J. Steiger

Confinement in a cryogenic penning trap of highest charge state ions from EBIT

The retrapping of highly charged Xe44+ and Th68+,72+ ions extracted from an ‘‘electron‐beam ion trap’’ (EBIT) is demonstrated after injection of the ions into RETRAP, a cryogenic Penning trap (up to 6 T magnetic field) currently with an open cylinder design. Ion extraction in a short pulse (5–20 μs) from EBIT, essential for efficient retrapping, is employed. The ions are slowed down upon entering a deceleration tube mounted above the trap within the magnetic field. The potential is then rapidly (100 ns) decreased, enabling low‐energy ions to enter the trap. Capture efficiencies up to 25% are observed via detection of the delayed ion release pulse with a detector below the trap. Signal voltages induced in a tuned circuit due to single and multiple ions have been observed by tuning the ion resonant axial oscillation frequencies for different ions. Results from transporting and retrapping of the ions, as well as their detection, are described and the trapping efficiency is discussed. The motivation for these...

Charge exchange between Xe44+ and H2 in an ion trap

Abstract Extracted Xe 44+ ions from an electron beam ion trap (EBIT) have been decelerated and captured in a cylindrical Penning trap. The voltage induced between the compensation electrodes by the axial ion oscillation is used to measure charge exchange rate coefficients from H 2 to Xe 44+ at low energies and the resistive cooling time constant as well. The experimentally determined reaction rates are found to be in reasonable agreement with the Langevin model for charge exchange.

In-situ hydrogen charging of thin Nb films and depth profiling with the 1H(15N, αγ)12C nuclear reaction

Abstract The hydrogen concentration in Nb films in equilibrium with an external H2-gas was measured by the 15N-NRA method using a differential pumping system. We find that the hydrogen solubility in films is reduced compared to that of bulk samples. This can be explained by the clamping of epitaxial films to the substrate. These first direct measurements of solubility curves for films are in disagreement with earlier investigations by other authors, who found — based on indirect concentration determinations — an increased solubility in films. We think that the discrepancy is due to incorrect concentration determinations in these earlier studies.

Collisions and spectroscopy of cold, highly charged high-Z ions in RETRAP

Abstract Recent experimental results from the RETRAP apparatus, including electron capture measurements on highly charged high-Z ions and laser cooling of a mixed cloud of Be+ and Be2+ ions, are briefly described. These results are used as a basis for discussion of planned spectroscopy measurements on hydrogen-like and beryllium-like high-Z highly charged ions. Experimental parameters for potential measurements of the ground state hyperfine structure of a hydrogen-like high-Z ion, and the g-factor of the electron bound in that ion, are emphasized.

Observation of sequential electron capture to individual highly-charged Th ions

Electron transfer from H2 to Th79+ was studied in a cryogenic Penning trap by non-destructively observing the sequential development with time of the charge state of one or a few stored particles. The ratio of the true double capture cross section to the total capture cross section was found to be 0.21 ± 0.11 at a mean center-of-mass energy near 6 eV.

Highly charged ion Coulomb crystallization in mixed strongly coupled plasmas

The investigation of highly charged ion Coulomb crystallization in mixed strongly coupled plasmas is of interest in many areas: white dwarf astrophysical plasmas are believed to have very similar thermodynamic properties, cold highly charged ions can be used as an object for high precision laser spectroscopy of fine and hyperfine transitions in the visible due to the absence of Doppler broadening and, an entirely new area of research is the potential application to highly charged ion based quantum computing schemes.We report the formation of such plasmas in a cryogenic Penning trap. These plasmas consisting of many species including Be+ and Xe44+ or Be+ and Xe15+ ions, are formed at a temperature of less than 4 K. The temperatures were obtained by applying a laser based sympathetic cooling scheme. The determination of the temperature and density from the laser resonance width and the fluorescence imaging of the Be+ clouds, respectively, yields a Coulomb coupling constant for the centrifugally separated Xe plasma high enough for crystallization.A molecular dynamics code, developed just for this purpose, was run to clarify the understanding of these plasmas and it was possible to show consistency between experiment and simulation.

Highly charged ion trapping and cooling

In the past few years a cryogenic Penning trap (RETRAP) has been operational at the Electron Beam Ion Trap (EBIT) facility at Lawrence Livermore National Laboratory. The combination of RETRAP and EBIT provides a unique possibility of producing and re-trapping highly charged ions and cooling them to very low temperatures. Due to the high Coulomb potentials in such an ensemble of cold highly charged ions the Coulomb coupling parameter (the ratio of Coulomb potential to the thermal energy) can easily reach values of 172 and more. To study such systems is not only of interest in astrophysics to simulate White Dwarf star interiors but opens up new possibilities in a variety of areas (e.g. laser spectroscopy, cold highly charged ion beams).

Collisions and spectroscopy of low-energy highly-charged ions using an ion trap

Electron transfer from H2 to highly-charged Xeq+ (q=35, 43–46) and Thq+ (q=73–80) ions at center-of-mass energies near 6 eV has been studied using the RETRAP system at Lawrence Livermore National Laboratory. The ions were produced in the Electron Beam Ion Trap and retrapped in the Penning ion trap. Initial cross section data are in reasonable accord with the predictions of the absorbing sphere model, and true double capture is found to be about 25% of the total. The development with time of the charge of a single ion undergoing collisions has been observed non-destructively. Certain spectroscopic measurements are planned, following cooling of the stored ions to cryogenic temperatures.