ion gun in regular air

[aussie_laser_dude]

Trying a fun thought experiment, a little stuck, figured someone on here may understand, or even have some practical experience in a similar technology like electron guns.

I'm trying to think how an ion propulsion system could work in regular air with no stored exhaust fuel (just pushes the air), my design so far is simple. Two highly charged parallel metal rings, the electric field causes dielectric breakdown and acceleration of the ions resulting in thrust. There's some parts I'm a bit unsure about:

Q1. In design a) For high electric fields, will current just leak between the rings? I've proposed a solution of encasing the rings in teflon, do you think this would actually work?

Q2. In design b) Will negative electrons "stick" on the teflon near the positive ring, and positive ions "stick" to the teflon near the negative ring, resulting in a low/zero electric field?

Cheers for any thoughts

[ChristofferB]

Your ions will be decelerated by hitting ambient air, I dont think you'll see any acceleration in air to be honest.

And yes, I'm fairly certain you'll see a current between the rings. It's wrong to call this leakage, as a charged particle beam by definition carries charge.

I'm not sure what you're trying to achieve. I guess you could have an accelerated beam generated in vacuum and then projected through a thin film out into air but that's just any old beamline.

[helius]

For an ion thruster you can build yourself in a day and actually see work, you can study the "lifter".
https://rimstar.org/sdprop/lifter/lifter.htm

The two electrodes need to be physically different shapes for the effect to work.

[sandalcandal]

Actually pretty well known and has been done in many forms including a small RC aircraft.


More rudimentary versions have been made by hackers and hobbyists for a long time with some frauds trying to sell them as anti gravity devices. I remember mythbusters made one wayback in an episode airing in 2006. Best I could find was this crappy video


Effect has also been used to make loudspeakers.

http://www.electrostatics.org/images/esa_2008_a2.pdf
http://tmms.co.jp/EFD/Industrial_issues/Plasmasonic.htm
https://hackaday.io/project/7875-ion-wind-loudspeaker-experiments

You just need some electrodes with some sharp edges to get E field concentration and a high enough voltage.

Big issue with these systems is the ozone and NOx they generate as a result of electric discharge into air.

Keywords: Ion wind, corona wind, ionocraft, ionic wind, "lifter"

Edit: Also a decent video explaining how lifters work

[sandalcandal]

Q1. In design a) For high electric fields, will current just leak between the rings? I've proposed a solution of encasing the rings in teflon, do you think this would actually work?

For high electric fields, air will be ionised near the electrodes and ionised molecules will drift between the electrodes causing a small current. You can't be accelerating particles without any current, that'd violate conservation of energy: air current is induced therefore there is kinetic energy being given, energy comes from in this case electrical current flow across high voltage potential of the electrodes P=IV

Q2. In design b) Will negative electrons "stick" on the teflon near the positive ring, and positive ions "stick" to the teflon near the negative ring, resulting in a low/zero electric field?

Covering an electrode in an insulator will indeed prevent electrons being transferred to/from the electrode but if the electric field is strong enough ions will still be generated on the insulated electrode but leave opposite ions directly on the insulated surface. Eventually charge build up will reduce the potential and E field to the point the it can no longer produce more ions as you have guessed.
Edit: The field can also be weakened without charge transfer through gathering molecules with induced dipoles or maybe not, not sure actually.
Edit2:  Gauss's law would indicate field should remain unless air volume is completely filled with dipoles? Attraction of dipoles should eventually stop if electrodes are not further charged though so maybe a slight reduction in E field as inducted dipoles are attracted and build up?

[aussie_laser_dude]

Thanks for the reply guys. The lifters link is interesting, I must admit youtube lifter videos inspired this design attempt.

