To some, magnets are just the things that hold  family photos and to-do lists to the fridge door  

but in reality, magnets and  magnetism make the world go around. 

Magnets are everywhere, every electric motor,  generator, loudspeaker, mechanical hard drive,  

microwave oven and of course equipment like  MRI machines which I recently found myself  

in and which was the inspiration for this video. 

Magnets are also the fundamental feature  of the new fusion reactors which will  

hopefully lead us to a clean energy world which  follows on nicely from our last video about  

the 3 mile island nuclear incident. So in this video we’ll look at how  

magnets are an often overlooked but  fundamental part of our modern world.

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Although this video is about magnets it  should really be about magnetic fields  

because a magnet is just an object or device  that creates a magnetic field and it's how we  

use these fields that makes them so very useful. Magnetic fields are everywhere too, the biggest  

nearest one is generated by the biggest  magnet.. the earth itself or to be more  

precise the ever-moving molten iron core at  the centre of the earth right under our feet. 

But even though the magnetic field that this  creates extends for tens of thousands of km  

into space and protects us from the charged  particle radiation given off by the sun,  

the power of that field is very weak on a local  scale. It only has enough strength to move the  

pointer of a compass and can easily be  overwhelmed by a tiny magnet nearby. 

So what is magnetism and what makes a magnet?  Well, Magnetism is defined as is a force  

generated in matter by the motion of electrons  within its atoms. Magnetism and electricity are  

two aspects of electromagnetism which is one  of the fundamental forces of the universe. 

Magnetism is the force that is created by the  orbit of electrons around the nucleus of an atom,  

a bit like the planets orbiting the sun  and the spin of the electrons themselves  

which is like the earth spinning on its axis. In most elements, there are pairs of electrons  

spinning in opposite directions which cancels this  force out. However, in some so-called transition  

metals such as iron, cobalt, and nickel  and rare earth elements cerium, neodymium,  

samarium, and europium, there are single unpaired  electrons and here the forces are not cancelled  

out making the electrons like a tiny magnets. When there are large groups of these electrons  

all spinning in the same direction the magnetic  force is added together creating magnetic domains  

and when are a lot of these magnetic domains  in a metal it is said to be magnetic. 

This creates magnetic field lines  in the space around it and the more  

lines there are the stronger the magnet is  and this is measured in gauss and teslas,  

one tesla being 10,000 guass. A typical fridge  magnet at its surface is about 100 guass  

and the earth’s magnetic field is about 0.5 guass. Because electricity and magnetism are intimately  

linked when a current is passed through  a conductor like a piece of copper wire,  

the movement of electrons in the wire  creates a magnetic field around the conductor  

but unlike natural permanent magnets this field  only exists for as long as a current is flowing  

and the greater the amount of current  flow the greater the magnetic field  

and these are known as electromagnets. The power required for an electromagnet  

is the square of the magnetic field, so to go from  1 tesla to 10 teslas requires 100 times the power. 

But using just copper wire there is  a limit to how much current can flow  

and as the wire heats up it’s resistance  increases decreasing the current. However,  

if superconducting materials are mixed with the  copper wire the amount of current can be much  

larger the magnetic field generated much stronger. But most superconductors only work when  

cryogenically frozen to as low as  -269C, limiting where they can be used. 

Until relatively recently most permanent magnets  were made from alloys of iron, nickel and cobalt  

but in 1984 both General Motors and the  Japanese company Sumitomo Special Metals,  

individually developed Neodymium magnets but  using different manufacturing techniques. 

These are now the most powerful commercially  available permanent magnets. This is because  

Neodymium has four unpaired electrons to the  three of iron and are capable of storing much more  

magnetic energy, typically 18 times that of normal  ferrite magnets by volume and 12 time by mass. 

This means that they can lift thousands of times  their own mass and have become commonplace in  

things high power motors of all sizes. Couple that  with high energy density Li-ion batteries and you  

have devices like battery-powered hand tools  that 30 years ago would have needed to be mains  

powered, tiny high power motors for  things for drones and of course the new  

powerful electric motors for electric vehicles. But as powerful as Neodymium magnets are there  

are some issues. Firstly when they are heated up  to beyond 100C the magnetic energy density drops  

dramatically till they reach the Curie point where  they permanently lose all their magnetic ability,  

though Dysprosium or terbium can be  added that will mitigate some of this  

to allow higher operating temperatures. The second is the supply of these rare  

earth elements is limited to just a few places  around the globe and mostly concentrated in China  

with dominates the supply chain, which limits the  competition and keeps the price artificially high. 

When we get the most powerful magnets,  Devices like MRI or Magnetic resonance  

imaging scanners which I happened to be  in one last year have to generate a very  

powerful but even magnetic field as possible. This is used to align the spin of the electrons  

in hydrogen atoms, and as our bodies are 70%  water which is 2 hydrogen atoms to one oxygen,  

this works very well to differentiate between fat,  water, muscle, and other soft tissue and bone. 

Around the core of the MRI scanner other  electromagnetic gradient coils then change  

that field in a rapid but controlled manner whist  radio waves are injected that affect the spin of  

the electrons. When the radio waves are turned  off the electrons return to their normal spin  

and this is picked up by other receiving coils  on and using this information the computer  

can build up a 3D image of the body in slices. The main electromagnet uses superconductors which  

have to be cooled with liquid helium to -269C or  4.2 kelvin to generate a field strength of about  

3 tesla which is why you can not enter the room  whilst it is on wearing or carrying anything made  

from ferrous metals or electronic devices  like pacemakers as these could be dislodged  

or heated up by the very strong magnetic field. There have been very rare incidents when safety  

protocols have not been followed where the  M.R.I. magnets have sucked in hospital beds,  

screwdrivers, oxygen tanks and other metal  objects into the core of the machine. 

https://static01.nyt.com/images/2017/06/27/science/ask-mri/ask-mri-jumbo-v2.jpg?quality=75&auto=webp 

Now as powerful as MRI magnets are, they far from  the largest magnets, that accolade will go to the  

experimental ITER fusion reactor currently being  built in France by an international consortium. 

