New type of accelerator

ERRORIST · 2004-11-04 10:04:55

Wow, this could propel a spacecraft once in space.

http://www.spacedaily.com/news/physics-04ze.html
http://www.spacedaily.com/news/physics-04ze.html

GCNRevenger · 2004-11-04 11:17:15

No, not really. Electrons don't make good reaction mass, and there are easier ways to ionize bulk gasses. Besides, they can't get the electron beam to go more then a millimeter or so, nor is there an easy way to get it out of the lasing chaimber. In any event, it would need huge power supplies and yeild very little propulsion, you would be better off using a regular ion engine.

chat · 2004-11-04 16:25:32

GCNRevenger,

I agree that a single electron gun will produce a dismal thrust, but 100 or 1000 might be a very different story.

The power requirements will indeed be high to power 100 electron guns, but then again ions cant be propelled at near C, electrons can.
Ions also require huge amounts of power to accelerate them to high speeds.

A small push at C vs a larger push at a smaller % of C still equates to the same power requirements to propel the vehicle to any equal speed.

Electrons might be the slow push version of space flight, but they keep pushing at near C until the power source runs out .
Probably better to think of electron guns as star ship engines and not space ship engines, they are just to slow to speed up for solar system travel.

Euler · 2004-11-04 17:10:35

A small push at C vs a larger push at a smaller % of C still equates to the same power requirements

Yes

to propel the vehicle to any equal speed.

No.

The two vehicles would use up the same amount of power, but the one with the lower exhaust velocity would have more thrust, so it would accelerate faster.

Electrons might be the slow push version of space flight, but they keep pushing at near C until the power source runs out .

Both methods keep pushing until the power runs out, and the power would run out at the same time in each ship. However, since the ion engine had a higher acceleration the whole time, it will end up at a much higher velocity.

chat · 2004-11-05 05:37:24

Euler,

The old bowling ball analogy comes to mind.

If you throw a bowling ball at 50 newtons or throw 50 newtons of ions the final speed will be exactly the same.

The bowling ball will simply take more power on one throw, and the ions less per throw.

Since ions weigh much more than electrons it will require more power to throw the ions and the power source will expend much earlier.

The electron gun version will run for years longer than the ion version and obtain the same final speed if ions and electrons run at the same efficiency.

A direct flow of electrons from a reactor will use near 100% of the power source.

Ions drives i believe are around 7% efficient.

Any engine to the stars will need a thrust as close to C as possible for as long a period as possible, and the speed up time is not to important.

Both ions and electrons are awful space ship engines for manned solar system travel, but pretty good engines for non manned star probes.

ERRORIST · 2004-11-05 08:00:59

The electrons are being exhausted at the speed of light where as the ions are being exhausted at much lower velocities.

GCNRevenger · 2004-11-05 08:26:37

I think what Euler is assuming in the comparison is that the power source (reactor) for each engine will run out of Uranium/Plutonium/Thorium at the same time, which will limit the length of each engine's burn time to the same length. Oh, and an electron beam engine can't be 100% thermally efficent either, you are limited to the efficency of the reactors' generators, which is around 30%.

In which case, since the electrons have so little momentum given an equal quantity of electricity to run each engine, then the ion engine will come out way on top over practical burn times. Its hard to emphasize how little thrust a cathode beam engine will produce, and stacking them up isn't practical because of the mass and energy requirements of the engine, even though it would be fuel efficent.

It must also be noted that you have to worry about building up an electrical charge on your vehicle, and if you are throwing vast quantities of electrons overboard, dozens or hundreds of times as much charge as an ion engine does, you are going to have big trouble. The only way to counter this huge buildup in positive charge is to throw positivly charged particles overboard, like Protons, which make it impossible to use electricity alone as your "reaction mass" and will require you to carry a pretty huge stock of "neutralization fuel."

A cathode beam engine, a bad idea no matter how you produce the beam.

