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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
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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. © 2010 American Institute of Physics.
Physics of Plasmas 01/2010; 17:073105. · 2.15 Impact Factor
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ABSTRACT: Various projects under study require an angular-momentum-dominated electron beam generated by a photoinjector. Some of the proposals directly use the angular-momentum-dominated beams (e.g. electron cooling of heavy ions), while others require the beam to be transformed into a flat beam (e.g. possible electron injectors for light sources and linear colliders). In this paper, we report our experimental study of an angular-momentum-dominated beam produced in a photoinjector, addressing the dependencies of angular momentum on initial conditions. We also briefly discuss the removal of angular momentum. The results of the experiment, carried out at the Fermilab/NICADD Photoinjector Laboratory, are found to be in good agreement with theoretical and numerical models.
12/2004;
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Y. Sun,
K.-J. Kim,
P. Piot,
K. Desler,
D. Edwards,
H. Edwards,
M. Huening,
J. Santucci, N. Barov,
D. Mihalcea,
R. Tikhoplav,
S. Lidia,
S.-H. Wang
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ABSTRACT: In the flat beam experiment at Fermilab/NICADD Photoinjector Laboratory(FNPL), it is essential to have a nonvanishing longitudinal magnetic field on the photocathode. The canonical angular momentum of the electron beam generated by this magnetic field is an important parameter in understanding the round to flat beam transformation. In this paper, we report our measurements of the canonical angular momentum, which is directly related to the skew diagonal elements of the beam matrix before beam is made flat. The measurements of the other elements of the beam matrix are also reported.
Particle Accelerator Conference, 2003. PAC 2003. Proceedings of the; 06/2003
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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 > 5 × 10<sup>14</sup> Amp/(m-rad)<sup>2</sup> 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 Northern Illinois University (MCADD). The goal of the experiment is to capture a ∼ 100 pC, 1.2 MeV beam with ∼ 4% rms energy spread out of a 2 × 10<sup>1</sup>3 cm<sup>-3</sup> peak density plasma using a ∼ 6 nC, 14 MeV drive beam. Status and progress on the experiment are reported.
Particle Accelerator Conference, 2003. PAC 2003. Proceedings of the; 06/2003
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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.
Physical Review E 08/2002; 66(1 Pt 2):016501. · 2.26 Impact Factor
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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. Comment: Submitted to Physical Review Letters
05/2002;
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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.
Physical Review Letters 03/2001; 86(6):1011-4. · 7.37 Impact Factor
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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<sup>14</sup> cm<sup>-3</sup> plasma,
this implies a 140 MeV/m deceleration and 72 MeV/m acceleration gradient
Particle Accelerator Conference, 2001. PAC 2001. Proceedings of the 2001; 02/2001
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ABSTRACT: When a short electron beam propagates in an underdense plasma
(plasma density n<sub>0</sub> < beam density n<sub>b</sub>) with a
downward density transition, it is known that some background plasma
electrons are trapped and accelerated by the plasma wakefield. The 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
Particle Accelerator Conference, 2001. PAC 2001. Proceedings of the 2001; 02/2001
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ABSTRACT: The A0 Photoinjector at Fermilab can produce high charge (10-14 nC) electron bunches of low emittance (20 pi mm-mrad for 12 nC). We have undertaken a study of the optimal compression conditions. Off-crest acceleration in the 9-cell capture cavity induces an energy-time correlation, which is rotated by the compressor chicane (4 dipoles). The bunch length is measured using streak camera images of optical transition radiation. We present measurements under various conditions, including the effect of the laser pulse length (2 ps sigma Gaussian vs. 10 ps FWHM flat top). The best compression to date is for a 13.2 nC bunch with sigma = 0.63 mm (1.89 ps), which corresponds to a peak current of 2.8 kA.
09/2000;
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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 MeVm in this regime of the PWFA, which is consistent with a peak acceleration gradient of 62 MeVm 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.
