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The use of dc glow discharges as undergraduate educational tools
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10.1119/1.4811435
/content/aapt/journal/ajp/81/9/10.1119/1.4811435
http://aip.metastore.ingenta.com/content/aapt/journal/ajp/81/9/10.1119/1.4811435
View: Figures

Figures

Image of Fig. 1.
Fig. 1.

General schematic of a glow discharge incorporating a movable cathode, a permanent magnet, a Helmholtz coil, and Langmuir probe. The dc glow has an anode (a) and a cathode (c) housed in a glass vessel. The electrodes are powered by a high-voltage power supply in series with a ballast resistor. The vacuum system controls the gas pressure via a coarse (ball) and fine (needle) valve that leaks gas into an inlet port while the vacuum pump removes gas through the outlet port.

Image of Fig. 2.
Fig. 2.

(Color online) Three educational plasma devices based on dc glow discharges: (a) a basic, introductory laboratory device, (b) and (c) an advanced dc glow discharge with magnets, (d) a discharge with Langmuir probes. See text for more details.

Image of Fig. 3.
Fig. 3.

The electrical breakdown voltage depends on the pressure of the gas and the distance between the high-voltage electrodes (circles, experimental data; curve, Eq. (1) with constants for air).

Image of Fig. 4.
Fig. 4.

The relationship between resistance and current for an air plasma at 3.2 Pa (circles, experimental data; curve, fit to Ohm's Law).

Image of Fig. 5.
Fig. 5.

Survey spectrum (a) and high-resolution spectrum (b) of argon taken in the 780–920 nm range yields spectral lines used to construct a Boltzmann plot (c) in the positive column. The linear fit yields an electron temperature of ∼0.5 eV.

Image of Fig. 6.
Fig. 6.

The ratio of visible plasma area inside and outside of the Helmholtz coil as a function of increasing magnetic field. The radius of the plasma in the vertical direction was estimated through a moment analysis that fits the visible plasma to an ellipse. The radius was then used to estimate for different field strengths (circles). A linear fit (curve) demonstrates that magnetic flux is conserved.

Image of Fig. 7.
Fig. 7.

Data set from the Langmuir probe. Below the floating potential , ion current is dominant; above, only electron current is collected. The inset shows the data in the electron collection region plotted on a semi-logarithmic scale.

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/content/aapt/journal/ajp/81/9/10.1119/1.4811435
2013-09-01
2014-04-18
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: The use of dc glow discharges as undergraduate educational tools
http://aip.metastore.ingenta.com/content/aapt/journal/ajp/81/9/10.1119/1.4811435
10.1119/1.4811435
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