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| MOPPH056 |
Generation of Attosecond X-ray Pulses with a Multi-Cycle Two-Color ESASE Scheme
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114 |
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- Y. T. Ding, P. H. Bucksbaum, Z. Huang
SLAC, Menlo Park, California
- H. Merdji
CEA, Gif-sur-Yvette
- D. F. Ratner
Stanford University, Stanford, Califormia
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Generation of attosecond x-ray pulses is attracting much attention within the x-ray free-electron laser (FEL) user community. Several schemes have been proposed based on manipulations of electron bunches with extremely short laser pulses. In this paper, we extend the attosecond two-color ESASE scheme* to the long optical cycle regime using a detuned second laser** and a tapered undulator. Both lasers can be about ten-optical-cycle long, with the second laser frequency detuned from the first one in order to optimize the contrast between the central and side current spikes. A tapered undulator can be used to mitigate the degradation effect of the longitudinal space charge force in the undulator*** as well as to suppress the FEL gain of all side current spikes. Simulations using the LCLS parameters show a single attosecond x-ray spike of ~100 attosecond can be produced with a good contrast ratio.
* A. A. Zholents and G. Penn, Phys. Rev. ST Accel. Beams 8, 050704 (2005).
** H. Merdji et al., Opt. Lett., 32, 3134 (2007).
*** G. Geloni et al., Nucl. Instrum. Methods A 583, 228 (2007).
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| MOCAU03 |
SASE FEL Polarization Control Using Crossed Undulator
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173 |
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- Y. T. Ding, Z. Huang
SLAC, Menlo Park, California
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There is a growing interest in producing intense, coherent x-ray radiation with an adjustable and arbitrary polarization state. In this paper, we study the crossed undulator scheme* for rapid polarization control in a self-amplified spontaneous emission (SASE) free electron laser (FEL). Because a SASE source is a temporally chaotic light, we perform a statistical analysis on the state of polarization using FEL theory and simulations**. We show that by adding a small phase shifter and a short (about 1.3 times the FEL power gain length), 90-degree rotated planar undulator after the main SASE planar undulator, one can obtain circularly polarized light - with over 80% polarization - near the FEL saturation.
* K.-J. Kim, Nucl. Instrum. Methods A 445, 329 (2000).
** Y. Ding and Z. Huang, Phys. Rev. ST Accel. Beams 11, 030702 (2008).
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Slides
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| TUPPH027 |
Measurements of Coherent Synchrotron Radiation and its Impact on the LCLS Electron Beam
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298 |
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- Z. Huang, K. L.F. Bane, F.-J. Decker, Y. T. Ding, D. Dowell, P. Emma, J. C. Frisch, R. H. Iverson, C. Limborg-Deprey, H. Loos, H.-D. Nuhn, G. V. Stupakov, J. L. Turner, J. J. Welch, J. Wu
SLAC, Menlo Park, California
- D. F. Ratner
Stanford University, Stanford, Califormia
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The Linac Coherent Light Source (LCLS) is a SASE x-ray Free-Electron Laser (FEL) project presently under construction at SLAC. Two separate magnetic dipole chicanes are used in the SLAC linac to compress the electron bunch length in stages, in order to reach the high peak current required for an x-ray FEL. In the bunch compressors, coherent synchrotron radiation (CSR) can be emitted–induced either by a short electron bunch, or by any longitudinal density modulation that may be on the bunch. We present measurements, simulations, and analysis of- the CSR-induced energy loss,
- the related transverse emittance growth, and
- the microbunching-induced CSR directly observed at optical wavelengths.
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| TUPPH041 |
Three-dimensional Analysis of Longitudinal Space Charge Microbunching Starting from Shot Noise
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338 |
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- D. F. Ratner
Stanford University, Stanford, Califormia
- A. Chao, Z. Huang
SLAC, Menlo Park, California
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The commissioning of the Linac Coherent Light Source injector shows unexpected coherent optical transition radiation (COTR) for an uncompressed electron bunch downstream of a dog-leg transport line*. In this paper, we develop a three-dimensional analysis of the longitudinal space charge microbunching in attempting to explain the phenomenon. The analysis takes into account the transverse correlation of the longitudinal space charge field due to shot-noise startup** and nonlinear transport optics. We also discuss its applications to the LCLS COTR observations***.
* R. Akre et al., PRST-AB 11, 030703 (2008).
