Plasma Railgun

[elementcollector1]

Why do I not see these being attempted more often? A plasma railgun works the same as a regular railgun, except the armature (and projectile) is ionized gas instead of anything physical. Now, the differences I would imagine are thus:

-The voltage would have to be very high - typical Jacob's Ladders take about 6 kV from a transformer to ionize air.

- Because the projectile isn't solid, it has a lot less friction (and therefore a lot better acceleration and force?)

 

Would the capacitor bank be different? I'm not sure whether plasma would need more or less energy...

[John Cuthber]

Have you ever tried to throw a ball of cotton wool across a room?

[Sensei]

-The voltage would have to be very high - typical Jacob's Ladders take about 6 kV from a transformer to ionize air.

 

6 kV is not very high.

 

I have Cockcroft-Walton generator producing ~40 kV (and expanding its capabilities with time).

It's used in experiments with x-rays in cloud chambers.

 

To fully load you need couple seconds (by 240 VAC @ 50 Hz). At least with electrolytic capacitors (which have pretty high capacitance).

 

These are screen-shots from video with ~25 kV setup.

I have videos showing difference between 6 kV, 10 kV, 25 kV, 40 kV setups.

I can send you videos privately if you're interested.

 

 

 

(whole "explosion" takes less than 1 frame of recording it camera, so sometimes there are misses, recorded just voice without actually picture. I will need to get high speed camera some day..)

 

Why do I not see these being attempted more often? A plasma railgun works the same as a regular railgun, except the armature (and projectile) is ionized gas instead of anything physical.

 

That sounds to me that you want to accelerate plasma using quickly changing magnetic field in barrel. Is that right?

Plasma is highly reactive. It will steal electrons from surrounding it matter, and unpredicted chemical reactions will happen.

Production of ozone is very high with mine above setup (especially with continuous coronal discharge when we will prevent "explosion").

You feel like after summer thunderstorm in seconds.

Edited May 11, 2014 by Sensei

[elementcollector1]

Hmm. Does this mean this cannot be utilized outside of a vacuum or inert atmosphere? If so, that's a damper. Is there risk of electrocution?

What is the container for those two wires in your pictures? It might be a trick of the light, but the second photo appears as if the wires are encased in a glass spheroid. Also, the wires weirdly remind me of those jumper wires I find in my Arduino kits.

John C: Yes. I couldn't get the smaller ones to go across, so I scaled it up a bit.

As for the chemical reactions, the two main ones that come to mind are production of NO₂ and O₃ (as mentioned). While this might result in a bit of a smell, you'd think the speed of the pulse would ensure that not much is produced... right?

When I Googled images of "plasma railgun", I came up with this:

 

 

It's actually a movie, and the picture above only appears for one frame, with a noise like a shotgun. (I wish there was some way to dampen the noise... ah well.)

 

Also, this is such a silly question, but is there any way to change the color of the plasma without resorting to pumping in gases like neon or krypton?

[Sensei]

Hmm. Does this mean this cannot be utilized outside of a vacuum

Vacuum would definitely increase distance plasma is traveling

 

Electron gun requires vacuum.

 

or inert atmosphere?

It will be ionized.

After all it's helium, neon, argon, xenon, etc. gas.

That's how these elements were discovered - by spectral lines present in air spectrum.

Scientists compared air spectrum (from discharge tube) with pure nitrogen and pure oxygen spectrum (from electrolysis or chemical reactions producing them) and noticed difference between them.

 

Is there risk of electrocution?

Yes, of course.

 

One mine colleague touched it when it was loaded 3 kV and since that moment he doesn't touch anything in lab anymore without asking..

You could smell of burning flesh (literally)..

I touched CW generator electrodes with 6 kV accidentally once too.

Somebody called me, in the middle of experiment, and I forgot to discharge capacitors entirely. When I returned, touched it and fall it..

Mine hand shake after several hours after that.

 

What is the container for those two wires in your pictures?

I had to use something that is not metal.

It's 1mm thick cardboard.

If we will place it between two electrodes with 25 kV, and wait couple seconds (double or triple as long as without cardboard between them) electric arc will be very powerful and will cut cardboard making pretty big hole in it.

 

It might be a trick of the light, but the second photo appears as if the wires are encased in a glass spheroid.

 

There is no glass, there is nothing surrounding it.

 

When you will take glass tube/pipe, attach electrodes from both sides and seal ends, and fill by some gas (hydrogen, oxygen, chlorine, I have created from electrolysis, CO₂ from dry ice, air), optionally lower pressure, you will have self made discharge tube.

 

Also, the wires weirdly remind me of those jumper wires I find in my Arduino kits.

