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Bulletin of the American Physical Society

Forming, trapping, and cooling neutral antimatter: strongly magnetized highly excited antihydrogen atoms

H. R. Sadeghpour

Published Jun 8, 2007• 0 citations
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Antimatter Advances Include Trapped Antihydrogen in Its Ground State

Phil Richerme

Bulletin of the American Physical Society•Jun 8, 2012•2 citations

Be+-Assisted Antihydrogen Synthesis and Trapping

Maria Eduarda Fagundes Gonçalves

Antihydrogen, the bound state of a positron and an antiproton, is a uniquely well-suited system for testing fundamental symmetries between matter and antimatter. The Antihydrogen Laser Physics Apparatus (ALPHA collaboration) synthesises antihydrogen atoms by slowly merging cold non-neutral positron and antiproton plasmas and traps the antiatoms in a magnetic minimum trap. While trapping efficiency has improved since its first demonstration in 2010, it plateaued after 2017.In ALPHA’s experimental conditions, antihydrogen is predominantly formed via three-body recombination, which has been theoretically and experimentally shown to strongly depend on the temperature of the positron plasma: lower positron temperatures yield higher antihydrogen trapping rates. In the ALPHA-2 trap, positrons alone reach a lower temperature limit of 15−20 K. The implementation of sympathetic cooling of positrons through collisions with laser-cooled Be+ions enabled stable lowering of these temperatures to below 10 K. This thesis describes the work towards antihydrogen synthesis with positrons prepared using this cooling method. A novel ion plasma preparation technique was developed to improve reproducibility, and a sophisticated control system with automated beam steering was implemented to ensure long-term operational stability. Moreover, the first demonstration of sympathetic cooling of positrons to < 10 K in a radially asymmetric magnetic field was carried out. Culminating in the first Be+-assisted antihydrogen synthesis and trapping. Careful optimisation of this technique resulted in a near eightfold increase in the antihydrogen trapping rate, and allowed for systematic studies of three-body recombination that were not possible before its implementation. Overall, this technique represents a paradigm shift for the ALPHA physics programme and provides a deeper understanding of antihydrogen synthesis, opening new avenues for precision studies of antimatter.

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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.

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Traps for Antimatter: The ALPHA Antihydrogen Apparatus

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ATRAP antihydrogen experiments

