Editing Electromagnet (section)

== High-field electromagnets ==

=== Superconducting electromagnets ===
[[Image:Small small IMG 0836.jpg|thumb|Figure 2. The most powerful electromagnet in the world, the 45&nbsp;T hybrid Bitter-superconducting magnet at the US National High Magnetic Field Laboratory, Tallahassee, Florida, USA]]

{{main|Superconducting magnet}}
When a magnetic field higher than the ferromagnetic limit of 1.6&nbsp;T is needed, [[Superconducting magnet|superconducting electromagnets]] can be used. Instead of using ferromagnetic materials, these use [[Superconductivity|superconducting]] windings cooled with [[liquid helium]], which conduct current without [[electrical resistance]]. These allow enormous currents to flow, which generate intense magnetic fields. Superconducting magnets are limited by the field strength at which the winding material ceases to be superconducting. Current designs are limited to 10–20&nbsp;T, with the current (2017) record of 32&nbsp;T.<ref name="nationalmaglab">{{cite web
 |title       = 32 Tesla All-Superconducting Magnet
 |publisher   = National High Magnetic Field Laboratory, USA
 |year        = 2018
 |url         = https://nationalmaglab.org/magnet-development/magnet-science-technology/magnet-projects/32-tesla-scm
 }}</ref><ref name="MagnetLab">{{cite web
 |title       = Mag Lab World Records
 |website     = Media Center
 |publisher   = National High Magnetic Field Laboratory, USA
 |year        = 2008
 |url         = http://www.magnet.fsu.edu/mediacenter/factsheets/records.html
 |access-date  = 2008-08-31
 |url-status  = dead
 |archive-url  = https://web.archive.org/web/20081007201258/http://www.magnet.fsu.edu/mediacenter/factsheets/records.html
 |archive-date = 2008-10-07
}}</ref> The necessary refrigeration equipment and [[cryostat]] make them much more expensive than ordinary electromagnets. However, in high-power applications this can be offset by lower operating costs, since after startup no power is required for the windings, since no energy is lost to ohmic heating. They are used in [[particle accelerator]]s and [[MRI]] machines.

=== Bitter electromagnets ===
{{main|Bitter electromagnet}}
Both iron-core and superconducting electromagnets have limits to the field they can produce. Therefore, the most powerful man-made magnetic fields have been generated by ''air-core'' non-superconducting electromagnets of a design invented by [[Francis Bitter]] in 1933, called Bitter electromagnets.<ref name="MagnetLabU">{{cite web
 |last        = Coyne
 |first       = Kristin
 |title       = Magnets: from Mini to Mighty
 |website     = Magnet Lab U
 |publisher   = National High Magnetic Field Laboratory
 |year        = 2008
 |url         = http://www.magnet.fsu.edu/education/tutorials/magnetacademy/magnets/fullarticle.html
 |access-date = 2008-08-31
 |url-status  = dead
 |archive-url = https://web.archive.org/web/20080917101425/http://www.magnet.fsu.edu/education/tutorials/magnetacademy/magnets/fullarticle.html
 |archive-date = 2008-09-17
}}</ref> Instead of wire windings, a Bitter magnet consists of a [[solenoid]] made of a stack of conducting disks, arranged so that the current moves in a helical path through them, with a hole through the center where the maximum field is created. This design has the mechanical strength to withstand the extreme [[Lorentz force]]s of the field, which increase with ''<math>B^2</math>''. The disks are pierced with holes through which cooling water passes to carry away the heat caused by the high current. The strongest continuous field achieved solely with a resistive magnet is 41.5&nbsp;T {{as of|2017|August|22|lc=y}}, produced by a Bitter electromagnet at the [[National High Magnetic Field Laboratory]] in [[Tallahassee]], [[Florida]].<ref name="NHMFL record">{{cite news |title=MagLab Reclaims Record for Strongest Resistive Magnet |url=https://nationalmaglab.org/news-events/news/strongest-resistive-magnet |access-date=14 May 2023 |publisher=National High Magnetic Field Laboratory |date=22 August 2017}}</ref><ref name="NHMFL Design and Testing 41.5T"> {{cite journal |last=Toth | first=J. | author2=Bole, S.T. |title="Design, Construction, and First Testing of a 41.5 T All-Resistive Magnet at the NHMFL in Tallahassee,"|journal=IEEE Transactions on Applied Superconductivity | volume=28 | issue=3|pages=1–4 |doi=10.1109/TASC.2017.2775578| publisher=IEEE | date=April 2018| s2cid=7923594 | doi-access=free | bibcode=2018ITAS...2875578T }} </ref> The previous record was 37.5&nbsp;T.<ref name="Dutch record">{{cite news |title=HFML sets world record with a new 37.5 tesla magnet |url=http://www.ru.nl/hfml/news/news/news-items/hfml-sets-world/ |access-date=21 May 2014 |publisher=High Field Magnet Laboratory |date=31 March 2014 |url-status=dead |archive-url=https://web.archive.org/web/20150904093407/http://www.ru.nl/hfml/news/news/news-items/hfml-sets-world/ |archive-date=4 September 2015 }}</ref> The strongest continuous magnetic field overall, 45&nbsp;T,<ref name="MagnetLabU" /> was achieved in June 2000 with a hybrid device consisting of a Bitter magnet inside a superconducting magnet.