Physical Review Special Topics - Accelerators and Beams 01/2000; 3(29):011301. · 1.52 Impact Factor
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J.-P. Carneiro,
R.A. Carrigan,
M.S. Champion,
P.L. Colestock,
H.T. Edwards,
J.D. Fuerst,
W.H. Hartung,
K.P. Koepke,
M. Kuchnir,
J.K. Santucci,
L.K. Spentzouris,
M.J. Fitch,
A.C. Melissinos,
P. Michelato,
C. Pagani,
D. Sertore, N. Barov,
J.B. Rosenzweig
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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 (<20 mm mrad) in
bunch spacing trains of 800 bunches separated by μs. 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
Particle Accelerator Conference, 1999. Proceedings of the 1999; 02/1999
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ABSTRACT: this paper have used the code NOVO [9], which solves the Maxwell equations, assuming that this solution is unchanging in a frame moving with the beam. The plasma electrons are assumed to behave like a cold fluid and are modeled with the Maxwell-Boltzman equation. We have added a beam model to this code which tracks a set of super-particles, consistent with the NOVO picture [8]. This contradicts the assumption that the fields are static in the beam's frame, but this discrepancy is not very large, if we can assure that the beam changes very slowly compared to a plasma oscillation ( k p >> 1 b ). A similar argument is used with spatial variations in the plasma density. In the most extreme case, the beam crosses a plasma/vacuum boundary, with the method and have been incorporated into the code. causing a transient response, which is neglected in our treatment. More gradual variations in the plasma density, like the droop at the ends of the column, are entirely consistent.
04/1998;
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Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 01/1998; 410:532. · 1.21 Impact Factor
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ABSTRACT: Short intense relativistic bunches, of the kind available from RF
photoinjectors, have been observed, through integrated and
time-dependent imaging, as well as collimator transmission, to
effectively self-guide in an underdense plasma over many times the
initial β-function. Picosecond resolution measurement of transverse
beam size displays the trumpet-shaped beam head predicted by simulations
and analysis. The simulations are in good quantitative agreement with
the beam sizes and transmissions obtained from experiment, with
deviations arising from the approximations involved in the simulation
model of the beam
Particle Accelerator Conference, 1997. Proceedings of the 1997; 06/1997
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ABSTRACT: The Argonne Wakefield Accelerator is comprised of two L-band
photocathode RF guns and standing wave linac structures. The high charge
bunches (20-100 nC) produced by the main gun (drive gun) allow us to
study the generation of wakefields in dielectric lined structures and
plasmas. The secondary gun (witness gun) generates low charge bunches
(80-300 pC) that are used to probe the wakefields excited by the drive
bunches. We use insertable phosphor screens for beam position
monitoring. Beam intensity is measured with Faraday cups and integrating
current transformers. Quartz or aerogel Cerenkov radiators are used in
conjunction with a Hamamatsu streak-camera for bunch length
measurements. The beam emittance is measured with a pepper-pot plate and
also by quadrupole scan techniques. We present a description of the
various diagnostics and the results of the measurements. These
measurements are of particular interest for the high current (drive)
linac, which operates in a much higher charge regime than other
photoinjector-based linacs
Particle Accelerator Conference, 1997. Proceedings of the 1997; 06/1997
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ABSTRACT: The Argonne Wakefield Accelerator (AWA) facility has begun its experimental program. This unique facility is designed to address advanced acceleration research which requires very short, intense electron bunches. The facility incorporates two photo-cathode based electron sources. One produces up to 100 nC, multi-kiloamp ‘drive’ bunches which are used to excite wakefields in dielectric loaded structures and in plasma. The second source produces much lower intensity ‘witness’ pulses which are used to probe the fields produced by the drive. The drive and witness pulses can be precisely timed as well as laterally positioned with respect to each other. We discuss commissioning, initial experiments, and outline plans for a proposed 1 GeV demonstration accelerator. © 1997 American Institute of Physics.
AIP Conference Proceedings. 03/1997; 398(1):116-125.
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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 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
IEEE Transactions on Plasma Science 05/1996; · 1.17 Impact Factor
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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
Particle Accelerator Conference, 1995., Proceedings of the 1995; 06/1995
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P. Schoessow,
E. Chojnacki,
G. Cox,
W. Gai,
C. Ho,
R. Konecny,
J. Power,
M. Rosing,
J. Simpson, N. Barov,
M. Conde
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ABSTRACT: The Argonne Wakefield Accelerator (AWA) is a new facility for
advanced accelerator research. A major component of the AWA is its drive
linac, consisting of a unique high current short pulse L-band
photocathode based gun and special standing wave preaccelerator designed
to produce 100 nC, 30 ps electron bunches at 20 MeV. Commissioning on
the drive linac is now underway. We report on our initial operating
experience with this novel machine, including bunch length and emittance
measurements
Particle Accelerator Conference, 1995., Proceedings of the 1995; 06/1995
