2002 II 2A

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The ion saturation current is at about -1.3 mA. The electron saturation current is about 12 mA.

The floating potential is at about 2 V. The space potential is at about 40 V.

We know:

V_{sp}-V_{f}=\left(3.3+\ln\mu\right)T

So, for hydrogen μ = 1, and so T\approx40/3.3\approx12\,\mathrm{eV}.

We use the ion saturation current:

Isi = − 0.6neCsA

The sound speed is:

C_{s}=9.79\times10^{5}\mu^{-1/2}T_{i}^{1/2}\mathrm{cm/s}\approx3\times10^{6}\mathrm{cm/s}

The area is:

A=\pi\left(.1\,\mathrm{cm}\right)\left(.5\,\mathrm{mm}\right)=.15\,\mathrm{cm}^{2}

So:

n_{e}\approx\frac{.0013\mathrm{A}}{0.6\cdot\left(.15\,\mathrm{cm}^{2}\right)\left(3\times10^{6}\mathrm{cm/s}\right)e}\approx3\times10^{10}\mathrm{cm}^{-3}

Sheath expansion effects could affect the accuracy of the density estimate, since it varies like the inverse of the sheath area.

This page was recovered in October 2009 from the Plasmagicians page on Generals_2002_II_2A dated 06:07, 14 May 2007.

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