Can we power our homes with the process that powers stars? Nuclear fusion offers to do just that, and scientists are looking for ways to harness this energy with experiments that run hotter than the Sun.
The Sun is heated by fusion – a process where the nuclei of two small atoms, such as hydrogen, fuse together into a larger one, such as helium. This releases a heap of energy. Making fusion work on Earth is a challenge scientists are working to meet. “In the Sun, gravity holds it all together,” says John Howard, from the Australian National University. “We don’t have enough gravity on Earth. Instead we can build a magnetic thermos flask to hold it together.”
The Australian Plasma Fusion Research Facility was upgraded last month to better understand the physics of fusion. Based on a type of magnetic bottle known as a stellarator, the machine uses radio waves and microwaves to heat gas until it forms plasma hotter than the centre of the Sun. “The reason it has to be so hot is because there’s so little of it there. It’s just a puff of gas in that machine,” says John.
The Joint European Torus in the United Kingdom showed that fusion really can provide us with energy. Using the same heavy hydrogen fuel mix, with a bigger machine, it produced 16 megawatts of energy in 1997 – the world record for fusion power.
The technology could work, but we’re not plugging in yet. “There are still some big technical challenges before you have a machine that can release power steadily back to the grid,” says John. The next leap forward in fusion research is ITER – a huge international project with a massive machine being built in France. Its goal is to produce 500 megawatts of power.
With the power of stars inside, is fusion safe? All current nuclear power stations use another process called fission, which breaks large atoms into smaller parts. Scientists say that fusion is safer than fission. “With fusion, there’s no chain reaction, it will never get out of control,” says John. “If you take the fuel away, it just stops.” Boyd Blackwell, who oversaw the upgrade of the Australian facility, agrees. “You’re talking about much smaller quantities and risk scenarios that are on a much less likely scale than fission,” says Boyd.
Want to explore the maths behind fusion? Look out for Maths and Stats by Email this Tuesday, which is all about donut-shaped magnetic fields.
A photograph of argon plasma produced inside the Australian Plasma Fusion Research Facility. The circular metallic coils are used to produce the magnetic field that confines the white hot plasma. Image: Tim Wetherell, Research School of Physics and Engineering, Australian National University
Quiz questions
How many vocal cords are used in the human body?
Which of these heats the inside of the Earth more? Is it a) radioactive decay, b) friction or c) electricity?
The word vaccine comes from the Latin word for which animal?
Which has the larger genome, bread wheat or rice?
What makes litmus paper change colour?
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Touch the magnet on the side of the aluminium foil. Does it stick?
Drop the coin through the middle of the tube of aluminium foil. Watch how fast it falls. Then try dropping the magnet.
Compare the speed of the falling magnet with the speed of the coin.
Safety: The magnet required for this experiment is very strong. Be careful not to put your fingers between the magnet and any other magnetic surface.
You will need
Roll of aluminium foil
20 cent coin
Strong magnet, such as a 2.5 cm diameter neodymium magnet. They are available in hobby and electronic stores. Make sure it is slightly smaller than the inside of the roll of aluminium foil.
What to do
Touch the magnet on the side of the aluminium foil. Does it stick?
Hold the roll of aluminium foil in front of you, so the tube is pointing straight up and down. You should be able to see the floor if you look through it.
Drop the coin through the middle of the tube. Watch how fast it falls.
Drop the magnet through the middle of the tube. Watch how fast it falls. Compare the speed of the falling magnet with the speed of the coin.
What’s happening?
The magnet falls much slower than the coin, but why? Electromagnetism is a force responsible for a variety of things. It holds atoms together to form matter, which means you can’t fall through the floor or walk through a wall. It also happens to have a lot to do with how light is made, how electricity works and why magnets stick together or push apart.
On the other hand, a moving magnet will also jiggle the charges in some materials, creating electricity. So a moving magnet makes electricity, which in turn creates another magnetic field.
Our dropped magnet won’t stick to the aluminium because it’s not made of the right material. The only elements that can attract magnets are iron, nickel and cobalt. However, some metals, such as copper and aluminium, will still conduct electricity if a magnet is moved over it. As the magnet falls, it moves past the aluminium, making a small amount of electricity. This electricity creates its own tiny magnetic field that pushes up against the falling magnet, slowing it down.
Applications
This activity is an example of magnetic braking, which is quite useful in situations where normal brakes aren’t as effective. For instance, most mechanical brakes rely on friction. Yet if the surfaces are too smooth or covered in a lubricant such as water or oil, mechanical brakes can slip and fail. Many roller coaster cars use magnetic brakes to slow them down.
Some brakes are similar to the one in our experiment, relying on the movement of neodymium magnets to create what are called ‘eddy currents’. The faster the magnets are moving, the stronger the eddy currents and the harder they’ll push, controlling the speed of the vehicle. Since they don’t rely on an electrical supply and work in most environments, they are a good way to make sure a roller coaster doesn’t malfunction.
How are stars made, and how do they live their lives? The best place to find answers is in the Milky Way. Click the video below to watch Naomi McClure-Griffiths from CSIRO share her research into a frothy and bubbly galaxy.
Quiz answers
There are two true vocal cords used in the human body, and two false vocal cords that do not directly make speech.
a) Radioactive decay produces more heat inside the Earth.
The word vaccine comes from the Latin word for cow, vacca. This is because a vaccine for smallpox was made from cowpox.
Bread wheat has a genome that is 40 times larger than rice.
Acids and bases make litmus paper change colour.
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