Here's why I'm doing this:
1. Rockets are heavy, mostly from fuel used to lift more fuel that is used to lift even more fuel etc. Ion propulsion of surrounding air means hundreds of tonnes of rocket weight can be shed. This is an attempt to rethink rocket engines.
2. Vacuum to air interface scares me, I want a 1atm pressure device, ie. a normal air ion gun, no vacuum.
3. "Lifters" are similar, but there is an important difference. Lifters are spitting out electrons from the negatively charged wires (charge is physically leaving the circuit). This requires a large battery current for large amounts of propulsion. In my design, the air ionises, creating pairs of charged particles, no circuit current needed to provide charges. My mistake, I'm just making different lifters, same working principal as my design ideas.

Sounds like design a) is going in the bin, can't be wasting electrical current. I've since pulled it out of the bin and added a laser.

Regarding the comment about ions hitting the ambient air and getting stuck in the tube, I could understand that collisions could result in positive ions ending up clumping around the negative terminal and electrons around the positive, but I don't understand how big of a problem it would be? Does this effect completely cancel out the applied electric field? Is the design already done for?

About the need for different shape electrodes, the design I'm considering doesn't need weird shapes, it just uses a really high applied voltage design a) should work with an added laser even with symmetric rings. I'm not intending to use electrodes oops looks like i will use electrodes, ideally current shouldn't leave or enter the metal rings. They might as well be statically charged. Two symmetric rings can create the dielectric breakdown of air and accelerate charged particles.

Omg that's a lot of links sandalcandal, will check them out.

[sandalcandal]

I think the links and the last video particularly should answer your questions. Also to reiterate what I said, you can't have zero electrical power the energy to produce movement and kinetic energy has to come from somewhere. At best you could maybe have zero average current by using some sort of AC?

[Gyro]

Thanks for the reply guys. The lifters link is interesting, I must admit youtube lifter videos inspired this design attempt.

An example from a little closer to home 

https://www.eevblog.com/forum/dodgy-technology/ionic-lifters-has-anyone-else-around-here-build-one/

[james_s]

1. Rockets are heavy, mostly from fuel used to lift more fuel that is used to lift even more fuel etc. Ion propulsion of surrounding air means hundreds of tonnes of rocket weight can be shed. This is an attempt to rethink rocket engines.

There is no way around this. The energy has to come from somewhere, and it is consumed by increasing the speed of the mass of the rocket. If you reduce the mass of the rocket you need less energy to accelerate it but you still need an incredible amount of energy to reach escape velocity from earth. Nothing known to man, save for a nuclear reaction  has the energy density of chemical fuel, batteries for storing electricity are not even close,  and additionally as fuel is burned the vehicle becomes lighter while batteries stay the same weight as they are drained. This is why you don't see Tesla building electric jumbo jets and won't unless there is some radical new method of storing electricity. Whether you move the air electrically, or by spinning a propeller, the fan in a turbofan engine or directly use only the energy of the expanding gas in a rocket engine you still have to put at least as much energy into the system as you get out, and your vehicle has to carry the source of this energy. The math governing all of this is well understood by people much smarter than I.

[Marco]

Big issue with these systems is the ozone and NOx they generate as a result of electric discharge into air.

Wire or edge discharge is a pretty piss poor way of generating electrons in air. Hell even tungsten tips are pretty bad, though you'll see them in all sorts of professional devices. You can't beat the humble carbon fibre brush for low ozone electron emitters.

I suspect multistage thrusters will be able to significantly increase the thrust to weight ratio of electrohydrodynamic thrusters. Single stage thrusters have a very limited design space.

PS. more relevant to fans than rocket engines though.

[aussie_laser_dude]

Thanks guys,
guess I have to eat some of my words, symmetric rings are no good because a uniform electric field causes the whole region to undergo dielectric breakdown which causes a short circuit ie electrical arching. It's also good to have a pointy end so the ion/electron pairs are generated at one end of the tube, giving maximum length of acceleration for maximum thrust. There is a way around this, using lasers to induce the ionisation, that way the electric field doesn't have to do be at dielectric breakdown values. Not sure if this could realistically be done in terms of energy efficiency? maybe?

