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N. Barov

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40 papers
title: Observations of low-aberration plasma lens focusing of relativistic electron beams at the underdense threshold
format: journal article
publisher: Physics of Plasmas
year: 21 July 2010
11 authors: M.C. Thompson | H. Badakov | J.B. Rosenzweig | G. Travish | N. Barov | P. Piot | R. Fliller | G.M. Kazakevich | J. Santucci | J. Li | R. Tikhoplav
abstract: Focusing of a 15 MeV electron bunch by a plasma lens operated at the threshold of the underdense regime has been demonstrated. The strong, 1.7 cm focal length, plasma lens focused both transverse directions simultaneously and reduced the minimum area of the beam spot by a factor of 23. It is shown through analytic analysis and simulation that the observed spherical aberration of this underdense lens, when expressed as the fractional departure of the focusing strength from its linear expectation, is ?K/K=0.08�0.04. This is significantly lower than the minimum theoretical value for the spherical aberration of an overdense plasma lens. Parameter scans showing the dependence of focusing performance on beam charge, as well as time resolved measurements of the focused electron bunch, are reported.
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title: Status of the UCLA/NICADD Plasma Density Transition Trapping Experiment
format: preprint
year: 2004
8 authors: M.C. Thompson | J.B. Rosenzweig | G. Travish | N. Barov | H. Edwards | P. Piot | J. Santucci | R. Tikhoplav
abstract: Plasma density transition trapping is a recently proposed self-injection scheme for plasma wake-field accelerators. This technique uses a sharp downward plasma density transition to trap and accelerate background plasma electrons in a plasma wake-field. This paper recounts the first attempt to demonstrate density transition trapping experimentally. The goal of the experiment is to capture a ∼ 100 pC, 1.5 MeV beam with 4% rms energy spread out of a 2.5x10^13 cm^−3 peak density plasma using a 6nC, 14 MeV drive beam. The first experimental run occurred at the Fermilab NICADD Photoinjector Laboratory (FNPL) between January and May 2004. While several key objectives were achieved, we were unable to achieve the drive beam parameters necessary for the experiment due to technical problems. We are in the process of resolving these problems in preparation for a second experimental run.
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title: Energy Loss of a High Charge Bunched Electron Beam in Plasma: Simulations, Scaling, and Accelerating Wakefields
format: preprint
year: 2004
4 authors: J.B. Rosenzweig | N. Barov | M.C. Thompson | R. B. Yoder
abstract: The energy loss and gain of a beam in the nonlinear, ��blowout�� regime of the plasma wakefield accelerator, which features ultrahigh accelerating fields, linear transverse focusing forces, and nonlinear plasma motion, has been asserted, through previous observations in simulations, to scale linearly with beam charge. Additionally, from a recent analysis by Barov et al., it has been concluded that for an infinitesimally short beam, the energy loss is indeed predicted to scale linearly with beam charge for arbitrarily large beam charge. This scaling is predicted to hold despite the onset of a relativistic, nonlinear response by the plasma, when the number of beam particles occupying a cubic plasma skin depth exceeds that of plasma electrons within the same volume. This paper is intended to explore the deviations from linear energy loss using 2D particle-in-cell simulations that arise in the case of experimentally relevant finite length beams. The peak accelerating field in the plasma wave excited behind the finite-length beam is also examined, with the artifact of wave spiking adding to the apparent persistence of linear scaling of the peak field amplitude into the nonlinear regime. At large enough normalized charge, the linear scaling of both decelerating and accelerating fields collapses, with serious consequences for plasma wave excitation efficiency. Using the results of parametric particle-in-cell studies, the implications of these results for observing severe deviations from linear scaling in present and planned experiments are discussed.
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title: Energy Loss and Accelerating Field in the Plasma Wakefield Accelerator
format: preprint
year: 2003
4 authors: J.B. Rosenzweig | R. B. Yoder | N. Barov | M.C. Thompson
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title: The UCLA/NICADD Plasma Density Transition Trapping Experiment
format: conference proceeding
conference: PAC 2003
year: 2003
6 authors: M.C. Thompson | W. Lu | W. Mori | J.B. Rosenzweig | G. Travish | N. Barov
abstract: Plasma density transition trapping is a recently purposed self-injection scheme for plasma wake-field accelerators. This technique uses a sharp downward plasma density transition to trap and accelerate background plasma electrons in a plasma wake-field. Two and three dimensional Particle-In-Cell (PIC) simulations show that electron beams of substantial charge can be captured using this technique, and that the beam parameters such as emittance, energy spread, and brightness can be optimized by manipulating the plasma density profile. These simulations also predict that transition trapping can produce beams with brightness > 5x10^14 Amp/(m-rad)^2 when scaled to high plasma density regimes. A proof-of-principle plasma density transition trapping experiment is planned for the near future. This experiment is a collaboration between UCLA and the Northern Illinois University (NICADD). The goal of experiment is to capture a ~100 pC beam with ~4% rms energy spread out of a 2 x 10^13 cm^-3 peak density plasma using a ~6nC, 14 MeV drive beam. Status and progress on the experiment are reported.
