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

1. Nov 27, 2017

### Sebastiaan

Alright, I'm trying to calculate the power requirements for a 30 Weber =( 30 Tesla/m2) Strong magnet

According to this document it would require about 88 MW using a steady-state copper coil magnet

The question is, how much power is required to do the same using cryogenicly cooled superconducting magnet?

The Document does mention the following
But how to convert this into power requirement into MegaWatt?

Here is one attempt:

120 A/mm2 = 12.2e+8 m2

Weber = Joule / Ampere

Joule = Ampere * Weber = 12.2e+8 * 30 = 3600000000 J = 3600 MJ = 3.6 GJ

Last edited: Nov 27, 2017
2. Nov 27, 2017

### phyzguy

The magnet itself will not require any continuous power once the magnetic field is established, although it will require a burst of electrical power to establish the circulating current. The power requirements will be determined by the power needed for the cryogenic refrigeration units to keep the magnet cold. This will depend on the size of the magnet. By the way, you have your units wrong. 1 Tesla = 1 Weber/m^2. I suspect you mean that you want a magnetic field of 30 Tesla = 30 Weber/m^2. I think this is beyond the range of high-temperature superconductors, meaning you will probably need liquid helium refrigeration.

3. Nov 27, 2017

### Sebastiaan

Interesting, so you would use a large bank of super capacitators charged to full power and then burst the magnetic field into life and then it is just a matter of maintaining below critical temperatures?

4. Nov 27, 2017

### phyzguy

No, I think it would be more typical to ramp up the field more slowly. Maybe someone else with experience at the LHC would know how and at what rate they ramp up the field. This Wikipedia page gives some more detail.

5. Nov 27, 2017

### sophiecentaur

@Sebastiaan : You ask a question about Power and provide a suggested answer in Energy. That doesn't actually make sense. The Energy in the field that you require can be supplied at almost any rate (Power) and it will just take different amounts of time.

6. Nov 27, 2017

### Staff: Mentor

Typically you just ramp a magnet to field using normal mains power. It can take a few hours, but the power is not particularly demanding.

7. Nov 27, 2017

### Sebastiaan

Alright but how much power needs to be provided to get it fully charged? Does my 3.6 GigaJoule result make any sense? Also what would be the minimum amount of power to charge it?

8. Nov 27, 2017

### phyzguy

Your energy calculation makes no sense. How did you go from 120 A/mm2 to 12.2e+8 m2? The units don't even agree. Then you ignored the m^2 in the next step of your calculation. The best way to do this is to figure out what the inductance of your coil will be. This will depend on the size of the coil. The energy to charge it is then given by 1/2*L*I^2. The power will then be this energy divided by how long you want to take to charge it up. But I suspect you will find that the refrigeration power will be the dominant power in your system.

How large is your magnet going to be?

9. Nov 27, 2017

### sophiecentaur

It is the total Energy that determines conversation about when it is 'fully charged'. You cannot mix and match your units if you want a sensible conversation about Physics and EE.
Why would you want to charge the magnet up in any particular time? What would be the point of using 'super capacitors" which would, themselves, need to be charged at well.
3.6GJ can be supplied over any time you want. The formula E = Pt applies (or the Integral version when the supplied power is not constant.

10. Nov 28, 2017

### Sebastiaan

Oh my mistake I meant 1.2e+8m2. I wanted extrapolate 120 A/mm2 to 1 square meter.
The goal is to find Joule = Amp * Wb

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

### Sebastiaan

The diameter of the magnet would be 100 meter, the initial goal is to to create a 10 km diameter mini magnetosphere as described in the linked document. This is all hypothetically of cource!
The whole contraption would like something like this

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

### Sebastiaan

I Want to make the magnetic field be able to quickly pulsate. I was hoping I could shift the energy between the super capacitors and the superconducting magnet. The Pulsating is required to make the mini mag become able to act as a magnetic scoop capable of collecting charged particles like solarwind ions

13. Nov 28, 2017

### sophiecentaur

You are proposing a resonant circuit now. This changes the situation somewhat. Supply power is not the only relevant factor here - you would still 'charge up' the resonator with energy slowly but now you have the resonant frequency of the LC oscillator to consider (the self Inductance of the coil) and, as you have heavy currents flowing in the leads to and in the massive C and the lead resistance would certainly not be Zero. Also, you could have significant peak volts across the capacitor. Super capacitors are not (afaik) high voltage devices.

14. Nov 28, 2017

Staff Emeritus
This whole thread is a confused mismash of units, where units are misdefined, or used to represent the wrong thing, or equated when they are not equal. It's like trying to answer the question "how many calories are in a mile".

That said, if you are trying to have a field of that magnitude over that area with a magnet rise time of minutes, it will take gigawatts of power. You have to provide all the stored energy in the magnetic field from your power source. This will almost certainly destroy your magnet.

15. Nov 28, 2017

### Sebastiaan

Ok, then how could we temporaily store the high current with high peak voltages?

16. Nov 28, 2017

### sophiecentaur

Did you read Vanadium's last post? He has introduced another thing for you to consider before you assume this is in any way workable.

17. Nov 28, 2017

### Sebastiaan

Besides making very gradual changes to the current, Is there anyway to prevent the edgy current causing a Magnet quench

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

Staff Emeritus
Facts, schmacts.

19. Nov 28, 2017

### Sebastiaan

Are you implying that based on your gut feeling it is imposible to create a pulsed magnetic field with super conducting magnets?

Ok but let me repharse my original question.

"How much power do you need to put into a 30 Weber super conduction magnet before it gets to full strength"

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

### Staff: Mentor

Its time to clarify your question. Are you asking what's practically possible, or what may be theoretically possible in the future given infinite power and money?

The power needed depends on what you mean by "quickly pulsate." The quicker, the more power. Give us a number in hertz.