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27 papers
| title: | Beam compression experiments using the UCLA/ATF compressor |
| format: | conference procceeding |
| conference: | |
| year: | 2006 |
| 13 authors: | | | | | | | | | | | | | |
| abstract: | We review recent experimental results from the BNL ATF using the compressor built by UCLA. The measurements discussed include: first observation of short wavelength coherent edge radiation angular/wavelength spectrum and spectrum, sub-100 fsec pulse-length coherent transition autocorrelation measurements, and longitudinal and transverse phase space distortions. Extension of these measurements, as well as those which can be made possible by a new X-band traveling wave deflector being developed in an industrial collaboration, are examined. |
| keywords: | quindi |
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| title: | Magnetic Chicane Radiation Studies at the BNL ATF |
| format: | conference procceeding |
| conference: | |
| year: | 2006 |
| 11 authors: | | | | | | | | | | | |
| abstract: | Radiation emitted by relativistic electrons traversing the magnetic field gradients of a chicane bunch compressor has been studied in an attempt to characterize coherent edge radiation (CER). The studies performed at the Accelerator Test Facility (ATF) at Brookhaven National Laboratory (BNL) include frequency spectrum, angular distribution, and polarization measurements. A reconstruction of the longitudinal charge profile from the measured spectrum shows that the bunch has been compressed to approximately 30 μm FWHM, with a peak current exceeding 1.5 kA. Measurements of radiation from the short pulses are compared to predictions from QUINDI, a new simulation code developed at UCLA to model the radiation. |
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| title: | Recent Results from and Future Plans for the VISA II SASE FEL |
| format: | conference procceeding |
| conference: | 2005 Particle Accelerator Conference |
| year: | 2005 |
| 19 authors: | | | | | | | | | | | | | | | | | | | |
| abstract: | The VISA II (Visible to Infrared SASE Amplifier) project, a consequent experiment to the succesful VISA enterprise, entails the use of a chirped electron beam to drive a high gain SASE FEL. The resulting ultra-short pulses will be characterized using an advanced FROG (Frequency Resolved Optical Gating) technique, as well as a double differential spectrum (angle/wavelength) diagnostic. Implementation of sextupole corrections to the longitudinal aberrations affecting the high energy-spread chirped beam during transport to the VISA undulator is studied. Start-end simulations, including radiation diagnostics, are discussed. Initial experimental results involving a highly chirped beam transported without sextupole corrections, the resulting high gain lasing, and computational analysis are briefly reported. |
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| title: | Experimental and Analytical Study of a High Gain Self Amplified Spontaneous Emission Free Electron Laser Operating in a Large Spectral Bandwidth Regime |
| format: | thesis |
| year: | 2005 |
| 1 author: | |
| abstract: | The drive to create and measure ultra-short pulses in the x-ray regime advances the ongoing development of free electron lasers (FEL). Several proposed schemes, to shorten the pulse length of the radiation, involve driving the FEL with a chirped (linear longitudinal phase space correlation) electron beam in the self amplified spontaneous emission (SASE) mode. This dissertation examines the experiments conducted under such conditions, canvassing analytical and numerical studies of beam dynamics and radiation properties, experimental observations, and descriptions of the development of novel diagnostics. The VISA (Visible-Infrared SASE Amplifier) program has achieved saturation at 840 nm within a 4 m long undulator. A novel bunch compression mechanism during transport was discovered and ultimately responsible for the high peak current required to drive the FEL. Start-to-end simulations, detailing the dynamics from electron beam inception at the photocathode to the FEL radiation properties at the undulator, were successfully benchmarked to observable data. |
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| title: | Observation of Anomalously Large Spectral Bandwidth in a High Gain Self-amplified Spontaneous Emission Free-Electron Laser |
| format: | preprint |
| year: | 2005 |
| 14 authors: | | | | | | | | | | | | | | |
