Centrifugal Plasma Accelerator Pulse Rocket Idea....

[Spacescifi]

Plasma rockets are known for low thrust despite high exhaust speeds because plasma is low mass to begin with. The only way I know of to get higher thrust out of low mass exhaust is to put more energy into shooting it out.

I remember how spin launch spins a projectile rocket at high speeds for a period of time before launch, and wondered if much the same could be done with plasma.

I don't know if plasma accelerators are a thing or if this is more a particle beam kind of thing. I was thinking that if plasma could be rotated at high speed for a long time and then released in pulses it could make for a good space drive.

Thoughts?

Question: Would the plasma necessarily get hotter the faster it is rotated? My gut tells me probably, which would put a limit on how fast you could rotate it before shooting it out as exhaust

Obviously we cannot SSTO with it, though a scifi version could at the expense of turning the ground onto molten lava with relativistic speed plasma exhaust.

Edited August 19, 2023 by Spacescifi

[darthgently]

2 hours ago, Spacescifi said:

Plasma rockets are known for low thrust despite high exhaust speeds because plasma is low mass to begin with. The only way I know of to get higher thrust out of low mass exhaust is to put more energy into shooting it out.

I remember how spin launch spins a projectile rocket at high speeds for a period of time before launch, and wondered if much the same could be done with plasma.

I don't know if plasma accelerators are a thing or if this is more a particle beam kind of thing. I was thinking that if plasma could be rotated at high speed for a long time and then released in pulses it could make for a good space drive.

Thoughts?

Question: Would the plasma necessarily get hotter the faster it is rotated? My gut tells me probably, which would put a limit on how fast you could rotate it before shooting it out as exhaust

Obviously we cannot SSTO with it, though a scifi version could at the expense of turning the ground onto molten lava with relativistic speed plasma exhaust.

Given what you wrote the average of the pulses would be no more than just direct plasma drive.   And there would be containment overhead for the "ring buffer".   Maybe if you need a higher thrust short burn in some corner case it would be worth it.  Something to ponder.

Just realize that the energy required to contain the radial force of the plasma in the ring would not be free at all

[KSK]

This sounds difficult.

Plasma, broadly speaking, is a hot gas of electrons and positive ions, the ions being what's left after you strip one or more electrons off an atom.

The basic principle behind a circular particle accelerator, is that you give the particles a burst of acceleration each time they go round the circle.  This means that the accelerating system (there are various systems used) can be relatively small, compared to a linear accelerator. The particles are charged and are steered around the circle by magnetic fields. The faster the particles are going, the stronger that magnetic field needs to be and, for a high energy accelerator, the magnetic field strength will be synchronized (hence synchrotron) to the particle speed.

Trying to accelerate a plasma, i.e. a mix of positively charged and negatively charged particles, is going to be difficult, because those particles will be deflected in opposite directions by the steering magnets. That's going to complicate the accelerator design.

There's also the additional problem that accelerating a charged particle creates electromagnetic radiation. Since the particles here are moving in a circle, they are constantly accelerating towards the centre of that circle, and so constantly emitting electromagnetic radiation. This is so-called synchrotron radiation or bremsstrahlung. 

Bremsstrahlung can either be the entire point of your accelerator (generating high intensity X-ray beams for crystallography and other material science applications) or an utter nuisance (wasting energy in high energy accelerators). The way you get around it is to either use heavier particles or a larger radius accelerator. The heavier particles aren't a problem in this scenario, but the accelerator radius  is going to be constrained by the spacecraft size

Long story short, a circular plasma accelerator small enough to form a practical space drive is probably going to have significant energy losses to bremsstrahlung and, along with that, will be emitting radiation in all directions.

 

I think. Any accelerator bods care to chip in?

[Spacescifi]

33 minutes ago, KSK said:

This sounds difficult.

Plasma, broadly speaking, is a hot gas of electrons and positive ions, the ions being what's left after you strip one or more electrons off an atom.

The basic principle behind a circular particle accelerator, is that you give the particles a burst of acceleration each time they go round the circle.  This means that the accelerating system (there are various systems used) can be relatively small, compared to a linear accelerator. The particles are charged and are steered around the circle by magnetic fields. The faster the particles are going, the stronger that magnetic field needs to be and, for a high energy accelerator, the magnetic field strength will be synchronized (hence synchrotron) to the particle speed.

Trying to accelerate a plasma, i.e. a mix of positively charged and negatively charged particles, is going to be difficult, because those particles will be deflected in opposite directions by the steering magnets. That's going to complicate the accelerator design.

There's also the additional problem that accelerating a charged particle creates electromagnetic radiation. Since the particles here are moving in a circle, they are constantly accelerating towards the centre of that circle, and so constantly emitting electromagnetic radiation. This is so-called synchrotron radiation or bremsstrahlung. 

Bremsstrahlung can either be the entire point of your accelerator (generating high intensity X-ray beams for crystallography and other material science applications) or an utter nuisance (wasting energy in high energy accelerators). The way you get around it is to either use heavier particles or a larger radius accelerator. The heavier particles aren't a problem in this scenario, but the accelerator radius  is going to be constrained by the spacecraft size

Long story short, a circular plasma accelerator small enough to form a practical space drive is probably going to have significant energy losses to bremsstrahlung and, along with that, will be emitting radiation in all directions.

