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Last Name: Hogan
Full Name: M. Hogan
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27 papers
| title: | PRELIMINARY RESULTS FROM THE UCLA/SLAC ULTRA-HIGH GRADIENT CERENKOV WAKEFIELD ACCELERATOR EXPERIMENT |
| format: | conference procceeding |
| conference: | Erice 2005 |
| year: | 2006 |
| 12 authors: | | | | | | | | | | | | |
| abstract: | The first phase of an experiment to study the performance of dielectric Cerenkov wakefield accelerating structures at extremely high gradients in the GV/m range has been completed. This experiment takes advantage of the unique SLAC FFTB electron beam and its demonstrated ultra-short pulse lengths and high currents (e.g., ?z = 20 ?m at Q = 3 nC). The FFTB electron beam has been successfully focused down and sent through varying lengths of fused silica capillary tubing with two different sizes: ID = 200 ?m / OD = 325 ?m and ID = 100 ?m / OD = 325 ?m. The pulse length of the electron beam was varied in the range 20 ?m < ?z < 100 ?m which produced a range of electric fields between 2 and 20 GV/m at the inner surface of the dielectric tubes. We observed a sharp increase in optical emissions from the capillaries in the middle part of this surface field range which we believe indicates the transition between sustainable field levels and breakdown. If this initial interpretation is correct, the surfaced fields that were sustained equate to on axis accelerating field of several GV/m. In future experiments we plan to collect and measure coherent Cerenkov radiation emitted from the capillary tube to gain more information about the strength of the accelerating fields. |
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| title: | An Ultra-High Gradient Cerenkov Wakefield Acceleration Experiment at SLAC FFTB |
| format: | conference procceeding |
| conference: | |
| year: | 2004 |
| 7 authors: | | | | | | | |
| abstract: | The creation of ultra-high current, ultra-short pulse beams (Q=3 nC, σz= 20 μm) at the SLAC FFTB has opened the way for very high gradient plasma wakefield acceleration experiments. We study here the use of these beams in a proposed Cerenkov wakefield experiment, where one may excite electromagnetic wakes in a simple dielectric tube with inner diameter of few 100 microns that exceed the GV/m level. We discuss the scaling of the fields with design geometric design parameters, and choice of dielectric. We also examine measurable aspects of the experiment, such as the total coherent Cerenkov radiation energy one may collect, and the expected aspects of dielectric breakdown at high fields. |
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| title: | An Ultra-High Gradient Cerenkov Wakefield Acceleration Experiment at SLAC FFTB |
| format: | conference procceeding |
| conference: | |
| year: | 2004 |
| 7 authors: | | | | | | | |
| abstract: | The creation of ultra-high current, ultra-short pulse beams (Q=3 nC, ) at the SLAC FFTB has opened the way for very high gradient plasma wakefield acceleration experiments. We study here the use of these beams in a proposed Cerenkov wakefield experiment, where one may excite electromagnetic wakes in a simple dielectric tube with inner diameter of few100 microns that exceed the GV/m level. We discuss the scaling of the fields with design geometric design parameters, and choice of dielectric. We also examine measurable aspects of the experiment, such as the total coherent Cerenkov radiation energy one may collect, and the expected aspects of dielectric breakdown at high fields. |
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| title: | ORION: An Advanced Accelerator Facility at SLAC |
| format: | conference procceeding |
| conference: | 2001 Particle Accelerator Conference |
| year: | 2001 |
| 13 authors: | | | | | | | | | | | | | |
| abstract: | Extending the center-of-mass energy frontier for high-energy physics depends on the research and development that is conducted now in the area of advanced accelerator physics and technology. In this article, we present the design and beam dynamics simulations for the emittance-compensated, RF photoinjector of the ORION Facility. (4 References). |
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| title: | A measurement of high gain SASE FEL induced electron beam micro-bunching using coherent transition radiation |
| format: | conference procceeding |
| conference: | 1999 Particle Accelerator Conference |
| year: | 1999 |
| 9 authors: | | | | | | | | | |
| abstract: | Coherent transition radiation (CTR) was used to study the longitudinal modulations of an electron beam exiting the UCLA/LANL high gain SASE FEL. The induced longitudinal micro-bunching of the electron beam at the exit of the undulator was measured with a frequency domain technique using the CTR emitted when this beam strikes a thin conducting foil. Formalisms for both CTR and SASE theories are related using the simulation code GINGER in which the SASE FEL gain of the output radiation and the micro-bunching of the electron beam are given. Experimental results from the CTR measurement will show the limit of standard transition radiation theory is being approached and new analysis is needed. (8 References). |