Pretty close.

They are standard wires for connecting breadboards.

Mine cascade generators are on breadboards, so I can freely connect/disconnect them together.

Although I saw on the net people are taking transparent kitchen plastic boxes like this one

 

making 4 holes, attaching banana connectors to it from both sides, and putting capacitor bank inside, filling by mineral oil, and sealing them permanently.

 

But if some capacitor will blow up, you have problem how to fix it.

 

Also, this is such a silly question, but is there any way to change the color of the plasma without resorting to pumping in gases like neon or krypton?

 

Free nucleus is attracting free (or not) electron.

Electron is emitting photon, or multiple photons with various frequencies, and is attracted more and more by nucleus.

And these photons is what we see as color of plasma.

 

With graphite electrodes I had red sparks.

Edited May 12, 2014 by Sensei

[elementcollector1]

So, to change the wavelength of the emitted photons, I would (might) have to change the electrodes? Sounds doable, thanks.

Although, could carbon electrodes even be used for a railgun?

What's your circuit for your cascade generator?

[Sensei]

So, to change the wavelength of the emitted photons, I would (might) have to change the electrodes? Sounds doable, thanks.

 

No. It's very small red spot. So small you probably wouldn't see it if I would make photo (something like 1-2 mm).

Mine point was- you cannot change color of plasma.

Edited May 12, 2014 by Sensei

[elementcollector1]

Ah. Unfortunate. Oh well, it was rather impractical.

Again, what circuit and power source do you use? I've seen a couple different variations.

[Sensei]

There are generally two.

I can switch between them, by just reconnecting wires.

 

 

(mine has more than 70 stages)

Edited May 12, 2014 by Sensei

[studiot]

 

One mine colleague touched it when it was loaded 3 kV and since that moment he doesn't touch anything in lab anymore without asking..

You could smell of burning flesh (literally)..

I touched CW generator electrodes with 6 kV accidentally once too.

Somebody called me, in the middle of experiment, and I forgot to discharge capacitors entirely. When I returned, touched it and fall it..

Mine hand shake after several hours after that.

 

 

If you are also experimenting with radar/microwaves please, please remove any rings, watches with metal straps or any complete circles of metal.

 

I know of at least one engineer who lost a finger becuase of this.

 

go well

[elementcollector1]

And I'm guessing the AC voltage source is an outlet, judging from this and your earlier comments on using 240 VAC. Personally, I'd rather avoid outlets, and instead use a battery or some such (probably leading to significantly less ability), but whatever. I've seen boost converters in those disposable cameras manage to ionize krypton for the flash at 350 V (DC?) while being powered by a single AA, so ionizing the gas with a battery is most likely not the problem.

 

From earlier experiments and questions, I've learned that the magnetic force a railgun exerts is limited by the current through the rails. Not knowing anything about the relationships of voltage and current for AC circuits, if the voltage were increased wouldn't the current fall proportionally?

[Sensei]

CW generator doesn't work with DC at all. It requires AC, AFAIK.

I have tried with 240 VDC, and it simply didn't load at all.

 

You can, or if you're using ceramic capacitors even have to, first convert 240 VAC to DC, then make your own AC from DC with required by device higher frequency than 50 Hz.

And then multiply voltage by CW to really high.

I've seen boost converters in those disposable cameras manage to ionize krypton for the flash at 350 V (DC?) while being powered by a single AA, so ionizing the gas with a battery is most likely not the problem.

A lot depends on pressure of gas. Krypton is inside of hermetic tube. It can have pretty low pressure. Checking it would require destroying device.

From earlier experiments and questions, I've learned that the magnetic force a railgun exerts is limited by the current through the rails. Not knowing anything about the relationships of voltage and current for AC circuits, if the voltage were increased wouldn't the current fall proportionally?

I don't have experience with rail guns nor plasma guns (who on this forum has? )

But I think you mixed two things.
(typical) electromagnet requires DC (with pretty low voltage, it's after all just wire with low resistance).
And the higher current you will provide to electromagnet (or just wire), the higher magnetic field you will receive surrounding them.
If you will swap direction, you will change electromagnet from attracting to repelling. But 50 Hz constantly switching back and forth directions will be probably completely useless for railgun (that's typical transformer). You want attract projectile once, then repel and done. When first stage is repelling, second stage has to be attracting with even more power, so projectile is accelerated in that direction.

AC for CW generator is another circuit, independent from electromagnets. CW current is always DC on output. It's purpose to ionize, and nothing more. You don't use such high voltage to power electromagnets (it would be senseless and most probably would blow up wires and/or capacitors).
In electron gun, indeed such high voltage is used to attract electrons. And they fly through hole in anode. Real magnets are disallowing them to join with anode, and then they continue flying further in vacuum.