The factor that limits the strength of electromagnets is the inability to dissipate the enormous waste heat, so more powerful fields, up to 100&nbsp;T,<ref name="MagnetLab" /> have been obtained from resistive magnets by sending brief pulses of high current through them; the inactive period after each pulse allows the heat produced during the pulse to be removed before the next pulse. 
{{breakafterimages}}

=== Explosively pumped flux compression ===
{{main|Explosively pumped flux compression generator}}
[[Image:Flux compression generator 1.png|thumb|upright=1.2|A hollow tube type of explosively pumped flux compression generator. The hollow copper tube acts like a single-turn secondary winding of a transformer; when the pulse of current from the capacitor in the windings creates a pulse of magnetic field, this creates a strong circumferential current in the tube, trapping the magnetic [[field line]]s within. The explosives then collapse the tube, reducing its diameter, and the field lines are forced closer together, increasing the field.]]
The most powerful man-made magnetic fields<ref name="Apex">{{cite web
 |title       = What is the strongest magnet in the world?
 |publisher   = Apex magnets
 |date        = November 2014
 |url         = https://www.apexmagnets.com/news-how-tos/what-is-the-strongest-magnet-in-the-world/
 |access-date = February 5, 2017
 |url-status  = live
 |archive-url = https://web.archive.org/web/20170205183546/https://www.apexmagnets.com/news-how-tos/what-is-the-strongest-magnet-in-the-world/
 |archive-date = February 5, 2017
}}</ref> have been created by using explosives to compress the magnetic field inside an electromagnet as it is pulsed; these are called [[explosively pumped flux compression generator]]s. The [[Implosion (mechanical process)|implosion]] compresses the magnetic field to values of around 1,000&nbsp;T<ref name="MagnetLabU" /> for a few microseconds. While this method may seem very destructive, [[Shaped charge|shaped charges]] redirect the blast outward to minimize harm to the experiment. These devices are known as ''destructive pulsed electromagnets''.<ref name="MagnetLab-pulsed">{{cite web
  |last=Coyne |first=Kristin
  |title=7. Pulsed Magnets: Brief Shining Moments
  |website=Magnets from Mini to Mighty
  |publisher=[[National High Magnetic Field Laboratory]]
  |year=2008
  |url=https://nationalmaglab.org/education/magnet-academy/learn-the-basics/stories/magnets-from-mini-to-mighty
  |archive-url=https://web.archive.org/web/20141220145448/http://www.magnet.fsu.edu/education/tutorials/magnetacademy/magnets/page7.html
  |archive-date=2014-12-20
  |access-date=2014-05-21 }}</ref> They are used in physics and materials science research to study the properties of materials at high magnetic fields.