Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Cancellation of RF Coupler-Induced Emittance Due to Astigmatism   It is well-known that the electron beam quality required for applications
such as FELs and ultra-fast electron diffraction can be degraded by the
asymmetric fields introduced by the RF couplers of superconducting linacs. This
effect is especially troublesome in the injector where the low energy beam from
the gun is captured into the first high gradient accelerator section.
Unfortunately modifying the established cavity design is expensive and time
consuming, especially considering that only one or two sections are needed for
an injector. Instead, it is important to analyze the coupler fields to
understand their characteristics and help find less costly solutions for their
cancellation and mitigation. This paper finds the RF coupler-induced emittance
for short bunches is mostly due to the transverse spatial sloping or tilt of
the field, rather than the field's time-dependence. It is shown that the
distorting effects of the coupler can be canceled with a static (DC) quadrupole
lens rotated about the z-axis.

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The categories of this paper are: hep-th
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The categories of this paper are: gr-qc
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The categories of this paper are: econ
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The categories of this paper are: chao-dyn
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The categories of this paper are: cs
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The categories of this paper are: hep-ex
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The categories of this paper are: solv-int
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The categories of this paper are: nucl-ex
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The categories of this paper are: patt-sol
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The categories of this paper are: chem-ph
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The categories of this paper are: quant-ph
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The categories of this paper are: q-alg
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The categories of this paper are: dg-ga
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The categories of this paper are: cmp-lg
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The categories of this paper are: astro-ph
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The categories of this paper are: bayes-an