| abstract: | Observation of ultra-wide bandwidth, up to a full width of 15%, high-gain operation of a self-amplified spontaneous emission free election laser (SASE FEL) is reported. This type of lasing is obtained with a strongly chirped beam (~ 1.7%) emitted from the accelerator. Because of non-linear pulse compression during beam transport, a short, high current pulse with strong mismatch errors is injected into the undulator, bringing about high FEL gain. Start-end simulations reproduce key features of the measured results, and provide insight into mechanisms, such as angular spread in both emitted photon and electron trajectory distributions, which yield novel features in the radiation spectrum. |
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| title: | Observation of Anomalously Large Spectral Bandwidth in a High-Gain Self-Amplified Spontaneous Emission Free Elctron Laser |
| format: | journal article |
| year: | 2005 |
| 14 authors: | | | | | | | | | | | | | | |
| abstract: | Observation of ultrawide bandwidth, up to 15% full-width, high-gain operation of a self-amplified spontaneous emission free-election laser (SASE FEL) is reported. This type of lasing is obtained with a strongly chirped beam (E=E 1:7%) emitted from the accelerator. Because of nonlinear pulse compression during transport, a short, high current bunch with strong mismatch errors is injected into the undulator, giving high FEL gain. Start-to-end simulations reproduce key features of the measurements and provide insight into mechanisms, such as angular spread in emitted photon and electron trajectory distributions, which yield novel features in the radiation spectrum. |
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| title: | Recent Results from and Future Plans for the VISA II SASE FEL |
| format: | preprint |
| year: | 2005 |
| 19 authors: | | | | | | | | | | | | | | | | | | | |
| abstract: | The VISA II (Visible to Infrared SASE Amplifier) project, a consequent experiment to the succesful VISA enterprise, entails the use of a chirped electron beam to drive a high gain SASE FEL. The resulting ultra-short pulses will be characterized using an advanced FROG (Frequency Resolved Optical Gating)technique, as well as a double differential spectrum (angle/wavelength) diagnostic. Implementation of sextupole corrections to the longitudinal aberrations affecting the high energy-spread chirped beam during transport to the VISA undulator is studied. Start-end simulations, including radiation diagnostics, are discussed. Initial experimental results involving a highly chirped beam transported without sextupole corrections, the resulting high gain lasing, and computational analysis are briefly reported. |
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| title: | Sextupole Correction of the Longitudinal Transport of Relativistic Beams in Dispersionless Translating Sections |
| format: | journal article |
| year: | |
| 6 authors: | | | | | | |
| abstract: | We examine the use of sextupole magnets to correct nonlinearities in the longitudinal phase space transformation of a relativistic beam of charged particles in a dispersionless translating section, or dogleg. Through heuristic analytical arguments and examples derived from recent experimental endeavors and augmented by simulations using the particle tracking codes PARMELA and ELEGANT, sextupole corrections are found to be potentially useful in facilitating the use of such structures for beam compression or for shaping the current profile of the beam, by manipulation of the second-order longitudinal dispersion (or T566). Recent experimental evidence of the use of sextupoles to manipulate second-order horizontal and longitudinal dispersion of the beam is presented. The theoretical and experimental results indicate that these manipulations could be used to create an electron bunch with a current profile having a long ramp followed by a sharp cut-off, which is optimal for driving large amplitude wake fields in a plasma wake field accelerator. |
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| title: | VISA IB: Ultra-High Bandwidth, High Gain SASE FEL |
| format: | journal article |
| year: | |
| 15 authors: | | | | | | | | | | | | | | | |
| abstract: | We report the results of a high energy spread SASE FEL experiment, the intermediary experiment linking the VISA I and VISA II projects. A highly chirped beam (1.7 %) was transported, without corrections of longitudinal aberrations in the ATF dogleg, and injected into the VISA undulator. The ouput radiation displayed an uncharacteristicly large bandwidth (12 %) with extremely stable lasing and mea- sured energy of about 2 μJ . Start-to-end simulations re- produced key features of the experiment and provided an insight into the michanisms giving rise to such a high band- width. These analyses have important implications on the VISA II experiment. |
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| title: | Design and Operation of Pegasus Thermionic Cathode |
| format: | conference procceeding |
| conference: | 2003 Particle Accelerator Conference |
| year: | 2003 |
| 6 authors: | | | | | | |