ERRORIST · 2004-11-05 08:45:36

Looks like this new engine has very little mass. Perhaps, you can slam the electrons into the ions in a chaimber before they leave the back end of the ship? This would further accelerate the ions.

GCNRevenger · 2004-11-05 09:05:43

Has very little mass? How do you know that? Um, an ion engine is only a few feet around, but this laser/plasma electron accelerator is probobly not going to be any smaller. (see talk of "university basement" sized accelerators)

As far as using an electron beam as a booster to conventional ion drives, that doesn't make alot of sense since it would be more efficent to just make a more powerful acceleration screen on the ion engine and it would be impossible to get efficent interaction of the electron beam and the ion stream, which is probobly going to be a large fraction of a meter across.

ERRORIST · 2004-11-05 09:23:47

As the article states:"Using the huge electric fields in laser-produced plasmas, they have accelerated beams of electrons close to the speed of light, in an important step towards the development of a working laser electron accelerator that could sit on a table top."

Electrons at such high velocities have very high energies including kinetic energy.Smash them into an ion and the ion accelerates away.

GCNRevenger · 2004-11-05 10:12:40

Yeees a small one. There are many different sizes of accelerators you know.

Why would you want to do that? You could generate more thrust just by making the regular ion engine more powerful, instead of bothering with an electron beam generator. Getting the electrons to "hit" the ions is also going to be all but impossible, and will never be very efficent.

In order to build signifigant thrust, how big or how many of these are you going to need? And each one of them will require quite a bit of energy (heavier reactors) and charge negation fuel.

ERRORIST · 2004-11-05 10:41:55

Why would you want to do that? You could generate more thrust just by making the regular ion engine more powerful, instead of bothering with an electron beam generator. Getting the electrons to "hit" the ions is also going to be all but impossible, and will never be very efficent.

Why? Less Mass.

Euler · 2004-11-05 11:33:10

Ions drives i believe are around 7% efficient.

No, they are about 70% efficient.

GCNRevenger · 2004-11-05 12:29:42

...Which gives ion engines about 25% thermal efficency from a nuclear reactor. That is, for every four watts of heat are generated, then one watt is effected for propulsion by the ion engine (assuming ~33% thermal-electric conversion).

How could adding a complex electron accelerator, which can't in any event boost the efficency of ion engines anyway, have less mass then simply increasing the current in the ion engine's accelerator grids?

John Creighton · 2004-11-05 12:42:17

How could adding a complex electron accelerator, which can't in any event boost the efficency of ion engines anyway, have less mass then simply increasing the current in the ion engine's accelerator grids?

What if you used the electron accelerator instead of the neutralizer in the ion engine. If the electrons went faster then the ions then magnetic interactions would cause the ions to catch up. Of course as has been pointed out many times before the key technology is the power source and not the engine.

GCNRevenger · 2004-11-05 12:50:32

No that wouldn't help:
-Ions in ion engines are so much heavier then electrons, by tens of thousands of times, that they can't drag the ions much at all. Nor can you use 100 electrons for one ion or somthing, since that would cause charge imbalence.

-The electrons would not cause a net acceleration on the ship anyway.

John Creighton · 2004-11-05 13:12:43

Didn’t we discuss something like this before. If a neutral beam of ions hits a strong enough magnetic field perpendicular to the velocity of the beam the positive ions will be deflected one way and the negative ones will be deflect another way. The resulting change in velocity will produce a reaction force on the space craft.
No that wouldn't help:
-Ions in ion engines are so much heavier then electrons, by tens of thousands of times, that they can't drag the ions much at all.

Oh are they that much heavier. Well then I guess it would make no difference unless the electrons were moving at relativistic speeds.

Nor can you use 100 electrons for one ion or somthing, since that would cause charge imbalence.

Hopfully we all agree with this.

-The electrons would not cause a net acceleration on the ship anyway.

Well, accelerating the electrons will cause the positive ions to accelerate because if the electrons are moving faster then the ions, then the changing curl in the current will create a changing magnetic field that will create an electric field that wants to slow down the electrons and speed up the positive ions. I guess you point is once the electrons leave the space craft they will slow down really fast and the positive ions will be barely accelerated at all. Of course if the electrons are moving at relativistic speeds they will have a much greater momentum and this will accelerate the positive ions.

