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10 papers
| title: | Virtual dielectric waveguide mode description of a high-gain free-electron laser. I. Theory |
| format: | journal article |
| year: | June 20, 2008 |
| 3 authors: | | | |
| abstract: | A set of mode-coupled excitation equations for the slowly growing amplitudes of dielectric waveguide eigenmodes is derived as a description of the electromagnetic signal field of a high-gain free-electron laser FEL, including the effects of longitudinal space charge. This approach of describing the field basis set has notable advantages for FEL analysis in providing an efficient characterization of eigenmodes, and in allowing a clear connection to free-space propagation of the input seeding and output radiation. The formulation describes the entire evolution of the radiation wave through the linear gain regime, prior to the onset of saturation, with arbitrary initial conditions. By virtue of the flexibility in the expansion basis, this technique can be used to find the direct coupling and amplification of a particular mode. A simple transformation converts the derived coupled differential excitation equations into a set of coupled algebraic equations and yields a matrix determinant equation for the FEL eigenmodes. A quadratic index medium is used as a model dielectric waveguide to obtain an expression for the predicted spot size of the dominant system eigenmode, in the approximation that it is a single Gaussian mode. |
| keywords: | pbpl pra |
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| title: | Virtual dielectric waveguide mode description of a high-gain free-electron laser. II. Modeling and numerical simulations |
| format: | journal article |
| year: | June 20, 2008 |
| 3 authors: | | | |
| abstract: | A high-gain free-electron laser is modeled using an expansion of the radiation field in terms of guided Laguerre-Gaussian modes of a virtual dielectric waveguide E. Hemsing, A. Gover, and J. Rosenzweig, preceding paper, Phys Rev. A 77, 063830 2008 . The radiation profile evolution, power gain, and detuning efficiency characteristics are investigated for seeding with fundamental Gaussian and higher-order Laguerre- Gaussian input modes on a Gaussian e-beam in the collective regime. The full wave evolution solution at different seed radiation injection conditions results in determination of the optimal waist size and waist position of the seed radiation beam for maximum power coupling efficiency. Results for guided mode evolution and power gain are shown to be consistent with simulations performed with the code GENESIS 1.3. The amplification and spontaneous generation of FEL radiation with orbital angular momentum is also considered. |
| keywords: | pbpl pra |
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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. |
| keywords: | |
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| 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: | 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 |
| Details | |
| 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: | The FINDER Photoinjector |
| format: | journal article |
| year: | 2007 |
| 6 authors: | | | | | | |
| abstract: | The FINDER photoinjector was developed for the inverse Compton scattering experiment under UCLA- LLNL collaboration. The improvements of this gun from SPARC gun [1, 2] at INFN-LNF (Frascati) and previous UCLA versions of the 1.6 cell S-band photoinjector are detailed here. The gun is designed to have large mode separation to suppress 0 mode excitation which may be a cause of the emittance degradation. In an effort to reduce the RF quadrupole effect the full cell tuners are replaced by vacuum ports. The laser ports are also omitted. Two openings of the solenoid shield are added to top and bottom of it where there were only two openings on the sides. S11 of the cavity was presented. The on-axis electric field was measured by the bead drop method to show the good field balance. The magnetic field in the emittance compensation solenoid was measured and the quadrupole components were derived. |
| 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: | 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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