[Show abstract][Hide abstract] ABSTRACT: Narrow bandwidth, high energy photon sources can be generated by Thomson
scattering of laser light from energetic electrons, and detailed control of the
interaction is needed to produce high quality sources. We present analytic
calculations of the energy-angular spectra and photon yield that parametrize
the influences of the electron and laser beam parameters to allow source
design. These calculations, combined with numerical simulations, are applied to
evaluate sources using conventional scattering in vacuum and methods for
improving the source via laser waveguides or plasma channels. We show that the
photon flux can be greatly increased by using a plasma channel to guide the
laser during the interaction. Conversely, we show that to produce a given
number of photons, the required laser energy can be reduced by an order of
magnitude through the use of a plasma channel. In addition, we show that a
plasma can be used as a compact beam dump, in which the electron beam is
decelerated in a short distance, thereby greatly reducing radiation shielding.
Realistic experimental errors such as transverse jitter are quantitatively
shown to be tolerable. Examples of designs for sources capable of performing
nuclear resonance fluorescence and photofission are provided.
[Show abstract][Hide abstract] ABSTRACT: Electrically discharged plasma channels can guide laser pulses, extending the laser-plasma interaction length to many Rayleigh ranges. In applications such as the laser-plasma accelerator, the laser group velocity in the channel plays a critical role. The laser travel time (and thus the averaged group velocity) was measured through two-pulse frequency-domain interferometry and was found to depend on the on-axis plasma density and laser spot size. The data is in agreement with theory.
Physical review. E, Statistical, nonlinear, and soft matter physics. 06/2014; 89(6-1):063103.
[Show abstract][Hide abstract] ABSTRACT: In a laser plasma accelerator (LPA), a short and intense laser pulse
propagating in a plasma drives a wakefield (a plasma wave with a relativistic
phase velocity) that can sustain extremely large electric fields, enabling
compact accelerating structures. Potential LPA applications include compact
radiation sources and high energy linear colliders. We propose and study plasma
wave excitation by an incoherent combination of a large number of low energy
laser pulses (i.e., without constraining the pulse phases). We show that, in
spite of the incoherent nature of electromagnetic fields within the volume
occupied by the pulses, the excited wakefield is regular and its amplitude is
comparable or equal to that obtained using a single, coherent pulse with the
same energy. These results provide a path to the next generation of LPA-based
applications, where incoherently combined multiple pulses may enable high
repetition rate, high average power LPAs.
[Show abstract][Hide abstract] ABSTRACT: A method is proposed to generate femtosecond, ultralow emittance (∼10-8 m rad), electron beams in a laser-plasma accelerator using two lasers of different colors. A long-wavelength pump pulse, with a large ponderomotive force and small peak electric field, excites a wake without fully ionizing a high-Z gas. A short-wavelength injection pulse, with a small ponderomotive force and large peak electric field, copropagating and delayed with respect to the pump laser, ionizes a fraction of the remaining bound electrons at a trapping wake phase, generating an electron beam that is accelerated in the wake.
[Show abstract][Hide abstract] ABSTRACT: Beam loading in laser-plasma accelerators using a near-hollow plasma channel is examined in the linear wake regime. It is shown that, by properly shaping and phasing the witness particle beam, high-gradient acceleration can be achieved with high-efficiency, and without induced energy spread or emittance growth. Both electron and positron beams can be accelerated in this plasma channel geometry. Matched propagation of electron beams can be achieved by the focusing force provided by the channel density. For positron beams, matched propagation can be achieved in a hollow plasma channel with external focusing. The efficiency of energy transfer from the wake to a witness beam is calculated for single ultra-short bunches and bunch trains.
[Show abstract][Hide abstract] ABSTRACT: Radiation Pressure Acceleration relies on high intensity laser pulse
interacting with solid target to obtain high maximum energy, quasimonoenergetic
ion beams. Either extremely high power laser pulses or tight focusing of laser
radiation is required. The latter would lead to the appearance of the maximum
attainable ion energy, which is determined by the laser group velocity and is
highly influenced by the transverse expansion of the target. Ion acceleration
is only possible with target velocities less than the group velocity of the
laser. The transverse expansion of the target makes it transparent for
radiation, thus reducing the effectiveness of acceleration. Utilization of an
external guiding structure for the accelerating laser pulse may provide a way
of compensating for the group velocity and transverse expansion effects.
