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B. O'Shea

First Name: Brendan

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Last Name: O'Shea

Full Name: B. O'Shea

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17 papers
title: Gigavolt-per-Meter Wakefields in Annular Dielectric Structures
format: thesis
year: 2014
1 author: B.O'Shea
abstract: A wakefield accelerator uses a medium capable of sustaining appropriate electric fields to transfer energy from a drive beam to a witness beam. Examples of such systems include electron beam driven plasma wakefields [1, 2], laser driven plasma wakefields [3] and electron beam driven dielectric wakefield structures [4, 5, 6]. Dielectrics and plasmas are of particular interest because they are capable of maintaining electric fields on the order of GVm −1 and in the case of plasmas upwards of TVm −1 [7]. These systems provide a significant step beyond current radiofrequency accelerating structures capable of peak electric fields on the order of 100 MVm −1 and average effective electric fields of 20 MVm −1 [8]. Furthermore, beam driven dielectric structures produce a wakefield which is phase synchronous with the beam, these structures do not suffer from transit time or dephasing effects [9, 10]. In the case of dielectric wakefield accelerators, the structures under study in this publication, the modes generated by the driving beam are in the terahertz (THz) regime. Thus development of dielectric wakefield accelerators is seen as a path to smaller, more compact accelerating systems and as a means to generate THz radiation [11]. Here we demonstrate a beam-driven iidielectric wakefield accelerating structure that produces sustained fields of 1.35 GVm −1 for many hundreds of thousands of drive beam pulses. In addition we show beam-driven dielectric structures have the potential to produce single mode, high spectral purity THZ radiation of unprecedented energy scale.
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title: Beyond Injection: Trojan Horse Underdense Photocathode Plasma Wakefield Acceleration
format: conference proceeding
conference: AAC 2012 15th
year: 2012
18 authors: B. Hidding | J.B. Rosenzweig | Y.Xi | B. O'Shea | G. Andonian | D. Schiller | S. Barber | O. Williams | G. Pretzler | T. Königstein | F. Kleeschulte | M.J. Hogan | M. Litos | S. Corde | W.W. White | P. Muggli | D.L. Bruhwiler | K. Lotov
abstract: An overview on the underlying principles of the hybrid plasma wakefield acceleration scheme dubbed ”Trojan Horse” acceleration is given. The concept is based on laser-controlled release of electrons directly into a particle-beam- driven plasma blowout, paving the way for controlled, shapeable electron bunches with ultralow emittance and ultrahigh brightness. Combining the virtues of a low-ionization-threshold underdense photocathode with the GV/m-scale electric fields of a practically dephasing-free beam-driven plasma blowout, this constitutes a 4th generation electron acceleration scheme. It is applicable as a beam brightness transformer for electron bunches from LWFA and PWFA systems alike. At FACET, the proof-of-concept experiment ”E-210: Trojan Horse Plasma Wakefield Acceleration” has recently been approved and is in preparation. At the same time, various LWFA facilities are currently considered to host experiments aiming at stabilizing and boosting the electron bunch output quality via a trojan horse afterburner stage. Since normalized emittance and brightness can be improved by many orders of magnitude, the scheme is an ideal candidate for light sources such as free-electron-lasers and those based on Thomson scattering and betatron radiation alike.
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title: Dielectric Wakefield Acceleration of a Relativistic Electron Beam in a Slab-Symmetric Dielectric Lined Waveguide
format: journal article
publisher: Physical Review Letters
year: 15 June 2012
13 authors: G. Andonian | D. Stratakis | M. Babzien | S. Barber | M. Fedurin | E. Hemsing | K. Kusche | P. Muggli | B. O'Shea | X. Wei | O. Williams | V. Yakimenko | and J.B. Rosenzweig
abstract: We report first evidence of wakefield acceleration of a relativistic electron beam in a dielectric-lined slab-symmetric structure. The high energy tail of a ?60??MeV electron beam was accelerated by ?150??keV in a 2 cm-long, slab-symmetric SiO2 waveguide, with the acceleration or deceleration clearly visible due to the use of a beam with a bifurcated longitudinal distribution that serves to approximate a driver-witness beam pair. This split-bunch distribution is verified by longitudinal reconstruction analysis of the emitted coherent transition radiation. The dielectric waveguide structure is further characterized by spectral analysis of the emitted coherent Cherenkov radiation at THz frequencies, from a single electron bunch, and from a relativistic bunch train with spacing selectively tuned to the second longitudinal mode (TM02). Start-to-end simulation results reproduce aspects of the electron beam bifurcation dynamics, emitted THz radiation properties, and the observation of acceleration in the dielectric-lined, slab-symmetric waveguide.
