelength (11 eV). The observed free-electron laser gain (approx. 3000) and
the radiation characteristics, such as dependency on bunch charge, angular
distribution, spectral width and intensity fluctuations all corroborate the
existing models for SASE FELs.Comment: 6 pages including 6 figures; e-mail: [email protected]
Isolated terawatt attosecond hard X-ray pulse generated from single current spike
Isolated terawatt (TW) attosecond (as) hard X-ray pulse is greatly desired for four-dimensional investigations of natural phenomena with picometer spatial and attosecond temporal resolutions. Since the demand for such sources is continuously increasing, the possibility of generating such pulse by a single current spike without the use of optical or electron delay units in an undulator line is addressed. The conditions of a current spike (width and height) and a modulation laser pulse (wavelength and power) is also discussed. We demonstrate that an isolated TW-level as a hard X-ray can be produced by a properly chosen single current spike in an electron bunch with simulation results. By using realistic specifications of an electron bunch of the Pohang Accelerator Laboratory X-ray Free-Electron Laser (PAL-XFEL), we show that an isolated, >1.0 TW and similar to 36 as X-ray pulse at 12.4 keV can be generated in an optimized-tapered undulator line. This result opens a new vista for current XFEL operation: the attosecond XFEL
Modified reverse tapering method to prevent frequency shift of the radiation in the planar undulator
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