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Bitter magnets

  1. May 27, 2009 #1
    anyone have equations for bitter magnets? or do i use the ones for solenoids?

    i need an electromagnet capable of 4T. that doesn't use super conductors >_>

    i have access to liquid nitrogen though.
  2. jcsd
  3. Jun 1, 2009 #2
    So you are saying that your only problem is not having liquid helium? Or do you care about the bore temperature?

    Magnets are a thing that you simply buy, there must be very special reasons to do home brew. If you use copper I think that the permeability is negligible and I assume we are talking about dc. You should be able to use Biot Savart with homogeneous current density and integrate, but the field should be very similar to a normal coil.

    But let's talk about the real problems: you will need massive current. This will resistively heat the copper. One of the purposes of the bitter configuration is fighting this heat, first by giving the "wire" a large cross section, and then adding pipes to use liquid coolant. A rough calculation should show that you would need massive amounts of LN2 to cool the magnet, even though the resistivity is decreased. The description I found on line uses deionized water for cooling.
    You will need a large cooling setup, a large power supply, then you need to think about mechanical stability...

    Why don't you just buy the thing? Otherwise you should probably use some simulation software.
  4. Jun 1, 2009 #3


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    I've never heard of anyone using a nitrogen cooled normal magnet (unless it is the experiment itself that needs to be cooled); most large normal magnets are simply water cooled. You don't really gain much in terms of reduces losses by colling copper wire and LN2 is not really a good coolant anyway.
    Hence; water cooling is both more efficient and easier to use.
    Moreover, winding a 4T magnet is far from trivial and needs specialist equipment. Unless you know what you are doing you are better off buying one.

    Also, as 0xDEADBEEF has already pointed out you need a current source as well. For a 4T normal magnet something like a 50A supply should work (with maybe 20V compliance).
    This is more or less a standard piece of kit (you can buy one from e.g. TTI) but they are still pretty expensive, at least a few thousand dollars.

    So, if you are asking: is there any way to DIY a 4T magnet without spending a lot of money, the answer is no.
  5. Jun 4, 2009 #4
    at the moment im only trying to make a penning trap. sounds trivial but its only part of a bigger project. i was going to use Y123 at first as a plate material, yea not to easy to get made >_> .... yea
    then i saw the penning design and how it uses copper and an efficient water cooling system. given the amount of LN2 needed to compensate for water, and the amount of power used in there systems, i though 4T would be a fraction of what they are doing.

    reply to f95toli
    im attempting to assemble a bitter magnet, using 50A will generate allot of heat from resistance /cry

    reply to 0xDEADBEEF
    i understand... kinda o_O

    im making it home brew because i have no funding other than a hobbyist's wages D:
    50A sounds doable though. is it possible to get that out of a duel MOT config? reversed ofcorse.
  6. Jun 4, 2009 #5
  7. Jun 18, 2009 #6
    2 points;
    You really don't need a bitter magnet to get up to 4T, a simple solenoid can do this easily.
    If you want to build a bitter magnet to get up to around 10T this can be done with equipment that is fairly commonly available and won't break an average budget.
    A 'buzz box' welding unit can supply around 200 amps at 6v and these are low cost as second hand / car-boot sale equipment.
    To produce the 'coil'; aluminium and acryllic sheet, available from your local DIY store, a 'junior' hacksaw, tinsnips and a drill / file plus some time and care will produce this.
    Plus a large mild steel bolt (don't use high tensile bolts - the high carbon content causes problems). Try to fit the whole inside a CD tower case (the 100 off style) adapted to take water flow - if you feel you need it. Air cooling generally will do for these relatively low field applications
    As for the formula, for a home-brew version, the standard solenoid equations will do best. A rough calculation is ;- Field intensity = (amps x turns)/coil area; ignoring coil length effects
  8. Jun 20, 2009 #7
    For some info on diy Bitter magnets see:


    Note that these coils are destroyed when used--but they are subjected to a pulse from 300 microfarads at multiple thousands of volts and with very low inductance.

    My usual advice: read, read, read, and then BE CAREFUL. The 'experiment' shown here uses deadly voltages/amperages.

    Last edited by a moderator: Apr 24, 2017
  9. Aug 9, 2009 #8
    first off :O!
    and second ty for giving me hope sir. i got 150 amps out of a modded MOT and some grounding wire i picked up at home depot. 15 windings is too much, so ill try one large multi-stranded winding insted.

    amateur question: when you said "coil area" in the equation did you mean planer? as in i calculate the area of one layer of the conductor and multi by the number of layers

    ps i didnt see your post till WAY later. thought the thread died...
    Last edited: Aug 9, 2009
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