I've attached an updated list of designs after reading through the comments.

but you still need an incredible amount of energy to reach escape velocity from earth. Nothing known to man, save for a nuclear reaction 

Exactly! Consider something like a small ~kg ball of plutonium with a controllable neutron reflector over the top, I believe these things get ~MW of power. What technologically would stop the development of a small, lightweight drone (say ~20 to 300kg drone with a ~1kg energy source) that takes lifters to the extreme and uses them for incredible maneuverability?

Question: Could someone (in theory) make a small drone craft that darts around the sky at high speeds it any direction it wants with high acceleration and precision control that can fly for at least a minute? Obviously the power source makes this an almost certain no since regular folk can't dabble in nuclear technology. Imagine a small, perhaps ball shaped craft that could move in any direction at impressive speeds and accelerations. It may be possible using non-heat ionisation of air to have an approximately ambient temperature exhaust, making for an advanced sci-fi like spy drone.

Here's a graph on the energy required for ionisation of nitrogen gas (N2) (the main energy drainer), calculations are assuming 100% efficiency.



hmmm, MW scale power should allow for lightweight crafts to fly.... interesting

How much air would have to be ionised per second?



hmmm, hundreds of grams or isn't a crazy high value. Might be possible? Especially when you go to higher voltages and use less air ions for the same thrust. I suppose it makes sense, even with a modest ~100-200V you're already getting momentum returns per ion better than what jets get per exhaust molecule.

An example from a little closer to home 
https://www.eevblog.com/forum/dodgy-technology/ionic-lifters-has-anyone-else-around-here-build-one/

These things are quite fun to watch. Haven't seen too many videos where people fly them and also measure the forces, voltages, currents etc. Would be interesting.

The math governing all of this is well understood by people much smarter than I.

The basic equations are actually pretty simple to derive. We have conservation of momentum, classical electric and kinetic energies and simple momentum conserving collisions in air. It's pretty easy to calculate stuff like required energy/power, lifting force, ion counts, etc. I happen to have a snapshot of some notes of the math in case anyone is interested.

[T3sl4co1l]

1. Rockets are heavy, mostly from fuel used to lift more fuel that is used to lift even more fuel etc. Ion propulsion of surrounding air means hundreds of tonnes of rocket weight can be shed. This is an attempt to rethink rocket engines.
2. Vacuum to air interface scares me, I want a 1atm pressure device, ie. a normal air ion gun, no vacuum.

Okay so -- which one is it?  Because whatever plasma physics works in 1atm, probably doesn't work even at low pressures, let alone in hard vacuum; and in a hard vacuum, you still have to bring your reaction mass along for the ride, you can't do any different from any other rocket.  (And ion thrusters are a solved problem at this point, they're working quite well.)

Not to mention the chemistry: Earth's atmosphere has a fair amount of electron affinity (oxide and hydroxide ions), which means you get a mixture of ion polarities, and therefore some wasted reaction (their motions oppose, giving little net thrust).  This might be different on another world, maybe CO2+ is dominant, maybe H2S- is, I don't know.

And there are far more efficient ways to work with 1atm gas: just push the damn stuff, no need to waste power ionizing and splitting molecules!

Tim

[aussie_laser_dude]

Okay so -- which one is it?  Because whatever plasma physics works in 1atm, probably doesn't work even at low pressures, let alone in hard vacuum; and in a hard vacuum, you still have to bring your reaction mass along for the ride, you can't do any different from any other rocket.  (And ion thrusters are a solved problem at this point, they're working quite well.)

You don't have to bring a reaction mass along, this is why this idea seems so amazing to me. Look at lifters, lifters don't carry reaction mass, they use the surrounding air as the reaction mass. The only thing they need to keep flying is a good battery. Unfortunately the DIY lifters made on youtube don't have enough power to lift their own chemical batteries.

I'm saying this, take a lifter, take the best batteries we have (nuclear) and we have a craft that can fly to high altitudes and back potentially thousands of times over and over without stopping, without refueling, without needing to store any propellent on board.

And there are far more efficient ways to work with 1atm gas: just push the damn stuff, no need to waste power ionizing and splitting molecules!

