Antiproton Decelerator

The Antiproton Decelerator (AD) is a storage ring at the CERN laboratory near Geneva. It was built as a successor to the Low Energy Antiproton Ring (LEAR) and started operation in the year 2000. Antiprotons are created by impinging a proton beam from the Proton Synchrotron on a metal target. The AD decelerates the resultant antiprotons to an energy of 5.3 MeV, which are then ejected to one of several connected experiments.

ELENA (Extra Low ENergy Antiproton) is a 30 m hexagonal storage ring situated inside the AD complex. It is designed to further decelerate the antiproton beam to an energy of 0.1 MeV for more precise measurements. The first beam circulated ELENA on the 18th November 2016. The ring is expected to be fully operational in 2017. GBAR will be the first experiment to use a beam from ELENA, with the rest of the AD experiments following suit in 2019-2020.

ATHENA was an antimatter research project that took place at the Antiproton Decelerator. In August 2002, it was the first experiment to produce 50,000 low-energy antihydrogen atoms, as reported in Nature. In 2005, ATHENA was disbanded and many of the former members worked on the subsequent ALPHA experiment.

The ATHENA apparatus comprises four main subsystems: the antiproton catching trap, the positron accumulator, the antiproton/positron mixing trap, and the antihydrogen annihilation detector. All traps in the experiment are variations on the Penning trap, which uses an axial magnetic field to transversely confine the charged particles, and a series of hollow cylindrical electrodes to trap them axially (Fig. 1a). The catching and mixing traps are adjacent to each other, and coaxial with a 3 T magnetic field from a superconducting solenoid. The positron accumulator has its own magnetic system, also a solenoid, of 0.14 T. A separate cryogenic heat exchanger in the bore of the superconducting magnet cools the catching and mixing traps to about 15 K. The ATHENA apparatus features an open, modular design that allows great experimental flexibility, particularly in introducing large numbers of positrons into the apparatus.

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