# Linear electro magnetic field

1. Sep 28, 2014

### Ajbot

how could i make a linear electromagnetic field to a great distance

2. Sep 28, 2014

### Staff: Mentor

What exactly do you mean with "linear"?
Make a large, strong source. The question is way to broad for a more specific answer.

3. Sep 29, 2014

### Ajbot

A Electro magnetic field that is in a straight line that could go to a great distance

4. Sep 29, 2014

### Drakkith

Staff Emeritus
Are you talking about something like a laser?

5. Sep 29, 2014

### Ajbot

no a electromagnetic field

6. Sep 29, 2014

### Drakkith

Staff Emeritus
"A electromagnetic field" is extremely vague. You're going to need to be more specific if you want help.

7. Sep 29, 2014

### Ajbot

something like this.that could work in open air

8. Sep 29, 2014

### Drakkith

Staff Emeritus
No, nothing like that can be built to create an electric or magnetic field that doesn't fall off in strength over such a large distance in the open air. You'd need a large tunnel filled with electromagnets in order to generate a 1 km long magnetic field, and I'm not sure it's even possible to do something similar with an electric field.

9. Sep 29, 2014

### Ajbot

10. Sep 29, 2014

### billslugg

A linear electromagnetic field might be interpreted as one that did not fall off with distance. When radiated through space from a point source, the field will fall off as the inverse square of the distance. By confining the EM field to a waveguide, a 'linear' field can be achieved. A waveguide is simply a long skinny cavity bounded by metal.

11. Sep 29, 2014

### dontbearrogant

A Hall effect thruster is still rather short range, you're probably better off trying a high energy cutting laser as a guide for pulsed em waves (I say a high energy cutting laser because it should have a slight atmospheric blooming effect) but I don't know if it would work at a distance or even work at all.

12. Sep 29, 2014

### billslugg

EM pulse will not follow ionized channel. Ionized channel will absorb the EM wave and simply convert it to heat. However, if you were to make a ring of lasers that could ionize a cylindrical shell maybe 10 cm in diameter extending to outer space, then the interior might be ionization free for a few milliseconds. We would have a conductive waveguide that could efficiently couple an EM pulse of comparable wavelength to 10 cm, or about 3 GHz. Once the EM wavefront left the far end of the tube, it would then obey the law of squares in falling off in intensity.

13. Sep 29, 2014

### dontbearrogant

I didn't think about the conversion of the em wave to heat but the laser may work.

14. Sep 29, 2014

### dontbearrogant

That is assuming the lasers don't absorb and convert the em wave before it reaches its destination.

15. Sep 29, 2014

### Staff: Mentor

To get a field that is not completely different from your sketch, you would need objects significantly larger than 100m on both sides (~500m is better). It is possible, but you would have to construct something like multiple large towers.