[en] We report an experimental confirmation of the power-law relationship between the critical anisotropy parameter and ion number for the linear-to-zigzag phase transition in an ionic crystal. Our experiment uses laser cooled calcium ions confined in a linear radio-frequency trap. Measurements for up to ten ions are in good agreement with theoretical and numeric predictions. Implications on an upper limit to the size of data registers in ion trap quantum computers are discussed. (c) 2000 The American Physical Society

[en] During the 2005 Los Alamos Neutron Science Center (LANSCE) beam runs, beam current and centroid-jitter data were observed, acquired, analyzed, and documented for both the LANSCE H+ and H- beams. These data were acquired using three beam position monitors (BPMs) from the 100-MeV Isotope Production Facility (IPF) beam line and three BPMs from the Switchyard transport line at the end of the LANSCE 800-MeV linac. The two types of data acquired, intermacropulse and intramacropulse, were analyzed for statistical and frequency characteristics as well as various other correlations including comparing their phase-space like characteristics in a coordinate system of transverse angle versus transverse position. This paper will briefly describe the measurements required to acquire these data, the initial analysis of these jitter data, and some interesting dilemmas these data presented

[en] Foil stripping of H^- directly to H⁺ is being considered for proton injection in the next generation of high-current proton storage rings. This technique can result in significant losses because excited states of HO, which are also produced in the foil, are field stripped in the downstream bending magnets. Without due care in the injection system design, many of the resulting protons will be outside the acceptance of the storage ring and will be quickly lost. We measured the production of such H⁰ excited states at the LAMPF High Resolution Atomic Beam Facility. An 800-MeV H^- beam was passed through carbon foils of thicknesses 70, 100, 200, and 300 μg/cm², and the excited states were analyzed by a special magnet downstream of the foil. The magnet had a linear field gradient so that the trajectories of the outgoing protons could be used to reconstruct the field values at which the various H⁰ stripped. We found that about 1% of the H⁰ emerge in excited states which can be stripped to protons by ring-bending magnets

[en] We report the first observation of nonresonant excess photon absorption (for ionization as well as detachment) in competition with the single photon process. A 35keV negative hydrogen ion beam is irradiated with focused Nd:YAG laser pulses; the 1.165eV photon energy exceeds the electron binding energy by 0.41eV. The time of flight spectrum of detached electrons exhibits the absorption of one and two photons. The detached electrons exit with a P wave angular distribution for the one-photon detachment and primarily a D wave for the two photon excess photon detachment. copyright 1997 The American Physical Society

[en] The realization of a paradigm chaotic system, namely, the harmonically driven oscillator, in the quantum domain using cold trapped ions driven by lasers is theoretically investigated. The simplest characteristics of regular and chaotic dynamics are calculated. The possibilities of experimental realization are discussed. (c) 2000 The American Physical Society

[en] One-photon detachment and two-photon nonresonant excess photon detachment of electrons from the H^- ion (outer-electron binding energy = 0.7542 eV) are observed with 1.165 eV laser pulses from a Nd:YAG laser (where YAG denotes yttrium aluminum garnet). A Penning ion source produces a pulsed 8 μA, 35 keV H^- beam that intersects a laser beam cylindrically focused down to a 17 μm full width at half maximum waist in the ion beam direction, creating a high-intensity interaction region with peak intensities of up to 10¹¹ W/cm². The interaction time is 7 ps. The detached electrons are detected by a time-of-flight apparatus enabling us to detect a very small two-photon signal in the presence of a very large signal from single photon detachments. By rotating the linear polarization angle, we study the angular distribution of the electrons for both one- and two-photon detachments. The spectra are modeled to determine the asymmetry parameters and one- and two-photon cross sections. We find β₂ to be 2.54+0.44/-0.60 and β₄ to be 2.29+0.07/-0.31, corresponding to a D state of 89+3/-12% of the S wave and D wave detachments for the two-photon results. The relative phase angle between the S and D amplitudes is measured to be less than 59 degree sign . The measured cross sections are found to be consistent with theoretical predictions. The one-photon photodetachment cross section is measured to be (3.6±1.7)x10^-17 cm². The two-photon photodetachment generalized cross section is (1.3±0.5)x10^-48 cm⁴ sec, consistent with theoretical calculations of the cross section. The three-photon generalized cross section is less than 4.4x10^-79 cm⁶ sec². (c) 1999 The American Physical Society

[en] We have measured the relative cross section for photodetachment from the K^- ion for the process K^- + hν→ K⁺ + 2e^- over the photon energy range 21- 24.5 eV. The structures in the measured cross section are associated with correlated processes involving the detachment or excitation of a 3p core electron, processes which are often accompanied by the excitation of one or more valence electrons. The most prominent feature in the cross section is a strong resonance arising from the excitation of a 3p electron from the core and a 4s valence electron. As in previous experiments on double excitation of valence electrons, electron correlation is seen to play an important role in the dynamics of negative ions

[en] The correlated process of photodetaching two electrons from the F^- ion following the absorption of a single photon has been investigated over an energy range 20-62 eV. In the experiment, a beam of photons from the Advanced Light Source was collinearly merged with a counter-propagating beam of F^- ions from a sputter ion source. The F⁺ ions produced in the interaction region were detected, and the normalized signal was used to monitor the relative cross section for the double-detachment reaction. An absolute scale for the cross section was established by measuring the spatial overlap of the two beams and by determining the efficiency for collection and detection of the F⁺ ions. The measured cross section is compared with R-matrix and random phase approximation calculations. These calculations show that the Auger decay of the 2s2p⁶ core-excited state of the F atom plays a minor role in the production of F⁺ ions and that double detachment is likely to be dominated by simultaneous correlated ejection of two valence electrons at energies well above threshold