Consider efficiencies of rockets vs a nuclear powered lifter:

a) chemical rocket: tens to hundreds of tonnes of fuel to lift a relatively small payload to space. Huge job, massive costs, each rocket gets up once only and needs to be remade.
b) nuclear rocket : does better, still carries perhaps tens to hundreds of tonnes of H2 propellent. Huge job, massive costs, each rocket gets up once only and needs to be remade.
b) nuclear powered lifter: Potentially hundreds of high altitude trips without stopping, the battery will last for MANY uses.

This might be different on another world, maybe CO2+ is dominant, maybe H2S- is, I don't know.

I'm using N2 gas because it composes most of the atmosphere, lifters should work in pretty much any atmosphere. Lifters will even work in space! WHAT? IMPOSSIBLE? Mythbusters checked them in vacuums and they failed to work, right?
  Well, space isn't a perfect vacuum. High altitudes and even the space in our solar system has a low density of molecules/ions. There's not many of them, but you can accelerate them to really high speeds using a really high voltage to make up for it. Also, when travelling fast, you'll sweep through a large volume of space. A 3 metre wide craft that orbits the Earth would sweep though 1 billion cubic metres of space. Here's the problem I'm having with lifters in space, metal electrodes in low atmosphere conditions leak electrons, lots of them. Think CRT technology, cathode ray tubes etc. My proposed solution is design b) where I coat the electrodes in teflon. Not 100% sure if design b) works in heavy atmosphere, but I think it may work in space. Will design b) work in low pressure conditions?

[Haenk]

Big issue with these systems is the ozone and NOx they generate as a result of electric discharge into air.

AFAIR Nelson Pass talked about this in an interview, they demo'd an electrostatic speaker at a fair and it produced a ton of toxic gases...

[helius]

Two symmetric rings can create the dielectric breakdown of air and accelerate charged particles.

Nope, they cannot. Dielectric breakdown always begins as charges jumping out of a conductor into an insulator, because that is how the neutral molecules of the insulator become ions. No charges, no ions. Your misapprehension appears to be that the electric dipoles of the insulator get so strained that they fly apart into - and + halves. That is not what happens.

You can see this happening with CRT monitors. The second anode wire is at EHT: a potential around 20-30 kV. It doesn't ionize the air around it because it is insulated. If the insulation cracks, ionization begins to occur around the cracked region: not because the E field in the air surrounding the wire is any different, but because charges can now exit the wire into the air. Coating the cracked wire with insulating varnish stops the ionization: showing that charge flowing into the air is a necessary component of dielectric breakdown.

Another demonstration is Lichtenberg figures, where the pattern starts at the metal contact and grows outwards. The dielectric breaks down where the field is strongest, and charges are available from the conductor to form ions. If you teflon insulate the conductor, you will not get any Lichtenberg figure until exceeding the breakdown potential of teflon.

[Marco]

Counter example, barrier discharge.

I wonder if you could do barrier discharge to create a macroscopically neutral plasma and then use a LINAC to create negative/positive charged zones and accelerate them.

[sandalcandal]

Dielectric breakdown always begins as charges jumping out of a conductor...

That is generally the case but not always true. Partial discharge and dielectric barrier discharge (and other RF/AC based breakdowns) don't require charge transfer from a conductor. Dielectric breakdown is motivated by a strong electric field dislocating covalently bonded electrons in the molecular structure of a dielectric material. Charge transfer to a conductor is required to sustain a dielectric breakdown however since without it a charge build up will occur and attenuate the electric field.

You can see this happening with CRT monitors. The second anode wire is at EHT: a potential around 20-30 kV. It doesn't ionize the air around it because it is insulated. If the insulation cracks, ionization begins to occur around the cracked region: not because the E field in the air surrounding the wire is any different, but because charges can now exit the wire into the air. Coating the cracked wire with insulating varnish stops the ionization: showing that charge flowing into the air is a necessary component of dielectric breakdown.

