Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Cumulation of High-current Electron Beams: Theory and Experiment   A drastic cumulation of current density caused by electrostatic repulsion in
relativistic vacuum diodes with ring-type cathodes is described theoretically
and confirmed experimentally. The distinctive feature of the suggested
cumulation mechanism over the conventional one, which relies on focusing a
high-current beam by its own magnetic field, is a very low energy spread of
electrons in the region of maximal current density that stems from a laminar
flow profile of the charged-particle beam.

16
The categories of this paper are: stat
6
The categories of this paper are: astro-ph
13
The categories of this paper are: quant-ph
34
The categories of this paper are: chem-ph
19
The categories of this paper are: eess
15
The categories of this paper are: nucl-ex
24
The categories of this paper are: dg-ga
12
The categories of this paper are: nucl-th
4
The categories of this paper are: cond-mat
27
The categories of this paper are: comp-gas
17
The categories of this paper are: q-fin
5
The categories of this paper are: gr-qc
29
The categories of this paper are: funct-an
33
The categories of this paper are: plasm-ph
7
The categories of this paper are: hep-th
18
The categories of this paper are: econ