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| title: | Measured free-electron laser microbunching using coherent transition radiation |
| format: | conference procceeding |
| conference: | 20th International Free Electron Laser Conference |
| year: | 1999 |
| 9 authors: | | | | | | | | | |
| abstract: | The microbunch distribution of an electron beam exiting a SASE free-electron laser has been measured using the emitted coherent transition radiation (CTR) produced from a thin aluminum foil placed at the end of the undulator. The wavelength of the coherent transition radiation is shown to be the same as the FEL wavelength, and thus a measure of the beam microbunch spacing. Also, the study of the CTR linewidth and angular acceptance of the radiation captured are shown to be derived from this coherent radiative process. Scattering effects on the forward emitted transition radiation from the electron beam traversing an aluminum foil are also considered. (11 References). |
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| title: | Measurements of gain larger than 10(5) at 12 mu m in a self-amplified spontaneous-emission free-electron laser |
| format: | unknown |
| year: | 1998 |
| 14 authors: | | | | | | | | | | | | | | |
| abstract: | We report measurements of very large output intensities corresponding to a gain larger than 10/sup 5/ for a single pass free-electron laser operating in the self-amplified spontaneous emission (SASE) mode at 12 mu m. We also report the observation and analysis of intensity fluctuations of the SASE radiation intensity in the high-gain regime. The results are compared with theoretical predictions and simulations. (18 References). |
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| title: | Measurements of High Gain and Intensity Fluctuations in a Self-Amplified, Spontaneous-Emission Free-Electron Laser |
| format: | journal article |
| year: | 1998 |
| 12 authors: | | | | | | | | | | | | |
| abstract: | We report measurements of large gain for a single pass free-electron laser operating in self-amplified spontaneous emission (SASE) at 16 mm starting from noise. We also report the first observation and analysis of intensity fluctuations of the SASE radiation intensity in the high gain regime. The results are compared with theoretical predictions and simulations. |
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| title: | Observation of High Gain and Intensity Fluctuations in Self-Amplified Spntaneous Emission free-Electron Lasers |
| format: | thesis |
| year: | 1998 |
| 1 author: | |
| abstract: | This thesis presents the results of two recent free electron laser (FEL) experiments operating in the self amplified spontaneous emission (SASE) mode. An X-ray laser would offer a unique way to explore the structure of matter at the atomic and molecular scale. Among the various schemes proposed to reach this wavelength region, the free electron laser, operating without mirrors in a self amplified spontaneous emission mode offers a favorable scaling law. It has also been shown that utilizing state of the art linear accelerators and electron sources it is possible to build an X-ray SASE FEL, and this has lead to two major proposals to build a SASE X-ray FEL, one at SLAC, the other at DESY. The theory on which the SASE X-ray FEL is based, has been developed over many years, but the experimental data to support it are few and incomplete. Very large gain in SASE has so fr been observed in the centimeter to millimeter waves, and in the medium infrared (IR) at Los Alamos; recently gain in the near IR has been observed at Orsay and at Brookhaven. The intensity distribution function has been previously measured only for spontaneous undulator radiation, with no amplification, and long bunches. This theseis analyzes two recent experiments designed to verify the models of high gain FELs. High gain FEL theory is reviewed with a emphasis on the characteristics of SASE measurable by these experiments. The accelerator, beamline components and diagnostics are described with an emphasis on the measurements. The FEL undulators and optical diagnostics are also described, again with an emphasis on the measurements. The experimental data are compared to analytic models, where applicable, and to computer simulation codes. |
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| title: | Observation of Self-Amplified Spontaneous-Emission-Induced Electron-Beam Microbunching Using Coherent Transition Radiation |
| format: | unknown |
| year: | 1998 |
| 9 authors: | | | | | | | | | |
| abstract: | We report the measurement of electron-beam microbunching at the exit of a self-amplified spontaneous-emission free-electron laser (SASE FEL), by observation of coherent transition radiation (CTR). The CTR was found to have an angular spectrum much narrower than spontaneous transition radiation and a narrow-band frequency spectrum. The central frequency of the fundamental CTR spectrum is found to differ slightly from that of the SASE, a finding in disagreement with previously invoked CTR theory. The CTR measurement establishes the uniformity of microbunching in the transverse dimension, indicating the SASE FEL operates in a dominant transverse mode. |
