How is antimatter stored?

In this section you will find answers to the following questions:

Can antimatter be stored?
How much antimatter can be stored?
For how long?
How is this done?
Why is it done?

One of the most characteristic properties of antimatter is the fact that it annihilates and completely disappears if it meets normal matter. For this reason, in order to store antimatter, devices called "traps" are used to hold antiparticles. These traps have the special property of keeping the particles away from the walls of the trap. Also, all the air inside the trap is removed to create a vacuum so that the antiparticles will not annihilate on the atoms in the air.

The type of trap used by these experiments is called a Penning trap. In this sort of device, charged positrons and antiprotons are held by electric and magnetic forces and stay in the center of the container without touching its walls. These traps are so effective that particles can be stored for months without ever encountering matter. However, we cannot store many particles in them because the particles naturally repel one another. If large quantities are accumulated, this repelling force eventually overcomes the electromagnetic field that keeps them in place.

Penning trap

Storing atoms with neutral charges, like antihydrogen, turns out to be much more complicated. Since they lack electrical charge, they cannot be subjected to electric forces, so they must be stored with a purely magnetic trap. Nobody has been capable of storing antihydrogen atoms so far, but this is the goal of our research collaboration in the ALPHA Project. The construction of this trap involves combining a number of different magnetic fields, including that of an octupole magnet.

Schematic design of an octupole magnet Tridimensional design of an octupole magnet

With this device, antihydrogen atoms will be stored for at least a few seconds (thousands of times longer than they would survive without a trap.) This short period of time is enough to conduct spectroscopy on the atoms (that is, to analyze what kind of light spectrum the particles generate). Spectral measurements give information about the forces that hold atoms together and are among the most accurate measurements available in Physics. This makes them a good tool to study even minute differences between matter and antimatter.

Assembling the prototype particle trap

The production and storage of antimatter is a costly process, both in terms of time and money. The production of a nanogram (a billionth of a gram) of antihydrogen costs a few hundred million euros. Considering these difficulties, why is antimatter worth researching?

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