Edited May 12, 2014 by Sensei

[John Cuthber]

What are people trying to do here?

Shooting plasma across the room is pretty much a non-starter.

Interestingly, though he didn't know anything about plasma, Newton could have explained the expected range of your weapon.

http://en.wikipedia.org/wiki/Impact_depth

 

He may, or may not, have experimented with throwing feathers and such.

[elementcollector1]

Maybe not across the room! Just enough to exert a force on an object without touching it.

While I read the page, I don't come across much to do with such low-density 'projectiles' as plasma, and wouldn't it *not* have a fixed volume, length or anything?

Hmm. So, I guess the analogy was imperfect - but then why does the plasma in a railgun accelerate in a specific direction? If the voltage constantly reversed, it would be accelerated in two different directions equally. My guess would be to include an AC/DC converter to charge up a massive capacitor bank for use in the railgun. But then, would it ionize? Probably not, if you're correct - unless ionization in this case has less to do with voltage and more to do with energy provided.

This has me wondering how a plasma railgun even works at all!

[Sensei]

Maybe not across the room! Just enough to exert a force on an object without touching it.

Result of plasma shot is destruction or damaging of thing that you shot, not "exerting a force" like it would be some kind of slowly moving ball...

On website's movies where you found above screen-shots you can see how they damaged target.

 

Space shuttles and space station look like Swiss cheese (under microscope) due to constant hitting them by protons accelerated to relativistic speeds from the Sun and other stars. Holes have diameter of single atom or so.

 

but then why does the plasma in a railgun accelerate in a specific direction?

Imagine you have piece of metal/iron, and turn on powerful electromagnet above it.

Metal "jumps" attracted to electromagnet.

So imagine couple electromagnets in row, one more powerful than the other.

And they are switching in right order, precisely synchronized.

When previous stops working, next one in queue is starting attracting...

 

Difference between particle accelerators and plasma railgun is just in details (like using vacuum in accelerators (which limits loses of energy), large size, and circular path).

 

If the voltage constantly reversed, it would be accelerated in two different directions equally. My guess would be to include an AC/DC converter to charge up a massive capacitor bank for use in the railgun. But then, would it ionize? Probably not, if you're correct - unless ionization in this case has less to do with voltage and more to do with energy provided.

This has me wondering how a plasma railgun even works at all!

 

Positive electrode of DC circuit attracts electrons.

Electron escape atom, and goes to circuit.

Then atom that's near first ionized atom gives its electron to previously ionized.

And it goes and goes through medium.

Electrons starts flowing through path made by positively charged atoms.

Negative electrode of circuit has excess of electrons (they are residing inside of capacitors) and gives them to ionized atoms.

 

At 10-12 kV of DC made by CW generator I can see how it SLOWLY happens.

It builds up a few seconds.

It's the best view in darkness. Violet photons are emitted by thin a few cm length thunderbolts.

http://en.wikipedia.org/wiki/Corona_discharge

http://en.wikipedia.org/wiki/Electrical_discharge

 

 

When these lines of ionized atoms from positive electrode join negative electrode, there is "explosion" and instant discharge of CW capacitors (and we see flash, loud voice, and sphere of plasma like in #3 post), and everything starts from beginning.

 

unless ionization in this case has less to do with voltage and more to do with energy provided.

 

Energy is charge in Coulombs * Voltage

E=Q*U

Q=I*t

 

Q divided by e is quantity of electrons in this case.

1 C/1.602*10^-19 C = 6.25*10^18 electrons.

 

If we have voltage like 6 kV it will make plasma when distance between electrodes is like 1-2 mm or so.

If we will move them a bit further, nothing will happen.

But when we will increase voltage to f.e. 12 kV, it will again start working.

After further moving away, it's stopping working again.

For really large distances there are needed millions of volts.

Edited May 14, 2014 by Sensei

[elementcollector1]

So, it's less like a true railgun and more akin to a multi-stage coilgun? Confusing.

The Wiki page for plasma railguns states that they can "produce controlled jets of given densities and velocities ranging from 5 to 200 km/s".

 

So, this is not a suitable method for "pushing" a given object without touching it, due to damage of the target. Does anyone know other means of accomplishing this? I'd rather not resort to electromagnetism, as that only affects magnets, and ferromagnetic and diamagnetic materials.

[Heroprime]

The main problem is maybe the efficiency of that sort of gun. I'm not sure how much uf plasma you'll need to burn though a tank.