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A.M. Cook

First Name: A. M.

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Last Name: Cook

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16 papers

title: Beam compression experiments using the UCLA/ATF compressor

format: conference procceeding

conference:

year: 2006

13 authors: D. Schiller | E. Hemsing | J. B. Rosenzweig | M.P. Dunning | G. Andonian | A. Murokh | A.M. Cook | S. Reiche | M. Babzien | K. Kusche | V. Yakimenko | L. Palumbo | C. Vicario

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.

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title: Magnetic Chicane Radiation Studies at the BNL ATF

format: conference procceeding

conference:

year: 2006

11 authors: M.Dunning | G. Andonian | A.M.Cook | E.Hemsing | A.Murokh | S. Reiche | J. B. Rosenzweig | D. Schiller | M. BABZIEN | K. Kusche | V. Yakimenko

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.

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title: Optinum Beam Creation In Photoinjectors Using Space-Charge Expansion

format: conference procceeding

conference:

year: 2006

16 authors: J. B. Rosenzweig | A.M. Cook | M. Dunning | R. J. England | M. Bellaveglia | M. Boscolo | L. Catani | A. Cianchi | G. Di Pirro | M. Gerrario | D. Filippetto | G. Gatti | P. Musumeci | L. Palumbo | C. Vicario | S. Jones

abstract: It has recently been shown that by illuminating a photocathode with an ultra-short laser pulse of appropriate transverse profile, a uniform density, ellipsoidally shaped bunch is dynamically formed, which then has linear space-charge fields in all dimensions inside of the bunch. We study here this process, and its marriage to the standard emittance compensation scenario that is implemented in most modern photoinjectors. It is seen that the two processes are compatible, with simulations indicating that a very high brightness beam can be obtained. The scheme has produced stimulus for a series of experiments at the SPARC injector at Frascati in 2006-2007. An initial time-resolved experiment has been performed involving Cerenkov radiation produced at an aerogel. We discuss the results of this preliminary experiment, as well as plans for future experiments to resolve the ellipsoidal bunch shape at low energy. Future measurements at high energy based on fs resolution RF sweepers are discussed.

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title: Dielectric Wakefield Accelerating Structure as a Source of Terahertz Coherent Cerenkov Radiation

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year:

8 authors: A.M. Cook | J. B. Rosenzweig | M.C Thompson | H. Badakov | G. Travish | R. Tikhoplav | O.B. Williams | R. J. England

abstract: We discuss future experimental work proposed to study the performance of a cylindrical dielectric wakefield accelerating structure as a coherent Cerenkov radiation source at the Neptune laboratory at UCLA. The Cerenkov wakefield acceleration experiment carried out recently by UCLA/SLAC/USC, using the ultrashort and high charge beam (Q = 3 nC, RMS bunch length = 20 micron) at the SLAC FFTB, demonstrated electromagnetic wakes at the few GV/m level. The motivation of our prospective experiment is to investigate the operation of a similar scenario using the comparatively long pulse, low charge beam (Q = 0.5 nC, RMS bunch length = 200 micron) at UCLA Neptune. The field amplitude produced in this setup would be one to two orders of magnitude lower, at the few tens to few 100 MV/m level. Such a decelerating field would extract a significant amount of energy from a low-energy beam in a distance on the order of a few centimeters, allowing the use of short dielectric structures. We discuss details of the geometry and composition of the structures to be used in the experiment. We also examine the possibility of a future dedicated facility at UCLA Neptune based on a hybrid photoinjector currently in development. The intrinsic bunch compression capabilities and improved beam parameters (RMS bunch length = 100 micron, Q = 1 nC) of the photoinjector would allow the creation of a high power radiation source in the terahertz regime.

