Biomedical subjects

C A Ordonez

Publications and source records attributed to C A Ordonez.

4 recordsLinked to original sources

PubMed2005

Adiabatic formation of quasibound states of antihydrogen.

The classical trajectory of an initially unbound positron within the electric field of an antiproton and a uniform magnetic field is simulated in three dimensions. Several simulations are run incorporating experimental parameters used for antihydrogen production, which has been achieved by two different groups [M. Amoretti, Nature (London) 419, 456 (2002); G. Gabrielse, Phys. Rev. Lett. 89, 213401 (2002)]. The simulations indicate that temporary bound states of antihydrogen can form at positive energies, where the energy of the system is defined to be zero when the positron and antiproton are at rest with infinite separation. Such quasibound states, which form only when the magnetic field is present, are typically smaller than in a dimension perpendicular to the magnetic field. An analytical model is developed for a formation cross section, and it is found that quasibound states may form more frequently than stable Rydberg states.

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PubMed2004

Plasma two-temperature equilibration rate.

A theory is developed that is suitable for describing a two-species thermalization process in a plasma with parameters suitable for recombination to take place. Recombining plasmas have recently been produced using positrons and antiprotons [M. Amoretti et al., Nature (London) 419, 456 (2002); G. Gabrielse et al., Phys. Rev. Lett. 89, 213401 (2002)]. The theory is not restricted to large Coulomb logarithm values, and correspondence with prior theory is shown in the limit of large Coulomb logarithm values. The theory applies for two plasma species, each having a Maxwellian velocity distribution and being weakly correlated.

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PubMed2003

Fully and partially non-neutral plasma equilibria in a variable-electrode-radius Malmberg-Penning trap.

Two types of plasma equilibria are self-consistently computed for a three-electrode Malmberg-Penning trap that has an increase in the radius of a section of the center electrode. When a single species, fully non-neutral plasma is confined within the trap, equilibria are predicted in which the plasma produces a three-dimensional electric potential well. Partially non-neutral plasma equilibria are predicted to be possible by confining a second, oppositely signed plasma species within the three-dimensional well produced by the first plasma species. Conditions that are necessary for partially non-neutral plasma equilibria to be self-consistently possible are reported. A partially non-neutral plasma formed of electrons and singly charged xenon ions is then specifically considered, first with the ions confined within a three-dimensional well produced by the electrons and next with the electrons confined within a three-dimensional well produced by the ions.

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PubMed1999

Confinement physics for thermal, neutral, high-charge-state plasmas in nested-well solenoidal traps.

A theoretical study is presented which indicates that it is possible to confine a neutral plasma using static electric and solenoidal magnetic fields. The plasma consists of equal temperature electrons and highly stripped ions. The solenoidal magnetic field provides radial confinement, while the electric field, which produces an axial nested-well potential profile, provides axial confinement. A self-consistent, multidimensional numerical solution for the electric potential is obtained, and a fully kinetic theoretical treatment on axial transport is used to determine an axial confinement time scale. The effect on confinement of the presence of a radial electric field is explored with the use of ion trajectory calculations. A thermal, neutral, high-charge-state plasma confined in a nested-well trap opens new possibilities for fundamental studies on plasma recombination and cross-field transport processes under highly controlled conditions.

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