Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Using pipe with corrugated walls for a sub-terahertz FEL   It has been noted in the past, in the study of the wall-roughness impedance,
that a metallic pipe with corrugated walls supports propagation of a
high-frequency mode that is in resonance with a relativistic beam. This mode
can be excited by a beam whose length is a fraction of the wavelength. In this
paper, we study another option of excitation of the resonant mode in a metallic
pipe with corrugated walls---via the mechanism of the free electron laser
instability. This mechanism works if the bunch length is much longer than the
wavelength of the radiation.

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The categories of this paper are: bayes-an
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The categories of this paper are: hep-lat
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The categories of this paper are: acc-phys
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The categories of this paper are: math
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The categories of this paper are: patt-sol
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The categories of this paper are: nucl-th
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The categories of this paper are: chao-dyn
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The categories of this paper are: alg-geom
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The categories of this paper are: math-ph
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The categories of this paper are: hep-ph
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The categories of this paper are: hep-th
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The categories of this paper are: dg-ga
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The categories of this paper are: stat
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The categories of this paper are: cmp-lg
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The categories of this paper are: eess
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The categories of this paper are: plasm-ph