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title: Energy Loss of a High Charge Bunched Electron Beam in Plasma: Analysis
format: thesis
year: 2003
4 authors: N. Barov | J.B. Rosenzweig | M.C. Thompson | R. Yoder
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title: Energy Loss of a High Charge Bunched Electron Beam in Plasma: Analysis
format: conference proceeding
conference: ICFA Workshop on Physics and Applications of High Brightness Electron Beams
year: 2003
3 authors: N. Barov | J.B. Rosenzweig | M.C. Thompson
abstract: There has been much interest in the blowout regime of plasma wakefield acceleration (PWFA), which features ultra-high fields and nonlinear plasma motion. Using an exact analysis, we examine here a fundamental limit of nonlinear PWFA excitation, by an infinitesimally short, relativistic electron beam. The beam energy loss in this case is shown to be linear in charge even for nonlinear plasma response, where a normalized, unitless charge exceeds unity. The physical basis for this effect is discussed, as are deviations from linear behavior observed in simulations with finite length beams.
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title: Energy Loss of a High Charge Bunched Electron Beam in Plasma: Nonlinear plasma response and linear scaling
format: conference proceeding
conference: AAC 2002 10th
year: 2002
4 authors: J.B. Rosenzweig | N. Barov | M.C. Thompson | R.B. Yoder
abstract: There has been much experimental and theoretical interest in blowout regime of plasma wakefield acceleration (PWFA), which features ultra-high accelerating fields, linear transverse focusing forces, and nonlinear plasma motion. Using an exact analysis, we examine here a fundamental limit of nonlinear PWFA excitation, by an infinitesimally short, relativistic electron beam. The beam energy loss in this case is shown to be linear in charge even for nonlinear plasma response, where a normalized, unitless charge exceeds unity, and relativistic plasma effects become important or dominant. The physical bases for this persistence of linear response are pointed out. As a byproduct of our analysis, we re-examine the issue of field divergence as the point-charge limit is approached, suggesting an important modification of commonly held views of evading unphysical energy loss. Deviations from linear behavior are investigated using simulations with finite length beams. The peak accelerating field in the plasma wave excited behind a finite-length beam is also examined, with the artifact of wave spiking adding to the apparent persistence of linear scaling of the peak field amplitude well into the nonlinear regime. On the other hand, at large enough normalized charge, linear scaling of fields collapses, with serious consequences for plasma wave excitation efficiency. The dramatic implications of these results for observing the collapse of linear scaling in planned experiments are discussed.
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title: Plasma electron fluid motion and wave breaking near a density transition
format: journal article
publisher: Physical Review E
year: 2002
3 authors: R. J. England | J.B. Rosenzweig | N. Barov
abstract: Recently, Suk, Barov, and Rosenzweig [Phys. Rev. Lett. 86, 1011 (2001)] proposed a scheme for trapping background electrons in a plasma wake field using a sudden downward transition in the background ion density, where the density transition length is small compared to the plasma skin depth. In the present paper we present a fluid dynamical description of this mechanism that is self-consistent up to the point of wave breaking. A one-dimensional nonlinear relativistic second-order differential equation is derived for the electron fluid velocity in Lagrangian coordinates. Numerical integrations of this equation are used to map out the regions of parameter space in which wave breaking occurs and to determine the extent of the downstream region of plasma involved in wave breaking. Comparisons with one-dimensional particle-in-cell (PIC) simulations show that the onset of trapping occurs at the parameter values where wave breaking begins in the fluid analysis, but that the downstream extent of plasma involved in wave breaking is not a reliable predictor of the number of trapped particles. The PIC simulations also reveal that particles initially located on the upstream side of the density transition may become trapped, although these particles do not participate in wave breaking in the fluid description.
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title: Plasma Wakefield Experiments
format: conference proceeding
conference: AAC 2002 10th
year: 2002
6 authors: N. Barov | M.C. Thompson | K. Bishofberger | J.B. Rosenzweig | H. Edwards | J. Santucci
abstract: We discuss the recent experiments in the field of Plasma Wakefield Acceleration (PWFA), with emphasis on the FNAL experiment. After completion of this work, the next round of experiments will need to push the envelope on accelerating gradient, interaction length, stability, and accelerated charge. We present theoretical results dealing with plasma accelerator performance in the limit of high driver charge, and short wavelengths. We comment on the impact of such results on both the afterburner (single module) and staged (multiple modules) approaches to plasma-based accelerators.