I speculate that prevention of corona discharge isn't primarily due to the prevention of conduction by the dielectric insulation but exclusion of air from extremely high E field concentration points at the surface of the electrode where initial ionisation can occur and propagate a corona discharge. (Most) corona discharges (there are multiple categories of corona discharges) aren't simple homogenous ionisations in a volume of air, they are a more complex interaction with initial ionisation "seeds" being accelerated then colliding with non-ionised molecules and producing avalanche type effects. I suspect accumulation of charge as ionisation occurs helps limit discharge as mentioned above but thin insulation will be quickly deteriorated by this. I recall from HV hobbyist forums that "thin" insulation tends to still have issues with deterioration and corona discharges appearing particularly for AC potentials where I assume charges are recycled and cannot accumulate and stop, hopefully someone can confirm that...

Another demonstration is Lichtenberg figures, where the pattern starts at the metal contact and grows outwards. The dielectric breaks down where the field is strongest, and charges are available from the conductor to form ions. If you teflon insulate the conductor, you will not get any Lichtenberg figure until exceeding the breakdown potential of teflon.

A Lichtenberg figures are fractal structures caused by distribution of current through self-forming conductive channels. They are a dielectric breakdown related phenomenon because they require a non-conductive material on/in which to form the conductive channels but have nothing to do with breakdowns fundamentally requiring a transfer of charge.

[sandalcandal]

I wonder if you could do barrier discharge to create a macroscopically neutral plasma and then use a LINAC to create negative/positive charged zones and accelerate them.

Because it is macroscopically neutral, application of an external electric field will cause separation of charged particles which will in turn produce a restoring field (e.g. Debye Shielding). Oscillations are common but not sure how you'd get net acceleration. It might be possible however, due to the difference in mobility between positive and negative charge carriers there would be something akin to a "phase lag" that could be used to "pull" the plasma along. It's been a bit since I studied plasma physics...not to mention I ended up going a different direction before getting very deep.

[aussie_laser_dude]

I wonder if you could do barrier discharge to create a macroscopically neutral plasma and then use a LINAC to create negative/positive charged zones and accelerate them.

These are the kind of ideas I like hearing, didn't know that was called a barrier discharge btw. Two things affecting lifter thrust and efficiency are the collisions of ions with air (drift velocity) and the recombination rate of ions / electrons to a neutral molecule before exiting the field. Different approaches / technologies like what you've suggested could affect factors like these and result in higher efficiencies / thrust than the typical youtube lifter, which I suspect is far from optimised.
   Having a quick think about this proposed design, we can get a large volume of air ionised, that's good, more ions gives more push. A downside is that there will be a lot of ion-electron recombinations, meaning very quickly we can't push them anymore. Compare this to a lifter design, ion/electron pairs are created at the positive pointy electrode, a small volume of air is ionised which may be bad. Electrons go left, ions go right, they don't really collide into each other to recombine, which is good.
  Which design is better? Maybe one gives more thrust and the other gives better energy efficiency?

[Marco]

AFAIK in a lifter most of the momentum is caused by electrons crashing into neutral molecules ... positive ions don't contribute much I think.

[Nerull]

I certainly hope you're aware that "Getting to high altitude" and "getting to orbit" are extremely different things. Getting to high altitude is relatively easy, and not what rockets spend most of their time doing.

Not bringing your own reaction mass and operating in low pressures are also mutually exclusive. If you don't' want to bring your own reaction mass, you are limited to low altitudes.

[aussie_laser_dude]

AFAIK in a lifter most of the momentum is caused by electrons crashing into neutral molecules ... positive ions don't contribute much I think.

