Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Comparison Between, and Validation Against an Experiment of, a
  Slowly-Varying Envelope Approximation Code and a Particle-in-Cell Simulation
  Code for Free-Electron Lasers   Free-electron lasers (FELs) operate at wavelengths down to hard x-rays, and
are either seeded or start from noise. There is increasing interest in x-ray
FELs that rely on Self-Amplified Spontaneous Emission (SASE), and this involves
increasing simulation activity in the design, optimization, and
characterization of these x-ray FELs. Most of the simulation codes in use rely
on the Slowly-Varying Envelope Approximation (SVEA) in which Maxwell's
equations are averaged over the fast time scale resulting in relatively small
computational requirements. While the SVEA codes are generally successful, the
predictions of these codes sometimes differ in various aspects of the FEL
interaction. In contrast, Particle-in-Cell (PiC) simulation codes do not
average Maxwell's equations and are considered to be a more complete model of
the underlying physics.Unfortunately, they require much longer run times than
SVEA codes and have not been validated by comparison with experiment as often
as the SVEA codes. In order to remedy this, and to resolve issues that arise
due to different predictions between the SVEA codes, we present a comparison
between one SVEA code (MINERVA) and a PiC simulation code (PUFFIN) with the
experimental measurements obtained at the SPARC SASE FEL experiment at ENEA
Frascati. The results show good agreement between the two codes and between the
codes and the experiment. Since the formulations of the two codes share no
common elements, this validates both formulations and demonstrates the
capability to model the FEL interaction from the start of teh undulator through
the undulator and into deep saturation.

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The categories of this paper are: cond-mat
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The categories of this paper are: cs
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The categories of this paper are: stat
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The categories of this paper are: adap-org
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The categories of this paper are: q-fin
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The categories of this paper are: nlin
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The categories of this paper are: atom-ph
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The categories of this paper are: hep-ex
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The categories of this paper are: cmp-lg
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The categories of this paper are: nucl-th
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The categories of this paper are: math-ph
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The categories of this paper are: hep-lat
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The categories of this paper are: funct-an
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The categories of this paper are: q-bio
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The categories of this paper are: math
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The categories of this paper are: ao-sci