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Penning-Malmberg and Minimum-B Trap Compatibility:theAdvantagesofHigher-Order Multipole Traps

J. Fajans, Andréa Schmidt

Published Feb 6, 2008• 0 citations
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Abstract

Abstract. The ATHENA and ATRAP collaborations have recently created large numbers of untrapped anti-hydrogen atoms. The most commonly suggested scheme for trapping the anti-hydrogen is to use a Minimum-B trap. Unfortunately, the Minimum-B fields are very likely to destroy the confinement of the anti-hydrogen constituents; the positrons and anti-protons, which are themselves held in double-well Penning-Malmberg traps. The reasons for the loss of confinement, and modifications to the Minimum-B trap that may alleviate this problem, are discussed in this paper.

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Abstract. The ATHENA and ATRAP collaborations have recently created large numbers of untrapped anti-hydrogen atoms. The most commonly suggested scheme for trapping the anti-hydrogen is to use a Minimum-B trap. Unfortunately, the Minimum-B fields are very likely to destroy the confinement of the anti-hydrogen constituents; the positrons and anti-protons, which are themselves held in double-well Penning-Malmberg traps. The reasons for the loss of confinement, and modifications to the Minimum-B trap that may alleviate this problem, are discussed in this paper.
A comparison of the 1S-2S transitions of hydrogen and antihydrogen will yield a stringent test of CPT conservation. Necessarily, the antihydrogen atoms need to be trapped to perform high precision spectroscopy measurements. Therefore, an approximately 0.75 T deep neutral atom trap, equivalent to about 0.5 K for ground state (anti)hydrogen atoms, has been superimposed on a Penning-Malmberg trap in which the anti-atoms are formed. The antihydrogen atoms are produced following a number of steps. A bunch of antiprotons from the CERN Antiproton Decelerator is caught in a Penning-Malmberg trap and subsequently sympathetically cooled and then compressed using rotating wall electric fields. A positron plasma, formed in a separate accumulator, is transported to the main system and also compressed. Antihydrogen atoms are then formed by mixing the antiprotons and positrons. The velocity of the anti-atoms, and their binding energies, will strongly depend on the initial conditions of the constituent particles, for example their temperatures and densities, and on the details of the mixing process. In this paper the complete lifecycle of antihydrogen atoms will be presented, starting with the production of the constituent antiparticles and the description of the manipulations necessary to prepare them appropriately for antihydrogen formation. The latter will also be described, as will the possible fates of the anti-atoms.
Only our ATRAP Collaboration is yet able to accumulate and store 4.2 K antiprotons and positrons. The antiprotons come initially from the new Antiproton Decelerator facility at CERN. Good control of such cold antimatter plasmas is key to aspirations to produce and study antihydrogen atoms that are cold enough to confine by their magnetic moments. In the closest approach to cold antihydrogen realized to date, the cold positrons have been used to cool antiprotons, the first time that positron cooling has ever been observed. The Penning-loffe trap, one possibility for simultaneously confining antihydrogen and the cold ingredients from which it is formed, is introduced and discussed.
We have demonstrated storage of plasmas of the charged constituents of the antihydrogen atom, antiprotons and positrons, in a Penning trap surrounded by a minimum-B magnetic trap designed for holding neutral antiatoms. The neutral trap comprises a superconducting octupole and two superconducting, solenoidal mirror coils. We have measured the storage lifetimes of antiproton and positron plasmas in the combined Penning-neutral trap, and compared these to lifetimes without the neutral trap fields. The magnetic well depth was 0.6 T, deep enough to trap ground state antihydrogen atoms of up to about 0.4 K in temperature. We have demonstrated that both particle species can be stored for times long enough to permit antihydrogen production and trapping studies.