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title: EXPERIMENTAL TESTING OF DYNAMICALLY OPTIMIZED PHOTOELECTRON BEAMS

format: conference procceeding

conference: Erice 2005

year: 2006

16 authors: James Rosenzweig | A.M. Cook | M. Dunning | R. J. England | P. Musumeci | M. Bellaveglia | M. Boscolo | L. Catani | A. Cianchi | G. Di Pirro | M. Ferrario | D. Fillipetto | G. Gatti | L. Palumbo | L. Sserafini | C. Vicario

abstract: We discuss the design of and initial results from an experiment in space-charge dominated beam dynamics which explores a new regime of high-brightness electron beam generation at the SPARC (located at INFN-LNF, Frascati) photoinjector. The scheme under study employs the natural tendency in intense electron beams to configure themselves to produce a uniform density, giving a nearly ideal beam from the viewpoint of space charge-induced emittance. The experiments are aimed at testing the marriage of this idea with a related concept, emittance compensation, We show that the existing infrastructure at SPARC is nearly ideal for the proposed tests, and that this new regime of operating photoinjector may be the preferred method of obtaining highest brightness beams with lower energy spread. We discuss the design of the experiment, including developing of a novel time-dependent, aerogel-based imaging system. This system has been installed at SPARC, and first evidence for nearly uniformly filled ellipsoidal charge distributions recorded.

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title: Effects of Ion Motion in Intense Beam-Driven Plasma Wakefield Accelerators

format: journal article

year: 2005

5 authors: J. B. Rosenzweig | A. M. Cook | A. Scott | M. C. Thompson | R. B. Yoder

abstract: Recent proposals for using plasma wakefield accelerators (PWFA) as a component of a linear collider have included intense electron beams with densities many times in excess of the plasma density. The beam’s electric fields expel the plasma electrons from the beam path to many beam radii in this regime. We analyze here the motion of plasma ions under the beam fields, and find for a proposed PWFA collider scenario that the ions completely collapse inside of the beam. Simulations of ion collapse are presented. Implications of ion motion on the feasibility of the PWFA-based colliders are discussed.

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title: RF AND MAGNETIC MEASUREMENTS ON THE SPARC PHOTOINJECTOR AND SOLENOID AT UCLA

format: conference procceeding

conference: 2005 Particle Accelerator Conference

year: 2005

8 authors: J. B. Rosenzweig | A.M. Cook | M.P. Dunning | P. Frigola | G. Travish | C. Sanelli | F. Tazzioli | D. T. Palmer

abstract: The rf photocathode gun and the solenoid for the SPARC project at INFN-LNF (Frascati) have been fabricated and undergone initial testing at UCLA. The advanced aspects of the design of these devices are detailed. Final diagnosis of the tuning of the RF gun performance, including operating mode frequency and field balance, is described. The emittance compensating solenoid magnet, which is designed to be tuned in longitudinal position by differential excitation of the coils, has been measured using Hall probe scans for field profiling, and pulsed wire methods to determine the field center. Comparisons between measurements and the predictions of design codes are made.

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title: Emittance compensation with dynamically optimized photoelectron beam profiles

format: journal article

year: 2005

4 authors: J. B. Rosenzweig | A.M. Cook | M. Dunning | M. Ferrario

abstract: Much of the theory and experimentation concerning creation of a high-brightness electron beam from a photocathode, and then applying emittance compensation techniques, assumes that one must strive for a uniform density electron beam, having a cylindrical shape. On the other hand, this shape has large nonlinearities in the space-charge field profiles near the beam

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title: Mitigation of RF Gun Breakdown by Removal of Tuning Rods in High Field Regions

format: conference procceeding

conference: 2007 Particle Accelerator Conference

year:

5 authors: A. M. Cook | M.P. Dunning | J. B. Rosenzweig | K. Serratto | P. Frigola

abstract: The pi-mode resonant frequency of the 1.6 cell SLAC/BNL/UCLA style RF photoinjector electron gun is conventionally tuned using cylindrical copper tuning pieces that extend into the full-cell cavity through holes in the side of the gun. This design begins to fail in many versions of this popular gun design at higher voltage levels, when the cavity undergoes electric breakdown in the vicinity of the tuners. In order to remove the tuners from the region of high electric field, mitigating this problem, one must change the full cell geometry significantly. We have investigated a method for accomplishing this, in which we stretch the gun structure to tune the resonant frequency up by over 2 MHz. We constructed a device to perform this stretching and tested the modified photoinjector in an RF test bed. We succeeded in putting approximately 8.4 MW of RF power into the gun, an improvement over the 4 MW routinely achieved with a similar gun using conventional tuning methods installed at the UCLA Neptune laboratory. Recent results in testing this gun with a magnesium cathode insert are reported as well.