[Show abstract][Hide abstract] ABSTRACT: The process of electron self-injection in the nonlinear bubble wake generated by a short and intense laser pulse propagating in a uniform underdense plasma is studied by means of fully self-consistent particle-in-cell simulations and test-particle simulations. We consider a wake generated by a non-evolving laser driver traveling with a prescribed velocity, which then sets the structure and the velocity of the wake, so the injection dynamics is decoupled from driver evolution, but a realistic structure for the wakefield is retained. We show that a threshold for self-injection into a non-evolving bubble wake exists, and we characterize the dependence of the self-injection threshold on laser intensity, wake velocity, and plasma temperature for a range of parameters of interest for current and future laser-plasma accelerators. V C 2013 AIP Publishing LLC.
Physics of Plasmas 10/2013; 20. · 2.38 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This is the working summary of the Accelerator Science working group of the
Computing Frontier of the Snowmass meeting 2013. It summarizes the computing
requirements to support accelerator technology in both Energy and Intensity
[Show abstract][Hide abstract] ABSTRACT: Laser plasma accelerators have the potential to reduce the size of future
linacs for high energy physics by more than an order of magnitude, due to their
high gradient. Research is in progress at current facilities, including the
BELLA PetaWatt laser at LBNL, towards high quality 10 GeV beams and staging of
multiple modules, as well as control of injection and beam quality. The path
towards high-energy physics applications will likely involve hundreds of such
stages, with beam transport, conditioning and focusing. Current research
focuses on addressing physics and R&D challenges required for a detailed
conceptual design of a future collider. Here, the tools used to model these
accelerators and their resource requirements are summarized, both for current
work and to support R&D addressing issues related to collider concepts.
[Show abstract][Hide abstract] ABSTRACT: Optical spectra of a drive laser exiting a channel guided laser-plasma accelerator (LPA) are analyzed through experiments and simulations to infer the magnitude of the excited wakefields. The experiments are performed at sufficiently low intensity levels and plasma densities to avoid electron beam generation via self-trapping. Spectral redshifting of the laser light is studied as an indicator of the efficiency of laser energy transfer into the plasma through the generation of coherent plasma wakefields. Influences of input laser energy, plasma density, temporal and spatial laser profiles, and laser focal location in a plasma channel are analyzed. Energy transfer is found to be sensitive to details of laser pulse shape and focal location. The experimental conditions for these critical parameters are modeled and included in particle-in-cell simulations. Simulations reproduce the redshift of the laser within uncertainties of the experiments and produce an estimate of the wake amplitudes in the experiments as a function of amount of redshift. The results support the practical use of laser redshifting to quantify the longitudinally averaged accelerating field that a particle would experience in an LPA powered below the self-trapping limit.
Physics of Plasmas 06/2013; 20(6). · 2.38 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The interaction of high energy electrons, positrons, and photons with intense
laser pulses is studied in head-on collision geometry. It is shown that
electrons and/or positrons undergo a cascade-type process involving multiple
emissions of photons. These photons can consequently convert into
electron-positron pairs. As a result charged particles quickly lose their
energy developing an exponentially decaying energy distribution, which
suppresses the emission of high energy photons, thus reducing the number of
electron-positron pairs being generated. Therefore, this type of interaction
suppresses the development of the electromagnetic avalanche-type discharge,
i.e., the exponential growth of the number of electrons, positrons, and photons
does not occur in the course of interaction. The suppression will occur when 3D
effects can be neglected in the transverse particle orbits, i.e., for
sufficiently broad laser pulses with intensities that are not too extreme. The
final distributions of electrons, positrons, and photons are calculated for the
case of a high energy e-beam interacting with a counter-streaming, short
intense laser pulse. The energy loss of the e-beam, which requires a
self-consistent quantum description, plays an important role in this process,
as well as provides a clear experimental observable for the transition from the
classical to quantum regime of interaction.
Physical Review A 06/2013; 87(6). · 3.04 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The growth of the beam self-modulation and hosing instabilities initiated by a seed wakefield is examined. Although the growth rates for the self-modulation and hosing instabilities are comparable, it is shown that an externally excited wakefield can be effective in selectively seeding the beam radial self-modulation, enabling the beam to fully modulate before strong beam hosing develops. Methods for coherent seeding are discussed.
Physics of Plasmas 05/2013; 20(5). · 2.38 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A method of creating plasma channels with controllable depth and transverse
profile for the guiding of short, high power laser pulses for efficient
electron acceleration is proposed. The plasma channel produced by the
hydrogen-filled capillary discharge waveguide is modified by a ns-scale laser
pulse, which heats the electrons near the capillary axis. This interaction
creates a deeper plasma channel within the capillary discharge that evolves on
a ns-time scale, allowing laser beams with smaller spot sizes than would
otherwise be possible in the unmodified capillary discharge.