| abstract: | A new thermionic cathode has been developed and installed for use on The PEGASUS plane wave transformer injector. The novel design of the LaB6 cathode allows for thermionic emission as well as photoinjector operation. Test stand measurements as well as in situ operational experience are reported. |
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| title: | Design and Status of the VISA II Experiment |
| format: | conference procceeding |
| conference: | 2003 Particle Accelerator Conference |
| year: | 2003 |
| 12 authors: | | | | | | | | | | | | |
| abstract: | VISA II is the follow-up project to the successful Visible to Infrared SASE Amplifier (VISA) experiment at the Accelerator Test Facility (ATF) in Brookhaven National Lab (BNL). This paper will report the motivation for and status of the two main experiments associated with the VISA II program. One goal of VISA II is to perform an experimental study of the physics of a chirped beam SASE FEL at the upgraded facilities of the ATF. This requires a linearization of the transport line to preserve energy chirping of the electron beam at injection. The other planned project is a strong bunch compression experiment, where the electron bunch is compressed in the chicane, and the dispersive beamline transport, allowing studies of deep saturation. |
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| title: | The UCLA Pegasus Plane-Wave Transformer Photoinjector |
| format: | conference procceeding |
| conference: | 2003 Particle Accelerator Conference |
| year: | 2003 |
| 6 authors: | | | | | | |
| abstract: | A photoinjector based on a multicell plane wave transformer accelerating structure has been commissioned at the UCLA Department of Physics' Pegasus Laboratory. Design and construction of the novel structure have been previously reported [J. Rosenzweig, et al. PAC Proceedings 1997], and recent operation with a thermionic cathode is being presented at this conference [P. Frigola, et al. these proceedings]. This paper describes the planned operation of the PWT gun as a photoinjector, including design and construction details of the drive laser. Progress to date and future plans are discussed. |
| keywords: | |
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| title: | Status of the UCLA PEGASUS Laboratory |
| format: | conference procceeding |
| conference: | 2003 Particle Accelerator Conference |
| year: | 2003 |
| 6 authors: | | | | | | |
| abstract: | The PEGASUS laboratory is a versatile radiation facility dedicated to the advancement of novel concepts in beam physics. The installation of a new LaB$_6$ cathode will allow for both thermionic emission and photoinjection operation. The PEGASUS plane wave transformer injector has been conditioned to 20 MW of RF power. Recent operations show a 15 MeV dark current beam that will be used for beam radiation studies. An upgrade to the drive laser system has been explored and will be realized shortly. This paper will describe and report the status of the various subsystems of the PEGASUS laboratory and outline the experiments underway, such as innovative beam instrumentation, surface effects in optical transition radiation, Thomson scattering, and waveguide SASE FEL. |
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| title: | The FEL Program at the PEGASUS Injector |
| format: | conference procceeding |
| conference: | 2003 Particle Accelerator Conference |
| year: | 2003 |
| 6 authors: | | | | | | |
| abstract: | The PEGASUS photo injector at UCLA can produce a photo electrons beam with a normalized emittance of 2 mm mrad at an energy of 12-15 MeV, capable of driving a Free-Electron Laser in the mid IR regime. The FEL program, associated with the PEGASUS injector and presented here, is based on a Self-Amplifying Spontaneous Emission (SASE) FEL. The studies focus on increasing the efficiency of an FEL by novel undulator design and compensation of diffraction effects, using waveguides of millimeter size. In this presentation we also discuss the possibility of the PEGASUS FEL as a THz user facility. |
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| title: | Status of the UCLA PEGASUS Injector Laboratory |
| format: | conference procceeding |
| conference: | 24th International Free Electron Laser Conference |
| year: | 2003 |
| 6 authors: | | | | | | |
| abstract: | The PEGASUS plane wave transformer injector has been conditioned to 20 MW of RF power. Initial operations show a 15 MeV dark current beam that will be used for beam radiation studies. The design of a new LaB_6 cathode will allow for both thermionic emission and photoinjection operation. Experiments currently planned include novel beam instrumentation, surface effects in optical transition radiation, and waveguide SASE FEL. |
| keywords: | |