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title: Dynamics of a Driver Beam Propagating in an Underdense Plasma with a Downward Density Transition
format: conference proceeding
conference: PAC 2001
year: 2001
7 authors: Suk, H. | N. Barov | R. J. England | E. Esarey | G. Kim | J.B. Rosenzweig | M.C. Thompson
abstract: When a short electron beam propagates in an underdense plasma (plasma density n_p < beam density n_b) with a downward density transition, it is known that some background plasma electrons are trapped and accelerated by the plasma wakefield[1]. Beam quality of the trapped plasma electrons is severely affected by the wakefield that is generated by the driving electron beam, so dynamics and instabilities of the driver beam are very important. In this paper, we present some simulation results on the self-trapping and driver beam dynamics.
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title: Plasma Electron Trapping and Acceleration in a Plasma Wake Field Using a Density Transition
format: journal article
publisher: Physical Review Letters
year: 2001
4 authors: Suk, H. | N. Barov | J.B. Rosenzweig | E. Esarey
abstract: A new scheme for plasma electron injection into an acceleration phase of a plasma wake field is presented. In this scheme, a single, short electron pulse travels through an underdense plasma with a sharp, localized, downward density transition. Near this transition, a number of background plasma electrons are trapped in the plasma wake field, due to the rapid wavelength increase of the induced wake wave in this region. The viability of this scheme is verified using two-dimensional particle-in-cell simulations. To investigate the trapping and acceleration mechanisms further, a 1D Hamiltonian analysis, as well as 1D simulations, has been performed, with the results presented and compared.
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title: Ultra high-gradient energy loss by a pulsed electron beam in a plasma
format: conference proceeding
conference: PAC 2001
year: 2001
9 authors: N. Barov | K. Bishofberger | J.B. Rosenzweig | J.P. Carneiro | P. Colestock | H. Edwards | Fitch, M. J. | W. Hartung | J. Santucci
abstract: The plasma wake-field mechanism can be used to couple energy at a high rate from a bunched electron beam into a plasma wave. We will present results from the Fermilab A0 facility where a beam with an initial energy of 14 MeV passes through the plasma to emerge with a much broader energy spread, spanning from a low of 3 MeV to a high of over 20 MeV. Over the 8 cm length of the 10(14) cm(-3) plasma, this implies a 140 MeV/m deceleration and 72 MeV/m acceleration gradient. (12 References).
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title: Trapping of background plasma electrons in a beam-driven plasma wake field using a downward density transition
format: conference proceeding
conference: AAC 2000 9th
year: 2001
4 authors: Suk, H. | N. Barov | J.B. Rosenzweig | E. Esarey
abstract: Trapping of background plasma electrons by a beam-driven plasma wake field is studied as a new self-injection method. In this scheme, a short electron beam pulse is sent through an underdense plasma with a downward density transition and some background plasma electrons are trapped by the strong wake field due to the sudden increase of the wake wave wavelength at the density transition. Two-dimensional PIC (Particle-In-Cell) simulations show that a significant amount of plasma electrons are trapped and accelerated to a higher energy than the driving beam energy. Furthermore, the trapped-beam quality is fairly good. In this paper, the 2-D simulation results, dynamics of the trapped beam and the driving beam, and the proposed experiment for the UCLA Neptune Laboratory are described. (15 References).
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title: Plasma Electron Trapping and Acceleration in a Plasma Wake Field Using a Density Transition
format: preprint
year: 2000
4 authors: E. Esarey | H. Suk | N. Barov | J.B. Rosenzweig
abstract: A new scheme for plasma electron injection into an acceleration phase of a plasma wakefield is presented. In this scheme, a short single electron beam bunch is sent through an underdense plasma with a sharp, localized downward density transition. Near this transition, a number of background plasma electrons are trapped in the plasma wake field due to the rapid wavelength increase of the wake wave in this region. The viability of this scheme is verified using two-dimensional particle-in-cell (PIC) simulations. To investigate the trapping and acceleration mechanism further, a 1-D Hamiltonian analysis as well as 1-D simulations have been performed, with the results are presented and compared.