This is the largest experiment fusion reactor  to date and hopefully will be the first to prove  

that fusion is viable on a commercial scale even  though it won't generate any electrical power,  

the heat created will just be  vented via a giant heat exchanger. 

Now if you're wondering why  this is such a big deal,  

then this quick explanation will show you why. Existing nuclear power stations use nuclear  

fission which takes heavy elements like  uranium and bombards them with neutrons,  

this splits the uranium atoms and in  the process releases more neutrons,  

some of which heat’s up cooling water  that surrounds the uranium fuel rods  

which is used to create steam to  power turbines and make electricity. 

The problem with fission is that once a fission  reaction takes place if things go wrong it can  

very quickly escalate out of control with  disastrous results, that’s what happened  

at 3 Miles Island, Chernobyl and Fukushima. It  also creates other highly radioactive elements  

which are the waste products and will remain  radioactive for hundreds or thousands of years. 

Nuclear fusion on the other hand is the same  process the sun and all stars use to convert the  

lightest element in the universe Hydrogen, into  helium. It does this under extreme pressure at  

the centre of the sun that fuses the Hydrogen  nuclei together to create heavier elements  

like helium and in the process, it releases energy  which we then capture and use to make electricity. 

Fusion reactions release four times the amount  of power compared to fission and 4 million times  

that of coal. Just 1 gram of deuterium-tritium,  isotopes of Hydrogen in a fusion process would  

produce 90,000-kilowatt hours of energy  or the same as burning 11 tonnes of coal. 

Fusion is also inherently safe, unlike fission  it is very difficult to start and maintain so  

it can not create runaway reactions. If anything  goes wrong with the process the reactions stop  

automatically and there is no nuclear waste other  than the irradiated reaction containment vessels  

when the plant is shut down or refurbished. The problem is that, unlike the sun, we can  

not recreate the extreme pressure here on earth,  at the centre of the sun the density of hydrogen,  

the lightest element in the  universe is 70x denser than steel. 

But fusion can occur on earth at just 10 times  atmospheric pressure if the temperature is high  

enough, about 10x hotter than the centre  of the sun or 150 million degrees Celsius. 

Now there is nothing on earth or in the universe  that withstand that kind of temperature but  

luckily for us matter at that high a temperature  is a plasma that reacts to magnetic fields.  

So if you have a very strong magnetic  field you can contain this super-hot plasma  

and that’s exactly what they do in a tokamak  fusion reactor but using deuterium & tritium  

as fuel instead of normal hydrogen because they  react better under less extreme conditions. 

ITER or the International Thermonuclear  Experimental Reactor is a magnetic confinement  

fusion reactor and will be the biggest tokamak  reactor built so far and the magnets used in it  

are the biggest ever built. The reactor itself is large  

torus shape, like a giant doughnut and will  use four types of superconducting Magnets,  

a central solenoid magnet, poloidal magnets,  toroidal-field coils, and correction coils.  

The central solenoid alone is the biggest at 18  metres high by 4.3m wide and weighing 1000 tonnes. 

Together, these create an intense magnetic  field between 11 and 13 tesla that will hold  

the plasma in a vacuum in the centre of the  reactor vessel away from the walls whilst it  

is heated to 150 million degrees by passing  huge electrical currents through the plasma. 

The central solenoid magnet is made up of  six sections stacked on top of each other.  

The combined magnets will produce a field  strength of 13 Telsa which about 280,000 times  

stronger than that of the earths. These will repel  each other when running, so they are held together  

with massive tie rods which applies 50,000 tons  of compression, so great is the magnetic field. 

In fact when the central solenoid is  active it could pick up the equivalent  

of an America class amphibious assault  ship weighing in at about 45,000 tons. 

The TF coils which surround the ring of  the torus generate a force of up to 40,000  

tonnes of pressure when active, in fact the whole  structure has to withstand the forces greater than  

twice that of the space shuttle at take-off. Whilst all this is going on the temperature of  

the plasma is 150 million degrees but just a meter  or so away the whole vacuum vessel structure and  

superconducting coils sits in a giant cryostat  tank that cools it to -269 degrees Celius. 

ITER will require 300MW of electrical power to  get the plasma to absorb 50MW of thermal power in  

order to release 500MW of heat in periods of 4-500  seconds when it is finally up and running in 2035. 

But if you could make the  magnets not only more powerful,  

use less power and work at higher temperatures  

then the whole fusion process would be much more  efficient and make even more power for its size. 

So to this end, the most powerful  superconducting magnet ever made  

has been built and tested by a joint team  from MIT and Commonwealth Fusion Systems. 

By using a new high-temperature superconducting  material it allowed them to make a  

record-breaking magnetic field of 20 Tesla's  in Sept 2021 in a much smaller space some  

40 times smaller than current low-temperature  superconducting coils making net power  

from fusion possible more quickly. The fusion power produced in a tokamak  

is proportional to the strength of the magnetic  field to the fourth power, so if you can double  

the magnetic field strength you can get a  16x increase in the amount of fusion power. 

These new coils will be used in  the SPARC fusion project which by  

2025 is hoping to produce net positive fusion  in smaller more easily manufactured reactors  

that can’t come fast enough if we are to move  to a net-zero carbon world any time soon. 

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