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title: Breaking the Attosecond, Angstrom and TV/m Field Barriers with Ultrafast Electron Beams
format: conference proceeding
conference: AAC 2010 14th
year: 2010
17 authors: J.B. Rosenzweig | G. Andonian | P. Bucksbaum | A. Fukasawa | M. Ferrario | M. Hogan | E. Hemsing | P. Krejcik | G. Marcus | A. Marinelli | P. Muggli | P. Musumeci | B. O'Shea | F. O'Shea | C. Pellegrini | D. Schiller | G. Travish
abstract: Recent initiatives at UCLA concerning ultra-short, GeV electron beam generation have been aimed at achieving sub-fs pulses capable of driving X-ray free-electron lasers (FELs) in single-spike mode. This scheme uses very low charge beams, which may allow existing FEL injectors to produce few-100 attosecond pulses, with very high brightness. Towards this end, recent experiments at the Stanford X-ray FEL (LCLS, first of its kind, built with essential UCLA leadership) have produced ~2 fs, 20 pC electron pulses. We discuss here extensions of this work, in which we seek to exploit the beam brightness in FELs, in tandem with new developments at UCLA in cryogenic undulator technology, to create compact accelerator/undulator systems that can lase below 0.15 Å, or be used to permit 1.5 Å operation at 4.5 GeV. In addition, we are now developing experiments which use the present LCLS fs pulses to excite plasma wakefields exceeding 1 TV/m, permitting a table-top TeV accelerator for frontier high energy physics applications. We discuss the experimental issues associated with this initiative.
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title: DEVELOPMENT OF A 1.5+0.5 CELL PHOTOINJECTOR
format: journal article
publisher: PAC 09 Proceedings
year: 2009
6 authors: B. O'Shea | J.B. Rosenzweig | Luigi Faillace | A. Fukasawa | Joshua Moody | Pietro Musumeci
abstract: We present the development and status of a traditional UCLA/BNL/SLAC style 1.5 cell photoinjector with an additional half cell downstream to aid in longitudinal pulse compression. The work presented includes radio frequency design via SuperFish and HFSS as well as beam dynamics simulation using PARMELA. We investigate longitudinal compression of an electron beam in this extra downstream half cell and show shorter final beam lengths at the cost of transverse beam quality, when compared with traditional 1.6 cell systems.
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title: Novel Radio-Frequency Gun Structures For Ultrafast Relativistic Electron Diffraction
format: journal article
publisher: Microscopy and Microanalysis
year: 2009
7 authors: P. Musumeci | L. Faillace | A. Fukasawa | J.T. Moody | B. O'Shea | J.B. Rosenzweig | C.M. Scoby
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: Status of the Fermi@Elettra Photoinjector
format: conference proceeding
conference: EPAC 2008
year: 2008
21 authors: M. Trovo | L. Badano | S. Biedron | D. Castronovo | F. Cianciosi | P. Craievich | M.D. Danailov | G.DAuria | M. Ferianis | S.V. Milton | G. Penco | L. Pivetta | L. Rumiz | D. Wang | M. Eriksson | D. Kumbaro | F. Lindau | H. Badakov | A. Fukasawa | B. O'Shea | J.B. Rosenzweig
abstract: The new FERMI@Elettra photoinjector is presently undergoing high-power testing and characterization at MAXlab in Lund, Sweden. This effort is a collaboration between Sincrotrone Trieste, MAX-lab and UCLA. The 1.6-cell RF gun cavity and the focusing solenoid were successfully designed and built by the Particle Beam Physics Laboratory at UCLA, delivered to Sincrotrone Trieste at the beginning of 2008, and installed in the linac tunnel at MAX-lab. Use of the MAX-lab facility will allow the FERMI project to progress significantly with the photoinjector while waiting for the completion of the new linac building extension at Sincrotrone Trieste. We report here on the high-power conditioning of the RF cavity and the first beam tests.
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title: commissioning of the UCLA Neptune X-Band Deflecting Cavity and Applications to Current Profile Measurement of Ramped Electron Bunches
format: conference proceeding
conference: PAC 2007
year: 2007
5 authors: R. J. England | B. O'Shea | J.B. Rosenzweig | G. Travish | D. Alesini
abstract: A 9-cell standing wave deflecting cavity has recently been constructed and installed at the UCLA Neptune Laboratory for use as a temporal diagnostic for the 13 MeV, 300 to 700 pC electron bunches generated by the Neptune photoinjector beamline. The cavity is a center-fed Glid-Cop structure operating in at TM110-like deflecting mode at 9.59616 GHz with a pi phase advance per cell. At the maximum deflecting voltage of 500 kV, the theoretical resolution limit of the device is 50 fs, although with current beam parameters and a spot size of 460 microns RMS the effective resolution is approximately 400 fs. We discuss the operation and testing of the cavity as well as its intended application: measuring the temporal current profile of ramped electron bunches generated using the Neptune dogleg compressor, and we present the first measurements of the electron beam current profile obtained using the deflecting cavity.