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title: Observation of plasma wakefield acceleration in the underdense regime
format: journal article
publisher: Physical Review Special Topics-Accelerators & Beams
year: 2000
5 authors: N. Barov | J.B. Rosenzweig | M. E. Conde | W. Gai | J. G. Power
abstract: Initial experiments which have explored the physics of the underdense (blowout) regime of the plasma wakefield accelerator (PWFA) at the Argonne Wakefield Accelerator facility are reported. In this regime, the relativistic electron beam is denser than the plasma, causing the beam channel to completely rarefy, and leaving a high quality accelerating region which also contains a uniform ion column. This ion column in turn allows the drive and accelerating beams to be well guided over many initial beam beta-function lengths. The results of these experiments, which have taken place over several years, are reviewed. Notable achievements in the course of these studies include the creation and measurement of drive and witness beam generated in an rf photoinjector, as well as previously published studies on drive beam guiding in the underdense regime. In addition, these experiments allowed measurement of both beam energy loss and gain, at a maximum average rate of 25 MeV/m in this regime of the PWFA, which is consistent with a peak acceleration gradient of 62 MeV/m in the excited waves. Difficulties associated with this type of experiment are discussed, as are prospects for mitigating these difficulties and achieving high gradient acceleration in planned future experiments.
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title: Energy Loss of a High Charge Bunched Electron Beam in Plasma
format: preprint
year: 2000
3 authors: N. Barov | J.B. Rosenzweig | M.C. Thompson
abstract: There has been much interest in the regime of plasma wake-field acceleration (PWFA) having ultra-high fields, and associated nonlinear plasma motion. With an exact analytical approach, we examine here a fundamental limit of PWFA excitation, by an infinitesimally short relativistic bunched beam. The beam energy loss in this case is shown to be linear in charge even for nonlinear plasma response, where a normalized, unitless charge exceeds unity. The physical basis for this effect is discussed, as are deviations from linear behavior observed in simulations with finite length beams.
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title: Plasma electron trapping and acceleration in a plasma wake field using a density transition
format: conference proceeding
conference: ICFA Advanced Accelerator Workshop on the Physics of High Brightness Beams 2nd
year: 2000
4 authors: Suk, H. | N. Barov | J.B. Rosenzweig | E. Esarey
abstract: A new scheme for plasma electron injection into an acceleration phase of a plasma wake field is presented. In this scheme, a short single electron beam bunch is sent through an underdense plasma with a sharp downward density transition and some plasma electrons are trapped in the plasma wake field due to the rapid wavelength increase of the wake wave at the density transition. To investigate the trapping and acceleration mechanism, two-dimensional particle-in-cell (PIC) simulations were performed, and the illustrative 2-D simulation shows that the new injection method can produce a relatively large charge (~0.5 nC), short (~1 ps) and high energy (> driving beam energy) electron beam pulse with a plasma density transition from 5x10(13) cm(-3) to 3.5x10(13) cm(-3). In addition to the 2-D simulations, 1-D analytic work based on the Hamiltonian formalism and 1D simulations have been performed and the results are also presented. Finally, a proposed experiment at the Neptune Laboratory of UCLA is described.
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title: First results of the Fermilab high-brightness RF photoinjector
format: conference proceeding
conference: PAC 1999
year: 1999
18 authors: J.P. Carneiro | R.A. Carrigan | Champion, M. S. | P. L. Colestock | H. T. Edwards | Fuerst, J. D. | W. H. Hartung | Koepke, K. P. | Kuchnir, M. | J. K. Santucci | Spentzouris, L. K. | Fitch, M. J. | Melissinos, A. C. | P. Michelato | C. Pagani | Sertore, D. | N. Barov | J.B. Rosenzweig
abstract: A collaboration has been formed between FNAL, UCLA, LNFN Milano, the University of Rochester, and DESY to develop the technology of an RF photoinjector, followed by a superconducting cavity, to produce high bunch charge (8 nC) with low normalized emittance ([left angle bracket]20 mm mrad) in bunch spacing trains of 800 bunches separated by mu s. The activities of bunch charge the collaboration fall into two categories: 1. the development of Injector II for the TeSLA/TTF accelerator. This photoinjector (TTF RF Gun) was tested at Fermilab in September and October 1998 and installed at DESY in November 1998. 2. the installation at the A0 Hall of Fermilab of a modified version of the TTF photoinjector, for photoinjector R&D and to study novel applications of high-brightness, pulsed electron beams. This photoinjector (A0 RF Gun) produced its first beam in March 1999. This paper presents a summary of the tests done at Fermilab on the TITF Injector II and the first results obtained on the new Fermilab photoinjector.
