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AIP conference proceedings

Progress toward cold antihydrogen

G. Gabrielse, J. Estrada, Steven Peil, Timothy Roach, Jun Tan, P. Yesley

Published Jan 1, 1999• 1 citation
Publisher

Abstract

The production and study of cold antihydrogen will require the manipulation of dense and cold, single component plasmas of antiprotons and positrons. The undertaking will build upon the experience of the nonneutral plasma physics community. Annihilations of the antimatter particles in the plasmas can be imaged, offering unique diagnostic opportunities not available to this community when electrons and protons are used. The techniques developed by our TRAP collaboration to capture and cool antiprotons will certainly be used by our expanded ATRAP collaboration, and by the competing ATHENA Collaboration, both working at the nearly completed AD facility of CERN. We recently demonstrated a new techniques for accumulating cold positrons directly into a cryogenic vacuum system. The closest we have come to low energy antihydrogen so far is to confine cold positrons and cold antiprotons within the same trap structure and vacuum container. Finally, we mention that stored electrons have been cooled to 70 mK, the first time that elementary particles have been cooled below 4 K. In such an apparatus it should be possible to study highly magnetized plasmas of electrons or positrons at this new low temperature.

DOI
10.1063/1.1302098

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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.

AIP conference proceedings•Jan 1, 2002•0 citations

Antihydrogen Trapped in the ALPHA Experiment

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<!--HTML-->In 2010 the ALPHA collaboration succeeded in trapping antihydrogen atoms for the first time.[i] Stored antihydrogen promises to be a unique tool for making high precision measurements of the structure of this first anti-atom. Achieving this milestone presented several substantial experimental challenges and this talk will describe how they were overcome. The unique design features of the ALPHA apparatus will be explained.[ii] These allow a high intensity positron source and an antiproton imaging detector similar to the one used in the ATHENA[iii] experiment to be combined with an innovative magnet design of the anti-atom trap. This seeks to minimise the perturbations to trapped charged particles which may cause particle loss and heating[iv]. The diagnostic techniques used to measure the diameter, number, density, and temperatures of both plasmas will be presented as will the methods developed to actively compress and cool of both plasma species to sizes and temperatures [v],[vi], [vii] where trapping attempts with a reasonable chance of success can be tried. The results of the successful trapping experiments will be outlined as well as some subsequent experiments to improve the trapping rate and storage time. [i] 'Trapped antihydrogen' G.B. Andresen et al., Nature 468, 673 (2010) [ii]'A Magnetic Trap for Antihydrogen Confinement' W. Bertsche et al., Nucl. Instr. Meth. Phys. Res. A566, 746 (2006) [iii] Production and detection of cold antihydrogen atoms M.Amoretti et al., Nature 419, 456 (2002). [iv]' Antihydrogen formation dynamics in a multipolar neutral anti-atom trap' G.B. Andresen et al., Phys. Lett. B 685, 141 (2010) [v]' Evaporative Cooling of Antiprotons to Cryogenic Temperatures', G.B. Andresen et al. Phys. Rev. Lett 105, 013003 (2010) [vi]'Compression of Antiproton Clouds for Antihydrogen Trapping' G. B. Andresen et al. Phys. Rev. Lett 100, 203401 (2008) [vii] 'Autoresonant Excitation of Antiproton Plasmas' G.B. Andresen et al., Phys. Rev. Lett. 106, 025002 (2011) Organizer: Ferdinand Hahn PH/DT Detector Seminar webpage

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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.

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The merging of antiprotons with a positron plasma is the predominant and highest efficient method for cold antihydrogen formation used to date. We present experimental evidence that this method has serious disadvantages for producing antihydrogen cold enough to be trapped. Antihydrogen is neutral but may be trapped in a magnetic field minimum. However, the depth of such traps are of order 1 K, shallow compared to the kinetic energies in current antihydrogen experiments. Studying the spatial distribution of the antihydrogen emerging from the ATHENA positron plasma we have, by comparison with a simple model, extracted information about the temperature of the antihydrogen formed. We find that antihydrogen is formed before thermal equilibrium is attained between the antiprotons and the positrons, and thus that further positron cooling may not be sufficient for producing antihydrogen cold enough to be trapped. We discuss the implications for trapping of antihydrogen in a magnetic trap, important for ongoing work by the ALPHA collaboration.

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Over the last decades it has become routine to form beams of positrons and antiprotons and to use them to produce trapped samples of both species for a variety of purposes. Positrons can be captured efficiently, for instance using a buffer-gas system, and in such quantities to form dense, single component plasmas useful for antihydrogen formation. The latter is possible using developments of techniques for dynamically capturing and then cooling antiprotons ejected from the Antiproton Decelerator at CERN. The antiprotons can then be manipulated by cloud compression and evaporative cooling to form tailored plasmas. We will review recent advances that have allowed antihydrogen atoms to be confined for the first time in a shallow magnetic minimum neutral atom trap superimposed upon the region in which the antiparticles are held and mixed. A new mixing technique has been developed to help achieve this using autoresonant excitation of the centreofmass longitudinal motion of an antiproton cloud. This allows efficient antihydrogen formation without imparting excess energy to the antiprotons and helps enhance the probability of trapping the anti-atom. © 2012 American Institute of Physics.

AIP conference proceedings•Jan 1, 2012•0 citations

Antihydrogen Formation using Cold Plasmas

N. Madsen

Antihydrogen, the antimatter counterpart of the hydrogen atom, can be formed by mixing cold samples of antiprotons and positrons. In 2002 the ATHENA collaboration succeeded in the first production of cold antihydrogen. By observing and imaging the annihilation products of the neutral, non‐confined, antihydrogen atoms annihilating on the walls of the trap we can observe the production in quasi‐real‐time and study the dynamics of the formation mechanism. The formation mechanism strongly influences the final state of the formed antihydrogen atoms, important for future spectroscopic comparison with hydrogen. This paper briefly summarizes the current understanding of the antihydrogen formation in ATHENA.