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title: The Effects of Ion Motion in Very Intense Beam-driven Plasma Wakefield Accelerators

format: conference procceeding

conference:

year: 2004

4 authors: J. B. Rosenzweig | A.M. Cook | M.C. Thompson | R. B. Yoder

abstract: Recent proposals for using plasma wakefield accelerators in the blowout regime as a component of a linear collider have included very intense driver and accelerating beams, which have densities many times in excess of the ambient plasma density. The electric fields of these beams are widely known to be large enough to completely expel plasma electrons from the beam path; the expelled electrons often attain relativistic velocities in the process. We examine here another aspect of this high-beam density scenario: the motion of ions. In the lowest order analysis, for both cylindrically symmetric and

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title: Beam-Driven Dielectric Wakefield Accelerating Structure as a THz Radiation Source

format: preprint

year: 2007

9 authors: A. Kanareykin | O.B. Williams | R. Tikhoplav | A.M. Cook | H. Badakov | J. B. Rosenzweig | G. Travish | M.C Thompson | R. J. England

abstract: Experimental work is planned to study the performance of a beam-driven cylindrical dielectric wakefield accelerating structure as a source of THz coherent Cerenkov radiation (CCR). For an appropriate choice of dielectric tube geometry and driving electron bunch parameters, the device operates in a single-mode regime, producing radiation in the THz range. This source can potentially produce high power levels relative to currently available sources, with ~50 uJ radiated energy per pulse achievable using the electron beam currently in operation at the Neptune advanced accelerator laboratory at UCLA (~13 MeV beam energy, ~200 um RMS bunch length, ~500 pC bunch charge). Preparations underway for installation of the experiment are discussed.

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title: MITIGATION OF ELECTRIC BREAKDOWN IN AN RF PHOTOINJECTOR BY REMOVAL OF TUNING RODS IN HIGH-FIELD REGIONS

format: preprint

year: 2007

5 authors: K. Serratto | P. Frigola | J. B. Rosenzweig | M.P. Dunning | A.M. Cook

abstract: The pi-mode resonant frequency of the 1.6 cell SLAC/BNL/UCLA style RF photoinjector electron gun is conventionally tuned using cylindrical copper tuning pieces that extend into the full-cell cavity through holes in the side of the gun. This design begins to fail in many versions of this popular gun design at higher voltage levels, when the cavity undergoes electric breakdown in the vicinity of the tuners. In order to remove the tuners from the region of high electric field, mitigating this problem, the full cell geometry must be changed significantly. We report on a method of accomplishing this, in which we use a mechanical device of custom design to stretch the cavity structure of an existing photoinjector in order to tune the resonant frequency up by over 2 MHz. We present results of testing the modified photoinjector in an RF test bed with both copper and magnesium cathodes, succeeding in putting approximately 8 - 10 MW of RF power into the gun. This is an improvement over the 4 MW routinely achieved in a similar gun using conventional tuning methods installed at the UCLA Neptune laboratory.

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title: Chicane Radiation Measurements with a Compressed Electron Beam at the BNL ATF

format: journal article

year: 2007

12 authors: G. Andonian | R. B. Agustsson | A. M. Cook | M. P. Dunning | E. Hemsing | A. Y. Murokh | S. Reiche | J. B. Rosenzweig | M. Babzien | K. Kusche | R. Malone | V. Yakimenko

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title: OPTIMUM ELECTRON BUNCH CREATION IN A PHOTOINJECTOR

format: journal article

year: 2007

16 authors: J.B. Rosenzweig | A.M. Cook | M. Dunning | R.J. England | P. Musumeci | M. Bellaveglia | M. Boscolo | L. Catani | A. Cianchi | G. Di Pirro | M. Ferrario | D. Filippetto | G. Gatti | L. Palumbo | C. Vicario | S. Jones

abstract: Recent studies have shown that by illuminating a pho- tocathode with an ultra-short laser pulse of appropriate transverse profile, a uniform density, ellipsoidally shaped electron bunch can be dynamically formed. Linear space- charge fields then exist in all dimensions inside of the bunch, which minimizes emittance growth. Here we study this process, and its marriage to the standard emittance compensation scenario that is implemented in most modern photoinjectors. We show that the two processes are com- patible, with simulations indicating that a very high bright- ness beam can be obtained. An initial time-resolved experi- ment has been performed at the SPARC injector in Frascati, involving Cerenkov radiation produced at an aerogel. We discuss the results of this preliminary experiment, as well as plans for future experiments at the UCLA Pegasus labo- ratory to resolve the ellipsoidal bunch shape at low energy. Future measurements at high energy based on fs resolution RF sweepers are discussed.