C. H. Storry, M. M. Aggarwal, A. Akbari +37 more

Abstract Antihydrogen (Hbar) was first produced at CERN in 1996. Over the past decade our ATRAP collaboration has made massive progress toward our goal of producing large numbers of cold Hbar atoms that will be captured in a magnetic gradient trap for precise comparison between the atomic spectra of matter and antimatter. The AD at CERN provides bunches of 3 × 107 low energy Pbars every 100 seconds. We capture and cool to 4 K, 0.1% of these in a cryogenic Penning trap. By stacking many bunches we are able to do experiments with 3 × 105 Pbars. ∼100 e+/sec from a 22Na radioactive source are captured and cooled in the trap, with 5 × 106 available experiments.We have developed 2 ways to make Hbar from these cold ingredients, namely 3‐body collisions, and 2‐stage Rydberg charge exchange. In the first case, Pbars are injected into a nested trap containing e+. Hbar is formed when 2 e+ and 1 Pbar collide. In 2‐stage Rydberg charge exchange, laser‐excited caesium (Cs) enters the trap through a small hole. Rydberg positronium is formed when a e+ captures an e‐from a Cs. These atoms exit the trap, some passing through a nearby cloud of cold Pbars. A 2nd charge‐exchange results when a Pbar captures the e+, forming Hbar. We have also developed techniques to measure the excited‐state distribution of the Hbar and measure their velocity. I will present results from these experiments and discuss the next generation of apparatus to be commissioned this year. This new apparatus includes a e+ accumulator built at York University providing many more e+. The new Pbar annihilation detector provides spatial information of annihilations. Windows allow lasers to enter the trap for spectroscopic measurements and for laser cooling of the Hbar. Possibly the most exciting inclusion in this new apparatus is the inclusion of a neutral particle trap which may, for the first time, capture the Hbar and lead to the first atomic spectrum from antimatter. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Physica status solidi. C, Conferences and critical reviews/Physica status solidi. C, Current topics in solid state physics•Jul 11, 2007•3 citations
Antihydrogen, the bound state of a positron and an antiproton, is a uniquely well-suited system for testing fundamental symmetries between matter and antimatter. The Antihydrogen Laser Physics Apparatus (ALPHA collaboration) synthesises antihydrogen atoms by slowly merging cold non-neutral positron and antiproton plasmas and traps the antiatoms in a magnetic minimum trap. While trapping efficiency has improved since its first demonstration in 2010, it plateaued after 2017.In ALPHA’s experimental conditions, antihydrogen is predominantly formed via three-body recombination, which has been theoretically and experimentally shown to strongly depend on the temperature of the positron plasma: lower positron temperatures yield higher antihydrogen trapping rates. In the ALPHA-2 trap, positrons alone reach a lower temperature limit of 15−20 K. The implementation of sympathetic cooling of positrons through collisions with laser-cooled Be+ions enabled stable lowering of these temperatures to below 10 K. This thesis describes the work towards antihydrogen synthesis with positrons prepared using this cooling method. A novel ion plasma preparation technique was developed to improve reproducibility, and a sophisticated control system with automated beam steering was implemented to ensure long-term operational stability. Moreover, the first demonstration of sympathetic cooling of positrons to < 10 K in a radially asymmetric magnetic field was carried out. Culminating in the first Be+-assisted antihydrogen synthesis and trapping. Careful optimisation of this technique resulted in a near eightfold increase in the antihydrogen trapping rate, and allowed for systematic studies of three-body recombination that were not possible before its implementation. Overall, this technique represents a paradigm shift for the ALPHA physics programme and provides a deeper understanding of antihydrogen synthesis, opening new avenues for precision studies of antimatter.
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.
Abstract Antihydrogen (Hbar) was first produced at CERN in 1996. Over the past decade our ATRAP collaboration has made massive progress toward our goal of producing large numbers of cold Hbar atoms that will be captured in a magnetic gradient trap for precise comparison between the atomic spectra of matter and antimatter. The AD at CERN provides bunches of 3 × 107 low energy Pbars every 100 seconds. We capture and cool to 4 K, 0.1% of these in a cryogenic Penning trap. By stacking many bunches we are able to do experiments with 3 × 105 Pbars. ∼100 e+/sec from a 22Na radioactive source are captured and cooled in the trap, with 5 × 106 available experiments.We have developed 2 ways to make Hbar from these cold ingredients, namely 3‐body collisions, and 2‐stage Rydberg charge exchange. In the first case, Pbars are injected into a nested trap containing e+. Hbar is formed when 2 e+ and 1 Pbar collide. In 2‐stage Rydberg charge exchange, laser‐excited caesium (Cs) enters the trap through a small hole. Rydberg positronium is formed when a e+ captures an e‐from a Cs. These atoms exit the trap, some passing through a nearby cloud of cold Pbars. A 2nd charge‐exchange results when a Pbar captures the e+, forming Hbar. We have also developed techniques to measure the excited‐state distribution of the Hbar and measure their velocity. I will present results from these experiments and discuss the next generation of apparatus to be commissioned this year. This new apparatus includes a e+ accumulator built at York University providing many more e+. The new Pbar annihilation detector provides spatial information of annihilations. Windows allow lasers to enter the trap for spectroscopic measurements and for laser cooling of the Hbar. Possibly the most exciting inclusion in this new apparatus is the inclusion of a neutral particle trap which may, for the first time, capture the Hbar and lead to the first atomic spectrum from antimatter. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)