Antiproton Decelerator

The Antiproton Decelerator (AD) is a storage ring at the CERN laboratory near Geneva. It was built from the Antiproton Collector (AC) to be 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. The major goals of experiments at AD are to spectroscopically observe the antihydrogen and to study the effects of gravity on antimatter. Though each experiment at AD has varied aims ranging from testing antimatter for cancer therapy to CPT symmetry and antigravity research. From 1982 to 1996, CERN operated the Low Energy Antiproton Ring (LEAR), through which several experiments with slow-moving antiprotons were carried out. During the end stages of LEAR, the physics community involved in those antimatter experiments wanted to continue their studies with the slow antiprotons. The motivation to build the AD grew out of the Antihydrogen Workshop held in Munich in 1992. This idea was carried forward quickly and AD's feasibility study was completed by 1995. In 1996, the CERN Council asked the Proton Synchrotron (PS) division to look into the possibility of generating slow antiproton beams. The PS division prepared a design study in 1996 with the solution to use the antiproton collector (AC), and transform it into a single Antiproton Decelerator Machine. The AD was approved in February 1997. AC modification, AD installation, and commissioning process were carried out in the next three years. By the end of 1999, the AC ring was modified into a decelerator and cooling system- forming the Antiproton Decelerator. AD's oval-shaped perimeter has four straight sections where the deceleration and cooling systems are placed. There are several dipole and quadrupole magnets in these sections to avoid beam dispersion. Antiprotons are cooled and decelerated in a single 100-second cycle in the AD synchrotron.