In order to synthesize antihydrogen, we need to combine antiprotons with positrons. We call this delicate process ‘Mixing’. We want to keep the antihydrogen for study, so we use a magnetic trap to confine (trap) it. The mixing process has been carefully planned such that the magnetic trap does not interfere with it. This allows us to repeat the ‘Mixing’ step inside our magnetic trap to ‘Stack’ (accumulate) antihydrogen in the trap.

Plasma is the fourth fundamental state of matter. It is a gas with so much energy the electrons orbiting the atoms have too much energy to remain in orbit, giving us ions and free electrons. Plasma can be artificially generated by heating (a lightning bolt is made of plasma), electromagnetic fields (see fluorescent light bulbs) or radiation.

Plasma at ALPHA

At ALPHA, we manipulate the ingredients to make antihydrogen as plasmas. We use several so-called non-neutral plasmas made up of either positrons, electrons or antiprotons (or mixtures of these). Each of these particle plasmas are prepared separately: the positrons and electrons have no ions to orbit, and the antiprotons have not (yet) got positrons orbiting them.

As charged plasmas, they are easy to manipulate in the vacuum of the experiment. We can confine them with magnetic and electric fields (see Penning Trap). Their charged nature also helps with diagnostic measurements (see Faraday Cup and MCP).

The second ingredient that is needed to create antihydrogen are antiprotons. The Antiproton, p, is the antimatter counterpart of a proton. Antiprotons can be produced in collisions involving cosmic rays, but do not occur on earth naturally. That’s why we need to produce them with the accelerators at CERN.

The first ingredient that is needed to create antihydrogen are positrons. The Positron (= positive electron), e+, is the antimatter counterpart of the electron, and was the first antimatter particle that was discovered. Positrons occur naturally at the β+ decay of radioactive material.