Stored positrons for antihydrogen production

The production of antihydrogen is examined in the light of recent experimental results on a technique for the efficient accumulation, manipulation, and storage of positrons. From these data, we argue that this high-efficiency positron trapping technique could be adapted for the production of antihydrogen and would offer significant advantages over other positron trapping techniques currently being proposed for this purpose. This revised version was published online in August 2006 with corrections to the Cover Date.     

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.     

Extremely cold positrons for antihydrogen production

The storage of extremely cold (4 K) antiprotons in a Penning trap is an important step toward the creation and study of cold antihydrogen. The other required ingredient, the largest possible number of comparably cold positrons, is still lacking. These would be recombined in a high vacuum with the trapped antiprotons, already stored at a pressure below 5×10⁻¹⁷ Torr, thereby avoiding annihilation of the antihydrogen atoms before they can be used in high accuracy measurements or in controlled collision experiments. In an exploratory experiment, positrons from a 18 mCi²²Na source follow fringing field lines of a 6 T superconducting solenoid through tiny apertures in the electrodes of a Penning trap to strike a tungsten (reflection) moderator. The positron beam is chopped mechanically and a lock-in directly detects a positron current of 2.5×10⁶e⁺/s on the moderator. The use of a moderator, unlike an earlier experiment in which < 100 positrons were confined in vacuum, should greatly increase the number of positrons trapped in high vacuum.     

Relativistic theory of atom-laser interactions at very high laser intensities

The high-frequency approximation of Kristi? and Mittleman is considered in detail as a basis for the relativistic theory of atom-laser interactions. The properties of the 3D potentials are discussed. Within a one-dimensional model similar to that employed by Kylstra, Ermolaev, and Joachain in ab initio calculations on the time-dependent Dirac equation, the electron mass-shift due to dressing by a superstrong laser field is investigated. In the full domain of the laser parameters, the frequency ω and the peak field strength ?₀, the 1D bound states exhibit remarkable features. The numerical calculations show the existence of a very wide intermediate range of the field strengths where, in the zeroth order of the high-frequency approximation, the binding is stabilized by the field.     

Positron accumulation and storage for antihydrogen production

We propose a scheme to stack and accumulate positrons, emitted randomly from a radioactive source. The positrons are moderated and accumulated at low energy.     

High rate production of antihydrogen

We show that antihydrogen production is the dominant process when mixing antiprotons and positrons in the ATHENA apparatus, and that the initial production rate exceeds 300 Hz, decaying to 30 Hz within 10 s. A fraction of 65% of all observed annihilations is due to antihydrogen.     

Trapping positrons for low energy antihydrogen production

A method of trapping large numbers of positrons at liquid helium temperatures in a 6 Tesla magnetic field is described. Positrons from a sodium-22 source are moderated to low energies with a tungsten reflection moderator. A Penning trap with hyperbolic electrodes holds the positrons in a magnetron (EXB) orbit. The positrons are then cooled via coupling to a tuned circuit that is in resonance with the axial oscillation of the positrons. At this point, many slow positrons are permanently trapped in the Penning trap. The positrons are centered in the trap by applying a radio-frequency field at a frequency near the sum of the axial and magnetron frequencies. This method promises to produce 10⁶ trapped positrons at a density of 10⁷ to 10⁸ per cm³. Such densities of positrons would be useful in producing antihydrogen in combination with existing antiproton plasmas.     

Driven production of cold antihydrogen and the first measured distribution of antihydrogen states

Cold antihydrogen is produced when antiprotons are repeatedly driven into collisions with cold positrons within a nested Penning trap. Efficient antihydrogen production takes place during many cycles of positron cooling of antiprotons. A first measurement of a distribution of antihydrogen states is made using a preionizing electric field between separated production and detection regions. Surviving antihydrogen is stripped in an ionization well that captures and stores the freed antiproton for background-free detection.     

A single trapped antiproton and antiprotons for antihydrogen production

During the last several years, our TRAP collaboration has pioneered techniques for slowing, trapping, cooling and indefinitely storing antiprotons to energies more than 10¹⁰ times lower than previously possible. The radio signal from a single trapped antiproton is now being used for precision measurements. Many cold antiprotons are stacked as another important step toward the eventual production of antihydrogen, and positrons have been trapped in vacuum.     

Positron plasma diagnostics and temperature control for antihydrogen production

Production of antihydrogen atoms by mixing antiprotons with a cold, confined, positron plasma depends critically on parameters such as the plasma density and temperature. We discuss nondestructive measurements, based on a novel, real-time analysis of excited, low-order plasma modes, that provide comprehensive characterization of the positron plasma in the ATHENA antihydrogen apparatus. The plasma length, radius, density, and total particle number are obtained. Measurement and control of plasma temperature variations, and the application to antihydrogen production experiments are discussed.     