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title: Optimum Beam Creation in Photoinjectors Using Space-Charge Expansion

format: journal article

year: 2006

4 authors: J.B. Rosenzweig | A.M. Cook | M. Dunning | R.J. England

abstract: It has recently been shown that by illuminating a photo- cathode with an ultra-short laser pulse of appropriate trans- verse profile, a uniform density, ellipsoidally shaped bunch is dynamically formed, which then has linear space-charge fields in all dimensions inside of the bunch. We study here this process, and its marriage to the standard emittance compensation scenario that is implemented in most modern photoinjectors. It is seen that the two processes are compat- ible, with simulations indicating that a very high brightness beam can be obtained. The scheme has produced stimulus for a series of experiments at the SPARC injector at Fras- cati in 2006-2007. An initial time-resolved experiment has been performed involving Cerenkov radiation produced at an aerogel. We discuss the results of this preliminary ex- periment, as well as plans for future experiments to resolve the ellipsoidal bunch shape at low energy. Future measure- ments at high energy based on fs resolution RF sweepers are discussed.

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title: DIELECTRIC WAKEFIELD ACCELERATOR EXPERIMENTS AT THE SABER FACILITY

format: preprint

year:

17 authors: G. Travish | H. Badakov | A.M. Cook | J. B. Rosenzweig | R. Tikhoplav | A. Kanareykin | M.C Thompson | M. K. Berry | I. Blumenfeld | F.J. Decker | M. J. Hogan | R. Ischebeck | R. Iverson | N. Kirby | R. Siemann | D. Walz | P. Muggli

