# Can we concentrate magnetic (electromagnetic) field in same way we concentrate light into laser?

Sorry if that question is too noobish but i wonder- we can make laser beam and it can go far in distance without loosing much of its power.

To my understanding magnetic field just propagates around its source (like magnet).

Can we do something to concentrate magnetic field so instead propagating in all directions it would "beam" into only one direction?

EDIT
Solenoid can "narrow" magnetic field inside of itself. I thought about something that could be done over air.

• Like a solenoid? – Jon Custer Oct 10 '16 at 15:32
• @JonCuster I considered something that could go via air but thank you for comment. – Eodj Oct 10 '16 at 20:53
• I think this is actually a pretty interesting question. I don't necessarily know the answer, but it's an interesting idea... at least I took it that you meant making something analogous to the laser for non-visible electromagnetic spectrum. Is that correct? – IntuitivePhysics Oct 11 '16 at 19:55

There is no way you can keep a large volume with a magnetic field lines going straight to infinity. Field lines are nothing like a laser, the laser is a wave (propagates according to wave equations) and field lines are abstract concepts that link points with the same value of magnetic field.

However, you can make those field lines very long if you have powerful magnets. Simply take a U-shaped magnet. You know lines are straight between the two legs. So make a bigger magnet, you will get longer lines!

Otherwise, note that the magnetic field can be frozen-in when over a plasma. The field lines follow the plasma. There might be some strange plasma configuration where you push a plasma in a straight line to extend the field lines. I don't know if that is possible and that does not sound like anything easy.

• It's worth noting that magnetic field lines don't go to infinity because of the absence of magnetic monopoles. Because there are no magnetic monopoles, field lines instead must loop back. – Mason Nov 30 '16 at 21:17

A confined "beam" of magnetic field lines, say along and close-to the z-axis, would have to have a strength that changed rapidly with x and y near the "edge" of the beam.

But a large $\partial B_z/\partial x$ or $\partial B_z/\partial y$, means a non-zero curl.

For time-independent fields, a non-zero curl for the B-field requires a current density at that point (Ampere's law). This is exactly what happens in a long solenoid.

So it is not possible to produce the beam you suggest without confining it with a current all the way along its length.