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| title: | Bunch length measurement of picosecond electron beams from a photoinjector using coherent transition radiation |
| format: | conference procceeding |
| conference: | ICFA Second Generation Plasma Acceleration Workshop |
| year: | 1998 |
| 6 authors: | | | | | | |
| abstract: | The bunch length of an electron beam derived from the UCLA Saturnus photoinjector has been measured using a 45 degrees CTR foil. The sudden change of electrons boundary conditions cause them to radiate (transition radiation) with the spectral power entirely dependent upon the degree of coherency, which strongly relates to the beam size. A polarizing Michelson interferometer allowed measurement of the auto-correlation of the coherent transition radiation signal. An analysis method was developed to compensate for undetected low-frequency radiation and systematically extract the bunch length information for a specific beam model. This analysis allowed observation of pulse lengthening due to the space charge, as well as compression with the variation of the RF injection phase. The hypothesis of a satellite beam has been also tested using this analysis. (8 References). |
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| title: | UCLA-KIAE focusing permanent magnet undulator for SASE experiment |
| format: | conference procceeding |
| conference: | 19th International Free Electron Laser Conference |
| year: | 1998 |
| 9 authors: | | | | | | | | | |
| abstract: | A description of a new 2 m undulator is presented which was specially designed and manufactured for a SASE mode FEL experiment. It is a one section two plane focusing permanent magnet construction. The uniform period length is 2.06 cm, total number of periods is 98. The peak field on the axis is 5.4 kG for a 5 mm gap. (8 References). |
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| title: | Measurements of high gain and noise fluctuations in a SASE free electron laser |
| format: | conference procceeding |
| conference: | Workshop on Single Pass, High Gain FELs Starting from Noise Aiming at Coherent X-Rays |
| year: | 1997 |
| 12 authors: | | | | | | | | | | | | |
| abstract: | We report measurements of large gain for a single pass Free Electron Laser operating in Self Amplified Spontaneous Emission (SASE) at 16 mu m starting from noise. We also report the first observation and analysis of intensity fluctuations of the SASE radiation intensity in the high gain regime. The results are compared with theoretical predictions and simulations. (11 References). |
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| title: | Experimental confirmation of transverse focusing and adiabatic damping in a standing wave linear accelerator |
| format: | journal article |
| year: | 1997 |
| 10 authors: | | | | | | | | | | |
| abstract: | The measurement of the transverse phase-space map, or transport matrix, of a relativistic electron in a high-gradient, radio-frequency linear accelerator (rf linac) at the UCLA photoinjector is reported. This matrix, which indicates the effects of acceleration (adiabatic damping), first-order transient focusing, and ponderomotive second-order focusing, is measured as a function of both rf field amplitude and phase in the linac. The elements of the matrix, determined by observation of centroid motion at a set of downstream diagnostics due to deflections induced by a set of upstream steering magnets, compare well with previously developed analytical theory [J. Rosenzweig and L. Serafini, Phys. Rev. E 49, 1599 (1994)]. The determinant of the matrix is obtained, yielding a direct confirmation of trace space adiabatic damping. Implications of these results on beam optics at moderate energy in high-gradient linear accelerators such as rf photoinjectors are discussed. |
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| title: | A Numerical Method of Calculating the Effective Start-Up Power in a High Gain Free Electron Laser |
| format: | conference procceeding |
| conference: | 8th International Free Electron Laser Conference |
| year: | 1997 |
| 2 authors: | | |
| abstract: | We present a simple model of the startup process in a high gain Free Electron Laser (FEL). The model is used to numerically calculate the power generated within the first gain length of the FEL, which is amplified by the remainder of the undulator. The model takes into account the bandwidth and angular limits imposed by the high-gain process. A brief comparison of the results of this model to an analytic approximation for calculating the start-up power is also given. |
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| title: | The UCLA high gain infrared free electron laser |
| format: | conference procceeding |
| conference: | 18th International Free-Electron Laser Conference |
| year: | 1997 |
| 5 authors: | | | | | |