AIP conference proceedings•Jan 1, 2004•1 citation
The production and study of cold antihydrogen will require the manipulation of dense and cold, single component plasmas of antiprotons and positrons. The undertaking will build upon the experience of the nonneutral plasma physics community. Annihilations of the antimatter particles in the plasmas can be imaged, offering unique diagnostic opportunities not available to this community when electrons and protons are used. The techniques developed by our TRAP collaboration to capture and cool antiprotons will certainly be used by our expanded ATRAP collaboration, and by the competing ATHENA Collaboration, both working at the nearly completed AD facility of CERN. We recently demonstrated a new techniques for accumulating cold positrons directly into a cryogenic vacuum system. The closest we have come to low energy antihydrogen so far is to confine cold positrons and cold antiprotons within the same trap structure and vacuum container. Finally, we mention that stored electrons have been cooled to 70 mK, the first time that elementary particles have been cooled below 4 K. In such an apparatus it should be possible to study highly magnetized plasmas of electrons or positrons at this new low temperature.
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.
<!--HTML-->In 2010 the ALPHA collaboration succeeded in trapping antihydrogen atoms for the first time.[i] Stored antihydrogen promises to be a unique tool for making high precision measurements of the structure of this first anti-atom. Achieving this milestone presented several substantial experimental challenges and this talk will describe how they were overcome. The unique design features of the ALPHA apparatus will be explained.[ii] These allow a high intensity positron source and an antiproton imaging detector similar to the one used in the ATHENA[iii] experiment to be combined with an innovative magnet design of the anti-atom trap. This seeks to minimise the perturbations to trapped charged particles which may cause particle loss and heating[iv]. The diagnostic techniques used to measure the diameter, number, density, and temperatures of both plasmas will be presented as will the methods developed to actively compress and cool of both plasma species to sizes and temperatures [v],[vi], [vii] where trapping attempts with a reasonable chance of success can be tried. The results of the successful trapping experiments will be outlined as well as some subsequent experiments to improve the trapping rate and storage time. [i] 'Trapped antihydrogen' G.B. Andresen et al., Nature 468, 673 (2010) [ii]'A Magnetic Trap for Antihydrogen Confinement' W. Bertsche et al., Nucl. Instr. Meth. Phys. Res. A566, 746 (2006) [iii] Production and detection of cold antihydrogen atoms M.Amoretti et al., Nature 419, 456 (2002). [iv]' Antihydrogen formation dynamics in a multipolar neutral anti-atom trap' G.B. Andresen et al., Phys. Lett. B 685, 141 (2010) [v]' Evaporative Cooling of Antiprotons to Cryogenic Temperatures', G.B. Andresen et al. Phys. Rev. Lett 105, 013003 (2010) [vi]'Compression of Antiproton Clouds for Antihydrogen Trapping' G. B. Andresen et al. Phys. Rev. Lett 100, 203401 (2008) [vii] 'Autoresonant Excitation of Antiproton Plasmas' G.B. Andresen et al., Phys. Rev. Lett. 106, 025002 (2011) Organizer: Ferdinand Hahn PH/DT Detector Seminar webpage
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.
The merging of antiprotons with a positron plasma is the predominant and highest efficient method for cold antihydrogen formation used to date. We present experimental evidence that this method has serious disadvantages for producing antihydrogen cold enough to be trapped. Antihydrogen is neutral but may be trapped in a magnetic field minimum. However, the depth of such traps are of order 1 K, shallow compared to the kinetic energies in current antihydrogen experiments. Studying the spatial distribution of the antihydrogen emerging from the ATHENA positron plasma we have, by comparison with a simple model, extracted information about the temperature of the antihydrogen formed. We find that antihydrogen is formed before thermal equilibrium is attained between the antiprotons and the positrons, and thus that further positron cooling may not be sufficient for producing antihydrogen cold enough to be trapped. We discuss the implications for trapping of antihydrogen in a magnetic trap, important for ongoing work by the ALPHA collaboration.
Over the last decades it has become routine to form beams of positrons and antiprotons and to use them to produce trapped samples of both species for a variety of purposes. Positrons can be captured efficiently, for instance using a buffer-gas system, and in such quantities to form dense, single component plasmas useful for antihydrogen formation. The latter is possible using developments of techniques for dynamically capturing and then cooling antiprotons ejected from the Antiproton Decelerator at CERN. The antiprotons can then be manipulated by cloud compression and evaporative cooling to form tailored plasmas. We will review recent advances that have allowed antihydrogen atoms to be confined for the first time in a shallow magnetic minimum neutral atom trap superimposed upon the region in which the antiparticles are held and mixed. A new mixing technique has been developed to help achieve this using autoresonant excitation of the centreofmass longitudinal motion of an antiproton cloud. This allows efficient antihydrogen formation without imparting excess energy to the antiprotons and helps enhance the probability of trapping the anti-atom. © 2012 American Institute of Physics.
Antihydrogen, the antimatter counterpart of the hydrogen atom, can be formed by mixing cold samples of antiprotons and positrons. In 2002 the ATHENA collaboration succeeded in the first production of cold antihydrogen. By observing and imaging the annihilation products of the neutral, non‐confined, antihydrogen atoms annihilating on the walls of the trap we can observe the production in quasi‐real‐time and study the dynamics of the formation mechanism. The formation mechanism strongly influences the final state of the formed antihydrogen atoms, important for future spectroscopic comparison with hydrogen. This paper briefly summarizes the current understanding of the antihydrogen formation in ATHENA.