Physics of Plasmas 03/2013; 20(2). · 2.38 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The development of models and the “Virtual Detector for Synchrotron Radiation” (vdsr) code that accurately describe the production of synchrotron radiation are described. These models and code are valid in the classical and linear (single-scattering) quantum regimes and are capable of describing radiation produced from laser-plasma accelerators (LPAs) through a variety of mechanisms including betatron radiation, undulator radiation, and Thomson/Compton scattering. Previous models of classical synchrotron radiation, such as those typically used for undulator radiation, are inadequate in describing the radiation spectra from electrons undergoing small numbers of oscillations. This is due to an improper treatment of a mathematical evaluation at the end points of an integration that leads to an unphysical plateau in the radiation spectrum at high frequencies, the magnitude of which increases as the number of oscillation periods decreases. This is important for betatron radiation from LPAs, in which the betatron strength parameter is large but the number of betatron periods is small. The code vdsr allows the radiation to be calculated in this regime by full integration over each electron trajectory, including end-point effects, and this code is used to calculate betatron radiation for cases of experimental interest. Radiation from Thomson scattering and Compton scattering is also studied with vdsr. For Thomson scattering, radiation reaction is included by using the Sokolov method for the calculation of the electron dynamics. For Compton scattering, quantum recoil effects are considered in vdsr by using Monte Carlo methods. The quantum calculation has been benchmarked with the classical calculation in a classical regime.
Physical Review Special Topics - Accelerators and Beams 03/2013; 16(3). · 1.57 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Methods for the calculation of laser tunneling ionization in explicit particle-in-cell codes used for modeling laser–plasma interactions are compared and validated against theoret-ical predictions. Improved accuracy is obtained by using the direct current form for the ion-ization rate. Multi level ionization in a single time step and energy conservation have been considered during the ionization process. The effects of grid resolution and number of macro-particles per cell are examined. Implementation of the ionization algorithm in two different particle-in-cell codes is compared for the case of ionization-based electron injection in a laser–plasma accelerator.
Journal of Computational Physics 01/2013; 236:220-228. · 2.14 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Because of their ultra-high accelerating gradient, laser plasma based accelerators (LPA) are contemplated for the next generation of high energy colliders and light sources. The upcoming BELLA project will explore acceleration of electron bunches to 10 GeV in a meter long plasma, where a wakefield is driven by a PW-class laser. Particle-in-cell (PIC) simulations are used to design the upcoming experiments. Simulations are challenging because of the disparity of length scale between the laser wavelength (~1 micron) that needs to be resolved and the simulation length (~ 1 m). We report on recent developments of the Laser Envelope Model, a reduced model for laser-plasma interactions that has previously demonstrated orders of magnitude speedup. In particular, we present the implementation of the model in cylindrical coordinates, allowing for quite rapid prototyping of laser acceleration stages. We discuss the performance benefits as well as the limitations and trade-offs of this model. In parallel, high frequency noise in PIC simulations makes it difficult to accurately represent beam energy spread and emittance. We show that calculating the beam self-fields using a static Poisson solve in the beam frame dramatically reduces particle noise, allowing for more accurate simulation of the beam evolution.
Plasma Science (ICOPS), 2013 Abstracts IEEE International Conference on; 01/2013
[Show abstract][Hide abstract] ABSTRACT: Radiation pressure is an effective mechanism of momentum transfer to ions in laser plasmas. The energy of ions accelerated by the radiation pressure can be greatly enhanced due to a transverse expansion of a thin target. The ion velocity cannot exceed the pulse group velocity. The beams of accelerated ions are unstable against various instabilities, which results in the target modulations and broadening of the ion energy spectrum.
Lasers and Electro-Optics Pacific Rim (CLEO-PR), 2013 Conference on; 01/2013
[Show abstract][Hide abstract] ABSTRACT: The Virtual Detector for Synchrotron Radiation (VDSR) is a parallel C++ code developed to calculate the incoherent radiation from a single charged particle or a beam moving in given external electro-magnetic fields. In this proceedings the code structure and features are introduced. An example of radiation generation from the betatron motion of a beam in the focusing fields of the wake in a laser-plasma accelerator is presented.
[Show abstract][Hide abstract] ABSTRACT: The operational plasma density and laser parameters for future colliders based on laser-plasma accelerators are discussed. Beamstrahlung limits the charge per bunch at low plasma densities. Reduced laser intensity is examined to improve accelerator efficiency in the beamstrahlung-limited regime.