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title: Propagation of short electron pulses in a plasma channel
format: journal article
publisher: Physical Review Letters
year: 1998
4 authors: N. Barov | M. E. Conde | W. Gai | J.B. Rosenzweig
abstract: We report the near-steady-state propagation over long distance of a 25 psec, tightly focused relativistic electron beam which creates, by radial ejection of plasma electrons, a focusing ion channel in a plasma of electron density smaller than the beam. A dense beam core, close in radius to the injected beam, which was nearly matched to the ion focusing strength, is observed at the plasma exit. Time-resolved imaging confirms that this core is situated in the trailing half of the beam, as predicted by analytical and computer models. We discuss the impact of these results on plasma wake field acceleration schemes. (16 References).
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title: Plasma Wake-field Acceleration in the Blowout Regime
format: thesis
year: 1998
1 author: N. Barov
abstract: The blowout regime is a limiting case of a nonlinearly excited plasma wave that overcomes problems identified in past linear regime studies of the plasma wake-field accelerator. Here, it is studied with the aid of simulations and by conducting experiments. Fluid model and particle-in-cell simulations have been used to study the propagation of drive pulses short enough to couple to the plasma mode, over distances comparable to the energy depletion length. Evolution of the beam radial dynamics in the simulations, and the associated wake-field phase shifts, outline phenomena important for achieving the maximum energy gain for the accelerated electrons. An experiment to demonstrate long-term drive beam propagation of a short electron pulse in an underdense plasma shows good agreement with simulations, with minor differences thought to originate from the limitation of simulating only a two-dimensional system. An experiment to measure electron acceleration is part of an ongoing effort, and has shown a 2.6 MeV energy gain and a 22 MeV/m acceleration gradient.
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title: Results of blowout regime propagation experiments of an electron beam in a plasma
format: conference proceeding
conference: PAC 1997
year: 1998
4 authors: N. Barov | M. Conde | W. Gai | J.B. Rosenzweig
abstract: When a tightly focused electron beam propagates in an underdense plasma (beam density greater than the plasma electron density, n b > n 0 ), the plasma electrons are expelled radially by the space-charge of the beam, forming an ion channel which in turn provides a uniform, linear focusing force on the beam. When the beam is short ( σ z < 2 k p − 1 ), making it suitable as a driver for plasma wake-field acceleration (PWFA)[3], requirements on the beam properties (current, eminence and energy) to achieve ion channel self-focusing become more difficult to satisfy[10]. If the beam is initially β - matched to the focusing gradient, that is, the β -function is initially equal to βγπ eq e rn = /2 0 , where σ r and ε , are the rms transverse beam radius and emittance, the transverse distribution in the body of the beam is nearly stationary, while that near the head expands radially. The loss in beam density near the head associated with this expansion further retards the plasma electron response and causes the pinch point (where sufficient focusing gradient develops) to move backwards in the beam frame. The fast relaxation distance for these beam head dynamics is roughly 4 β eq , or 5 cm for our experimental conditions, which is less than half of the plasma length, L p = 12 cm. The present experiments were motivated by the proposed use of the underdense regime as the basis for a PWFA[8] (the blowout regime) which is very attractive in terms of drive and accelerating beam guiding, in that when a plasma-electron free ion column is formed, the focusing force in this region is linear and the acceleration gradient is independent of radius.
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title: Towards a plasma wake-field acceleration-based linear collider
format: conference proceeding
conference: ICFA Second Generation Plasma Acceleration Workshop
year: 1998
5 authors: J.B. Rosenzweig | N. Barov | A. Murokh | E. Colby | P. Colestock
abstract: A proposal for a linear collider based on an advanced accelerator scheme, plasma wake-field acceleration in the extremely nonlinear regime, is discussed. In this regime, many of the drawbacks associated with preservation of beam quality during acceleration in plasma are mitigated. The scaling of all beam and wake parameters with respect to plasma wavelength is examined. Experimental progress towards high-gradient acceleration in this scheme is reviewed. We then examine a linear collider based on staging of many modules of plasma wake-field accelerator, all driven by a high average current, pulse compressed, RF photoinjector-fed linac. Issue of beam lending, efficiency, optimized stage length, and power efficiency are discussed. A proof-of-principle experimental test of the staging concept at the Fermilab test facility is discussed.
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title: A Linear Collider Based on Nonlinear Plasma Wake-field Acceleration
format: conference proceeding
conference: Summer Study on New Directions for High Energy Physics
year: 1997
3 authors: J.B. Rosenzweig | N. Barov | E. Colby
abstract: A proposal for a linear collider based on an advanced accelerator scheme, plasma wake-field acceleration in the extremely nonlinear regime is discussed. In this regime, many of the drawbacks associated with preservation of beam quality during acceleration in plasma are mitigated. Experimental progress towards high-gradient acceleration in this scheme is reviewed. We then examine a linear collider based on staging of many modules of plasma wake-field accelerator, all driven by a high average current, pulse compressed, rf photoinjector-fed linac. Issues of beam loading, efficiency, optimized stage length, and power efficiency are discussed. A proof-of-principle experimental test of the staging concept and the Fermilab Test Facility is discussed.
