Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Spectrally peaked proton beams shock accelerated from an optically
  shaped overdense gas jet by a near-infrared laser   We report on the generation of impurity-free proton beams from an overdense
gas jet driven by a near-infrared laser ($\lambda_L=1.053$ $\mathrm{\mu} m$).
The gas profile was shaped prior to the interaction using a controlled
prepulse. Without this optical shaping, a 30$\pm$4 nCsr$^{-1}$ thermal spectrum
was detected transversely to the laser propagation direction with a high energy
8.27$\pm$7 MeV, narrow energy spread (6$\pm$2 %) bunch containing 45$\pm$7
pCsr$^{-1}$. In contrast, with optical shaping the radial component was not
detected and instead forward going protons were detected with energy 1.32$\pm$2
MeV, 12.9$\pm$3 % energy spread, and charge 400$\pm$30 pCsr$^{-1}$. Both the
forward going and radial narrow energy spread features are indicative of
collisionless shock acceleration of the protons.

9
The categories of this paper are: nlin
22
The categories of this paper are: chao-dyn
11
The categories of this paper are: hep-lat
6
The categories of this paper are: astro-ph
24
The categories of this paper are: dg-ga
2
The categories of this paper are: math
31
The categories of this paper are: ao-sci
23
The categories of this paper are: solv-int
33
The categories of this paper are: plasm-ph
18
The categories of this paper are: econ
13
The categories of this paper are: quant-ph
37
The categories of this paper are: supr-con
0
The categories of this paper are: hep-ph
32
The categories of this paper are: atom-ph
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The categories of this paper are: hep-th
25
The categories of this paper are: patt-sol