Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: High brightness and fully coherent x-ray pulses from XFELO seeded
  high-gain FEL schemes   The successful operation of the hard x-ray self-seeding experiment at the
LCLS opens the era of fully coherent hard x-ray free electron lasers (FELs).
However, the shot-to-shot radiation fluctuation is still a serious issue. In
this paper, high-gain, single-pass x-ray FEL schemes seeded by the narrow
bandwidth radiation signal from an x-ray FEL oscillator were proposed and
investigated, which are expected to generate high brightness, fully coherent
and stable x-ray pulse. A simple model has been developed to figure out the
temporal and the spectral structures of the output pulses in x-ray FEL
oscillator. And options using two synchronized accelerators and using one
accelerator were considered, respectively.

19
The categories of this paper are: eess
23
The categories of this paper are: solv-int
34
The categories of this paper are: chem-ph
4
The categories of this paper are: cond-mat
27
The categories of this paper are: comp-gas
18
The categories of this paper are: econ
17
The categories of this paper are: q-fin
2
The categories of this paper are: math
20
The categories of this paper are: acc-phys
36
The categories of this paper are: cmp-lg
29
The categories of this paper are: funct-an
10
The categories of this paper are: q-bio
8
The categories of this paper are: hep-ex
33
The categories of this paper are: plasm-ph
21
The categories of this paper are: adap-org
16
The categories of this paper are: stat