Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Characterization of hydrogen plasma in a permanent ring magnet based
  helicon plasma source for negative ion source research   HELicon Experiment for Negative ion source (HELEN-I) with single driver is
developed with a focus on the production of negative hydrogen ions. In the
Helicon wave heated plasmas, very high plasma densities ($\sim10^{19} m^{-3}$)
can be attained with electron temperatures as low as $\sim$1 eV in the
downstream region. These conditions favor the production of negative hydrogen
ions. In HELEN-I device at IPR, helicon plasma is produced using Hydrogen gas
in a diverging magnetic field, created by a permanent ring magnet. RF Power
($P_{RF}$) of 800-1000W at 13.56 MHz frequency is applied to a Nagoya-III
antenna to excite m = 1 helicon mode in the plasma. The plasma is confined by a
multi-cusp field configuration in the expansion chamber. The transition from
inductively coupled mode to Helicon mode is observed near $P_{RF}$ 700W with
plasma density $\sim 10^{18} m^{-3}$ and electron temperature $\sim$ 5 eV in
the driver and $\sim$ 1eV in the expansion volume. Line integrated negative
hydrogen ion density is measured in the expansion chamber by employing an
Optical Emission Spectroscopy (OES) diagnostic technique using
$H_\alpha/H_\beta$ ratio and Laser photo-detachment based Cavity Ring Down
spectroscopic (CRDS) diagnostic technique. The measured value of negative
hydrogen ion density is in the order of $10^{16} m^{-3}$ at 6 mTorr pressure
and does not vary significantly with power in the helicon mode, pressure and
downstream axial magnetic field variation. The negative ion density
measurements are compared with theoretically estimated values calculated using
particle balance method considering different reaction rates responsible for
negative hydrogen ion creation and destruction. It is to be noted that at
present Caesium (Cs) is not injected in the plasma discharge to enhance $H^-$
ion density.

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The categories of this paper are: q-alg
27
The categories of this paper are: comp-gas
0
The categories of this paper are: hep-ph
7
The categories of this paper are: hep-th
35
The categories of this paper are: mtrl-th
23
The categories of this paper are: solv-int
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The categories of this paper are: ao-sci
36
The categories of this paper are: cmp-lg
8
The categories of this paper are: hep-ex
6
The categories of this paper are: astro-ph
5
The categories of this paper are: gr-qc
22
The categories of this paper are: chao-dyn
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The categories of this paper are: quant-ph
9
The categories of this paper are: nlin
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The categories of this paper are: math-ph
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The categories of this paper are: dg-ga