GCNRevenger · 2004-11-05 13:15:56

Yeah, an electron weighs about 1/2000th of a proton or neutron, so for Xenon ion engine fuel you are looking at ~260,000X mass difference.

My thinking is that accelerating the ions with the neutralization beam after they have left the engine doesn't do you any good, all the propulsion in an ion engine happens between the charge grids.

chat · 2004-11-05 15:26:46

GCNRevenger,

Making a simpler electron engine isn't that hard.
An ark of a few million or billion volts focused on a fuel source.
You should be able to accelerate it to a good percent of C when the fuel becomes plasma and explodes and you give it only 1 escape route.

A simple way of converting the low mass of electrons into high mass thrust.

It wont be a starship, but just might be a good solar system vehicle with quick acceleration.

A great fuel might be a titanium rod that simply extends as the leading edge of the rod is turned into plasma.
The rod would also act nicely as a plasma explosion blocker.

In effect a plasma rocket with no moving parts.

The main reactor power could probably be focused to do the same job with most of the reaction, but don't stand behind it when it fires up:)
A nuclear belcher for sure.

The main problem for any such idea isn't the idea of the engine, its the reactor needed to power it.

For any respectable space or star engine i think we are talking a minimum of 50mw.

Ion and electron engines without some secondary reaction are painfully slow to accelerate.
Neither will probably ever be useful manned space engines.

Who said space travel was going to be easy or cheap anyway

GCNRevenger · 2004-11-05 15:40:35

What you have just described is an "Arcjet" engine, which has been around for some time. Although they are electric and produce okay thrust, they are NOT super-efficent. Nor is there any coupling of the momentum of the electons to the target material in any efficent fasion.

ERRORIST · 2004-11-05 16:50:21

My thinking is that accelerating the ions with the neutralization beam after they have left the engine doesn't do you any good, all the propulsion in an ion engine happens between the charge grids.

And that is where you hit them with the electrons between the charge grids. This should accelerate them faster before they leave the ship.

chat · 2004-11-06 05:10:37

GCNRevenger,

If you can work around the efficiency problem the ark jet works really well.

In todays semiconductor world i can believe that anyone hasn't invented a layered titanium rod that will ark with much better efficiency.

It shouldn't be that hard to make layers of micro circuitry embedded into the titanium that are efficient ark machines.

Heck my TV arks all the time without any design plan.

ERRORIST,

Hmmm that is an interesting idea.
You would have to redesign the ion charge plates a bit to allow a secondary push from the electrons, but i think your on to something.

Its a bit of a tech monster to incorporate both systems though.

Since electrons are simple to accelerate to near C, i think the best way to accelerate ions is to have an acceleration coil with ions inside it.
Use the electron beam to accelerate the ions, then expel the ions at peek speed.

No need to rush the electron to ion speed transfer as the ions can continue to accelerate inside the accelerator until they peek in speed.

I proposed this idea quite some time ago with the minor problem of a 50mw reactor being needed to power it.

GCNRevenger · 2004-11-06 12:35:47

You don't "hit" particles with electons! Its not like that, it doesn't work that way... billiard ball mechanics is not the whole story, atoms don't react like solid spheres when struck by free electrons. You entire way of thinking about such an engine is fundimentally incorrect... The best it would do is charge up the particles a little more and fling a huge amount of free electrons out the back, which will short out the whole system.

The problem with the Arcjet concept is that it is largely a thermal engine, albeit an electrically heated one, and those will never be super efficent no matter what you try. Putting circutry in a Ti rod won't make any difference at all, it is a problem of fundimental physics again, and not anything to do with how the rod would be consumed.

chat · 2004-11-06 15:17:09

GCNRevenger,

I was probably a distorted on how to accelerate the ions in my post.

