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W.J. Brown

First Name: W.

Middle Name: J.

Last Name: Brown

Full Name: W.J. Brown

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7 papers

title: Adjustable, short focal length permanent-magnet quadrupole based electron beam final focus system

format: journal article

year: 2005

9 authors: J. K. Lim | P. Frigola | G. Travish | J. B. Rosenzweig | S.G. Anderson | W. J. Brown | J.S. Jacob | C.L. Robbins | A.M. Tremaine

abstract: Advanced high-brightness beam applicaitons such as inverse-Compton scattering (ICS) depend on achieving of ultra-small spot sizes in high current beams. Modern injectors and compressors enable the production of high-brightness beams having needed short bunch lengths and small emittances. Along with these beam properties comes the need to produce tighter foci, using stronger, shorter focal length optics. An approach to creating such strong focusing-systems using high field, small-bore permanent-magnet quadrupoles (PMQs) is reported here. A final focus system employing three PMQs, each composed of 16 neodymium iron boride sectors in a Halbach geometry has been installed in the PLEIADES ICS experiment. The field gradient in these PMQs is 560 T/m, the highest ever reported in a magnetic optics system. As the magnets are of a fixed field-strength, the focusing system is tuned by adjusting the position of the three magnets along the beamline axis, in analogy to familiar camera optics. This paper discusses the details of the focusing system, simulation, design, fabrication and experimental procedure in creating ultra-small beams at PLEIADES.

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title: Velocity bunching of high-brightness electron beams

format: journal article

year: 2005

11 authors: S. G. Anderson | P. Musumeci | J. B. Rosenzweig | W. J. Brown | R. J. England | M. Ferrario | J. S. Jacob | M. C. Thompson | G. Travish | A. M. Tremaine | R. Yoder

abstract: Velocity bunching has been recently proposed as a tool for compressing electron beam pulses in modernhigh brightness photoinjector sources. This tool is familiar from earlier schemes implemented for bunching dc electron sources, but presents peculiar challenges when applied to high current, low emittance beams from photoinjectors. The main difficulty foreseen is control of emittance oscillations in the beam in this scheme, which can be naturally considered as an extension of the emittance compensation process at moderate energies. This paper presents two scenarios in which velocity bunching, combined with emittance control, is to play a role in nascent projects. The first is termed ballistic bunching, where the changing of relative particle velocities and positions occur in distinct regions, a short high gradient linac, and a drift length. This scenario is discussed in the context of the proposed ORION photoinjector. Simulations are used to explore the relationship between the degree of bunching, and the emittance compensation process. Experimental measurements performed at the UCLA Neptune Laboratory of the surprisingly robust bunching process, as well as accompanying deleterious transverse effects, are presented. An unanticipated mechanism for emittance growth in bends for highly momentum chirped beam was identified and studied in these experiments. The second scenario may be designated as phase space rotation, and corresponds closely to the recent proposal of Ferrario and Serafini. Its implementation for the compression of the electron beam pulse length in the PLEIADES inverse Compton scattering (ICS) experiment at LLNL is discussed. It is shown in simulations that optimum compression may be obtained by manipulation of the phases in low gradient traveling wave accelerator sections. Measurements of the bunching and emittance control achieved in such an implementation at PLEIADES, as well as aspects of the use of velocity-bunched beam directly in ICS experiments, are presented.

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title: Ultra-High Density Electron Beams for Beam Radiation and Beam Plasma Interaction

format: conference procceeding

conference: 2005 Particle Accelerator Conference

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11 authors: G. Anderson | W.J. Brown | D.J. Gibson | F.V. Hartemann | J.S. Jacob | A.M. Tremaine | J.K. Lim | P. Frigola | P. Musumeci | J.B. Rosenzweig | G. Travish

abstract: Current and future applications of high brightness electron beams, which include advanced accelerators such as the plasma wake-field accelerator (PWFA) and beam radiation interactions such as inverse-Compton scattering (ICS), require both transverse and longitudinal beam sizes on the order of tens of microns. Ultra-high density beams may be produced at moderate energy (50 MeV) by compression and subsequent strong focusing of low emittance, photoinjector sources. We describe the implementation of this method used at the PLEIADES ICS x-ray source in which the photoinjector-generated beam has been compressed to 300 fsec duration using the velocity bunching technique and focused to 20 um rms size using an extremely high gradient, permanent magnet quadrupole (PMQ) focusing system.

