Storage of an electron plasma in a sextupole radial antihydrogen trap

This work reports for the first time experimental data obtained with electrons stored in a Penning–Malmberg trap surrounded by a sextupole radial magnetic field. This trap geometry is one of the candidates for trapping antihydrogen atoms in the place where they are produced starting from cold antiprotons and positrons or positronium. The measurements show that electron plasmas with parameters matching the range used for positrons and electrons in the antihydrogen experiments (number of particles ranging from few 10⁶ up to several 10⁷ and densities of the order of 10⁸–10⁹ cm⁻³, radius of the order of 1–2 mm) can be transported with 100% efficiency in a trap region that simultaneously confines completely the charged particles and the neutral antihydrogen in the radial plane. Inside this trap plasma storage times of the order of several tens of seconds up to some hundreds of seconds are measured. The plasma storage times are consistent with those needed for antihydrogen production; however the increase of the plasma temperature due to the expansion is not negligible; the consequences of this effect on the antihydrogen trapping are outlined.     

Quadrupole-induced resonant-particle transport in a pure electron plasma

Small transverse magnetic quadrupole fields sharply degrade the confinement of non-neutral plasmas held in Malmberg-Penning traps. For example, a quadrupole magnetic field of only 0.02 G/cm doubles the diffusion rate in a trap with a 100 G axial magnetic field. Larger quadrupole fields noticeably change the shape of the plasma. The transport is greatest at an orbital resonance. These results cast doubt on plans to use magnetic quadrupole neutral atom traps to confine antihydrogen atoms created in double-well positron/antiproton Malmberg-Penning traps.     

Development of a pure cryogenic positron plasma using a LINAC positron source

The development of a high density cryogenic pure positron plasma trap at the LLNL positron beam facility opens new possibilities for antihydrogen research. We discuss a planned measurement of the three-body collisional recombination rate in magnetized plasmas, a possible antihydrogen atomic beam experiment, and other applications of pure positron plasmas.     

Alternative method for reconstruction of antihydrogen annihilation vertices

The ALPHA experiment, located at CERN, aims to compare the properties of antihydrogen atoms with those of hydrogen atoms. The neutral antihydrogen atoms are trapped using an octupole magnetic trap. The trap region is surrounded by a three layered silicon detector used to reconstruct the antiproton annihilation vertices. This paper describes a method we have devised that can be used for reconstructing annihilation vertices with a good resolution and is more efficient than the standard method currently used for the same purpose.     

The ASACUSA CUSP: an antihydrogen experiment

In order to test CPT symmetry between antihydrogen and its counterpart hydrogen, the ASACUSA collaboration plans to perform high precision microwave spectroscopy of ground-state hyperfine splitting of antihydrogen atom in-flight. We have developed an apparatus (“cusp trap”) which consists of a superconducting anti-Helmholtz coil and multiple ring electrodes. For the preparation of slow antiprotons and positrons, Penning-Malmberg type traps were utilized. The spectrometer line was positioned downstream of the cusp trap. At the end of the beamline, an antihydrogen beam detector was located, which comprises an inorganic Bismuth Germanium Oxide (BGO) single-crystal scintillator housed in a vacuum duct and surrounding plastic scintillators. A significant fraction of antihydrogen atoms flowing out the cusp trap were detected.     

Inward transport and compression of a positron plasma by a rotating electric field

Inward transport of a magnetized pure positron plasma confined in a Penning-Malmberg trap is produced by applying a rotating electric field to the plasma. Compression is observed over a broad range of frequencies. Compression factors up to 20 in central density were obtained. Positron collisions with a neutral buffer gas are used to counteract the heating due to the rotating electric field. The results have implications for a variety of applications including the production of brightness enhanced positron beams, the study of electron-positron plasmas, and antihydrogen production.     

Magnetic trapping of long-lived cold Rydberg atoms

We report on the trapping of long-lived strongly magnetized Rydberg atoms. 85Rb atoms are laser cooled and collected in a superconducting magnetic trap with a strong bias field (2.9 T) and laser excited to Rydberg states. Collisions scatter a small fraction of the Rydberg atoms into long-lived high-angular momentum "guiding-center" Rydberg states, which are magnetically trapped. The Rydberg atomic cloud is examined using a time-delayed, position-sensitive probe. We observe magnetic trapping of these Rydberg atoms for times up to 200 ms. Oscillations of the Rydberg-atom cloud in the trap reveal an average magnetic moment of the trapped Rydberg atoms of approximately -8microB. These results provide guidance for other Rydberg-atom trapping schemes and illuminate a possible route for trapping antihydrogen.     

Synthesis of cold antihydrogen in a cusp trap

We report here the first successful synthesis of cold antihydrogen atoms employing a cusp trap, which consists of a superconducting anti-Helmholtz coil and a stack of multiple ring electrodes. This success opens a new path to make a stringent test of the CPT symmetry via high precision microwave spectroscopy of ground-state hyperfine transitions of antihydrogen atoms.     

Antihydrogen atom formation in a CUSP trap towards spin polarized beams

The ASACUSA collaboration has been making a path to realize high precision microwave spectroscopy of ground-state hyperfine transitions of antihydrogen atom in flight for stringent test of the CPT symmetry. For this purpose, an efficient extraction of a spin polarized antihydrogen beam is essential. In 2010, we have succeeded in synthesizing our first cold antihydrogen atoms employing a CUSP trap. The CUSP trap confines antiprotons and positrons simultaneously with its axially symmetric magnetic field to form antihydrogen atoms. It is expected that antihydrogen atoms in the low-field-seeking states are preferentially focused along the cusp magnetic field axis whereas those in the high-field-seeking states are defocused, resulting in the formation of a spin-polarized antihydrogen beam.     

