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Measurement and modeling of a diamond deposition reactor: Hydrogen atom and electron number densities in an arc jet discharge
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Image of FIG. 1.
FIG. 1.

Cross-sectional schematic diagrams of the torch heads and the arc jet reactor chamber. Labels are defined in the main text. The torch assembly is mounted so that the N torch points towards the center of the substrate holder (i.e., vertically in the main figure).

Image of FIG. 2.
FIG. 2.

Optical emission images of the arc jet plume for an plasma. The right-hand column shows 2D camera images obtained using an interference filter to transmit only H Balmer- emission; the images from top to bottom were taken for flow rates of 0.2, 0.5, 1.0, and of added . Emission was accumulated through neutral-density filters with respective optical densities (OD) of 4.5, 4.5, 3.5, and 2.0, and the contrasts within the images have been arbitrarily scaled for clarity. The left-hand column shows plots of accumulated emission along the central axis of the plume for the same flow rates as the adjacent images, with intensities corrected for the ODs of the neutral-density filters. The front face of the substrate is at .

Image of FIG. 3.
FIG. 3.

The diagonal lines connecting open circles show calculated variations of the required power coupled into the plasma within the N-torch and P-torch head for a range of flows to establish the specified gas temperatures at the nozzle orifice, NZRC. The connected black circles show the experimentally measured power coupled into the plasma (as determined by calorimetric measurements of the power lost to the water flow cooling the torches), from which a gas temperature of is deduced. Argon flow rates were [slm] and in the N and P torches, respectively.

Image of FIG. 4.
FIG. 4.

(Color online) and flow fields for “base” plasma conditions ( and flowing into the N torch, with a further into the P torch), with coupled into the N-torch plasma.

Image of FIG. 5.
FIG. 5.

(Color online) Plots showing the calculated dependence of (—); and the number densities of the eight species included in the chemical kinetic model [i.e., (red 엯), (black ◻), (blue ▵), (violet ▿), Ar (violet ⋆), (cerise ▷), (khaki ◁), and electrons (turquoise ◇)] for input flows in the N torch of (a) , and (b) , . (c) shows the calculated dependencies of all of the corresponding quantities bar , for the case of . Conditions at NZRC in the model are the following: , , for (a) and (b), and , (a); , (b).

Image of FIG. 6.
FIG. 6.

(Color online) Calculated variations of the number densities of , , , and with distance from the nozzle, for two different radial distances . Closed symbols are for and open symbols are for . The different shapes denote the flow rates of , (black squares); (red circles); and (blue triangles).

Image of FIG. 7.
FIG. 7.

The left-hand column shows experimental CRDS measurements (in black) of H Balmer- lines in absorption at four different flow rates of : from top to bottom these are , 0.5, 1.0, and . Also shown overlaid (in grey) are simulations of the absorption features carried out using data from the model calculations of spatially resolved number densities (∎) and electron densities (◻), as plotted in the right-hand column. For clearer comparison with the experimental data, the simulated profiles have been scaled vertically by factors of , , , and for respective flows of , 0.5, 1.0, and .

Image of FIG. 8.
FIG. 8.

A comparison of the model and experimental column densities and electron densities (see details of how these values are derived). The data shown are from the model (∎) and experimental measurements (●), and model (◻) and measured (엯) electron densities. In the constructed absorption profiles at 1.0- and (shown in Fig. 7), no significant Lorentzian contribution can be observed, and thus experimental electron densities are not plotted for these .

Image of FIG. 9.
FIG. 9.

The variation of electron density as determined by measurement of the Stark broadening of the Balmer- line by CRDS, with power delivered to the arc jet, . The dashed line shows a linear fit through the data and the origin.

Image of FIG. 10.
FIG. 10.

Computed electron mole fractions (엯 and left-hand axis) and temperatures (● and right-hand axis) at the nozzle inlet, NZRC, as function of the power to the inlet equilibrium plasma.

Image of FIG. 11.
FIG. 11.

Calculated axial behavior of electron densities at (circles) and (triangles) for different inlet ionization degrees with (open symbols) and corresponding temperatures and .


Generic image for table
Table I.

The kinetic scheme employed in the model. Rate constants are calculated using , with the following units: cal, mol, K, cm, and s.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Measurement and modeling of a diamond deposition reactor: Hydrogen atom and electron number densities in an Ar∕H2 arc jet discharge