| title: | Updates to QUINDI |
| format: | conference procceeding |
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| year: | |
| 2 authors: | | |
| abstract: | QUINDI has been developed to address the numerical challenge of calculating the radiation spectra from electron bunches in bending magnet systems. Since the introduction of QUINDI, many improvements and features have been added. QUINDI now supports a 3D model for bending magnets which includes fringing fields. A more modular approach has been achieved which allows better interoperability with other tracking and radiation codes. There have been many updates to the electric field calculation and spectrum processing, as well as to the post-processor, SpecGUI. |
| keywords: | quindi |
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| title: | High brightness electron beam emittance evolution measurements in an rf photoinjector |
| format: | journal article |
| year: | 2008 |
| 48 authors: | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
| abstract: | The new generation of linac injectors driving free electron lasers in the self-amplified stimulated emission (SASE-FEL) regime requires high brightness electron beams to generate radiation in the wavelength range from UV to x rays. The choice of the injector working point and its matching to the linac structure are the key factors to meet this requirement. An emittance compensation scheme presently applied in several photoinjectors worldwide is known as the ‘‘Ferrario’’ working point. In spite of its great importance there was, so far, no direct measurement of the beam parameters, such as emittance, transverse envelope, and energy spread, in the region downstream the rf gun and the solenoid of a photoinjector to validate the effectiveness of this approach. In order to fully characterize the beam dynamics with this scheme, an innovative beam diagnostic device, the emittance meter, consisting of a movable emittance measurement system, has been designed and built. With the emittance meter, measurements of the main beam parameters in both transverse phase spaces can be performed in a wide range of positions downstream the photoinjector. These measurements help in tuning the injector to optimize the working point and provide an important benchmark for the validation of simulation codes. We report the results of these measurements in the SPARC photoinjector and, in particular, the first experimental evidence of the double minimum in the emittance oscillation, which provides the optimized matching to the SPARC linac. |
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| title: | Virtual dielectric waveguide mode description of a high-gain free-electron laser. I. Theory |
| format: | journal article |
| year: | 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 highgain 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. |
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| title: | Virtual dielectric waveguide mode description of a high-gain free-electron laser. |
| format: | journal article |
| year: | 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. |
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| title: | Efficient harmonic microbunching in a 7th-order inverse-free-electron laser interaction |
| format: | journal article |
| year: | 2009 |
| 8 authors: | | | | | | | | |
| abstract: | We have shown that a seventh-order inverse-free-electron laser (IFEL) interaction, where the radiation frequency is the seventh harmonic of the fundamental resonant frequency, can microbunch a beam of relativistic electrons inside an undulator. Using coherent transition radiation (CTR) emitted by the bunched 12.3 MeV beam as a diagnostic, strong microbunching of the beam is inferred from the observation of CTR at the first, second, and third harmonics of the seed 10 m radiation. Threedimensional IFEL simulations show that the observed harmonic ratios can be explained only if transverse spatial distribution of the steepened bunched beam is taken into account. |
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| title: | Helical Electron-Beam Microbunching by Harmonic Coupling in a Helical Undulator |
| format: | journal article |
| year: | 2009 |
| 7 authors: | | | | | | | |
| abstract: | Microbunching of a relativistic electron beam into a helix is examined analytically and in simulation. Helical microbunching is shown to occur naturally when an e beam interacts resonantly at the harmonics of the combined field of a helical magnetic undulator and an axisymmetric input laser beam. This type of interaction is proposed as a method to generate a strongly prebunched e beam for coherent emission of light with orbital angular momentum at virtually any wavelength. The results from the linear microbunching theory show excellent agreement with three-dimensional numerical simulations. |
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| title: | Observation of coherent terahertz edge radiation from compressed electron beams |
| format: | journal article |
| year: | 2009 |
| 9 authors: | | | | | | | | | |
| abstract: | Coherent radiation emitted from a compressed electron bunch as it traverses the sharp edge regions of a magnetic chicane has been investigated at the Brookhaven National Laboratory Accelerator Test Facility. Electron beam measurements using coherent transition radiation interferometry indicate a 100 fs rms bunch accompanied by distinct distortions in energy spectrum due to strong self-fields. These self-fields are manifested in emitted high power THz radiation, which displays signatures of the phenomenon known as coherent edge radiation. Radiation characterization studies undertaken include spectral analysis, farfield intensity distribution, polarization, and dependence on the electron bunch length. The observed aspects of the beam and radiation allow detailed comparisons with start-to-end simulations. |
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| title: | Electron Emission Characterization of Mg Photocathode Grown by Pulsed Laser Deposition Within an S-band RF Gun |
| format: | journal article |
| year: | 2009 |
| 7 authors: | | | | | | | |
| abstract: | Pulsed laser deposition (PLD) has been proposed several years ago as a suitable technique to deposit a pure Mg film over a radio frequency (rf ) gun Cu backflange in order to obtain a high efficiency photocathode surface for the generation of high brightness electron beams. In this paper we report preliminary experimental results on the emission properties of a PLD grown Mg film within the high electric field gradients of a rf gun showing the effects of the rf conditioning process on the cathode surface. Even though a laser cleaning process should be performed on the sample surface in order to remove contaminated layers, the results presented here are very promising for the realization of a final Mg-based photocathode. |
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| title: | Novel Radio-Frequency Gun Structures For Ultrafast Relativistic Electron Diffraction |
| format: | journal article |
| year: | 2009 |
| 7 authors: | | | | | | | |
| abstract: | Radio-frequency (RF) photoinjector-based relativistic ultrafast electron diffraction (UED) is a promising new technique that has the potential to probe structural changes at the atomic scale with sub-100 fs temporal resolution in a single shot. We analyze the limitations on the temporal and spatial resolution of this technique considering the operating parameters of a standard 1.6 cell RF gun (which is the RF photoinjector used for the first experimental tests of relativistic UED at Stanford Linear Accelerator Center; University of California, Los Angeles; Brookhaven National Laboratory), and study the possibility of employing novel RF structures to circumvent some of these limits. |
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| title: | Generation of Narrow-Band Terahertz Coherent Cherenkov Radiation in a Dielectric Wakefield Structure |
| format: | thesis |
| year: | June 2009 |
| 1 author: | |
| abstract: | |
| keywords: | Thesis |
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