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title: Pulse Compression via Velocity Bunching with the LLNL Thomson X-Ray Source Photoinjector

format: conference procceeding

conference: 2003 Particle Accelerator Conference

year: 2003

5 authors: S.G. Anderson | W. J. Brown | A.M. Tremaine | P. Musumeci | J. B. Rosenzweig

abstract: We report the compression of a high brightness, relativistic electron beam to rms lengths below 300 femtoseconds using the velocity compression technique in the LLNL Thomson X-ray source photoinjector. The results are consistent with analytical and computational models of this process. The emittance evolution of the beam during compression is investigated in simulation and found to be controllable with solenoid focusing.

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title: Generation of High Brightness X-Rays with the PLEIADES Thomson X-Ray Source

format: conference procceeding

conference: 2003 Particle Accelerator Conference

year: 2003

14 authors: W. J. Brown | S. Anderson | C. P. J. Barty | J. K. Crane | R. R. Cross | D. N. Fittinghoff | F. V. Hartemann | J. Kuba | G. P. Le Sage | D. R. Slaughter | P. T. Springer | A. Tremaine | J. B. Rosenzweig | D. J. Gibson

abstract: The use of short laser pulses to generate high peak intensity, ultra-short x-ray pulses enables exciting new experimental capabilities, such as femtosecond pump-probe experiments used to temporally resolve material structural dynamics on atomic time scales. PLEIADES (Picosecond Laser Electron InterAction for the Dynamic Evaluation of Structures) is a next generation Thomson scattering x-ray source being developed at Lawrence Livermore National Laboratory (LLNL). Ultra-fast picosecond x-rays (10-200 keV) are generated by colliding an energetic electron beam (20-100 MeV) with a high intensity, sub-ps, 800 nm laser pulse. The peak brightness of the source is expected to exceed 1020 photons/s/0.1 bandwidth/mm2/mrad2. Simulations of the electron beam production, transport, and final focus are presented. Electron beam measurements, including emittance and final focus spot size are also presented and compared to simulation results. Measurements of x-ray production are also reported and compared to theoretical calculations.

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title: Electron Beam Production and Characterization for the PLEIADES Thomson X-Ray Source

format: conference procceeding

conference: 10th Advanced Accelerator Concepts Workshop

year: 2002

13 authors: W. J. Brown | F. V. Hartemann | A. Tremaine | P. T. Springer | G. P. Le Sage | C. P. J. Barty | J. B. Rosenzweig | J. K. Crane | R. R. Cross | D. N. Fittinghoff | D. J. Gibson | D. R. Slaughter | S. Anderson

abstract: We report on the performance of an S-band RF photocathode electron gun and accelerator for operation with the PLEIADES Thomson x-ray source at LLNL. Simulations of beam production, transport, and focus are presented. It is shown that a 1 ps, 500 pC electron bunch with a normalized emittance of less than 5 Tcmm-mrad can be delivered to the interaction point. Initial electron measurements are presented. Calculations of expected x-ray flux are also performed, demonstrating an expected peak spectral brightness of 1020 photons/s/mm2/mrad2/0.1% bandwidth. Effects of RF phase jitter are also presented, and planned phase measurements and control methods are discussed.

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title: Experimental characterization of an ultrafast Thomson scattering x-ray source with three-dimensional time and frequency-domain analysis

format: journal article

year: 2004

18 authors: W. J. Brown | S. G. Anderson | C. P. J. Barty | S. M. Betts | R. Booth | J. K. Crane | R. R. Cross | D. N. Fittinghoff | D. J. Gibson | F. V. Hartemann | E. P. Hartouni | J. Kuba | G. P. Le Sage | D. R. Slaughter | A. M. Tremaine | A. J. Wootton | P. T. Springer | J. B. Rosenzweig

abstract: We present a detailed comparison of the measured characteristics of Thomson backscattered xrays produced at the Picosecond Laser-Electron Interaction for the Dynamic Evaluation of Structures facility at Lawrence Livermore National Laboratory to predicted results from a newly developed, fully three-dimensional time and frequency-domain code. Based on the relativistic differential cross section, this code has the capability to calculate time and space dependent spectra of the x-ray photons produced from linear Thomson scattering for both bandwidth-limited and chirped incident laser pulses. Spectral broadening of the scattered x-ray pulse resulting from the incident laser bandwidth, perpendicular wave vector components in the laser focus, and the transverse and longitudinal phase spaces of the electron beam are included. Electron beam energy, energy spread, and transverse phase space measurements of the electron beam at the interaction point are presented, and the corresponding predicted x-ray characteristics are determined. In addition, time-integrated measurements of the xrays produced from the interaction are presented and shown to agree well with the simulations.

