Never before had the ingredients of cold antihydrogen (antiprotons and positrons) been simultaneously confined within the same ultra high vacuum system. The challenge was to manipulate two different type of antimatter particles at the same time, especially because the sources for these antimatter particles were completely different.  The antiprotons were created at CERN, then were slowed, captured and cooled by the TRAP collaboration.  The positrons originated in a radioactive source.  These positrons were captured and cooled using techniques developed and demonstrated by the TRAP members from Harvard.  The simultaneous confinement took place in the last week the LEAR operated.

An interaction of the trapped antimatter particles was also observed.  This first demonstrated interaction between the ingredients of cold antihydrogen was an exciting step forward, the closest by far that anyone had ever come to producing cold antihydrogen.
 

(a) Trap used to confine the ingredients of cold antihydrogen for the first time.  The positrons (e+) are initially confined within the same vacuum and trap structure as are the antiprotons (p).   (b) Potential "wells" which confine the positrons and antiprotons arise when the appropriate voltages are applied to the electrodes in (a).   The electrical signals from the simultaneously trapped positrons (c) and antiprotons (d).

When trapped antiprotons were made to pass through the simultaneously trapped positrons, the electrical signal from the cold positrons (a) was clearly heated (b).