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title: Status of UCLA IR FEL
format: preprint
year: 1996
21 authors: C. Pellegrini | G. Baranov | N. Barov | P. Davis | M. Fauver | B. Gitter | G. Hairapetian | S. Hartman | M. Hogan | S. Ivanchenkov | C. Joshi | A. Khlebnikov | P. Kwok | N. Luhmann | S. Park | J.B. Rosenzweig | K. Schenk | Smolin, J. A. | P. Tran | G. Travish | A. A. Varfolomeev
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title: Pulse compression in radio frequency photoinjectors: applications to advanced accelerators
format: conference proceeding
conference: Workshop on Second Generation Plasma Accelerators
year: 1996
3 authors: J.B. Rosenzweig | N. Barov | E. Colby
abstract: While RF photoinjectors are an excellent source of high brightness electron beams, there are constraints to tying together the expected emittance and peak current performance of a given photoinjector system. These constraints, which arise from the complicated dynamics of the electrons due to the interplay of RF and space-charge forces within the photoinjector, tend to favor lower peak current operation. For some ultimate uses of photoinjector beams, such as linear collider test beams, wakefield accelerators, and free-electron lasers (FEL's), one may desire much higher peak currents. In this case, an inexpensive and reliable method for producing extremely short high-current electron bunches is to use magnetic compression. We examine this scheme analytically and by computer simulation. Many applications are illustrated, including the TESLA Test Facility/FEL injector, ultra-high current beams for plasma wakefields and generation of femtosecond electron pulses for injection ultra-high current beams for injection into short wavelength laser-based accelerators. It is shown that the injection timing jitter associated with the laser can be nearly eliminated using this scheme, making it an indispensable component in many of the advanced accelerator injectors we consider.
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title: Measurements of plasma wake-fields in the blow-out regime
format: conference proceeding
conference: PAC 1995
year: 1995
9 authors: N. Barov | M. Conde | J.B. Rosenzweig | Schoessow, P. | Cox, G. | W. Gai | Konecny, R. | J. Power | J. Simpson
abstract: Initial results from nonlinear plasma wake-field experiments at the Argonne Wakefield Accelerator (AWA) test facility are reported. This nonlinear "blow-out" regime is characterized by the complete ejection of the plasma electrons from the beam channel. The wake-fields in this case are of notably high quality for acceleration of electrons, as the acceleration is independent of transverse position, and the focusing is linear and independent of longitudinal position within the electron depleted region, allowing self-consistent guiding of the majority of the driving electron beam. Initial measurements of the energy gain in a witness beam indicate a positive shift in its energy distribution of at least 0.5 MeV. (9 References).
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title: Pulse Compression in RF Photoinjectors: Applications to Advanced Accelerators
format: preprint
year: 1995
3 authors: J.B. Rosenzweig | N. Barov | E. Colby
abstract: While rf photoinjectors are an excellent source of high brightness electron beams, there are constraints tying together the expected emittance and peak current performance of a given photoinjector system. These constraints, which arise from the complicated dynamics of the electrons due to the interplay of rf and space-charge forces within the photoinjector, tend to favor lowe peak current operation. For some ultimate uses of photoinjector beams, such as linear collider test beams, wake-field accelerators and FELs, one may desire much higher peak currents. In this case, an inexpensive and reliable method for producing extramely short, high-current electron bunches is to use magnetic compression. We examine this scheme alalytically and by computer simulation. Many applications are illustrated, including the TESLA Test Facility/FEL injector, ulta-high current beams for plasma wake-fields, and generation of femtosecond electron pulses for injection into short wavelength laser-based accelerators. It is show that the injection timing jitter associated with the laser can be nearly eliminated using this scheme, making it an indispensable component in many of the advanced acclerator injectors we consider.