Magnet coils charged by the electrons in the accelerator to transfer electron energy to ion propulsion.

Closest example is a linear induction accelerator.
Guess you would have to call it a linear ion accelerator.

Similar to deep space, but different in the way you speed the ions in a continuous push, and the amount of power that can be em parted to each ion.

Deep space is a one push engine, with a liner accelerator and no rush to push the ions i believe ion speeds of .50c are possible.

It would be a big power consumer though, but a fast craft after time.
Still slow to accelerate though with a single acceleration coil.

The ark jet probably has a solution to its host of problems,
but in theory its a good solar system engine.
Or at least a good way to get going at respectable time frames.

John Creighton · 2004-11-06 15:51:25

Since we are on the topic of various accelerators I have a physics thought experiment which I don’t seem to be able to answer buy visualization. If you have a changing magnetic field around a toroid it will it will produce an electric field though the axis of a torrid. Now if an electron is stationary in the center of the toroid the magnetic field around the electron is constant. However it the electron is moving along the axis of the toroid the magnetic field around the electron is changing. In the reference frame of the electron the curl of the magnetic field is changing and thus there should be an electric field.

Now consider several toroids stacked on top of each other like doughnuts. Each one having a stronger magnetic field around it. If the electron moves through the axis of these toroids then the field around the electron is either continuously increasing or continuously decreasing. To me it almost sounds like I created an accelerator that could be constructed with permanent magnets. Where is the fallacy. Or is there no fallacy but when the electrons get so far past the end they come back.

My guess is that you can’t accelerate electrons with permanent magnets without them coming back to where they started. However this to me suggests that the right magnetic field profile could be used to compress a charged stream of particles. Thinking to the far future I wonder if such principles could be applied as an advanced form of anti matter storage. Picture toroids (A.K.A doughnuts connected end to end in a ring) The fields for a standing wave structure and are such the positive ions are compelled to travel one way around the ring and the negative ions are compelled to travel another way. The charge of the medium would be natural and all the particles of the same charge would be compelled to move at the same velocity. Since the distribution of velocities will have two narrow peaks the entropy will be low. Usually low entropy implies a low temperature. Thus the medium will have neutral change and be at a low temperature. Thus it should be fairly compressed.

Hmmm…I think this post is dabbling beyond my level of physics.

New Mars Forums

Announcement

#1 2004-11-04 10:04:55

Re: New type of accelerator

#2 2004-11-04 11:17:15

Re: New type of accelerator

#3 2004-11-04 16:25:32

Re: New type of accelerator

#4 2004-11-04 17:10:35

Re: New type of accelerator

#5 2004-11-05 05:37:24

Re: New type of accelerator

#6 2004-11-05 08:00:59

Re: New type of accelerator

#7 2004-11-05 08:26:37

Re: New type of accelerator

#8 2004-11-05 08:45:36

Re: New type of accelerator

#9 2004-11-05 09:05:43

Re: New type of accelerator

#10 2004-11-05 09:23:47

Re: New type of accelerator

#11 2004-11-05 10:12:40

Re: New type of accelerator

#12 2004-11-05 10:41:55

Re: New type of accelerator

#13 2004-11-05 11:33:10

Re: New type of accelerator

#14 2004-11-05 12:29:42

Re: New type of accelerator

#15 2004-11-05 12:42:17

Re: New type of accelerator

#16 2004-11-05 12:50:32

Re: New type of accelerator

#17 2004-11-05 13:12:43

Re: New type of accelerator

#18 2004-11-05 13:15:56

Re: New type of accelerator

#19 2004-11-05 15:26:46

Re: New type of accelerator

#20 2004-11-05 15:40:35

Re: New type of accelerator

#21 2004-11-05 16:50:21

Re: New type of accelerator

#22 2004-11-06 05:10:37

Re: New type of accelerator

#23 2004-11-06 12:35:47

Re: New type of accelerator

#24 2004-11-06 15:17:09

Re: New type of accelerator

#25 2004-11-06 15:51:25

Re: New type of accelerator

Board footer