Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Negative-hydrogen-ion production from a nanoporous 12CaO $\cdot$ 7Al2O3
  (C12A7) electride surface   A high production rate of negative hydrogen ion was observed from a
nanoporous C12A7 electride surface immersed in hydrogen/deuterium low-pressure
plasmas. The target was biased at 10-170 V negatively and the target surface
was bombarded by H3 + ions from the plasma. The production rate was 1-2 orders
higher than a clean molybdenum surface. The measured H-energy spectrum
indicates that the major production mechanism is desorption by sputtering. This
material has potential to be used as production surface of cesium-free negative
ion sources for accelerators, heating beams in nuclear fusion, and surface
modification for industrial applications.

37
The categories of this paper are: supr-con
29
The categories of this paper are: funct-an
26
The categories of this paper are: bayes-an
6
The categories of this paper are: astro-ph
10
The categories of this paper are: q-bio
9
The categories of this paper are: nlin
2
The categories of this paper are: math
24
The categories of this paper are: dg-ga
36
The categories of this paper are: cmp-lg
1
The categories of this paper are: cs
25
The categories of this paper are: patt-sol
4
The categories of this paper are: cond-mat
31
The categories of this paper are: ao-sci
5
The categories of this paper are: gr-qc
16
The categories of this paper are: stat
32
The categories of this paper are: atom-ph