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AIP conference proceedings

Extraction of ultra-slow antiproton beams and their physics application

Hiroyuki A. Torii

Published Jan 1, 2005• 3 citations
Publisher

Abstract

The Trap group of ASACUSA collaboration has decelerated and confined millions of cooled antiprotons in an electromagnetic trap, 50 times more efficiently than conventional methods. They were then extracted out of the magnetic field of 2.5 T and transported at 10–500 eV. This unique ultra‐slow antiproton beam from our apparatus named MUSASHI is expected to open up a new field of atomic and nuclear physics.

DOI
10.1063/1.2130204

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The Trap group of ASACUSA collaboration has decelerated and confined millions of cooled antiprotons in an electromagnetic trap, 50 times more efficiently than conventional methods. They were then extracted out of the magnetic field of 2.5 T and transported at 10–500 eV. This unique ultra‐slow antiproton beam from our apparatus named MUSASHI is expected to open up a new field of atomic and nuclear physics.
We have recently succeeded in decelerating and confining millions of antiprotons, 50 times more efficiently than conventional methods, in an electromagnetic trap. These antiprotons were cooled by preloaded electron plasma to an energy below an electronvolt. They were then extracted out of the magnetic field of 2.5 T and transported typically at 250 eV along a beamline, designed for efficient transport at 10–1000 eV. This unique beam from our apparatus named MUSASHI opens up a new field of atomic and nuclear physics probed by ultra‐slow antiprotons.In this paper, the whole experimental setup and procedure will be overviewed: deceleration, capture, cooling and extraction of antiprotons will be discussed in detail, including technical description of diagnostic devices.
Ultra slow mono-energetic antiproton beams are under preparation combining novel techniques to decelerate antiprotons with an RFQD (Radio Frequency Quadrupole Decelerator), to trap, cool, and compress in an electromagnetic trap, and finally to extract as an ultra slow mono-energetic beam. This unique beam will make it possible to study the ionization processes around adiabatic energy regions, channeling, stopping power, antiprotonic atom formation processes under single collision conditions, to prepare metastable antiprotonic atoms such as p̄p, p̄He+, p̄He++, p̄Li+ in vacuum, and to make high precision laser spectroscopy of them. This project named ASACUSA (Atomic Spectroscopy And Collisions Using Slow Antiprotons) is expected to open a new physics regime in antimatter science under well controlled conditions.
Recently, slow and ultra‐slow antiprotons are now available, which will open a new field of research in atomic physics as well as in related fields. In realizing this, the combination of an RFQD (Radio Frequency Quadrupole Decelerator) and a large multi‐ring trap (MRT) installed in a super‐conducting solenoid has been employed. Several million antiprotons have already been accumulated, and a mono‐energetic antiproton beam of 10 eV has been extracted and transported through a specially designed beam line. A couple of basic experiments which get feasible by the developments of ultra slow antiproton beam are discussed, which include ionization and antiprotonic atom formation processes and also to study spectroscopic nature of various meta‐stable antiprotonic atoms under single collision conditions. A so‐called cusp trap configuration is also discussed, which could for the first time synthesize intense spin‐polarized antihydrogen beams. At the same time, it could trap antihydrogen atoms for a macroscopic time.
We have developed techniques to decelerate, cool and confine antiprotons in vacuo with an electromagnetic trap, for production of a Monoenergetic Ultra‐Slow Antiproton Source for High‐precision Investigation (MUSASHI) over the last several years. The ultra‐slow antiproton beam which can now be extracted stably has opened up the possibility to study ionization and atomic capture processes between an antiproton and an atom at an unprecedented low energy under the single‐collision condition for the first time. The collision energy can be tuned from 10 eV to 1 keV either by varying the beam transport energy or by biasing the voltages at the collision region.Since the number of available antiprotons is very much limited, the reaction probability must be maximized in order to make best use of them. We have prepared a powerful supersonic helium gas jet with a density of 3×1012 atoms/cm3 to be crossed with the antiproton beam. For rigorous identification of particles (e−, p̄ and (p̄A+)0) needed for reduction of huge background signals, we developed a detection system with two microchannel plates each with a delay‐line two‐dimensional position sensitive detector, and a box of scintillator plates. A set of electrodes and coils were placed near the collision point to guide electromagnetically the electrons perpendicular to the antiproton beam. The reaction events will be recognized by an electron signal followed by an antiproton annihilation with an appropriate time of flight. Our design and strategy of the experiment are discussed.
We have used a radio frequency quadrupole decelerator to decelerate antiprotons emerging from the CERN Antiproton Decelerator from MeV- to keV-scale energy, and collected five decelerated pulses in a multiring trap. Some 5 x 10(6) antiprotons were stacked in this way. Cooling of the trapped antiprotons by a simultaneously trapped electron plasma was studied nondestructively via shifts in plasma mode frequencies. We have also demonstrated the first step in extracting a 10-500 eV antiproton beam from the trap.