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Download fileAtmospheric Helium Capillary Dielectric Barrier Discharge for Soft Ionization: Determination of Atom Number Densities in the Lowest Excited and Metastable States
journal contribution
posted on 07.01.2014, 00:00 authored by Vlasta Horvatic, Saskia Müller, Damir Veza, Cedomil Vadla, Joachim FranzkeThe populations of the lowest excited
helium states 2s 3S1, 2s 1S, 2p 3P0J, and 2p 1P0 created in an atmospheric
helium capillary dielectric barrier discharge were determined by means
of optical emission spectroscopy. The emitted intensities of 388,
501, 587, and 667 nm lines were measured side-on and end-on with respect
to the discharge axis. The comparison of optically thin side-on spectra
with end-on spectra, which exhibited the absorption effects in the
line kernels, enabled the determination of the average values of the
number densities n1 in the considered
He states along the plasma length L. The field of
the theoretical profiles for a series of the n1L parameters pertinent to the experimental
conditions was calculated for each line. By introducing the experimental
data into the field of calculated curves, n1L corresponding to the particular state could be
obtained. The measurements of the emission profiles were done as a
function of the discharge voltage in the range covering homogeneous
as well as filamentary DBD operation mode. Due to nonuniformity of
the excited atom density distribution along the plasma, the values
of n1 could be obtained only in the homogeneous
operation mode where the nonuniformity was small. The following maximum
values were found for the number densities in the investigated states: n1av (2s 3S1) = (2.9 ± 1.1) × 1013 cm–3, n1av (2s 1S) = (1.4 ±
0.5) × 1013 cm–3, n1av (2p 3P0J) = (1.1 ± 0.4) × 1013 cm–3, n1av (2p 1P0) = (4.2 ± 1.6) × 1012 cm–3, and they represent the average populations along the plasma column
in the capillary.
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number densities n 1filamentary DBD operation mode2 p 3 P 0J2 p 1 P 0n 1L parametershelium states 21avcmatom density distributionAtmospheric Helium Capillary Dielectric Barrier DischargeMetastable StatesThe populations1 Semissionnonuniformity667 nm linesprofileplasma length Lhelium capillary dielectric barrier dischargespectraAtom Number Densities