Terawatt x-ray free-electron-laser optimization by transverse electron distribution shaping

Emma, Claudio; Wu, Juhao; Fang, Kun; Chen, S.; Serkez, Svitozar; Pellegrini, C.

doi:10.1103/physrevstab.17.110701

Cited by 18 publications

(13 citation statements)

References 16 publications

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“…The strength of the guiding (given by the electron beam refractive index [141]) is proportional to the beam bunching which underscores the importance of maintaining a large fraction of the beam trapped and bunched in the tapered wiggler for maximum output efficiency. Recent numerical studies have suggested improving the effect of the guiding by varying the electron beam spot-size in the tapered section [77] or shaping the electron transverse distribution from Gaussian to parabolic or uniform [100], yielding a relative improvement in the efficiency around 10-40%.…”

Section: Transverse Effectsmentioning

confidence: 99%

Superradiant and stimulated-superradiant emission of bunched electron beams

et al. 2019

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We outline the fundamental coherent radiation emission processes from a bunched charged particles beam. In contrast to spontaneous emission of radiation from a random electron beam that is proportional to the number of particles, a pre-bunched electron beam can emit spontaneously coherent radiation proportional to the number of particles -squared, through the process of (spontaneous) superradiance (SP-SR) (in the sense of Dicke's). The coherent SP-SR emission of a bunched electron beam can be even further enhanced by a process of stimulated-superradiance (ST-SR) in the presence of a seed injected radiation field. In this review, these coherent radiation emission processes for both single bunch and periodically bunched beams are considered in a model of radiation mode expansion.We also analyze here the SP-SR and ST-SR processes in the nonlinear regime, in the context of enhanced undulator radiation from a uniform undulator (wiggler) and in the case of wiggler Tapering-Enhanced Stimulated Superradiant Amplification (TESSA).The processes of SP-SR and TESSA take place also in tapered wiggler seed-injected FELs. In such FELs, operating in the X-Ray regime, these processes are convoluted with other effects. However these fundamental emission concepts are useful guidelines in efficiency enhancement strategy of wiggler tapering. Based on this model we review previous works on coherent radiation sources based on SP-SR (coherent undulator radiation, synchrotron radiation, Smith-Purcell radiation etc.), primarily in the THz regime and on-going works on tapered wiggler efficiency-enhancement concepts in various frequency regimes.

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Section: Transverse Effectsmentioning

confidence: 99%

Superradiant and stimulated-superradiant emission of bunched electron beams

et al. 2019

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“…Finally, we note that there is a strong demand in the FEL science community for higher photon flux per pulse, to reach the level needed for imaging large systems such as protein molecules [42]. These applications require peak powers in the multi-TW range, contained in 25-100 fs pulses, to permit imaging before the destruction of the target.…”

Section: Introductionmentioning

confidence: 99%

Next generation high brightness electron beams from ultrahigh field cryogenic rf photocathode sources

Rosenzweig

Cahill

Dolgashev

et al. 2019

Phys. Rev. Accel. Beams

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Recent studies of the performance of radio-frequency (rf) copper cavities operated at cryogenic temperatures have shown a dramatic increase in the maximum achievable surface electric field. We propose to exploit this development to enable a new generation of photoinjectors operated at cryogenic temperatures that may attain, through enhancement of the launch field at the photocathode, a significant increase in fivedimensional electron beam brightness. We present detailed studies of the beam dynamics associated with such a system, by examining an S-band photoinjector operated at 250 MV=m peak electric field that reaches normalized emittances in the 40 nm-rad range at charges (100-200 pC) suitable for use in a hard x-ray free-electron laser (XFEL) scenario based on the LCLS. In this case, we show by start-to-end simulations that the properties of this source may give rise to high efficiency operation of an XFEL, and permit extension of the photon energy reach by an order of magnitude, to over 80 keV. The brightness needed for such XFELs is achieved through low source emittances in tandem with high current after compression. In the XFEL examples analyzed, the emittances during final compression are preserved using microbunching techniques. Extreme low emittance scenarios obtained at pC charge, appropriate for significantly extending temporal resolution limits of ultrafast electron diffraction and microscopy experiments, are also reviewed. While the increase in brightness in a cryogenic photoinjector is mainly due to the augmentation of the emission current density via field enhancement, further possible increases in performance arising from lowering the intrinsic cathode emittance in cryogenic operation are also analyzed. Issues in experimental implementation, including cavity optimization for lowering cryogenic thermal dissipation, external coupling, and cryocooler system, are discussed. We identify future directions in ultrahigh field cryogenic photoinjectors, including scaling to higher frequency, use of novel rf structures, and enabling of an extremely compact hard x-ray FEL.

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“…The drive laser strikes the photocathode surface to emit electrons. The temporal and transverse shape of the laser pulse, together with the quantum efficiency (QE) of the photocathode surface, determines the temporal and transverse distribution of the electron beam upon emission, which has a significant impact on beam brightness and FEL performance [5][6][7][8][9][10]. The temporal distribution can be manipulated with techniques such as polarization based pulse stacking with birefringent crystals [11], acousto-optic modulators [12,13] or spatial modulators at a dispersion region [14].…”

Section: Introductionmentioning

confidence: 99%

Ultraviolet laser transverse profile shaping for improving x-ray free electron laser performance

Alverson

Bohler

et al. 2017

Phys. Rev. Accel. Beams

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The photocathode rf gun is one of the most critical components in x-ray free electron lasers. The drive laser strikes the photocathode surface, which emits electrons with properties that depend on the shape of the drive laser. Most free electron lasers use photocathodes with work function in the ultraviolet, a wavelength where direct laser manipulation becomes challenging. In this paper, we present a novel application of a digital micromirror device (DMD) for the 253 nm drive laser at the Linear Coherent Light Source. Laser profile shaping is accomplished through an iterative algorithm that takes into account shaping error and efficiency. Next, we use laser shaping to control the X-ray laser output via an online optimizer, which shows improvement in FEL pulse energy. Lastly, as a preparation for electron beam shaping, we use the DMD to measure the photocathode quantum efficiency across cathode surface with an averaged laser rms spot size of 59 μm. Our experiments demonstrate promising outlook of using DMD to shape ultraviolet lasers for photocathode rf guns with various applications.

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Terawatt x-ray free-electron-laser optimization by transverse electron distribution shaping

Cited by 18 publications

References 16 publications

Superradiant and stimulated-superradiant emission of bunched electron beams

Superradiant and stimulated-superradiant emission of bunched electron beams

Next generation high brightness electron beams from ultrahigh field cryogenic rf photocathode sources

Ultraviolet laser transverse profile shaping for improving x-ray free electron laser performance

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