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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title:	Beam compression experiments using the UCLA/ATF compressor
format:	conference procceeding
conference:
year:	2006
13 authors:	D. Schiller \| E. Hemsing \| J. B. Rosenzweig \| M.P. Dunning \| G. Andonian \| A. Murokh \| A.M. Cook \| S. Reiche \| M. Babzien \| K. Kusche \| V. Yakimenko \| L. Palumbo \| C. Vicario
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:	Magnetic Chicane Radiation Studies at the BNL ATF
format:	conference procceeding
conference:
year:	2006
11 authors:	M.Dunning \| G. Andonian \| A.M.Cook \| E.Hemsing \| A.Murokh \| S. Reiche \| J. B. Rosenzweig \| D. Schiller \| M. BABZIEN \| K. Kusche \| V. Yakimenko
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.
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title:	Optinum Beam Creation In Photoinjectors Using Space-Charge Expansion
format:	conference procceeding
conference:
year:	2006
16 authors:	J. B. Rosenzweig \| A.M. Cook \| M. Dunning \| R. J. England \| M. Bellaveglia \| M. Boscolo \| L. Catani \| A. Cianchi \| G. Di Pirro \| M. Gerrario \| D. Filippetto \| G. Gatti \| P. Musumeci \| L. Palumbo \| C. Vicario \| S. Jones
abstract:	It has recently been shown that by illuminating a photocathode with an ultra-short laser pulse of appropriate transverse profile, a uniform density, ellipsoidally shaped bunch is dynamically formed, which then has linear space-charge fields in all dimensions inside of the bunch. We study here this process, and its marriage to the standard emittance compensation scenario that is implemented in most modern photoinjectors. It is seen that the two processes are compatible, with simulations indicating that a very high brightness beam can be obtained. The scheme has produced stimulus for a series of experiments at the SPARC injector at Frascati in 2006-2007. An initial time-resolved experiment has been performed involving Cerenkov radiation produced at an aerogel. We discuss the results of this preliminary experiment, as well as plans for future experiments to resolve the ellipsoidal bunch shape at low energy. Future measurements at high energy based on fs resolution RF sweepers are discussed.
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title:	Dielectric Wakefield Accelerating Structure as a Source of Terahertz Coherent Cerenkov Radiation
format:	conference procceeding
conference:
year:
8 authors:	A.M. Cook \| J. B. Rosenzweig \| M.C Thompson \| H. Badakov \| G. Travish \| R. Tikhoplav \| O.B. Williams \| R. J. England
abstract:	We discuss future experimental work proposed to study the performance of a cylindrical dielectric wakefield accelerating structure as a coherent Cerenkov radiation source at the Neptune laboratory at UCLA. The Cerenkov wakefield acceleration experiment carried out recently by UCLA/SLAC/USC, using the ultrashort and high charge beam (Q = 3 nC, RMS bunch length = 20 micron) at the SLAC FFTB, demonstrated electromagnetic wakes at the few GV/m level. The motivation of our prospective experiment is to investigate the operation of a similar scenario using the comparatively long pulse, low charge beam (Q = 0.5 nC, RMS bunch length = 200 micron) at UCLA Neptune. The field amplitude produced in this setup would be one to two orders of magnitude lower, at the few tens to few 100 MV/m level. Such a decelerating field would extract a significant amount of energy from a low-energy beam in a distance on the order of a few centimeters, allowing the use of short dielectric structures. We discuss details of the geometry and composition of the structures to be used in the experiment. We also examine the possibility of a future dedicated facility at UCLA Neptune based on a hybrid photoinjector currently in development. The intrinsic bunch compression capabilities and improved beam parameters (RMS bunch length = 100 micron, Q = 1 nC) of the photoinjector would allow the creation of a high power radiation source in the terahertz regime.
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title:	EXPERIMENTAL TESTING OF DYNAMICALLY OPTIMIZED PHOTOELECTRON BEAMS
format:	conference procceeding
conference:	Erice 2005
year:	2006
16 authors:	James Rosenzweig \| A.M. Cook \| M. Dunning \| R. J. England \| P. Musumeci \| M. Bellaveglia \| M. Boscolo \| L. Catani \| A. Cianchi \| G. Di Pirro \| M. Ferrario \| D. Fillipetto \| G. Gatti \| L. Palumbo \| L. Sserafini \| C. Vicario
abstract:	We discuss the design of and initial results from an experiment in space-charge dominated beam dynamics which explores a new regime of high-brightness electron beam generation at the SPARC (located at INFN-LNF, Frascati) photoinjector. The scheme under study employs the natural tendency in intense electron beams to configure themselves to produce a uniform density, giving a nearly ideal beam from the viewpoint of space charge-induced emittance. The experiments are aimed at testing the marriage of this idea with a related concept, emittance compensation, We show that the existing infrastructure at SPARC is nearly ideal for the proposed tests, and that this new regime of operating photoinjector may be the preferred method of obtaining highest brightness beams with lower energy spread. We discuss the design of the experiment, including developing of a novel time-dependent, aerogel-based imaging system. This system has been installed at SPARC, and first evidence for nearly uniformly filled ellipsoidal charge distributions recorded.