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title:	Adjustable, short focal length permanent-magnet quadrupole based electron beam final focus system
format:	journal article
year:	2005
9 authors:	J. K. Lim \| P. Frigola \| G. Travish \| J. B. Rosenzweig \| S.G. Anderson \| W. J. Brown \| J.S. Jacob \| C.L. Robbins \| A.M. Tremaine
abstract:	Advanced high-brightness beam applicaitons such as inverse-Compton scattering (ICS) depend on achieving of ultra-small spot sizes in high current beams. Modern injectors and compressors enable the production of high-brightness beams having needed short bunch lengths and small emittances. Along with these beam properties comes the need to produce tighter foci, using stronger, shorter focal length optics. An approach to creating such strong focusing-systems using high field, small-bore permanent-magnet quadrupoles (PMQs) is reported here. A final focus system employing three PMQs, each composed of 16 neodymium iron boride sectors in a Halbach geometry has been installed in the PLEIADES ICS experiment. The field gradient in these PMQs is 560 T/m, the highest ever reported in a magnetic optics system. As the magnets are of a fixed field-strength, the focusing system is tuned by adjusting the position of the three magnets along the beamline axis, in analogy to familiar camera optics. This paper discusses the details of the focusing system, simulation, design, fabrication and experimental procedure in creating ultra-small beams at PLEIADES.
keywords:
Download \| View \| Details \| edit \| delete

title:	Velocity bunching of high-brightness electron beams
format:	journal article
year:	2005
11 authors:	S. G. Anderson \| P. Musumeci \| J. B. Rosenzweig \| W. J. Brown \| R. J. England \| M. Ferrario \| J. S. Jacob \| M. C. Thompson \| G. Travish \| A. M. Tremaine \| R. Yoder
abstract:	Velocity bunching has been recently proposed as a tool for compressing electron beam pulses in modernhigh brightness photoinjector sources. This tool is familiar from earlier schemes implemented for bunching dc electron sources, but presents peculiar challenges when applied to high current, low emittance beams from photoinjectors. The main difficulty foreseen is control of emittance oscillations in the beam in this scheme, which can be naturally considered as an extension of the emittance compensation process at moderate energies. This paper presents two scenarios in which velocity bunching, combined with emittance control, is to play a role in nascent projects. The first is termed ballistic bunching, where the changing of relative particle velocities and positions occur in distinct regions, a short high gradient linac, and a drift length. This scenario is discussed in the context of the proposed ORION photoinjector. Simulations are used to explore the relationship between the degree of bunching, and the emittance compensation process. Experimental measurements performed at the UCLA Neptune Laboratory of the surprisingly robust bunching process, as well as accompanying deleterious transverse effects, are presented. An unanticipated mechanism for emittance growth in bends for highly momentum chirped beam was identified and studied in these experiments. The second scenario may be designated as phase space rotation, and corresponds closely to the recent proposal of Ferrario and Serafini. Its implementation for the compression of the electron beam pulse length in the PLEIADES inverse Compton scattering (ICS) experiment at LLNL is discussed. It is shown in simulations that optimum compression may be obtained by manipulation of the phases in low gradient traveling wave accelerator sections. Measurements of the bunching and emittance control achieved in such an implementation at PLEIADES, as well as aspects of the use of velocity-bunched beam directly in ICS experiments, are presented.
keywords:
Download \| View \| Details \| edit \| delete

title:	Ultra-High Density Electron Beams for Beam Radiation and Beam Plasma Interaction
format:	conference procceeding
conference:	2005 Particle Accelerator Conference
year:
11 authors:	G. Anderson \| W.J. Brown \| D.J. Gibson \| F.V. Hartemann \| J.S. Jacob \| A.M. Tremaine \| J.K. Lim \| P. Frigola \| P. Musumeci \| J.B. Rosenzweig \| G. Travish
abstract:	Current and future applications of high brightness electron beams, which include advanced accelerators such as the plasma wake-field accelerator (PWFA) and beam radiation interactions such as inverse-Compton scattering (ICS), require both transverse and longitudinal beam sizes on the order of tens of microns. Ultra-high density beams may be produced at moderate energy (50 MeV) by compression and subsequent strong focusing of low emittance, photoinjector sources. We describe the implementation of this method used at the PLEIADES ICS x-ray source in which the photoinjector-generated beam has been compressed to 300 fsec duration using the velocity bunching technique and focused to 20 um rms size using an extremely high gradient, permanent magnet quadrupole (PMQ) focusing system.
keywords:	pbpl
Download \| View \| Details \| edit \| delete

title:	Pulse Compression via Velocity Bunching with the LLNL Thomson X-Ray Source Photoinjector
format:	conference procceeding
conference:	2003 Particle Accelerator Conference
year:	2003
5 authors:	S.G. Anderson \| W. J. Brown \| A.M. Tremaine \| P. Musumeci \| J. B. Rosenzweig
abstract:	We report the compression of a high brightness, relativistic electron beam to rms lengths below 300 femtoseconds using the velocity compression technique in the LLNL Thomson X-ray source photoinjector. The results are consistent with analytical and computational models of this process. The emittance evolution of the beam during compression is investigated in simulation and found to be controllable with solenoid focusing.
keywords:
Download \| View \| Details \| edit \| delete

