# I How To calculate the Power required for a Superconducting Magnet

1. Nov 28, 2017

Staff Emeritus
You see, that's mixing units again. How many volts are in a liter?

More than a gut feeling. It's an order of magnitude calculation, by someone who actually knows what these units are. And who knows the difference between magnetic flux and magnetic fied.

2. Nov 28, 2017

### Sebastiaan

sorry, I mean energy (in joules), not power (in voltage). Given is the Magnetic Flux strength of 30 Weber and current density of 120 A/mm2 (= 1.2e+8 A/ m2?) , I know that Wb = J / A , can I use this to calculate J ?

Last edited: Nov 28, 2017
3. Nov 28, 2017

### Sebastiaan

What is theoretically possible given near outrageous power and money. I need it for the construction of a hard science-fiction game simulation. So as long as there are no fundamental physics laws broken and not too outrageous it can fly. Think 24 century level technology, not current 21 century technology

Last edited: Nov 28, 2017
4. Nov 28, 2017

### Sebastiaan

I don't know but I guess it need to be fast enough to reel in the stuff catched in the magnetic field. My guess is it is linked to the speed of whatever I want to capture, which in the case of solar wind on average travels at 500 km/s. Given the radius of 5 km, a minimum pulse frequency Herz of 500 / 5 = 100 Herz is required

Last edited: Nov 28, 2017
5. Nov 28, 2017

Staff Emeritus
Then you need terawatts of power, not gigawatts. Probably several tens of terawatts, which exceeds all the power produced on earth. You might think this is acceptable in your story, but I can pretty much guarantee if you tried to feed your magnet this much power, it would vaporize.

6. Nov 29, 2017

### Sebastiaan

Perhaps you are right, but could you please illustrate that with a calculation example?

Last edited: Nov 29, 2017
7. Nov 29, 2017

Staff Emeritus
Your picture gives a magnetic field strength. Energy density goes as the square of field strength, the volume is given, and the power goes as the frequency.

8. Nov 29, 2017

### f95toli

Note also that creating a "pulsing" strong magnetic field is actually quite difficult since large inductance also implies a large time constant. Hence,. you want to keep the inductance as low as possible which means using a coil with fewer turns and instead using a large current. Now you have the problem that you have to find power supply that can generate a VERY large AC current; in your case the current would be so large that is probably not possible even in principle.
You also need even more energy since you have that W=LI^2/2

Experiments that require fast changes of large magnetic fields are very, very difficult and in some cases fairly extreme solutions are used. One way is to instead quickly change the geometry of the coil. This can also be used to generate very large magnetic fields; especially if explosives are used (there is actually a facility in the US where this is done)

9. Nov 30, 2017

### Sebastiaan

Could you explain what "L" and "I" represent here? Or provide a reference?

10. Nov 30, 2017

### Asymptotic

Energy stored in an electromagnetic field. L is inductance. I is current. Per Hyperphysics.