I initially thought this too, turns out to be the opposite, it's the positive ions which obtain momentum 5000 times greater than electrons, here is the equation for the ratio of momentums of an ion and electron both passed though the same potential difference:

[ Specified attachment is not available ]

Another argument is this, ions and electrons are generated at the edge of the positive terminal (in most lifter setups). The electric field can't do any more work on the electrons, they are already pretty much out of the field, so actually the electrons will gain almost zero momentum and ions will take it all for themselves. Draw a diagram with the created charge pair and the electric field lines with directions, this makes it easy to understand what I'm describing.
[EDIT: I suspect N2- anions could also play a role in certain setups, i don't have a device to perform measurements on currently, but anions could be a mechanism of momentum transfer if the uncommon case of the pointy electrode being negatively charged, resulting in the weird case of the thrust being in the same direction when swapping electrical polarity]

I certainly hope you're aware that "Getting to high altitude" and "getting to orbit" are extremely different things.

If you don't' want to bring your own reaction mass, you are limited to low altitudes.

Getting to space is easy, staying there is hard, right? High kinetic energy needed to maintain orbit, low gravitational potential energy to get up.
Think of a solar sail, they are being worked on even though they don't have much push when in the solar system. Could a lifter in the solar system beat a solar sail in the solar system under certain circumstances?
How about in low earth orbit where we want a craft to maintain a constant orbital altitude, fighting against orbital decay? Could lifters beat the ion exhaust engines in certain circumstances?

Can a ionocraft / lifter with a really good battery get to orbit? I think theoretically they can, but how ridiculous does the battery and engineering have to be? Where is the line of "our best engineering with no limits on money can get us this high and this fast with lifter technology"? I want to at least calculate some rough numbers to try and answer this, i'm part way there.

If none of these reasons convince you that this idea is worth investigating further, then how about the following. Wouldn't it be the coolest thing ever to make a UFO like craft that can silently hover and fly around? Who cares if it even has a practical use, imagine showing that at a party or playing pranks on the airforce, I think it's fun to think about.

[aussie_laser_dude]

Need equipment advice.

So I've developed a set of equations / models to describe lifters. The equations give relationships between about thrust, energy consumption, current, voltage, displacement of electrodes as well as other stuff like atmospheric density, atmospheric composition etc. As far as I can tell from scattered data I've viewed online, my calculations are close in every case I've tested. I think I have a reliable set of equations that work under a range of conditions. Nearly ready to try an experiment.

I want to make the electrodes a really low voltage (about 50V) and place a separate ion generator next to one electrode. Can i get some help in understanding how to do this? See the attachment for visuals. Can I get criticism / comment on my ion generator ideas, particularly idea c) in the image file. Will it work? (By "work", i mean, will this result in a current flowing between the rings?)

I've attached 3 ideas on how to do this:

[Marco]

These are the kind of ideas I like hearing, didn't know that was called a barrier discharge btw. Two things affecting lifter thrust and efficiency are the collisions of ions with air (drift velocity) and the recombination rate of ions / electrons to a neutral molecule before exiting the field. Different approaches / technologies like what you've suggested could affect factors like these and result in higher efficiencies / thrust than the typical youtube lifter, which I suspect is far from optimised.

Due to complexity and weight it's not really be tried for lifters, but for electrohydrodynamic fans multistage designs have been able to show greater speed/pressure/efficiency than single stage designs. They simply don't worry about recombination, every stage completely neutralizes the air again before the next stage ... but that seems inefficient.

I've never seen anyone try to build up air "packets" of alternating charge and accelerate those like a LINAC ... it might work, dunno.

[aussie_laser_dude]

every stage completely neutralizes the air again before the next stage ... but that seems inefficient.

To be fair to the designers, they were probably making a device for cooling laptop parts where the force to power consumption ratio isn't the main priority, they had other are other engineering constraints like making it compact. Having said that, the ionisation of air accounts for only a small part of the total energy consumption in this design (and every other design I've seen on the internet).
[See the attached graph]

At low electrode potentials, lifters must ionise lots of air, that's the sharp vertical line on the left. The slow rise on the right of the graph is due to kinetic energy given to ions. I think you can tell where on the curve most internet lifter designs sit...  If you can use the correct voltages, you can get orders of magnitudes improvement in power consumption for the same amount of lift. The low part of the curve (high efficiency of Force to Power consumption) is inaccessible with current lifter designs, I have some ideas on how to solve this.