Electronic and positronic guiding-center drift ions

A novel type of guiding-center drift ion is described. These ions occur only in strong magnetic fields. They consist of a neutral atom to which either an electron or positron is weakly bound, at a sufficiently large radius that it may be described by ExB drift dynamics. Such ions may occur naturally in astrophysical plasmas and may have been formed in recent antihydrogen experiments, where their presence would provide proof that deeply bound H atoms are being created.     

Antihydrogen synthesis by the reaction of antiprotons with excited state positronium atoms

Aspects of the possible reactions of trapped antiprotons with excited state positronium atoms to form antihydrogen are discussed. Conditions are identified whereby the antihydrogen produced may be suitable for capture in a neutral trap. A discussion is given of possible use of antihydrogen to test the quantization of electric charge involving precision comparisons of hydrogen and antihydrogen (Rydberg constants), and proton and antiproton cyclotron frequencies.     

ASACUSA MUSASHI: New progress with intense ultra slow antiproton beam

Our group “ASACUSA MUSASHI” has established an efficient way for accumulating antiprotons and extracting them as intense ultra-slow mono-energetic beams at the CERN-AD facility. This novel beam opens new frontiers for investigating a variety of physics. For realizing H? spectroscopy and the test for charge-parity-time symmetry, we have also developed the cusp trap, a combination of an anti-Helmholz superconducting coil and a multi-ring electrode trap, for trapping both antiprotons and positrons and then synthesizing antihydrogens. Recently, the cusp trap was practically used to accumulate antiprotons. The last piece for synthesizing antihydrogens in the cusp trap is the positron accumulator. We have developed a compact system to effectively accumulate positrons based on N₂ gas-buffer scheme with a specially designed high precision cylindrical multi-ring electrode trap. The recent progress of the developing work is an important milestone for upcoming antihydrogen science of ASACUSA MUSASHI.     

Magnetostatic traps for charged and neutral particles

We have constructed magnetostatic traps from permanent magnets for trapping charged and neutral atoms. Two storage experiments are presented: a compact Penning trap for light ions and magnetic trapping of single neutral atoms. The dynamics of cold neutral atoms and their loss mechanisms in a quadrupole magnetostatic trap are discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Possible antihydrogen production using trapped plasmas

Since antiprotons have been captured in an ion trap, we consider the possibility of producing antihydrogen by merging cold trapped plasmas of antiprotons and positrons. The calculated, instantaneous rate for antihydrogen production by the 3-body recombination is much higher than for other proposed techniques, opening up intriguing experimental possibilities.     

A versatile gas-flow proportional counter for Mössbauer spectroscopy

We discuss the need for neutral atom traps instead of atomic beams for the high-precision spectroscopic comparison of anithydrogen and hydrogen. We also describe recent proposals and advances towards a new trap for hydrogen and briefly discuss traps for antihydrogen.     

Extremely cold antiprotons for antihydrogen production

The possibility to produce, trap and study antihydrogen atoms rests upon the recent availability of extremely cold antiprotons in a Penning trap. Over the last five years, our TRAP Collaboration has slowed, cooled and stored antiprotons at energies 10¹⁰ lower than was previously possible. The storage time exceeds 3.4 months despite the extremely low energy, which corresponds to 4.2 K in temperature units. The first example of measurements which become possible with extremely cold antiprotons is a comparison of the antiproton inertial masses which shows they are the same to a fractional accuracy of 4×10⁻⁸. (This is 1000 times more accurate than previous comparisons and large additional increases in accuracy are anticipated.) To increase the number of trapped antiprotons available for antihydrogen production, we have demonstrated that we can accumulate or “stack” antiprotons cooled from successive pulsed injections into our trap.     

The method of invariants applied to the analysis of 57Fe Mössbauer spectra

The performance of proposed antihydrogen spectroscopy or gravity experiments will crucially depend on the temperature of the initial antihydrogen sample. Measurements by ATRAP and ATHENA have shown that antihydrogen produced with the nested-trap technique is much hotter than the temperature of the surrounding trap. Therefore, novel schemes for antihydrogen recombination as well as for the pre-cooling of antiprotons are being considered. We are investigating a possible antiproton cooling technique based on the laser cooling of negative osmium ions. If demonstrated to be successful, it will allow the sympathetic cooling of antiprotons—or any negatively charged particles—to microkelvin temperatures. As a first milestone toward the laser cooling of negative ions, we have performed collinear laser spectroscopy on negative osmium and determined the transition frequency and the cross-section of the relevant bound–bound electric-dipole transition.     

Combined Trap and Related Experiments

The regions of stability for simultaneous storage of positive and negative ions in the Combined trap are studied. It is shown that the regions of stability for the Combined trap are significantly larger than that for the Paul trap. The possibilities of making antihydrogen by simultaneous storage of antiprotons and positron clouds in this trap are also discussed.     

ALPHA: antihydrogen and fundamental physics

Detailed comparisons of antihydrogen with hydrogen promise to be a fruitful test bed of fundamental symmetries such as the CPT theorem for quantum field theory or studies of gravitational influence on antimatter. With a string of recent successes, starting with the first trapped antihydrogen and recently resulting in the first measurement of a quantum transition in anti-hydrogen, the ALPHA collaboration is well on its way to perform such precision comparisons. We will discuss the key innovative steps that have made these results possible and in particular focus on the detailed work on positron and antiproton preparation to achieve antihydrogen cold enough to trap as well as the unique features of the ALPHA apparatus that has allowed the first quantum transitions in anti-hydrogen to be measured with only a single trapped antihydrogen atom per experiment. We will also look at how ALPHA plans to step from here towards more precise comparisons of matter and antimatter.