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title: The FINDER Photoinjector
format: conference proceeding
conference: PAC 2007
year: 2007
6 authors: A. Fukasawa | H. Badakov | B. O'Shea | E. Hemsing | J.B. Rosenzweig | S. G. Anderson
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.
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title: Commissioning of the UCLA Neptune X-band Deflecting Cavity and Applications to Current Profile Measurement of Ramped Electron Bunches
format: conference proceeding
conference: PAC 2007
year: 2007
5 authors: R.J. England | B. O'Shea | J.B. Rosenzweig | G. Travish | D. Alesini
abstract: A 9-cell standing-wave deflecting cavity has recently been constructed and installed at the UCLA Neptune Lab- oratory for use as a temporal diagnostic for the 13 MeV, 300 to 700 pC electron bunches generated by the Neptune photoinjector beamline. The cavity is a center-fed Glid- Cop structure operating in at TM110-like deflecting mode at 9.59616 GHz with a ? phase advance per cell. At the maximum deflecting voltage of 530 kV, the theoretical res- olution limit of the device is 50 fs, although with current beam parameters and a RMS spot size of 460 ?m the ef- fective resolution is approximately 400 fs. We discuss the operation and testing of the cavity as well as its intended application of measuring the temporal current profile of ramped electron bunches generated using the Neptune dog- leg compressor, and we present the first measurements of the electron beam current profile obtained using the deflect- ing cavity.
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title: The New Photoinjector for the Fermi Project
format: conference proceeding
conference: PAC 2007
year: 2007
14 authors: G. D'Auria | D. Bacescu | L. Badano | F. Cianciosi | P. Craievich | M. Danailov | G. Penco | L. Rumiz | M. Trovo' | A. Turchet | H. Badakov | A. Fukusawa | B. O'Shea | J.B. Rosenzweig
abstract: FERMI@elettra is a single-pass FEL user facility covering the spectral range 100-10 nm. It will be located near the Italian third generation Synchrotron Light Source facility ELETTRA and will make use of the existing 1.0 GeV normal conducting Linac [1]. To obtain the high beam brightness required by the project, the present Linac electron source will be substituted with a photocathode RF gun now under development in the framework of a collaboration between Sincrotrone Trieste (ST) and Particle Beam Physics Laboratory (PBPL) at UCLA. The new gun will use an improved design of the 1.6 cell accelerating structure already developed at PBPL, scaled to 2998 MHz. We expect that the new gun design will allow a beam brightness increase by a factor 3-4 over the older version of the device. Some technical choices of the new design, including the enhancement of the mode separation, removal of the RF tuners, full cell symmetrization to limit the dipole and quadrupole RF field as well as an improved solenoid yoke design for multipole field corrections, will be discussed.
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title: Commissioning of a High-Brightness Photoinjector for Compton Scattering X-Ray Sources
format: conference proceeding
conference: PAC 2007
year: 2007
13 authors: S. G. Anderson | C. P. J. Barty | D. J. Gibson | F. V. Hartemann | M. Messerly | M. Shverdin | C. W. Siders | A. M. Tremaine | H. Badakov | P. Frigola | A. Fukasawa | B. O'Shea | J.B. Rosenzweig
abstract: Compton scattering of intense laser pulses with ultra- relativistic electron beams has proven to be an attractive source of high-brightness x-rays with keV to MeV ener- gies. This type of x-ray source requires the electron beam brightness to be comparable with that used in x-ray free- electron lasers and laser and plasma based advanced accel- erators. We describe the development and commissioning of a 1.6 cell RF photoinjector for use in Compton scatter- ing experiments at LLNL. Injector development issues such as RF cavity design, beam dynamics simulations, emit- tance diagnostic development, results of sputtered magne- sium photo-cathode experiments, and UV laser pulse shap- ing are discussed. Initial operation of the photoinjector is described.
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title: Experiment to Measure Ramped Electron Bunches at the UCLA Neptune Laboratory Using a Transverse Deflecting Cavity
format: conference proceeding
conference: AAC 2006 12th
year: 2006
5 authors: R. J. England | D. Alesini | B. O'Shea | J.B. Rosenzweig | G. Travish
abstract: A proof of principle experiment is underway at the UCLA Neptune laboratory to test the concept of generating linearly ramped relativistic electron bunches (rising in density from head to tail followed by a sharp cutoff) by using a sextupole-corrected dogleg section as a bunch compressor. Bunches with this structure have been predicted to be ideal for use as a plasma wake-field drive beam. The diagnostic being developed to measure the time profile of the beam is an X-Band (9.6 GHz) deflecting cavity. The recently completed cavity is a 9-cell standing wave structure operating in a TM110-like mode, designed to measure the temporal structure of the 2 to 10 ps, 14 MeV electron bunches generated by the Neptune S-band photoinjector and plane-wave transformer (PWT) accelerator beamline, with 50 fs resolution. We discuss the experimental plan for the ramped bunch experiment and present preliminary data related to the tuning and operation of the deflecting cavity.