Off-axial plasma displacement suitable for antihydrogen production in AEgIS experiment

Antihydrogen experiments are currently based on non neutral electron, positron or antiproton plasma manipulation techniques in cylindrical Malmberg-Penning traps. An experimental study of a plasma manipulation technique based on off-axis diocotron displacement is presented. The use of the autoresonant excitation of (1, 0) diocotron mode of pure electron plasma allows a precise positioning of the plasma by moving it across the magnetic field and allows dumping such plasma in a desired angular position. The experimental procedure described here will pave the way to positron loading into an off-axial Penning trap terminated with a positronium converter target as it is proposed for the AEgIS experimental apparatus. The technique was studied over a range of confining magnetic field values and reproduces experimental conditions similar to most of the currently running antihydrogen experiments. The efficiency of the autoresonant excitation – in terms of plasma expansion rate and particle loss – is analyzed, studying the behaviour of electron plasma subjected to large off-axial displacements, showing that this method fulfills the requirements imposed by the AEgIS experiment.     

Self-focusing and its related interactions at very high laser intensities for fast ignition at Osaka University

At the Institute of Laser Engineering, various type of experiments related to fast ignition were performed with the 12-beam laser system GEKKO XII and the newly added 100 TW beams line. Using both X-ray and UV laser probes, drilling via ponderomotive laser light self-focusing was studied to show drilling well into the overdense plasma over a distance of 100 μ m at a self-focused laser intensity of 10¹⁸ W / cm ² . This type of self-focusing accelerated electrons up to 0.1 to 1 MeV and was also applied to an imploding shell.     

Observation of antihydrogen production in flight at CERN

The observation of the production of antihydrogen atoms \overlineH ⁰\equiv\barpe⁺, the simplest atomic bound state of antimatter, is presented. A method has been used by the PS210 collaboration at LEAR which assumes that the production of \overlineH⁰ is predominantly mediated by the e⁺e^--pair creation via the two-photon mechanism in the antiproton--nucleus interaction. Neutral \overlineH⁰ atoms are indentified by a unique sequence of characteristics. In principle \overlineH⁰ is well suited for investigations of fundamental CPT violation studies under different forces, however, in our investigations we concentrate on the production of this antimatter object, since so far it had not been observed. The production of eleven antihydrogen atoms is reported including possibly 2± 1 background signals, the observed yield agrees with theoretical predictions. This revised version was published online in August 2006 with corrections to the Cover Date.     

Temperature measurements in plasmas generated by using lasers at different intensities

The temperature of laser-generated pulsed plasmas is an important property that depends on many parameters, such as the particle species and the time elapsed from the laser interaction with the matter and the surface characteristics.

Laser-generated plasmas with low intensity (<10¹⁰ W/cm²) at INFN-LNS of Catania and with high intensity (>10¹⁴ W/cm²) in PALS laboratory in Prague have been investigated in terms of temperatures relative to ions, electrons, and neutral species. Time-of-flight (ToF) measurements have been performed with an electrostatic ion energy analyzer (IEA) and with different Faraday cups, in order to measure the ion and electron average velocities. The IEA was also used to measure the ion energy, the ion charge state, and the ion energy distribution.

The Maxwell–Boltzmann function permitted to fit the experimental data and to extrapolate the ion temperature of the plasma core.

The velocity of the neutrals was measured with a special mass quadrupole spectrometer. The Nd:Yag laser operating at low intensity produced an ion temperature core of the order of 400 eV and a neutral temperature of the order of 100 eV for many ablated materials. The ToF of electrons indicates the presence of hot electron emission with an energy of ～1 keV.     

Efficient Rydberg positronium laser excitation for antihydrogen production in a magnetic field

Antihydrogen production by charge exchange reaction between positronium (Ps) and antiprotons requires an efficient excitation of Ps atoms up to high-n levels (Rydberg levels). We propose a two-step laser light excitation, the first from ground to n?=?3 and the second from this level to a Rydberg level n?>?15. In this study it is assumed that a Ps cloud is produced by positrons hitting a target converter located in a Penning-Malmberg trap within a uniform ~ 1 T magnetic field. We model the optical transition structure by taking into account Doppler and motional Stark effects. The predicted efficiency for population deposition in high n states is of ~30%.     

Muon pair production in very high energy nucleus-nucleus collisions

Characteristics of muon pair production in very high energy nucleus-nucleus collisions are discussed. Particular attention is given to comparing the rate of muon pairs produced from thermalized quark-gluon matter to that of pairs produced via the usual Drell-Yan mechanism. The thermal rate is at least of the same order of magnitude as the direct Drell-Yan rate and will certainly dominate whenx _F for the pair approaches 1. Beyondx _F =1 the thermal rate is also substantial. This region is particularly easily accessible in fixed target experiments.     

Confinement of electrons and ions in a combined trap with the potential for antihydrogen production

Experiments with electrons and ions in a combined trap are reported. The unique capability to confine particles with opposite charge and very different mass simultaneously in the same spatial region makes the combined trap a promising device for future synthesis of antihydrogen.