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Homemade electromagnet.

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iJim

Sat Feb 04 2017, 07:08PM

Registered Member #2662 Joined: Fri Jan 29 2010, 10:14AM
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Posts: 36

Hi all,

I'm just after opinions on whether one could build a 2T electromagnet at home? It needn't be a continuos field, so a pulsed magnet seems like the obvious thing. Back of the envelope calculation suggests hundreds if not thousands of Amps would be required and that would have to be squeezed into a relatively small solenoid!

Cheers

Jim

Carbon_Rod

Sun Feb 05 2017, 12:32AM

Registered Member #65 Joined: Thu Feb 09 2006, 06:43AM
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Posts: 1155

Most equipment uses a double walled dewar for keeping liquid nitrogen around liquid helium.
Thus, the cryogenically cooled super-conducting electromagnet can maintain its field for weeks with almost no electrical power required.
Note, the odds of finding a functional surplus unit is low given their scarcity among labs.

Doing this at home would pose some significant challenges... unless you lived in a particle physics lab.

klugesmith

Sun Feb 05 2017, 06:13AM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1714

Hi Jim.

2T is barely within the range where you can get the benefit of iron in the flux path.
In how large a space do you need that strong a flux density?

Would you be content with electromagnet for lifting things, or holding them down? 2 T isn't unreasonable (IMHO) if the magnet pole pieces are in contact with the attracted object.
Electromagnets made from microwave oven transformer are all over the Internet.

I'm guessing that with the original 120-volt primary winding, 15 or 20 amps DC would get you close to the saturation flux density. To do it with less current and power, add windings to fill the space formerly occupied by the secondary winding and core shunts. You could use pre-wound primary coils from one or two identical MOT's.

Hazmatt_(The Underdog)

Sun Feb 05 2017, 06:47AM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

Magnet

iJim

Mon Feb 06 2017, 07:45PM

Registered Member #2662 Joined: Fri Jan 29 2010, 10:14AM
Location:
Posts: 36

Pretty much as I thought, it knew it was going to be a big ask!! Apparently one can buy a table top 2T magnet these days for about 100k, I suspect the magnet may fit on a table top, but the power supply will be bigger than the table.

The reason I asked was because I'm interested in what happens to a plasma when it passes through such a high field. I'm not in a particle physics lab, but actually a plasma physics lab and the strongest magnets we have tend to be found in magnetrons. Actually, just across the road there's an MRI scanner with an 8T magnet, funnily enough the owner is not as keen as I am to give it a try!

klugesmith

Tue Feb 07 2017, 04:37AM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1714

>> Apparently one can buy a table top 2T magnet these days for about 100k...

OK Jim, it looks like you want B = 2 T in a mostly empty space.
But you still never said what size you are thinking of.
For a volume similar to that of a pencil eraser,

I bet it could be done with permanent magnets, with the whole thing no bigger than a soda can.

Sulaiman

Tue Feb 07 2017, 08:45AM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

AFAIK there are no phenomena that occur at 2T that do not occur at 1T, or 10T

I too would go for a couple of NdFeB permanent magnets with transformer steel for a yoke and as pole concentrators
1.7T easy, 2T marginal.

have a look here

iJim

Wed Feb 08 2017, 10:27AM

Registered Member #2662 Joined: Fri Jan 29 2010, 10:14AM
Location:
Posts: 36

Hi Sulaiman,

'there are no phenomena that occur at 2T that do not occur at 1T, or 10T'... Actually, under atmospheric pressure conditions, the gyration frequency of the electrons in the plasma approaches their collisional frequency in the 2 - 4 T range. There's potentially some interesting physics that might pop out in this range, but as noted, it's pretty hard to find out.

It's actually the same phenomena that is exploited in low pressure magnetised plasmas from materials processing applications. Critically, in these systems the collisional frequency is much lower, hence the required magnetic field is also much lower. So they tend to use rings of permanent magnets.

In terms of size, something small would be fine (the plasma passing through a high field region on the order of a cubic cm would be ideal).

Permanent magnets sound like they could certainly get me close and it's worth a try (as long as they aren't too expensive). An electromagnet would have the advantage of being able to trigger the field at different points during the discharge, which would add to what we could find out.

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