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title: Beam Dynamics in a Hybrid Standing Wave-Traveling Wave Photoinjector
format: conference proceeding
conference: AAC 2006 12th
year: 2006
11 authors: J.B. Rosenzweig | D. Alesini | A. Boni | M. Ferrario | L. Ficcadenti | A. Fukusawa | A. Mostacci | B. O'Shea | L. Palumbo | B. Spataro | V. Fusco
abstract: We discuss the dynamics of of a photoinjector beam in a hybrid traveling wave-standing wave photoinjector. With the field profile deduced from electromagnetic simulations, it is seen that the acceleration program induces strong velocity bunching. The beam dynamics in this scenario are explored using UCLA PARMELA. With a solenoid field overlaid on the TW section one may control emittance oscillations during bunching and acceleration. It is seen that the S-band device currently under development at UCLA may produce a 1 nC, 21 MeV, 100 micron rms pulse length beam, with emittance of 3 mm-mrad. Applications of this beam for creating coherent radiation are discussed.
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title: RF Design of the UCLA/INFN Hybrid SW/TW Photoinjector
format: conference proceeding
conference:
year: 2006
9 authors: J.B. Rosenzweig | Alessandro Boni | A. Fukasawa | D. Alesini | Massimo Ferrario | Bruno Spataro | Luca Ficcadenti | Andrea Palumbo | B. O'Shea
abstract: With increasing demand for high brightness, low emittance beams for use with freeelectron lasers, Compton scattering systems and wake-field accelerator experiments, stringent requirements have been placed on the design and operation of the 1.6 cell photoinjector. The proposed hybrid photoinjector combines the BNL/UCLA/SLAC style 1.5/1.6 cell standing wave gun with a traveling wave accelerator. Our goal is an injector that meets todays requirements and is scalable in design to meet tomorrows demands: emittances in the region of 1 mm-mrad for higher brightness as well as higher currents. The hybrid photoinjector also offers higher energy operation, enhanced cost effectiveness and better scalability than current designs such as integrated PWT photoinjectors and split gun/accelerating sections. The use of both SW and TW systems allows for higher gradients (Eo = 70 MV/m) in the SW gun for effective capture at lower emittances, while the lower energy acceleration in the TW sections (Eo = 13.5 MV/m) allows generation of higher energy beams which are less sensitive to space charge effects. We note the current results of simulation of beam dynamics, en,x = 3 mm-mrad, an energy spread of 1.5% with beam energies of 21 MeV at currents as high as 1.2 kA. Further we explore the possibilities of scalability to higher frequencies, analysis of coupling design, present cold test preparations and simulated RF analysis of the structure.
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title: The Design of a Hybrid Photoinjector for High Brightness Beam Applications
format: conference proceeding
conference: EPAC 2006
year: 2006
10 authors: D. Alesini | M. Ferrario | V. Fusco | B. Spataro | L. Ficcadenti | A. Mostacci | L. Palumbo | B. O'Shea | J.B. Rosenzweig | G. Travish
abstract: In this paper, we illustrate the electromagnetic and beam dynamics design procedure of a new class of photoinjector, a hybrid standing/traveling wave structure. In this device a standing wave RF gun section is integrated with a downstream traveling wave structure through a coupling cell that feeds simultaneously the two sections. We discuss the advantages in RF and beam performance of the hybrid photoinjector compared to conventional systems. The electromagnetic design has been performed using the 3D electromagnetic code HFSS. Results of beam dynamics simulations in different operating conditions are also discussed.
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title: X-Band Dipole Mode Deflecting Cavity for the UCLA Neptune Beamline
format: conference proceeding
conference: PAC 2005
year: 2005
5 authors: R. J. England | B. O'Shea | J.B. Rosenzweig | G. Travish | D. Alesini
abstract: We report progress on the design and construction of a nine-cell cavity operating in a TM110-like dipole mode for use as a temporal diagnostic of the 14 MeV, 300 pC electron bunches generated at the UCLA Neptune Laboratory linear accelerator, with an anticipated temporal resolution of 50 fs at a peak input power of 50 kW. The cavity is a center-fed standing-wave pi-mode structure, operating at 9.6 GHz, and incorporating a knife-edge and gasket assembly which minimizes the need for brazing or welding. Results of initial RF testing of the prototype cavity are discussed and compared with simulation results obtained using the commercial code HFSS.
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