keywords:
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title:	Effects of Ion Motion in Intense Beam-Driven Plasma Wakefield Accelerators
format:	journal article
year:	2005
5 authors:	J. B. Rosenzweig \| A. M. Cook \| A. Scott \| M. C. Thompson \| R. B. Yoder
abstract:	Recent proposals for using plasma wakefield accelerators (PWFA) as a component of a linear collider have included intense electron beams with densities many times in excess of the plasma density. The beam’s electric fields expel the plasma electrons from the beam path to many beam radii in this regime. We analyze here the motion of plasma ions under the beam fields, and find for a proposed PWFA collider scenario that the ions completely collapse inside of the beam. Simulations of ion collapse are presented. Implications of ion motion on the feasibility of the PWFA-based colliders are discussed.
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title:	RF AND MAGNETIC MEASUREMENTS ON THE SPARC PHOTOINJECTOR AND SOLENOID AT UCLA
format:	conference procceeding
conference:	2005 Particle Accelerator Conference
year:	2005
8 authors:	J. B. Rosenzweig \| A.M. Cook \| M.P. Dunning \| P. Frigola \| G. Travish \| C. Sanelli \| F. Tazzioli \| D. T. Palmer
abstract:	The rf photocathode gun and the solenoid for the SPARC project at INFN-LNF (Frascati) have been fabricated and undergone initial testing at UCLA. The advanced aspects of the design of these devices are detailed. Final diagnosis of the tuning of the RF gun performance, including operating mode frequency and field balance, is described. The emittance compensating solenoid magnet, which is designed to be tuned in longitudinal position by differential excitation of the coils, has been measured using Hall probe scans for field profiling, and pulsed wire methods to determine the field center. Comparisons between measurements and the predictions of design codes are made.
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title:	Emittance compensation with dynamically optimized photoelectron beam profiles
format:	journal article
year:	2005
4 authors:	J. B. Rosenzweig \| A.M. Cook \| M. Dunning \| M. Ferrario
abstract:	Much of the theory and experimentation concerning creation of a high-brightness electron beam from a photocathode, and then applying emittance compensation techniques, assumes that one must strive for a uniform density electron beam, having a cylindrical shape. On the other hand, this shape has large nonlinearities in the space-charge field profiles near the beam
keywords:
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title:	Mitigation of RF Gun Breakdown by Removal of Tuning Rods in High Field Regions
format:	conference procceeding
conference:	2007 Particle Accelerator Conference
year:
5 authors:	A. M. Cook \| M.P. Dunning \| J. B. Rosenzweig \| K. Serratto \| P. Frigola
abstract:	The pi-mode resonant frequency of the 1.6 cell SLAC/BNL/UCLA style RF photoinjector electron gun is conventionally tuned using cylindrical copper tuning pieces that extend into the full-cell cavity through holes in the side of the gun. This design begins to fail in many versions of this popular gun design at higher voltage levels, when the cavity undergoes electric breakdown in the vicinity of the tuners. In order to remove the tuners from the region of high electric field, mitigating this problem, one must change the full cell geometry significantly. We have investigated a method for accomplishing this, in which we stretch the gun structure to tune the resonant frequency up by over 2 MHz. We constructed a device to perform this stretching and tested the modified photoinjector in an RF test bed. We succeeded in putting approximately 8.4 MW of RF power into the gun, an improvement over the 4 MW routinely achieved with a similar gun using conventional tuning methods installed at the UCLA Neptune laboratory. Recent results in testing this gun with a magnesium cathode insert are reported as well.
keywords:	pbpl
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title:	The Effects of Ion Motion in Very Intense Beam-driven Plasma Wakefield Accelerators
format:	conference procceeding
conference:
year:	2004
4 authors:	J. B. Rosenzweig \| A.M. Cook \| M.C. Thompson \| R. B. Yoder
abstract:	Recent proposals for using plasma wakefield accelerators in the blowout regime as a component of a linear collider have included very intense driver and accelerating beams, which have densities many times in excess of the ambient plasma density. The electric fields of these beams are widely known to be large enough to completely expel plasma electrons from the beam path; the expelled electrons often attain relativistic velocities in the process. We examine here another aspect of this high-beam density scenario: the motion of ions. In the lowest order analysis, for both cylindrically symmetric and
keywords:
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title:	Beam-Driven Dielectric Wakefield Accelerating Structure as a THz Radiation Source
format:	preprint
year:	2007
9 authors:	A. Kanareykin \| O.B. Williams \| R. Tikhoplav \| A.M. Cook \| H. Badakov \| J. B. Rosenzweig \| G. Travish \| M.C Thompson \| R. J. England