** M. Venturini, PRST-AB 11, 034401 (2008).
*** H. Loos et al., these proceedings.
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| MOPPH051 |
Beam Stability Studies in the LCLS Linac
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94 |
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- J. L. Turner, R. Akre, A. Brachmann, F.-J. Decker, Y. T. Ding, D. Dowell, P. Emma, J. C. Frisch, A. Gilevich, G. R. Hays, P. Hering, Z. Huang, R. H. Iverson, C. Limborg-Deprey, H. Loos, A. Miahnahri, S. Molloy, H.-D. Nuhn, J. J. Welch, W. E. White, J. Wu
SLAC, Menlo Park, California
- D. F. Ratner
Stanford University, Stanford, Califormia
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The beam stability specifications for the Linac Coherent Light Source (LCLS) Free-Electron Laser (FEL) at Stanford Linear Accelerator Center (SLAC) are critical for X-Ray power, pointing, and timing stability. Studies of the transverse, longitudinal, and intensity stability of the electron beam are presented. Some sources are identified, correlated, and quantified.
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| MOPPH052 |
Commissioning Experience with the Linac Coherent Light Source Feedback Systems
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98 |
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- J. Wu, R. Akre, A. Brachmann, F.-J. Decker, Y. T. Ding, D. Dowell, P. Emma, D. Fairley, J. C. Frisch, A. Gilevich, G. R. Hays, P. Hering, Z. Huang, R. H. Iverson, C. Limborg-Deprey, H. Loos, A. Miahnahri, S. Molloy, H.-D. Nuhn, J. L. Turner, J. J. Welch, W. E. White
SLAC, Menlo Park, California
- D. F. Ratner
Stanford University, Stanford, Califormia
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The Linac Coherent Light Source (LCLS) is a SASE x-ray Free-Electron Laser (FEL) project under construction at SLAC. The machine commissioning includes the injector, the first and second bunch compressor stages, the linac up to 14 GeV, and the various beam diagnostics. To ensure the vitality of FEL lasing, it is critical to generate and preserve the high quality of the electron beam during acceleration and compression. The final beam quality can be very sensitive to system jitter. To minimize jitter, various transverse and longitudinal feedback systems are required. Here, we report the commissioning experience with these systems during the two phases of commissioning in 2007 - 2008.
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| THBAU01 |
Observation of Coherent Optical Transition Radiation in the LCLS Linac
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485 |
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- H. Loos, R. Akre, A. Brachmann, F.-J. Decker, Y. T. Ding, D. Dowell, P. Emma, J. C. Frisch, A. Gilevich, G. R. Hays, P. Hering, Z. Huang, R. H. Iverson, C. Limborg-Deprey, A. Miahnahri, S. Molloy, H.-D. Nuhn, J. L. Turner, J. J. Welch, W. E. White, J. Wu
SLAC, Menlo Park, California
- D. F. Ratner
Stanford University, Stanford, Califormia
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The beam diagnostics in the linac for the Linac Coherent Light Source (LCLS) X-ray FEL project at SLAC includes optical transition radiation (OTR) screens for measurements of transverse and longitudinal beam properties. We report on observations of coherent light emission from the OTR screens (COTR) at visible, near-IR and UV wavelengths from the uncompressed and compressed electron beam at various stages in the accelerator.
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Slides
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| FRAAU04 |
Commissioning of the LCLS Linac and Bunch Compressors
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548 |
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- P. Emma, R. Akre, A. Brachmann, F.-J. Decker, Y. T. Ding, D. Dowell, J. C. Frisch, A. Gilevich, G. R. Hays, P. Hering, Z. Huang, R. H. Iverson, C. Limborg-Deprey, H. Loos, A. Miahnahri, S. Molloy, H.-D. Nuhn, J. L. Turner, J. J. Welch, W. E. White, J. Wu
SLAC, Menlo Park, California
- D. F. Ratner
Stanford University, Stanford, Califormia
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The Linac Coherent Light Source (LCLS) is a SASE x-ray Free-Electron Laser (FEL) project under construction at SLAC*. The injector section, from drive-laser and RF photocathode gun through the first bunch compressor chicane, was commissioned in the spring and summer of 2007. The second phase of commissioning, including the second bunch compressor chicane and various main linac modifications, was completed in January through August of 2008. We report here on experience gained during this second phase of machine commissioning, including the injector, the first and second bunch compressor stages, the linac up to 14 GeV, and the various beam diagnostics and measurements. The final commissioning phase, including the undulator and the long transport line from the linac, is set to begin in December 2008, with first light in July 2009.
* J. Arthur et al. SLAC-R-593, April 2002.
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