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title: Propagation of short electron pulses in underdense plasmas
format: journal article
publisher: Physical Review E
year: 1994
2 authors: N. Barov | J.B. Rosenzweig
abstract: Dense relativistic electron beams traversing a plasma, in what is known as the underdense, or ion focusing, regime experience a strong, linear transverse restoring force. This force arises from the nearly immobile ions which form a channel of uncompensated positive charge when the plasma electrons are ejected in response to the introduction of the beam charge. This phenomenon can be used for focusing the electron beam to very high densities over long propagation distances. Several schemes have been proposed, including the nonlinear plasma wake-field accelerator, the adiabatic plasma lens, and the ion-channel laser, whose viability is based on this focusing effect for very short pulse, high current electron beams propagating in plasma. In this paper we examine, analytically and numerically, the self-consistent requirements on plasma density, beam current, length, and transverse emittance which must be satisfied in order for ion-channel formation and near equilibrium beam propagation to exist over the majority of the length of the electron beam. The dynamics of the beam-plasma system are modeled by a simultaneous solution of the plasma electron cold-fluid equations, and the Maxwell-Vlasov equation governing the beam's thermal equilibrium. The effects of introducing a strong axial magnetic field on the plasma response and beam equilibria are examined. In addition to developing criteria for self-consistent equilibrium focusing, a time-dependent analysis where the beam particles are treated as mobile particles in cells is developed in order to study the dynamical approach of this equilibrium. Inherently time-dependent phenomena, such as matching of the beam into the plasma and adiabatic lenses, are then examined with this method.
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title: Initial measurements of the UCLA RF photoinjector
format: conference proceeding
conference: Conference on High Intensity Electron Sources
year: 1994
14 authors: S. Hartman | M. Hogan | S. C. Hartman | N. Barov | C. Pellegrini | S. Park | J.B. Rosenzweig | G. Travish | R. Zhang | C. Clayton | P. Davis | M. Everett | C. Joshi | G. Hairapetian
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: An inverse free electron laser driven linear collider electron-positron B-factory
format: conference proceeding
conference: PAC 1993
year: 1993
3 authors: N. Barov | C. Pellegrini | Sandweiss, J.
abstract: We discuss an electron-positron linear collider B-Factory using Inverse Free Electron Lasers (IFEL) to accelerate the beams. The requirements on luminosity, larger than 10/sup 33/ cm/sup -2/ s/sup -1/, and energy spread of a B Factory introduce stringent conditions on the accelerator and the interaction region. We study the longitudinal dynamics through the IFEL, the efficiency of the acceleration process, and the ratio of particles which become accelerated, and fall within the resonance. The device is found to perform well in the presence of large variations in the laser field intensity over the beam. We also discuss the laser system powering the IFEL, and some of the system tolerances. (7 References).
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title: Propagation of Short Electron Pulses in Underdense Plasmas
format: conference proceeding
conference: PAC 1993
year: 1993
2 authors: N. Barov | J.B. Rosenzweig
abstract: Our program for an experimental plasma wake field accelerator (PWFA) to take place at the Argonne Wakefield Accelerator (AWA) facility, in the recently proposed blow-out regime relies on the propagation of an intense electron beam through an underdense plasma with a minimum of degradation. This paper presents a near-equilibrium model of beam propagation using the Maxwell-Vlasov equations governing the beam?s transverse behavior. Numerical results are presented which use this model simultaneously with the plasma electron cold fluid equations. A solenoidal magnetic field, which is necessary for high density plasma containment, also provides an initial beam equilibrium to begin the calculation. We compare the equilibrium model with a discrete beam particle simulation, which verifies the basic conclusions of the equilibrium model, and shows the collisionless damping approach to equilibrium in the beam head. The initial matching requirements for the beam?s entry into the plasma are examined. We also discuss the possibility of performing an adiabatic lens experiment.
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title: Initial operation and beam characteristics of the UCLA S-band RF photo-injector
format: conference proceeding
conference: PAC 1993
year: 1993
10 authors: C. Pellegrini | N. Barov | S. C. Hartman | S. Park | J.B. Rosenzweig | G. Travish | R. Zhang | P. Davis | C. Joshi | G. Hairapetian
abstract: The UCLA RF photo-injector system has been commissioned. All of the sub-components such as the high power RF, pico-second laser, RF photo-injector cavity, diagnostics, and supporting hardware have been tested and are operational. We briefly discuss the performance of the various components since the details of each subsystem are very lengthy. The laser delivers a sub 4 ps pulse containing 0-300 mu J of energy per pulse. The photo-injector produces 0-3 nC per bunch with an RF induced emittance of 1.5 pi (mm-mrad). (5 References).
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title: Emittance measurements of the 4.5 MeV UCLA RF photoinjector
format: conference proceeding
conference: PAC 1993
year: 1993
10 authors: S. C. Hartman | N. Barov | S. Park | C. Pellegrini | J.B. Rosenzweig | G. Travish | R. Zhang | P. Davis | C. Joshi | G. Hairapetian
abstract: The 1.5 cell RF photoinjector has been operated for the past several months using a copper cathode illuminated by 4 ps long pulses of UV (246 nm light, with a variable energy of between 0 to 300 mu J. This typically produces up to 3 nC of charge per bunch. Because space charge forces dominate the electron beam transport a pepper pot measurement system is used to measure the emittance. The emittance is measured as a function of charge, peak accelerating field, laser spot size and initial phase with respect to the RF field. This is accomplished with an automated control and data acquisition system which can measure single shot emittances at a rate of 5 Hz developed at UCLA. The experimental results obtained are then compared with theory and simulations. (4 References).
