Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Undulator radiation in the THz range   The experimental device for generation of undulator radiation in terahertz
wavelength region by use of undulator on ferromagnets is created. The device is
based on a beam of a microtrone with the energy 7.5 MeV. The radiation
wavelength is 200 micron. Registered spontaneous radiation has a power of 10
microwatt at a current of a beam 2 mA in a pulse. With the optical resonator,
in a mode, the amplification of 6 percent is received, that in some times is
more than expected value. This effect is explained as a result of partial
coherence of radiation.

18
The categories of this paper are: econ
27
The categories of this paper are: comp-gas
37
The categories of this paper are: supr-con
6
The categories of this paper are: astro-ph
28
The categories of this paper are: alg-geom
30
The categories of this paper are: q-alg
1
The categories of this paper are: cs
31
The categories of this paper are: ao-sci
8
The categories of this paper are: hep-ex
14
The categories of this paper are: math-ph
26
The categories of this paper are: bayes-an
34
The categories of this paper are: chem-ph
11
The categories of this paper are: hep-lat
9
The categories of this paper are: nlin
22
The categories of this paper are: chao-dyn
17
The categories of this paper are: q-fin