Generation of Large Electrostatic field

Hello,

I'm trying to figure out a simple way in which to create a large, static electric field (at least 10^4 V/m, if not 10^5 or even higher) over a short distance (about, or less than, 1cm). Could I simply hook some high voltage source up to a parallel plate type configuration and put them close together? Obviously if the field is larger than the dielectric strength of air this would have to be done in vacuum, but are there any other special considerations for generating large electric fields? Can this large field be created with "standard" lab equipment?

Reply to
diogenes500
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snipped-for-privacy@gmail.com a écrit :

Yes.

The most important is to keep your hands away.

Yes.

André Michaud

Reply to
srp

Since you have 1cm or less you need only 100, if not only 1000 volts to generate your 10^4 V/m or 10^5 V/m. 1000 volt dc bench supplies aren't that hard to buy or build.

Now if you wanted it with the plates separated by 10 meters, then that would be more challenging :) And perhaps something for Van De Graff.

Reply to
Don Taylor

You might try re-posting your query over in sci.space.science. A couple of regular posters there are active participants in space experiments that involve such equipment.

ciao,

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Jonathan Thornburg -- remove -

Hi,

Try this link:

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Tesla coils and at the bottom the Van de Graaf generators.

Reply to
KC

10^5 volts/meter is not a particularly high field. For example, At 1 cm, and normal temperature and pressure, the breakdown voltage of a 1 cm gap is about 30KV (doesn't increase linearly with gap width). This is for a uniform gap - either large plates with radiused edges (to eliminate edge effects), or, as used in labs, spheres of the order of 20 to 30cm diameter.

Now, if you are going to put something into this field, the breakdown voltage may be significantly reduced.

However, from the tenor of your question, I strongly suggest that you stay away from high voltage experimentation until you learn more.

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Reply to
Don Kelly

sure, no problem. 10^4 v/m is only 100v across 1cm, easy. 10^5 v/m is only

1000v at 1cm, you can get up to about 10,000 v across 1cm of air or 10^6v/m before it breaks down if its dry and clean. beyond that you need something better, like a vacuum or some other dielectric material. you should also have smooth and flat plates, have them bend in a wide radius away from each others at the ends to limit fringe effects, and lots of safeties and interlocks. high voltage power supplies are available up to at least 100kv dc, beyond that it starts to really get expensive.
Reply to
Dave

That's not really very large. Wires carrying house current (120 V in the U.S.) can be stripped and held ~3 mm apart without breaking down the air (60 Hz ac is essentially dc as far as breakdown is concerned). That's

4*10^4 V/m. A classroom Van De Graff machine generates ~200,000 Volts over ~0.5 meter, which is 4*10^5 V/m -- in this case ionization of the air is usually quite apparent.

In modern particle accelerators, gradients of 5 MegaVolts/meter are common, but this is using RF frequencies, not dc. In tests we have achieved over 80 MegaVolts/meter (in high pressure hydrogen gas, using RF at 805 MHz).

10^4 V/m over 1 cm is just 100 Volts. That's easy. Doing 10^5 V/m you'll need to be sure that all surfaces are smooth (because sharp corners will ionize the air, and could initiate sparking).

Plates connected to a lab ~100 Volt power supply and separated by 1 cm is easy.

Watch your fingers! -- you seem quite unknowledgeable about this sort of apparatus. I recommend getting someone with experience to assist -- these things can be dangerous.

Tom Roberts snipped-for-privacy@lucent.com

Reply to
Tom Roberts

Have not done any calculations, but a simple vacuum does not necessarily add much to dielectric strength. It probably would arc easily. So i would suggest an insulator that would do two things for you: 1) the higher dielectric constant, therby making it easier to get a larger electric field for a given voltage source, and 2) the possibility of standing off that much field strength without arcing.

Reply to
Robert Baer

It makes matters worse, in fact, till you get to really good vacuum. On pumping down from atmospheric pressure to 1 torr dielecetric strength decreases dramatically and remains quite poor to around

10^(-2)-10^(-3) torr. Then it starts improving but ou have to get to circa 10^(-5) or so before you get back to atmospheric levels.

Mati Meron | "When you argue with a fool, snipped-for-privacy@cars.uchicago.edu | chances are he is doing just the same"

Reply to
mmeron

snipped-for-privacy@gmail.com wrote in news: snipped-for-privacy@g44g2000cwa.googlegroups.com:

Take a look at Wimshurst Static Generator,

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I made one, go to sunday flea market, buy two 33rpm records. Buy copper snail tape and tape small 1/2" copper to vinyl record, spaced evenly apart. Buy two toothbrushes. These will rub against the record and copper tape. You can design the round probes your way. Turn the crank, a twisted rubber band will make one record spin in the opposite direction.

Try aluminum tape for air condition duct, instead of copper tape. Try other plastic discs that are about 12" in diameter. Try a small motor to turn the discs.

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Reply to
nobody home

First off, dry air breaks down at around 30kV/cm. Use a vacuum or something like SF6 if you want higher field strengths. Getting the required voltage is no problem, unless you want it very precise - use a toy Van Der Graaf generator.

However, that is the least of your problems. The major problem is that field strengths increase as the radius of curvature of the conductor decreases. That's why field strength at a needle point can be millions of volts mer metre while the applied voltage is in the hundreds or thousands. It's why ion wind streams from needle points.

If you have a parallel plate capacitor it's the *edges* that are very sharp (comparatively) and where the breakdown or ion winds will start.

You need two oblate spheroids whose flat portions face each other in order to get a uniform field over a small area.

Dirk

Reply to
Dirk Bruere

Which reminds me. Do not on any account use a high current PSU! You will probably die! Even a TV CRT HV supply at 25kV and a few mA will cause a massive shock and possibly burns if you mess with it. The only bonus being that it will probably not kill you, unless you are unlucky.

30kV at amperes will blast the flesh from your bones. 10mA will hurt, 100mA will kill.

Dirk

Reply to
Dirk Bruere

Check

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Reply to
AntiSPAM_g9u5dd43

This site might be of interest since part of it deals with HV circuits and discharges in a relatively safe manner

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Dirk

Reply to
Dirk Bruere

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