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Physical Review Letters

Effects of Extreme Magnetic Quadrupole Fields on Penning Traps and the Consequences for Antihydrogen Trapping

J. Fajans, William Alan Bertsche, Kieron Burke, Steven F. Chapman, Dirk Peter van der Werf

Published Oct 4, 2005• 59 citations
Publisher

Abstract

Measurements on electrons confined in a Penning trap show that extreme quadrupole fields destroy particle confinement. Much of the particle loss comes from the hitherto unrecognized ballistic transport of particles directly into the wall. The measurements scale to the parameter regime used by ATHENA and ATRAP to create antihydrogen, and suggest that quadrupoles cannot be used to trap antihydrogen.

DOI
10.1103/physrevlett.95.155001

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Measurements on electrons confined in a Penning trap show that extreme quadrupole fields destroy particle confinement. Much of the particle loss comes from the hitherto unrecognized ballistic transport of particles directly into the wall. The measurements scale to the parameter regime used by ATHENA and ATRAP to create antihydrogen, and suggest that quadrupoles cannot be used to trap antihydrogen.
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Numerous antihydrogen atoms are created at CERN, by ATRAP and ATHENA experiments, by bringing together positrons and antiprotons in a magnetic Penning trap. Most of these atoms are created in exotic, highly excited states, such that the magnetic forces on positrons are greater than the Coulomb attraction of antiprotons. This paper presents an overview of the recent progress made toward theoretical understanding of the complicated dynamics which leads to the formation and detection of antihydrogen atoms. There is no formal difference between the plasmas described here and normal, electron‐proton, matter plasmas, except the reversed sign of electrical charges. The next generation of experiments need to bring the antihydrogen atoms to the ground state and to cool them to sub‐milliKelvin temperature. Only then, high resolution spectroscopy can expose differences between matter and antimatter due to CPT violations. Suggestions are made for possible pathways toward this goal.
ATRAP has made many important improvements since CERN's Antiproton Decelerator (AD) was restarted in 2006. These include substantial increases in the number of positrons (e+) and antiprotons (Pbars) used to make antihydrogen (Hbar) atoms, a new technique for loading electrons (e−) that are used to cool Pbars and e+, implementation of a completely new, larger and more robust apparatus in our second experimental zone and the inclusion of a quadrupole Ioffe trap intended to trap the coldest Hbar atoms produced. Using this new apparatus we have produced large numbers of Hbar atoms within a Penning trap that is located within this quadrupole Ioffe trap using a new technique which shows promise for producing even colder atoms. These observed Hbar atoms resolve a debate about whether positrons and antiprotons can be brought together to form atoms within the divergent magnetic fields of a quadrupole Ioffe trap.
High-accuracy spectroscopic comparisons of trapped antihydrogen atoms (H¯) and hydrogen atoms (H) promise to stringently test the fundamental CPT symmetry invariance of the standard model of particle physics. ATRAP’s nested Penning-Ioffe trap was developed for such studies. The first of its unique features is that its magnetic Ioffe trap for H¯atoms can be switched between quadrupole and octupole symmetries. The second is that it allows laser and microwave access perpendicular to the central axis of the traps.