Railgun: Significant magnetic field where projectile is?

  • #1
greypilgrim
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Hi.
Very simplified schematics of railguns all look like this:
Railgun-1.svg.png

I have trouble properly understanding this. So apparently there is still a significant magnetic field where the projectile is, even though that's where the current stops flowing through the rails? Of course the magnetic field doesn't just stop there, there's a fringe field, but that has to be a lot weaker than the magnetic field between two wires far from the ends, doesn't it?

Would it make sense to build the projectile like this to move the crossing wire further inside the magnetic field:
Railgun-3.svg.png

Of course, the parts of the projectile (anti-)parallel to the rails would create an opposing magnetic field. But since this field is created by the projectile itself, it shouldn't be taken into account for the Lorentz force acting on the projectile. Or should it?
 
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  • #2
Can you clarify the second configuration? Are the orange conductors that parallel the black rails insulated from those rails, or in electrical contact with them? If they're in contact, isn't this the same as the first configuration, just with slightly thicker rails ahead of the projectile?
 
  • #3
They are part of the projectile and insulated from the rails, apart from the very front where there's contact (at the places where the projectile in the initial configuration was).

EDIT: I uploaded a clarified version.
 
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  • #4
But the orange current flowing anti-parallel to the black current will cancel, so no net increase in the field past the projectile.
 
  • #5
That's what I was wondering, does the field created by the anti-parallel parts count when calculating the Lorentz force onto the projectile? Wouldn't that mean that the orange part would create a net force on itself, contradicting 3rd Newton?

Imagine we only have the isolated orange part at rest, but with a huge inital charge separation that leads to a current. That shouldn't start moving, should it?
Railgun-4.svg.png
 
  • #6
greypilgrim said:
does the field created by the anti-parallel parts count when calculating the Lorentz force onto the projectile?
It cancels the force from the black wire next to it. You can say that they each create an opposite force, if you like. I prefer to say that there is no net current in that area so no field is created, but it is ultimately the same thing.
 
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  • #7
greypilgrim said:
That's what I was wondering, does the field created by the anti-parallel parts count when calculating the Lorentz force onto the projectile? Wouldn't that mean that the orange part would create a net force on itself, contradicting 3rd Newton?
Yes, the "anti-parallel parts count". On your diagram, I've marked non-existent magnetic field loops with red Xs:
1699127582316.png

The field in that region is zero because the net current through those loops vanishes: the black and orange currents are antiparallel and exactly balance to zero. So the only region of magnetic field propelling the projectile is behind it. Your "alternative" is really just the standard railgun.
 
  • #8
Okay, thanks. I think my question comes down to the thought experiment in #5. I refined it a bit and formulated it more clearly in this other thread.
 
  • #9
greypilgrim said:
Okay, thanks. I think my question comes down to the thought experiment in #5. I refined it a bit and formulated it more clearly in this other thread.
This thread here is now closed. Please continue the discussion in that other thread. Thanks.
 

FAQ: Railgun: Significant magnetic field where projectile is?

What is a railgun and how does it work?

A railgun is a device that uses electromagnetic forces to launch high-velocity projectiles. It consists of two parallel metal rails and a conductive projectile. When an electric current flows through the rails and the projectile, it creates a strong magnetic field that propels the projectile along the rails at high speeds.

How significant is the magnetic field where the projectile is located in a railgun?

The magnetic field where the projectile is located in a railgun is extremely significant and strong. It is this magnetic field that generates the Lorentz force, which propels the projectile forward. The strength of the magnetic field can reach several teslas, depending on the current and the design of the railgun.

What are the challenges associated with the magnetic field in a railgun?

The intense magnetic field in a railgun poses several challenges, including the need for materials that can withstand high electromagnetic forces and thermal stresses. Additionally, managing the electromagnetic interference and ensuring the stability of the magnetic field are critical for the efficient operation of the railgun.

Can the magnetic field in a railgun affect nearby electronic devices?

Yes, the magnetic field generated by a railgun can potentially affect nearby electronic devices. The strong electromagnetic pulses (EMPs) can induce currents in nearby conductive materials, potentially damaging or disrupting electronic equipment. Shielding and proper design are necessary to mitigate these effects.

What advancements are being made to improve the magnetic field control in railguns?

Advancements in railgun technology focus on improving magnetic field control through better materials, advanced cooling systems, and precise current regulation. Researchers are also exploring new rail designs and configurations to enhance the efficiency and stability of the magnetic field, thereby improving the overall performance of railguns.

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