How the ATHENA Experiment works     ATHENA

   In order to make antihydrogen, we have to first capture and prepare the ingredients: antiprotons and anti-electrons (a.k.a. positrons). When we make antihydrogen we need to be able to tell that we have made it. Therefore we need a high resolution detector that will be able to distinguish between when we make antihydrogen and any background that there might be. Finally, once antihydrogen is made we want to look at the spectrum of it and compare it to that of hydrogen.
These considerations mean that our experimental apparatus is split into some natural subsections:
red ball The antiproton catching trap
red ball The positron accumulator trap
red ball The mixing trap
red ball The antihydrogen detector
red ball Experimental control and data analysis
red ball Laser spectroscopy of antihydrogen
red ball How it all comes together

All the traps used in our experiment are variations of Penning traps where the radial confinement is provided by an strong magnetic field and the axial confinement is provided by electrical potentials applied to a series of  cylindrical shaped electrodes. This is a standard technique for trapping charged particles and has been used for many years to trap electrons, protons, ions and also antiprotons and positrons. For the trapping scheme to work the particles, however, need to be charged. Thus neutral atoms are NOT trapped by these traps; a feature we use to observe antihydrogen.
The figure below shows an overview over our entire experiment. The antiprotons from CERNs Antiproton Decelerator come in from the left. The positron source is situated to the far right.  The mixing of the two particles, to try to get them to make antihydrogen, takes place in the Mixing Trap (here called Recombination Trap), which is situated inside a cryogenically cooled (~10 K) coldnose that is inserted into our 3 Tesla superconducting magnet. The trap is surrounded by the ATHENA detector, which detects the annihilation of the antiprotons as well as the positrons with a very good time and space resolution.

ATHENA overview

Further reading:

Antimatter: Mirror of the Universe (Live from CERN webcast)
What is antimatter?(Scientific American)
Antimatter Makers Chase Ultimate Energy Source (
Through the Looking Glass (Nature)
CERN's New Antimatter Factory (CERN announcement)

LVJ - Last  modified September  14, 2002