abstract:	Experimental work is planned to study the performance of a beam-driven cylindrical dielectric wakefield accelerating structure as a source of THz coherent Cerenkov radiation (CCR). For an appropriate choice of dielectric tube geometry and driving electron bunch parameters, the device operates in a single-mode regime, producing radiation in the THz range. This source can potentially produce high power levels relative to currently available sources, with ~50 uJ radiated energy per pulse achievable using the electron beam currently in operation at the Neptune advanced accelerator laboratory at UCLA (~13 MeV beam energy, ~200 um RMS bunch length, ~500 pC bunch charge). Preparations underway for installation of the experiment are discussed.
keywords:	pbpl
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title:	MITIGATION OF ELECTRIC BREAKDOWN IN AN RF PHOTOINJECTOR BY REMOVAL OF TUNING RODS IN HIGH-FIELD REGIONS
format:	preprint
year:	2007
5 authors:	K. Serratto \| P. Frigola \| J. B. Rosenzweig \| M.P. Dunning \| A.M. Cook
abstract:	The pi-mode resonant frequency of the 1.6 cell SLAC/BNL/UCLA style RF photoinjector electron gun is conventionally tuned using cylindrical copper tuning pieces that extend into the full-cell cavity through holes in the side of the gun. This design begins to fail in many versions of this popular gun design at higher voltage levels, when the cavity undergoes electric breakdown in the vicinity of the tuners. In order to remove the tuners from the region of high electric field, mitigating this problem, the full cell geometry must be changed significantly. We report on a method of accomplishing this, in which we use a mechanical device of custom design to stretch the cavity structure of an existing photoinjector in order to tune the resonant frequency up by over 2 MHz. We present results of testing the modified photoinjector in an RF test bed with both copper and magnesium cathodes, succeeding in putting approximately 8 - 10 MW of RF power into the gun. This is an improvement over the 4 MW routinely achieved in a similar gun using conventional tuning methods installed at the UCLA Neptune laboratory.
keywords:	pbpl
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title:	Chicane Radiation Measurements with a Compressed Electron Beam at the BNL ATF
format:	journal article
year:	2007
12 authors:	G. Andonian \| R. B. Agustsson \| A. M. Cook \| M. P. Dunning \| E. Hemsing \| A. Y. Murokh \| S. Reiche \| J. B. Rosenzweig \| M. Babzien \| K. Kusche \| R. Malone \| V. Yakimenko
abstract:
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title:	OPTIMUM ELECTRON BUNCH CREATION IN A PHOTOINJECTOR
format:	journal article
year:	2007
16 authors:	J.B. Rosenzweig \| A.M. Cook \| M. Dunning \| R.J. England \| P. Musumeci \| M. Bellaveglia \| M. Boscolo \| L. Catani \| A. Cianchi \| G. Di Pirro \| M. Ferrario \| D. Filippetto \| G. Gatti \| L. Palumbo \| C. Vicario \| S. Jones
abstract:	Recent studies have shown that by illuminating a pho- tocathode with an ultra-short laser pulse of appropriate transverse profile, a uniform density, ellipsoidally shaped electron bunch can be dynamically formed. Linear space- charge fields then exist in all dimensions inside of the bunch, which minimizes emittance growth. Here we study this process, and its marriage to the standard emittance compensation scenario that is implemented in most modern photoinjectors. We show that the two processes are com- patible, with simulations indicating that a very high bright- ness beam can be obtained. An initial time-resolved experi- ment has been performed at the SPARC injector in Frascati, involving Cerenkov radiation produced at an aerogel. We discuss the results of this preliminary experiment, as well as plans for future experiments at the UCLA Pegasus labo- ratory to resolve the ellipsoidal bunch shape at low energy. Future measurements at high energy based on fs resolution RF sweepers are discussed.
keywords:	pbpl
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title:	Optimum Beam Creation in Photoinjectors Using Space-Charge Expansion
format:	journal article
year:	2006
4 authors:	J.B. Rosenzweig \| A.M. Cook \| M. Dunning \| R.J. England
abstract:	It has recently been shown that by illuminating a photo- cathode with an ultra-short laser pulse of appropriate trans- verse profile, a uniform density, ellipsoidally shaped bunch is dynamically formed, which then has linear space-charge fields in all dimensions inside of the bunch. We study here this process, and its marriage to the standard emittance compensation scenario that is implemented in most modern photoinjectors. It is seen that the two processes are compat- ible, with simulations indicating that a very high brightness beam can be obtained. The scheme has produced stimulus for a series of experiments at the SPARC injector at Fras- cati in 2006-2007. An initial time-resolved experiment has been performed involving Cerenkov radiation produced at an aerogel. We discuss the results of this preliminary ex- periment, as well as plans for future experiments to resolve the ellipsoidal bunch shape at low energy. Future measure- ments at high energy based on fs resolution RF sweepers are discussed.
keywords:	pbpl
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title:	DIELECTRIC WAKEFIELD ACCELERATOR EXPERIMENTS AT THE SABER FACILITY
format:	preprint
year:
17 authors:	G. Travish \| H. Badakov \| A.M. Cook \| J. B. Rosenzweig \| R. Tikhoplav \| A. Kanareykin \| M.C Thompson \| M. K. Berry \| I. Blumenfeld \| F.J. Decker \| M. J. Hogan \| R. Ischebeck \| R. Iverson \| N. Kirby \| R. Siemann \| D. Walz \| P. Muggli
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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