Plasma Thruster Magnetic Nozzle Development

[Maol]

Some new concepts for plasma thrusters involve an expanding magnetic field called magnetic nozzle (MN), where the plasma is spontaneously accelerated to propel a spacecraft when exhausted into space.

https://phys.org/news/2017-06-road-elec ... lsion.html

Physical picture of the applied magnetic field lines (blue lines) and the magnetic field lines (red lines) modified by the plasma flow, i.e., sum of the applied and plasma-induced magnetic fields. The plasma decreases the axial field component at the upstream side of the magnetic nozzle and increases it at the downstream side of the nozzle as described by the insets, where the transition between these two states are identified as shown by the upper left inset. Credit: Kazunori Takahashi


Will someone please elucidate on this and explain the physics of how this magnetic phenomenon occurs. Is this the same or a similar phenomenon as the Astrophysical Jets issuing from black holes, neutron stars, and other objects?

[Zyxzevn]

With charged plates you can give speed to electrons or charged plasma.
The oldschool TV works this way.
With magnetic fields you can direct the flow of the charged plasma a bit.
The TVs used the same principle to direct the electrons beam to the screen.
It is fun to put a magnet near an old TV.

It is a bit of a puzzle to create a magnetic field to make a charged plasma flow into
a single direction. The charged particles will start spiralling along the field lines
of the magnetic field.

If we assume there would be rotating back holes, the magnetic field created by the rotating
will be likely similar to that of the earth. With a north-pole and a south-pole.
I don't think that this configuration can not produce a stable plasma beam.
The plasma will encounter a declining magnetic field, which causes currents inside the
plasma. And I think that these currents cause the plasma beam to disperse.

In plasma confinement fusion reactors
(see: https://en.wikipedia.org/wiki/Magnetic_ ... ent_fusion)
we see a constant magnetic field. This is necessary to keep the plasma stable.
So if the field is relatively constant, like the magnetic field of a whole galaxy,
this plasma beam might be more stable.

So from this principle, the source of the plasma beams must be different from a magnetic black hole.

The alternative is that this hypothetical black hole is charged, and consuming a heavy particles.
And this again has no direction, making it impossible to create a beam.

On the other hand, if we use some kind of electric model for an object in the centre of a galaxy,
this becomes much easier. We can now assume a charged object that expels charged plasma due to the
charge of the object itself. Its direction can be dependent of the galaxy, not the object itself.
This charged object can direct a beam of charged plasma to far outside the galaxy.
And this is exactly what we see.

While it does not rule out a black hole, it is not the "black hole" physics that causes the
behaviour of the plasma beam.

[Maol]

Thank you. That's all well and good, and most of us understand how CRT tubes work and have familiarity with the several explanations regarding jets from black holes, etc, however, what I was curious about was a more thorough description and explanation of the function of the Magnetic Nozzle described in the link.

The additional and somewhat rhetorical question is: Are the physical phenomena which provide the directional thrust of ions from the MN similar to the processes which cause emission of plasma jets from Astronomical bodies, black holes, etc?

[Zyxzevn]

To overcome this problem, researchers propose a scenario in which the magnetic field lines are stretched to infinity by the plasma flow.

This hints at a theoretical misunderstanding of the scientists.
Magnetic field-lines do not "stretch" to infinity.

They seem to mix magnetic reconnection pseudo-science with the actual science
that is used in magnetic containment fusion reactors. The field-lines are imaginary
lines that is used to describe the direction of the magnetic field. So each line goes
from north to south. Visualisations of these lines can show up with ferro-magnetic
materials,

The plasma circles around the magnetic field direction. It does not directly follow it.
This plasma counters the change in the magnetic field that the particles in the plasma perceive.
(E= dB/dt)
So the charged plasma will create a magnetic field in the same direction, so the change is reduced.
The plasma will extend the magnetic field a bit, just like any conducting material.

Somehow the scientists think that they can create thrust by configuring the plasma is such a way that
it creates a magnetic field in 180 degrees reversed to an existing magnetic field.
This is possible by giving it an initial direction through the magnetic field.
In this initial direction the 2 magnetic fields will repel each other.

Yet the charged plasma will counter the change in the magnetic field, so it will create a magnetic field
into the same direction. And this will stop the repelling magnetic field and cause an attraction
between the fields.
This undoes the imaginary thrust.
So this plasma nozzle simply does not work.

The variation of the field strength is only a few percent of the applied magnetic field strength for now, but..

No but. That is all.

Here is a good list to learn about electromagnetism.
I think the scientists missed these classes.

[D_Archer]

From the OP article:

The universe is made up of plasma

---

As for the thruster, this could work, but is there more information of the applied magnetic field? Where is it coming from? do they use throat magnets and exhaust magnets, where are they placed? This is information you need to be have to say anything, no schematic is provided....*

Regards,
Daniel

*abstract
An axial magnetic field induced by a plasma flow in a divergent magnetic nozzle is measured when injecting the plasma flow from a radio frequency (rf) plasma source located upstream of the nozzle. The source is operated with a pulsed rf power of 5 kW, and the high density plasma flow is sustained only for the initial ∼100 μ sec of the discharge. The measurement shows a decrease in the axial magnetic field near the source exit, whereas an increase in the field is detected at the downstream side of the magnetic nozzle. These results demonstrate a spatial transition of the plasma-flow state from diverging to stretching the magnetic nozzle, where the importance of both the Alfvén and ion Mach numbers is shown

[Maol]

To overcome this problem, researchers propose a scenario in which the magnetic field lines are stretched to infinity by the plasma flow.

This hints at a theoretical misunderstanding of the scientists.
Magnetic field-lines do not "stretch" to infinity.

Not sure I'm ready to buy into a magnetic field stretching to infinity, though in a sense all magnetic fields do, but subject to the inverse square law the field strength becomes infinitely small. I guess it could be said infinity is as small as it is big.

Is this Magnetic Nozzle something akin to the Coil Gun patented by Kristian Birkeland in 1904?

https://en.wikipedia.org/wiki/Coilgun

https://www.google.com/patents/US754637 ... CB8Q6AEwAA

https://en.wikipedia.org/wiki/Coilgun#cite_note-3

[Zyxzevn]

Is this Magnetic Nozzle something akin to the Coil Gun patented by Kristian Birkeland in 1904?

https://en.wikipedia.org/wiki/Coilgun

Does look very different to me.

The nozzle is based on the idea that we can give plasma a certain magnetic polarization,
which we then can use to repel the plasma.
With fixed materials this does actually work,
See: Magnetic levitation using Eddy currents

[stickwhistler]

If this was valid, then the plasma thruster nozzle should work anywhere, yet I don't see any hoverboards,
'anti-gravity' lifters or any other such sci-fi devices.

Magnetic levitation via eddy currents ie hover trains (eg 'Maglev') work on an entirely different principle
ie two opposing magnets (albeit elctro magnets). An experiment : Put two small magnets in a glass tube,
sealed at one end, so that the magnets do not fall out. Put them in so that one magnet repels the other.
The top magnet 'hovers' . No plasma gun/thruster nozzle needed.

Methinks it is wishful thinking.