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| title: | PEGASUS Safety Interlock System |
| format: | tech note |
| year: | 2002 |
| 1 author: | |
| abstract: | Describes the design and functioning of the safety interlock system in the PEGASUS lab. |
| keywords: | |
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| title: | Commissioning of the UCLA PEGASUS Photoinjector Laboratory |
| format: | conference procceeding |
| conference: | 2001 Particle Accelerator Conference |
| year: | 2001 |
| 5 authors: | | | | | |
| abstract: | The PEGASUS Photoinjector has been commissioned at UCLA. The Plane Wave Transformer Photoinjector provides a high-brightness 17 MeV beam that will be used for numerous beam-radiation studies. Some of these will include SASE FEL, transition radiation from non-standard surfaces, and monochromatic x-ray production via PXR and Thompson scattering. |
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| title: | Simulations, Diagnostics and Recent Results of the VISA II Experiment |
| format: | conference procceeding |
| conference: | Proceedings of the 27th International Free Electron Laser Conference |
| year: | August 2005 |
| 17 authors: | | | | | | | | | | | | | | | | | |
| abstract: | The VISA II experiment entails the use of a chirped electron beam to drive a high gain SASE FEL. Sextupoles are implemented to correct the longitudinal aberrations affecting the high energy spread chirped beam during transport to the undulator. The output radiation is diagnosed with a modified frequency resolved optical gating (FROG) technique. The double differential energy spectrum is measured with a pair of slits and a set of gratings. In this paper, we report on start-to-end simulations, radiation diagnostics, as well as initial experimental results. Technical considerations for future experimental methods are also addressed. |
| keywords: | pbpl |
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| title: | Chicane Radiation Measurements with a Compressed Electron Beam at the BNL ATF |
| format: | conference procceeding |
| conference: | 2007 Particle Accelerator Conference |
| year: | 2007 |
| 12 authors: | | | | | | | | | | | | |
| abstract: | The radiation emitted from a chicane compressor has been studied at the Brookhaven National Laboratory (BNL) Accelerator Test Facility (ATF). Coherent edge radiation (CER) is emitted from a compressed electron beam as it traverses sharp edge regions of a magnet. The compression is accompanied by strong self-fields, which are manifested as distortions in the momentum space called beam bifurcation. Recent measurements indicate that the bunch length is approximately 100 fs rms. The emitted THz chicane radiation displays strong signatures of CER. This paper reports on the experimental characterization and subsequent analysis of the chicane radiation measurements at the BNL ATF with a discussion of diagnostics development and implementation. The characterization includes spectral analysis, far-field intensity distribution, and polarization effects. Experimental data is benchmarked to a custom developed start-to-end simulation suite. |
| keywords: | CER radiation compressor chicane |
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| title: | Chicane Radiation Measurements with a Compressed Electron Beam at the BNL ATF |
| format: | journal article |
| year: | 2007 |
| 12 authors: | | | | | | | | | | | | |
| abstract: | |
| keywords: | pbpl |
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| title: | Characterization of Orbital Angular Momentum Modes in FEL Radiation |
| format: | journal article |
| year: | 2007 |
| 5 authors: | | | | | |
| abstract: | It is well known that Gaussian modes of paraxial light can possess orbital angular momentum (OAM) as a result of a exp( −ilφ) azimuthal angular dependence[1]. Recent experiments on the VISA free-electron laser operating as self-amplified spontaneous amplifier (SASE) at λ=840 nm have produced transverse electromagnetic radiation inten- sity patterns that suggest the presence of one or more OAM modes. Though the intensity profiles from VISA are com- pelling, work remains to discern the phase structure since OAM modes are revealed by a characteristic helical phase dependence, with a pathological singularity on axis. Here we discuss current efforts to characterize the mode content of the VISA FEL through experiments, theoretical mod- els, and simulations. Possible methods to generate OAM modes in situ are discussed. |
| keywords: | pbpl |
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| title: | Seeded VISA: A 1064 nm Laser-Seeded FEL Amplifier at the BNL ATF |
| format: | journal article |
| year: | 2007 |
| 7 authors: | | | | | | | |