title:	Generation of High Brightness X-Rays with the PLEIADES Thomson X-Ray Source
format:	conference procceeding
conference:	2003 Particle Accelerator Conference
year:	2003
14 authors:	W. J. Brown \| S. Anderson \| C. P. J. Barty \| J. K. Crane \| R. R. Cross \| D. N. Fittinghoff \| F. V. Hartemann \| J. Kuba \| G. P. Le Sage \| D. R. Slaughter \| P. T. Springer \| A. Tremaine \| J. B. Rosenzweig \| D. J. Gibson
abstract:	The use of short laser pulses to generate high peak intensity, ultra-short x-ray pulses enables exciting new experimental capabilities, such as femtosecond pump-probe experiments used to temporally resolve material structural dynamics on atomic time scales. PLEIADES (Picosecond Laser Electron InterAction for the Dynamic Evaluation of Structures) is a next generation Thomson scattering x-ray source being developed at Lawrence Livermore National Laboratory (LLNL). Ultra-fast picosecond x-rays (10-200 keV) are generated by colliding an energetic electron beam (20-100 MeV) with a high intensity, sub-ps, 800 nm laser pulse. The peak brightness of the source is expected to exceed 1020 photons/s/0.1 bandwidth/mm2/mrad2. Simulations of the electron beam production, transport, and final focus are presented. Electron beam measurements, including emittance and final focus spot size are also presented and compared to simulation results. Measurements of x-ray production are also reported and compared to theoretical calculations.
keywords:
Download \| View \| Details \| edit \| delete

title:	Electron Beam Production and Characterization for the PLEIADES Thomson X-Ray Source
format:	conference procceeding
conference:	10th Advanced Accelerator Concepts Workshop
year:	2002
13 authors:	W. J. Brown \| F. V. Hartemann \| A. Tremaine \| P. T. Springer \| G. P. Le Sage \| C. P. J. Barty \| J. B. Rosenzweig \| J. K. Crane \| R. R. Cross \| D. N. Fittinghoff \| D. J. Gibson \| D. R. Slaughter \| S. Anderson
abstract:	We report on the performance of an S-band RF photocathode electron gun and accelerator for operation with the PLEIADES Thomson x-ray source at LLNL. Simulations of beam production, transport, and focus are presented. It is shown that a 1 ps, 500 pC electron bunch with a normalized emittance of less than 5 Tcmm-mrad can be delivered to the interaction point. Initial electron measurements are presented. Calculations of expected x-ray flux are also performed, demonstrating an expected peak spectral brightness of 1020 photons/s/mm2/mrad2/0.1% bandwidth. Effects of RF phase jitter are also presented, and planned phase measurements and control methods are discussed.
keywords:
Download \| View \| Details \| edit \| delete

title:	Experimental characterization of an ultrafast Thomson scattering x-ray source with three-dimensional time and frequency-domain analysis
format:	journal article
year:	2004
18 authors:	W. J. Brown \| S. G. Anderson \| C. P. J. Barty \| S. M. Betts \| R. Booth \| J. K. Crane \| R. R. Cross \| D. N. Fittinghoff \| D. J. Gibson \| F. V. Hartemann \| E. P. Hartouni \| J. Kuba \| G. P. Le Sage \| D. R. Slaughter \| A. M. Tremaine \| A. J. Wootton \| P. T. Springer \| J. B. Rosenzweig
abstract:	We present a detailed comparison of the measured characteristics of Thomson backscattered xrays produced at the Picosecond Laser-Electron Interaction for the Dynamic Evaluation of Structures facility at Lawrence Livermore National Laboratory to predicted results from a newly developed, fully three-dimensional time and frequency-domain code. Based on the relativistic differential cross section, this code has the capability to calculate time and space dependent spectra of the x-ray photons produced from linear Thomson scattering for both bandwidth-limited and chirped incident laser pulses. Spectral broadening of the scattered x-ray pulse resulting from the incident laser bandwidth, perpendicular wave vector components in the laser focus, and the transverse and longitudinal phase spaces of the electron beam are included. Electron beam energy, energy spread, and transverse phase space measurements of the electron beam at the interaction point are presented, and the corresponding predicted x-ray characteristics are determined. In addition, time-integrated measurements of the xrays produced from the interaction are presented and shown to agree well with the simulations.
keywords:	pbpl
Download \| View \| Details \| edit \| delete

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