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title: Measurement of the Dipole Magnets
format: preprint
year: 1993
4 authors: N. Barov | Tran, P. | M.C. Thompson | B. Gitter
abstract: The four Saturnus dipole magnets were calibrated with a Hall probe using a machinist's rotary table and a stepping motor to vary position. The setup was controlled by a Macintosh LC computer using LabView software. The field vs. current relationship was also measured. Single particle motion through the magnet was simulated, making a comparison of the real magnet to an ideal one.
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title: The UCLA IR FEL project
format: conference proceeding
conference: FEL 1992 14th
year: 1993
21 authors: G. Baranov | N. Barov | P. Davis | M. Fauver | B. Gitter | G. Hairapetian | S. Hartman | M. Hogan | S. Ivanchenkov | C. Joshi | A. Khlebnikov | P. Kwok | N. Luhmann | S. Park | C. Pellegrini | J.B. Rosenzweig | K. Schenk | Smolin, J. A. | P. Tran | G. Travish | A. A. Varfolomeev
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: Photoelectron beams from the UCLA RF gun
format: conference proceeding
conference: AAC 1992 3rd
year: 1993
12 authors: S. Park | N. Barov | S. Hartman | C. Pellegrini | J.B. Rosenzweig | P. Tran | G. Travish | R. Zhang | P. Davis | G. Hairapetian | C. Joshi | N. Luhmann
abstract: A high brightness, low emittance photocathode rf gun is starting operation at UCLA as an injector to a 20 MeV linac. This linac will initially be used to drive FELs, plasma wakefield accelerators, and to test plasma lenses. The gun is a 1 1/2 cell pi-mode standing wave structure running at 2.856 GHz, and has a copper photocathode. In the initial commissioning of the gun, photoelectron beams of up to 2.5 nC at 4.5 MeV have been produced. We report on the current status of the system, experimental data taken with 50 ps UV laser pulses, and plans for the future.
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title: Use of an inverse free electron laser in a linear collider B factory
format: conference proceeding
conference: AAC 1992 3rd
year: 1993
3 authors: C. Pellegrini | J. Sandweiss | N. Barov
abstract: The authors examine the possibility of using an IFEL as an accelerator in a linear collider B Factory. An IFEL is able to utilize a sizeable fraction of the energy of the laser pulse used to accelerate the beams. It is also able to meet the stringent requirements imposed on the energy spread and luminosity at the interaction point. Two separate examples are considered, differing in the way the laser pulse energy is coupled to the electron beam. The first maximizes the slippage between the beam bunch and the radiation, in order to decrease the peak laser power. In the second example the slippage is minimized. This results in uniform beam loading and may in principle be run at higher efficiency and lower average power. The authors also address the laser required to drive this accelerator. The power and frequency requirements suggest the use of a FEL drive laser. The design for this system includes the use of superconducting cavities to accelerate the drive beam, which is then propagated through an initially constant period undulator that is tapered after saturation.
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title: Status of RF photoinjector and PWT linac at UCLA
format: conference proceeding
conference: Linear Accelerator Conference 1992
year: 1992
12 authors: S. Park | N. Barov | S. Hartman | C. Pellegrini | J.B. Rosenzweig | P. Tran | G. Travish | R. Zhang | P. Davis | G. Hairapetian | C. Joshi | N. Luhmann
abstract: The authors report the present status of RF photoinjector and plane wave transformer (PWT) linac for the production of 20 MeV/c electron beam. The photoinjector is a 1/sup 1///sub 2/ cell pi -mode standing wave structure operating at 2.856 GHz with photoelectrons generated on a copper cathode by 4 ps long laser pulse at 206 nm. Measurements of the beam of photoelectrons are underway at various experimental parameters. The PWT has been tested at low power to investigate its mode structure. An overview of the system, latest data, and future directions are presented. (5 References).
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title: Quadrupole Magnets Measurement
format: preprint
year: 1992
3 authors: N. Barov | Tran, P. | M.C. Thompson
abstract: Field measurement as a function of position and current of the SATURNUS compact accelerator's quadrupole magnets was carried out using a Hall probe mounted on a simple carriage setup consisting of 3 precision linear translators and a 360-degree rotator. From this measurement, the displacement of the magnetic center from the geometric center and the effective length of each quadrupole were calculated. Also, changes in the measured magnetic field of one quadrupole due to the effect of its disassembly and reassembling were investigated. The results are reported in this paper.
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