| abstract: | An experimental study of a seeded Free Electron Laser (FEL) using the VISA undulator and a Nd:YAG seed laser will be performed at the Accelerator Test Facility (ATF) at Brookhaven National Laboratory. The study is motivated by the demand for a short Rayleigh length FEL amplifier at 1 micron to allow for high power transmission with min- imal damage of transport optics. Planned measurements include transverse and longitudinal coherence, angular dis- tribution, and wavelength spectrum of the FEL radiation. The effects of detuning the electron beam energy will be studied, with an emphasis on control of the radiation emis- sion angles and increase of the amplifier efficiency. Results of start-to-end simulations are also presented. |
| keywords: | pbpl |
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| title: | Experimental Characterization of the Transverse Phase Space of a 60-MeV Electron Beam through a Compressor Chicane |
| format: | journal article |
| year: | 2007 |
| 8 authors: | | | | | | | | |
| abstract: | Space charge and coherent synchrotron radiation may deteriorate electron beam quality when the beam passes through a magnetic bunch compressor. This paper presents the transverse phase-space tomographic measurements for a compressed beam at 60MeV, around which energy the first stage of magnetic bunch compression takes place in most advanced linacs. Transverse phase-space bifurcation of a compressed beam is observed at that energy, but the degree of the space charge-induced bifurcation is appreciably lower than the one observed at 12MeV. |
| keywords: | pbpl |
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| title: | Future FEL Studies at the VISA Experiment in the SASE and Seeded Modes |
| format: | journal article |
| year: | 2006 |
| 9 authors: | | | | | | | | | |
| abstract: | The VISA (Visible to Infrared SASE Amplifier) experiment at BNL (Brookhaven National Laboratory) has previously demonstrated saturation at 840 nm in 2001. Further SASE studies, in 2003, have demonstrated an anomalously large bandwidth spread of the FEL spectrum due to off-angle emissions. This paper disseminates the current and future program of the VISA program at BNL. This includes a study of a seeded FEL, using a 1 micron YAG laser as a seed, and the accompanying diagnostics to characterize the radiation. Diagnostics include the double differential spectrometer, a mode converter to investigate the orbital angular momentum of light in the FEL, and an optical pepper-pot for coherence measurements. As usual, start-to-end simulations are presented. |
| keywords: | pbpl |
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| title: | Experimental characterization of the transverse phase space of a 60-MeV electron beam through a compressor chicane |
| format: | journal article |
| year: | 2006 |
| 8 authors: | | | | | | | | |
| abstract: | Space charge and coherent synchrotron radiation may deteriorate electron beam quality when the beam passes through a magnetic bunch compressor. This paper presents the transverse phase-space tomographic measurements for a compressed beam at 60 MeV, around which energy the first stage of magnetic bunch compression takes place in most advanced linacs. Transverse phase-space bifurcation of a compressed beam is observed at that energy, but the degree of the space charge-induced bifurcation is appreciably lower than the one observed at 12 MeV. |
| keywords: | pbpl |
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| title: | Observation of Coherent Edge Radiation Emitted by a 100 Femtosecond Compressed Electron Beam |
| format: | journal article |
| year: | 2006 |
| 13 authors: | | | | | | | | | | | | | |
| abstract: | A chicane compressor developed by UCLA for the production of ultra-short, 60 MeV electron beams at the Brookhaven National Laboratory Accelerator Test Facility has been commissioned, and initial beam physics experiments have been performed. These measurements have established the compression of electron beams to the 100 femtosecond (1 kA peak current) regime, via coherent transition radiation (CTR) based measurements. Investigations of coherent edge radiation (CER) include signatures that differentiate it from coherent synchrotron radiation (CSR), such as polarization and far-field angular distribution. Additionally, the radiation wavelength spectrum is determined from autocorrelation measurements. Radiation properties are compared to detailed start-to-end simulations derived from PARMELA and QUINDI (a Lienard-Wiechert code developed at UCLA). Plans for future experiments which further explore the observed wavelength spectra are presented. |
| keywords: | pbpl |
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| title: | Experimental Characterization of 4-D Transverse Phase-Space of a Compressed Beam |
| format: | journal article |
| year: | 2005 |
| 8 authors: | | | | | | | | |
| abstract: | |
| keywords: | pbpl |
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