Paper | Title | Other Keywords | Page |
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MOOCNO01 | Emittance Control in the Presence of Collective Effects in the FERMI@Elettra Free Electron Laser Linac Driver | emittance, FEL, electron, linac | 6 |
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Recent beam transport experiments conducted on the the linac driving the FERMI@Elettra free electron laser have provided new insights concerning the transverse emittance degradation due to both coherent synchrotron radiation (CSR) and geometric transverse wakefield (GTW), together with methods to counteract such degradation. For beam charges of several 100's of pC, optics control in a magnetic compressor results to minimize the CSR once the H-function is considered*. We successfully extended this approach to the case of a modified double bend achromat system, opening the door to relatively large bending angles and compact transfer lines**. At the same time, the GTWs excited in few mm diameter iris collimators*** and accelerating structures have been characterized in terms of the induced emittance growth. A model integrating both CSR and GTW effects suggests that there is a limit on the maximum obtainable electron beam brightness in the presence of such collective effects.
* S. Di Mitri et al., PRST-AB 15, 020701 (2012) ** S. Di Mitri et al., PRL 110, 014801 (2013) *** S. Di Mitri et al., PRST-AB 15, 061001 (2012) |
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Slides MOOCNO01 [6.919 MB] | |||
TUOANO04 | PITZ Experience on the Experimental Optimization of the RF Photo Injector for the European XFEL | emittance, laser, electron, cathode | 160 |
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The Photo Injector Test facility at DESY, Zeuthen site (PITZ), develops high brightness electron sources for modern free electron lasers. A continuous experimental optimization of the L-band photo injector for such FEL facilities like FLASH and the European XFEL has been performed for a wide range of electron bunch charges – from 20 pC to 2 nC – yielding very small emittance values for all charge levels. Experience and results of the experimental optimization will be presented in comparison with beam dynamics simulations. The influence of various parameters onto the photo injector performance will be discussed.
Phys. Rev. ST Accel. Beams 15, 100701 (2012) |
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Slides TUOANO04 [3.126 MB] | |||
TUPSO33 | The Commissioning of Tess: An Experimental Facility for Measuring the Electron Energy Distribution From Photocathodes | electron, cathode, laser, vacuum | 290 |
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ASTeC have developed a Transverse Energy Spread Spectrometer (TESS) – an experimental facility to characterise the energy distribution of electrons emitted by a photocathode. Electron injector brightness is fundamentally limited by the width of this distribution or energy spread, and brightness will be increased significantly by reducing the longitudinal and transverse energy spread at source. TESS supports photocathode performance measurements at room and LN2-temperature under illumination from a range of fixed- and variable-wavelength light sources, allowing characterisation of both metal and semiconductor photocathodes. Preliminary work with GaAs* has shown that electron energy spread is dependent on the quantum efficiency (Q.E.) of the photocathode source, and TESS includes a piezo-electric leak valve to allow controlled degradation of the photocathode Q.E. whilst monitoring the energy spread of emitted electrons. This system offers huge potential to support future photocathode R&D work into a range of photocathode materials. Using GaAs photocathodes activated to high levels of Q.E. in our photocathode preparation facility**, we present commissioning results for TESS.
* Proc. IPAC ’12, TUPPD067, 1557-1559 ** Proc. IPAC ’11, THPC129, 3185-3187 |
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TUPSO57 | Generation of Ultrafast, High-brightness Electron Beams | gun, cathode, electron, cavity | 355 |
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Funding: This work was supported by the U.S. Department of Energy, under Contract No. DE-SC0009556. The production and preservation of ultrafast, high-brightness electron beams is a major R&D challenge for free electron laser (FEL) and ultrafast electron diffraction (UED) because transverse and longitudinal space charge forces drive emittance dilution and bunch lengthening in such beams. Several approaches, such as velocity bunching and magnetic compression, have been considered to solve this problem but each has drawbacks. We present a concept that uses radial bunch compression in an X-band photocathode radio frequency electron gun. By compensating for the path length differential with a curved cathode in an extremely high acceleration gradient cavity, we have demonstrated numerically the possibility of achieving more than an order of magnitude increase in beam brightness over existing electron guns. The initial thermo-structural analysis and mechanical conceptual design of this electron source are presented. |
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TUPSO76 | In Situ Characterization of ALKALI Antimonide Photocathodes | cathode, scattering, emittance, synchrotron | 403 |
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Funding: The authors wish to acknowledge the support of the US DOE, under Contract No. KC0407-ALSJNT-I0013, DE-AC02-98CH10886 and DE-SC0005713. Use of CHESS is supported by NSF award DMR-0936384. Alkali antimonide photocathodes are a prime candidate for use in high-brightness photoinjectors of free electron lasers and 4th generation light sources. These materials have complex growth kinetics - many methods exist for forming the compounds, each with different grain size, roughness, and crystalline texture. These parameters impact the performance of the cathodes, including efficiency, intrinsic emittance and lifetime. In situ analysis of the growth of these materials has allowed investigation of correlations between cathode structure and growth parameters and the resulting quantum efficiency (QE). The best cathodes have a QE at 532 nm in excess of 6% and are structurally textured K2CsSb with grain sizes in excess of 20 nm. X-ray reflection (XRR) has been used to characterize the roughness evolution of the cathode, while X-ray Diffraction (XRD) has been used to characterize the texture, grain size and stoichometry. |
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TUPSO83 | Quantum Efficiency and Transverse Momentum From Metals | electron, FEL, vacuum, laser | 424 |
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Funding: Work supported by US DOE contracts DE-AC02-05CH11231, KC0407-ALSJNT-I0013, and DE-SC000571. QE and transverse momentum are key parameters limiting the achievable brightness of FELs. Despite the importance, little data is available to substantiate current models. Expressions for each and experimental confirmation of each expression with respect to excess energy are presented. Novel instrumentation and analysis techniques developed are described. |
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WEPSO17 | High-resolution Seeding Monochromator Design for NGLS | FEL, optics, electron, undulator | 529 |
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Funding: DOE/BES A high-resolution soft X-ray seeding monochromator has been designed for self-seeding the Next-Generation Light Source (NGLS). The seeding monochromator system consists of a single variable-line-spacing grating, three mirrors and an exit slit and operates in the “fixed-focus” mode to achieve complete tuning of the seeding energy in range from 200 to 2000 eV with a nearly constant resolving power of over 2x104. The optical delay is less than 1 ps. The design is based upon a fully coherent treatment of the SASE FEL beam propagating from the upstream SASE undulator through the entire seeding monochromator system. This approach guides the design optimization in order to preserve the transverse beam profile entering the seeding undulator to ensure maximum efficiency. |
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