 

I think. Any accelerator bods care to chip in?

 

I see... lots of power virtually always means radiation if you go small.

The key is to utilize what would be energy losses by making them strengths.

Lots of radiation/waste heat?

That is ALSO a source of energy if you can harness it

Either absorb it with lead and conduct the heat into your exhaust, or reflect and focus it into your exhaust using scifi ray mirrors.

It would be really nice if we could change a short wave ray into a longer wave length by passing it through a force field, but that sounds more like make believe.

Ray conversion (RC) fields would be incredibly useful, but would not always save you, but would enable you to always find a way to make use of high energy rays by reflecting, focusing, or radiating them.

 

[Spacescifi]

 

Another method would be to use a large vacuum chamber to detonate a fusion reaction which is contained and directed with magnetic fields.

Come to think of it, if we had scifi magnetic beams we could shoot like laser beams, you woul not even need a magnetic nozzle... would you?

You could fire off two fusion pellets to smash at a prescribed distance and then fire magnetic beams to push off the plasma.... like a magnetic pusher plate.

Or you could rotate the beams fast like a spiral so that you had a ridiculously long magnetic funnel/nozzle at a distance to fire your fusion pellets down before you detonate them.

Coincidentally, this would also enable the plasma bolt weapons in space that we often see in scifi, only the bolts would be moving so fast you would not see them with the naked eye unless it was directly ahead of you OR if you were far enough away to watch the plasma travel the distance.

I guess it would look like project Orion, but minus the pusher plate, and a flash that keeps moving.away from the ship and expanding until it disappears.

Edited August 19, 2023 by Spacescifi

[farmerben]

1 hour ago, KSK said:

 

 

I think. Any accelerator bods care to chip in?

The ions in cyclotron go in a spiral.  They can all be made to exit in the same place and then travel in straight line.  

https://en.wikipedia.org/wiki/Cyclotron#/media/File:Cyclotron_diagram.png

 

A cyclotron 4.7m in diameter throws alpha particles at 0.82c

You could have a second accelerator for the stripped electrons and unite the beams behind the spacecraft.

 

Edited August 19, 2023 by farmerben

[Spacescifi]

14 minutes ago, farmerben said:

The ions in cyclotron go in a spiral.  They can all be made to exit in the same place and then travel in straight line.  

https://en.wikipedia.org/wiki/Cyclotron#/media/File:Cyclotron_diagram.png

 

A cyclotron 4.7m in diameter throws alpha particles at 0.82c

You could have a second accelerator for the stripped electrons and unite the beams behind the spacecraft.

 

 

So you are saying the original idea is at least somewhat viable, only with real constraints cyclotrons have?

I wonder how good a space drive it would be? From orbit to orbit only?

[farmerben]

 

double post

 

Edited August 19, 2023 by farmerben

[farmerben]

Much of the electrical energy you put in would come out radially as X rays.  Unlike gamma rays, X rays can be redirected by mirrors.  So there might be a sweet spot which is as energetic as possible, while mirrors still work, and thus all your exhausted momentum goes the same direction.

The thrust to weight ratio is lousy, but the ISP is good.  It might be suitable for interstellar travel if you could run for decades.  You can turn it on or off, unlike some drives.

You could also potentially use this device like a weapon to deflect small debris.  If lasers detect debris but are not quite enough to push it, and steering the whole ship is wasteful, then a helium wind machine might be the next best option, and then a railgun slug.  

The same basic cyclotron can be used for anything from electrons to heavy ions.  Although you need a separate device for the negative charges because they go the opposite direction.

Edited August 19, 2023 by farmerben

[Spacescifi]

7 hours ago, farmerben said:

Much of the electrical energy you put in would come out radially as X rays.  Unlike gamma rays, X rays can be redirected by mirrors.  So there might be a sweet spot which is as energetic as possible, while mirrors still work, and thus all your exhausted momentum goes the same direction.

The thrust to weight ratio is lousy, but the ISP is good.  It might be suitable for interstellar travel if you could run for decades.  You can turn it on or off, unlike some drives.

You could also potentially use this device like a weapon to deflect small debris.  If lasers detect debris but are not quite enough to push it, and steering the whole ship is wasteful, then a helium wind machine might be the next best option, and then a railgun slug.  

The same basic cyclotron can be used for anything from electrons to heavy ions.  Although you need a separate device for the negative charges because they go the opposite direction.

 

If you wanted to increase thrust while keeping some simplicity could these next ideas be viable?

1.  For extra thrust shunt the plasma and X-ray exhaust into a reaction chamber with molten lead (because lead absorbs X-rays). Like an afterburner mode... less efficient but more thrust when you need or want it.

2. Probably a single main engine exhaust nozzle would make engine design somewhat simpler. Since as is we are talking about relativistic plasma, reflected X-rays, and shunting all of that into an auxilliary reaction chamber with molten lead. While the main engine reaction chamber would be simply for plasma and X-rays to leave in the exhayst together.

[farmerben]

Then you're back to thermal propulsion and limited by the temperature the reaction chamber can handle.  Our best materials go up to about 4000 degrees which determines the temperature of the propellant.  Hydrogen or helium gives much better ISP than lead, and is currently our best orbit to orbit engine.