| abstract: | A high gain SASE FEL amplifier designed to operate in the infrared (near 10 mu m) is being commissioned in the particle beam physics laboratory at UCLA. The high brightness beam needed to drive the FEL is provided by an RF photocathode gun employing solenoidal emittance compensation. A novel linac (a plane wave transformer) accelerates the beam to a final energy [left angle bracket]or=15 MeV. This beam is to be sent through a 60 cm long undulator with a period of 1.5 cm and an undulator parameter K approximately=1. Near future experiments will focus on FEL physics relevant to proposed short wavelength devices. Investigations of start-up from noise (SASE), effects of beam parameters on gain as well as noise fluctuations are of particular interest. Here we present an overview of the hardware including relevant diagnostics, measured beam parameters, FEL simulation results and the status of proposed experiments. (9 References). |
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| title: | Status of UCLA IR FEL |
| format: | preprint |
| year: | 1996 |
| 21 authors: | | | | | | | | | | | | | | | | | | | | | |
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| title: | Status of the UCLA high-gain infrared free electron laser |
| format: | conference procceeding |
| conference: | 1995 Particle Accelerator Conference |
| year: | 1995 |
| 5 authors: | | | | | |
| abstract: | A compact, infrared (10-20 mu m), high-gain FEL is being commissioned at the Particle Beam Physics Laboratory (PBPL) at UCLA. A 60 cm long undulator with a period of 1.5 cm and an undulator parameter K-l has been built to be used in conjunction with the PBPL beam. Experiments will focus on EEL physics pertinent to proposed short wavelength devices. Of particular interest is exploration of startup from noise, self amplified spontaneous emission (SASE), beam parameter effects on gain, and output power fluctuations. Beam micro-bunching due to the FEL action will also be measured using coherent transition radiation. Here we present an overview of the relevant diagnostics, FEL simulation results and proposed experiments. (13 References). |
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| title: | The UCLA compact high brightness electron accelerator |
| format: | conference procceeding |
| conference: | 1995 Particle Accelerator Conference |
| year: | 1995 |
| 10 authors: | | | | | | | | | | |
| abstract: | We report the characteristics and performance of the UCLA S-band compact electron accelerator, consisting of a high brightness, 8 cm long, photo-injector with a copper cathode, followed by a 42 cm long plane wave transformer accelerating structure, delivering a beam energy of 10 MeV. The photo-electrons are produced by a 266 nm laser pulse of less than 4 ps in duration. Over time the laser induced electron emission decreases and the emission from the cathode surface becomes structured. Measurements of the quantum efficiency for Cu before and after this degradation are presented along with images of the non uniform electron emission. (8 References). |
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| title: | Initial operation of the UCLA plane wave transformer (PWT) linac |
| format: | conference procceeding |
| conference: | 1995 Particle Accelerator Conference |
| year: | 1995 |
| 10 authors: | | | | | | | | | | |
| abstract: | We report on the initial operation of a novel compact rf linac-the plane wave transformer (PWT). The PWT is a 42 cm long, 8 cell standing-wave structure, operated at S-band, in a pi -mode. We present the properties of this linac at rf power levels from 4 MW to 8 MW and beam energy from 7 MeV to 10 MeV, measured initially using both dark current and photo-electrons. Some technical issues associated with the operation are discussed. Future improvements of the PWT, using a modified design, are also studied. (6 References). |
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| title: | The UCLA high gain infrared FEL |
| format: | conference procceeding |
| conference: | 16th International Free Electron Laser Conference |
| year: | 1995 |
| 4 authors: | | | | |
| abstract: | The particle beam physics laboratory (PBPL) at UCLA is constructing a short period FEL which will operate in the high gain regime. The focus of the work has been the production of a high brightness electron beam suitable for short wavelength FELs. Once operational the FEL will be used to study phenomena of significance to short wavelength devices such as SASE and performance sensitivity to various beam parameters. Future studies may include the addition of a second undulator or amplification of an input source (CO/sub 2/ laser) to study saturation, superradiance, and optical guiding. (11 References). |
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| title: | Cold Test Measurements of the UCLA Photo-Injector |
| format: | preprint |
| year: | April 30, 1993 |
| 2 authors: | | |
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| title: | Initial measurements of the UCLA RF photoinjector |
| format: | conference procceeding |
| conference: | Conference on High Intensity Electron Sources |
| year: | 1994 |
| 14 authors: | | | | | | | | | | | | | | |
| abstract: | The 1.5 cell standing wave RF photoinjector has been operated for the past several months using a copper cathode. The photoinjector drive laser produces sub 2 ps pulses of UV ( lambda =256 nm) light with up to 200 mu J/pulse which generates up to 3 nC of charge, The emittance of the photoinjector was measured as a function of charge, RF launching phase, and peak accelerating field. Also, the quantum efficiency and pulse lengths of the laser beam and the electron beam were measured. (15 References). |
