| Paper | Title | Page |
|---|---|---|
| THPRO008 | Obtaining High Degree of Circular Polarization at X-ray FELs via a Reverse Undulator Taper | 2870 |
|
||
|
Baseline design of a typical X-ray FEL undulator assumes a planar configuration which results in a linear polarization of the FEL radiation. However, many experiments at X-ray FEL user facilities would profit from using a circularly polarized radiation. As a cheap upgrade one can consider an installation of a short helical (or cross-planar) afterburner, but then one should have an efficient method to suppress powerful linearly polarized background from the main undulator. In this paper we propose a new method for such a suppression: an application of the reverse taper in the main undulator. We discover that in a certain range of the taper strength, the density modulation (bunching) at saturation is practically the same as in the case of non-tapered undulator while the power of linearly polarized radiation is suppressed by orders of magnitude. Then strongly modulated electron beam radiates at full power in the afterburner. Considering SASE3 undulator of the European XFEL as a practical example, we demonstrate that soft X-ray radiation pulses with peak power in excess of 100 GW and an ultimately high degree of circular polarization can be produced.
Phys. Rev. ST-AB 16(2013)110702 |
||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-THPRO008 | |
| Export • | reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml) | |
| THPRO009 | Harmonic Lasing in X-ray FELs | 2873 |
|
||
| Contrary to nonlinear harmonic generation, harmonic lasing in a high-gain FEL can provide much more intense, stable, and narrow-band FEL beam which is easier to handle if the fundamental is suppressed. We perform a parametrization of the solution of eigenvalue equation for lasing at odd harmonics, and present explicit expression for FEL gain length, taking into account all essential effects. We propose and discuss methods for suppression of the fundamental. We also suggest a combined use of harmonic lasing and lasing at the retuned fundamental wavelength in order to reduce bandwidth and to increase brilliance of X-ray beam. We discover that in a part of the parameter space, corresponding to the operating range of soft X-ray beamlines of X-ray FEL facilities, harmonics can grow faster than the fundamental. We suggest that harmonic lasing can be widely used in the existing or planned X-ray FEL facilities. LCLS after a minor modification can lase at the 3rd harmonic up to the photon energy of 25-30 keV providing multi-gigawatt power level. At the European XFEL the harmonic lasing would allow to extend operating range up to 100 keV, to reduce bandwidth and increase brilliance. | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-THPRO009 | |
| Export • | reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml) | |
| THPRO010 | Analysis of Operation of Harmonic Lasing Self-seeded FEL | 2876 |
|
||
| Harmonic lasing self-seeded FEL holds great potential for significant improvement of the the longitudinal coherence of the radiation. A gap-tunable undulator is divided into two parts by setting two different undulator parameters such that the first part is tuned to a sub-harmonic of the second part. Harmonic lasing occurs in the exponential gain regime in the first part of the undulator, also the fundamental stays well below saturation. In the second part of the undulator the fundamental mode is resonant to the wavelength, previously amplified as the harmonic. The amplification process proceeds in the fundamental mode up to saturation. In this case the bandwidth is defined by the harmonic lasing (i.e. it is reduced by a significant factor depending on harmonic number) but the saturation power is still as high as in the reference case of lasing at the fundamental in the whole undulator, i.e. the spectral brightness increases. Application of the undulator tapering in the deep nonlinear regime would allow to generate higher peak powers approaching TW level. The scheme is illustrated with the parameters of the European XFEL. | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-THPRO010 | |
| Export • | reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml) | |
| THPRO011 | Investigation of the Coherence Properties of the Radiation at FLASH | 2879 |
|
||
| We present the results of the studies of coherence properties of the radiation from FLASH for fundamental harmonic and higher odd harmonics. General overview of the parameter space is performed including peak current, emittance, and external focusing. The results of our studies show that present configuration of FLASH free electron laser is not optimal for providing ultimate quality of the output radiation. We find that the physical origin of the problem is mode degeneration. The way for improving quality of the radiation is proposed. | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-THPRO011 | |
| Export • | reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml) | |