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Plasma as wire?

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Selenite

Fri Aug 05 2011, 04:59AM

Registered Member #4046 Joined: Fri Aug 05 2011, 03:55AM
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Is it possible to use plasma as conducting 'wire' to conduct direct current electricity at low(where low is preferably under 100 V) voltages and high currents without the plasma pinching up and melting the electrodes? Would RF excited/microwave plasma pass large amounts of current at low voltages without the plasma pinching, or at the very least not melting/eroding/vaporizing the electrodes?

Or is there a way to prevent a plasma arc between two large area electrodes from pinching so that the area of the arc covers the whole electrode, thus preventing the electrode from being ablated?

Forty

Fri Aug 05 2011, 06:12AM

Registered Member #3888 Joined: Sun May 15 2011, 09:50PM
Location: Erie, PA
Posts: 649

for plasma to be your conductor at that low of a voltage, you'd need the plasma to practically be in direct contact with the electrodes. If you don't want the electrodes to melt, you'd need a relatively cold plasma. i've only read into one method for making cold plasma, and it involved high voltages. and i'm sure the rf and microwave coupled plasmas would involve hv too. (it sounds like you want to avoid high voltage)

parallel and smooth electrodes should theoretically spread an arc out evenly, but that's pretty unlikely in reality. if it's a switch that you need to not ablate, then slamming the electrodes plates together really fast helps.
If it has to be an arc between two electrodes, then maybe a triggered spark gap would work. if you could set up the triggering electrode in such a way that it generates a uniform E field between the conductor electrodes when it fires, then it may cause an even breakdown between the plates. (i'm picturing two round plates as the conductors, and a ring of wire around the gap between them, spaced evenly from the plates)

are you trying to solve a problem you're having, or just brainstorming? a little more of a description of what you're trying to do would help.

Conundrum

Fri Aug 05 2011, 06:47AM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4061

Fascinating.

Some research was done into cold plasmas for medical applications, but my understanding was that the plasma behaved in this way because it was a poor conductor.

Yes you can use ion rich plasmas as conductors i.e. flame triode, but the conductivity is likely to be very limited due to the low number of ions compared with even a liquid such as sodium bicarbonate.

Unless some bright spark figures out how to make a plasma superconduct, but AFAIK this is not possible.

-A

Ash Small

Fri Aug 05 2011, 09:07AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Selenite wrote ...

Is it possible to use plasma as conducting 'wire' to conduct direct current electricity at low(where low is preferably under 100 V) voltages and high currents without the plasma pinching up and melting the electrodes?

HF TIG welders do exactly this. The HV HF keeps the plasma going (or, at least, ignites it), and low voltage AC or DC ~25V @ up to 300-400 amps (for aluminium welding) flows through the plasma. Tungsten electrodes are used, which do wear away slowly.

(Also, RIE, PECVD, etc (reactive ion etching, plasma enhanced chemical vapour deposition) use inductively coupled plasma and electrodes at ~similar voltages, but does require vacuum equipment)

Selenite

Fri Aug 12 2011, 12:57AM

Registered Member #4046 Joined: Fri Aug 05 2011, 03:55AM
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@Forty, looked into using cold plasmas, problem is most cold plasma can only conduct electricity through very short distances(~1 cm). That's hardly enough to be considered wire.

Triggered spark gaps work well for low currents, but experience ablation when operating at high currents. This happens because small arcs form over the electrode plate, each arcs creates a magnetic field which attracts other arcs(pinching). Thus the small arcs pull together into one arc increasing the current density to the point of destroying the electrodes.

@Ash Small, I thought RIE, PECVD, etc used low currents and high voltages? How much of a vacuum is required for this sort of thing? Can these processes be carried out around 2-10 torr?

Pinky's Brain

Fri Aug 12 2011, 08:46PM

Registered Member #2901 Joined: Thu Jun 03 2010, 01:25PM
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Posts: 837

For pulsed switching they occasionally use lasers powerful enough to create a plasma across the entire gap volume ... but at 100 volt you're probably not switching pulses.

Maybe you could walk the plasma with electromagnets to move it around the electrode and spread the heating even with the pinching?

Ash Small

Fri Aug 12 2011, 09:28PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Selenite wrote ...

.
@Ash Small, I thought RIE, PECVD, etc used low currents and high voltages? How much of a vacuum is required for this sort of thing? Can these processes be carried out around 2-10 torr?

Some processes use DC bias as low as 100V. I'm sorry I can't provide a full explanation, I'm still researching this subject myself.

Mattski

Sat Aug 13 2011, 03:53AM

Registered Member #1792 Joined: Fri Oct 31 2008, 08:12PM
Location: University of California
Posts: 527

What will your current return path be? There has to be one, and for a DC current it would have to be earth ground, a conductor, or another plasma arc. Otherwise you would need an AC current as this can flow across whatever capacitance exists between your target and your current return path, but to get much current this way frequency must be large, or capacitance must be large.

Selenite

Thu Aug 18 2011, 02:58AM

Registered Member #4046 Joined: Fri Aug 05 2011, 03:55AM
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Return path would be another conductor.

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