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| title: | Initial measurements of the UCLA RF photoinjector |
| format: | conference procceeding |
| conference: | 15th International Free Electron Laser Conference |
| year: | 1994 |
| 2 authors: | | |
| abstract: | An RF photocathode gun which, along with a compact linac, forms the injection system for a planned 10 mm free-electron laser amplifier experiment, has been commissioned in the Particle Beam Physics Laboratory at UCLA. This high-gradient gun, based on the Brookhaven design, has emitted several picosecond, [right angle bracket]100 A electron beams of up to 4 MeV in energy. These beams have been characterized by a variety of diagnostics. The quantum efficiency of the copper cathode used has been measured at normal incidence, and at 70 degrees incidence, where the polarization dependence was also examined. Limits on laser intensity due to surface damage, and to longitudinal space charge suppression of photoemission have been explored. The energy and energy spread of the beam were characterized using a dipole spectrometer, while the time structure was examined using a picosecond resolution streak camera. Both energy spread and pulse length were found to be adversely affected by longitundinal space charge forces. The emittance of the beam was measured using the pepper pot Technique, and its dependence on space charge and rf phase were found. The impact of these results on imporving the design and operation of high brightness photoinjectors is discussed, in particular with respect to SASE FEL amplifiers such as the UCLA 10mm FEL, and the proposed SLAC X-ray FEL. |
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| title: | Longitudinal Beam-Beam Effects in Circular Colliders |
| format: | conference procceeding |
| conference: | 1993 Particle Accelerator Conference |
| year: | 1993 |
| 2 authors: | | |
| abstract: | The longitudinal beam-beam interaction, which can lead to incoherent heating, synchrobctatron coupling, and coherent longitudinal instabilities in circular colliders, is examined. This analysis discusses two types of energy kicks, those due to the transverse particle motion coupling to the electric portion of the transverse kick, and those derived from the inductive electric field induced near the interaction, which is obtained from the transverse kick through use of a generalization of the Panofsky-Wenzel Theorem. Implications for low energy e+e- colliders (phi & B factories) with beams crossing head-on, and at finite angles, with and without crab crossing, are discussed. |
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| title: | The UCLA IR FEL project |
| format: | conference procceeding |
| conference: | 14th International Free Electron Laser Conference |
| year: | 1993 |
| 21 authors: | | | | | | | | | | | | | | | | | | | | | |
| abstract: | A 10.6 mu m free electron laser (FEL) operating in the high gain regime is under construction at UCLA. FEL physics significant to future short wavelength operation is emphasized including optical guiding, superradiance, saturation and self-amplified spontaneous emission (SASE). A 5 MeV RF photocathode gun illuminated by a UV laser supplies a high brightness electron beam which is injected into a plane wave transformer (PWT) linac for acceleration to 20 MeV. Recent measurements of the gun emittance as well as quantum efficiency are presented. The undulator is of a modified hybrid design producing approximately 7.5 kG peak field on axis with 5 mm gap spacing and 1.5 cm pole period. Simulation results which include three-dimensional effects are furnished. The present status and future plans of the project are summarized. (16 References). |
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| title: | DIELECTRIC WAKEFIELD ACCELERATOR EXPERIMENTS AT THE SABER FACILITY |
| format: | preprint |
| year: | |
| 17 authors: | | | | | | | | | | | | | | | | | |
| abstract: | Electron bunches with the unparalleled combination of high charge, low emittances, and short time duration, as first produced at the SLAC Final Focus Test Beam (FFTB), are foreseen to be produced at the SABER facility. These types of bunches have enabled wakefield driven accelerating schemes of multi-GV/m in plasmas. In the context of the Dielectric Wakefield Accelerators (DWA) such beams, having rms bunch length as short as 20 um, have been used to drive 100 um and 200 um ID hollow tubes above 20 GV/m surface fields. These FFTB tests enabled the measurement of a breakdown threshold in fused silica (with full data analysis still ongoing) [1]. With the construction and commissioning of the SABER facility at SLAC, new experiments would be made possible to test further aspects of DWAs including materials, tube geometrical variations, direct measurements of the Cerenkov fields, and proof of acceleration in tubes >10 cm in length. This collaboration will investigate breakdown thresholds and accelerating fields in new materials including CVD diamond. Here we describe the experimental plans, beam parameters, simulations, and progress to date as well as future prospects for machines based of DWA structures. |
| keywords: | pac 2007 |
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