47 research outputs found
Efficient electron injection into plasma waves using higher-orderlaser modes
Using higher-order transverse laser modes as drivers forplasma wave excitation, and, in particular, using a ring laser beam withmaximum intensity off-axis, results in reversal of the focusinganddefocusing phase regions in a laser wakefield accelerator. Thisresults in improved performance of self-trapping and laser injectionschemes. Specifically, the trapping threshold required foropticalinjection is decreased and the maximum energy gain of the trappedelectrons is increased. This scheme could also be of interest for thegeneration of ring electron beams or for beam conditioning
The Isgur-Wise function in a relativistic model for system
We use the Dirac equation with a ``(asymptotically free) Coulomb + (Lorentz
scalar) linear '' potential to estimate the light quark wavefunction for mesons in the limit . We use these wavefunctions to
calculate the Isgur-Wise function for orbital and radial
ground states in the phenomenologically interesting range . We find a simple expression for the zero-recoil slope, , where is the energy eigenvalue
of the light quark, which can be identified with the parameter
of the Heavy Quark Effective Theory. This result implies an upper bound of
for the slope . Also, because for a very light quark the size of the meson is determined mainly by the
``confining'' term in the potential , the shape of
is seen to be mostly sensitive to the dimensionless
ratio . We present results for the ranges of
parameters , and
light quark masses and compare to existing
experimental data and other theoretical estimates. Fits to the data give:
,
and [ARGUS
'93]; , and
[CLEO '93]; ${\bar\Lambda_{u,d}}^2/Comment: 22 pages, Latex, 4 figures (not included) available by fax or via
email upon reques
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Physical Fidelity in Particle-In-Cell Modeling of Small Debye-Length Plasmas
The connection between macro-particle shape functions and non-physical phase-space "heating" in the particle-in-cell (PIC) algorithm is examined. The development of fine-scale phasespace structures starting from a cold initial condition is shown to be related to spatial correlations in the interpolated fields used in the Lorentz force. It is shown that the plasma evolution via the PIC algorithm from a cold initial condition leads to a state that is not consistent with that of a thermal plasma
Nonlinear laser energy depletion in laser-plasma accelerators
Energy depletion of intense, short-pulse lasers via excitation of plasma waves is investigated numerically and analytically. The evolution of a resonant laser pulse proceeds in two phases. In the first phase, the pulse steepens, compresses, and frequency red-shifts as energy is deposited in the plasma. The second phase of evolution occurs after the pulse reaches a minimum length at which point the pulse rapidly lengthens, losing resonance with the plasma. Expressions for the rate of laser energy loss and rate of laser red-shifting are derived and are found to be in excellent agreement with the direct numerical solution of the laser field evolution coupled to the plasma response. Both processes are shown to have the same characteristic length-scale. In the high intensity limit, for nearly-resonant Gaussian laser pulses, this scale length is shown to be independent of laser intensity
Physical Fidelity in Particle-In-Cell Modeling of Small Debye-Length Plasmas
The connection between macro-particle shape functions and non-physical phase-space "heating" in the particle-in-cell (PIC) algorithm is examined. The development of fine-scale phasespace structures starting from a cold initial condition is shown to be related to spatial correlations in the interpolated fields used in the Lorentz force. It is shown that the plasma evolution via the PIC algorithm from a cold initial condition leads to a state that is not consistent with that of a thermal plasma
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Physical Fidelity in Particle-In-Cell Modeling of Small Debye-Length Plasmas
The connection between macro-particle shape functions and non-physical phase-space"heating" in the particle-in-cell (PIC) algorithm is examined. The development of fine-scale phasespace structures starting from a cold initial condition is shown to be related to spatial correlations in the interpolated fields used in the Lorentz force. It is shown that the plasma evolution via the PIC algorithm from a cold initial condition leads to a state that is not consistent with that of a thermal plasma
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Higher-order differencing schemes for modeling intense laser-plasma interactions
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Warm wavebreaking of nonlinear plasma waves with arbitrary phase velocities
A warm, relativistic fluid theory of a nonequilibrium, collisionless plasma is developed to analyze nonlinear plasma waves excited byintense drive beams. The maximum amplitude and wavelength are calculated for nonrelativistic plasma temperatures and arbitrary plasma wave phase velocities. The maximum amplitude is shown to increase in the presence of a laser field. These results set a limit to the achievable gradient in plasma-based accelerators
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Warm wavebreaking of nonlinear plasma waves with arbitrary phase velocities
A warm, relativistic fluid theory of a nonequilibrium, collisionless plasma is developed to analyze nonlinear plasma waves excited byintense drive beams. The maximum amplitude and wavelength are calculated for nonrelativistic plasma temperatures and arbitrary plasma wave phase velocities. The maximum amplitude is shown to increase in the presence of a laser field. These results set a limit to the achievable gradient in plasma-based accelerators
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Thermal effects in intense laser-plasma interactions
We present an overview of a new warm fluid model that incorporates leading-order kinetic corrections to the cold fluid model without making any near-equilibrium assumptions. In the quasi-static limit we obtain analytical expressions for the momentum spread and show excellent agreement with solutions of the full time-dependant equations. It is shown that over a large range of initial plasma temperatures, the fields are relatively insensitive to the pressure force. We discus implications of this work for model validation