D.A. Church

Confinement of injected beam ions in a Kingdon trap

Abstract Ions from a 2 keV hydrogen beam (a few nA current) were captured into an electrostatic ion trap (Kingdon trap) and stored for as long as 100 ms. The containment time was limited by the chamber pressure. The trap was made of an Al cylinder, 4 in. in diameter by 6 in. long, with a central tungsten wire of diameter 0.0025 in. Fast (100 ns fall time), high voltage pulses (1.9 kV → 0 V) with various durations of up to 100 ms were fed to the wire to turn the trap on and off. The cylinder was held at a constant potential ≈ 1.9 kV. The ions were dumped at the end of each storage interval and a fraction of them was measured by a microchannel plate. A signal to background ratio of 10 was achieved. The number of ions was found to decrease exponentially with a time constant of 60 ms due to collisions with the residual gas. The technique is being extended to slow, highly-charged ions and lower pressures.

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.

Considerations for retrapping, cooling, and crystallizing highly-charged high-Z ions

Abstract The recent extraction of ∽ 10 4 ions per pulse with both high charge and high atomic number Z from the electron beam ion trap (EBIT) encourages consideration of methods for retrapping and cooling these ions to approximately 4 K. Anticipated stored ion densities near this temperature should result in the formation of crystalline arrays of these ions in the trap. Standard techniques for pulsed injection of ions into the trap, followed by resistive damping of the translational motion and collisional cooling with cold charged particles, are expected to optimize the cooling process. Expected ion storage times based on extrapolated electron transfer collision rates are favorable. Interesting potential measurements suited to cold, highly-charged ions are also discussed.

Sequential photoionization of ions using synchrotron radiation and a Penning ion trap

Abstract Sequential photoionization has the potential of making available for study highly charged low energy ions. Synchrotron radiation was used to create a multicharged xenon ion target for further ionization by synchrotron radiation inside a Penning ion trap. Evidence of sequential photoionization was seen, though the yields were small. Improvements in the apparatus and radiation from third generation synchrotrons are expected to increase sequential photoionization yields significantly.

Lifetime of the 2 sup 3 S sub 1 state of heliumlike sup 79 Br sup 33

We report a measurement of the lifetime of the 2{sup 3}{ital S}{sub 1} level in heliumlike {sup 79}Br{sup 33+}. Our result is {tau}{sup exp}(2 {sup 3}{ital S}{sub 1})=224.1(7.1) ps. This agrees with the theoretical calculation of 230(2) ps and provides a test of {ital O}({ital Z}{sup 2}{alpha}{sup 2}) corrections to the lifetime. The experimental error is dominated by uncertainties in the correction required to account for long-lived cascades from highly excited states.

Production and storage of highly charged ions at room temperature

Selective production and storage at thermal energies of highly charged ions (e.g. hydrogen-like argon, Ar17+) are imminently feasible. Multi-step photoionisation by wiggler-enhanced synchrotron radiation of thermal ions stored in a Penning trap is discussed. Potential applications of these ions to electron transfer and photoionisation measurements are pointed out.

Collision spectroscopy of low-energy-beam U 5+ ions

The sixth spectrum of uranium (U vi) between 80 and 115 nm is studied by observation of transitions following low-energy electron capture by a U6+-ion beam in a H2 gas target. Emission cross sections of several identified transitions are obtained, the energy dependence investigated, and the spectra compared with the predictions of single-configuration Dirac–Fock (SCDF) calculations. Based on tentative identifications, a Rydberg–Ritz parameterization yields a predicted ionization potential only 0.3% above the SCDF result.

Atomic physics with the Texas A&M ECR ion source

Abstract An electron-cyclotron-resonance (ECR) ion source has been constructed to provide highly charged ions for injection into the K500 superconducting cyclotron. The source is also available approximately 30% of the time for use in experiments independent of the cyclotron. An atomic physics beamline has been constructed for this purpose and is now operational. A variety of experiments pertaining to neutralization processes, laser spectroscopy and charge exchange are currently in progress.

Traps and rings: Is small beautiful?

Abstract In recent years ion traps of various types have served in studies of collision interactions and spectroscopy of low energy multicharged ions. With large storage rings for multicharged heavy ions, dedicated to atomic physics research, now planned or coming into operation, it is useful to consider the role of ion traps in future experimental work. The capabilities and current limitations of multicharged ion research using traps are discussed, and a comparison with storage rings for the purposes of ion spectroscopy is made. Recent experimental investigations to develop techniques for the study of multicharged ions in traps using laser or synchrotron radiation are discussed, including a UHV pulsed gas source and an atom beam as ionization targets.

Charge state evolution in an ion trap irradiated by VUV synchrotron radiation

Abstract The energies of photons obtainable from the VUV ring at the National Synchrotron Light Source (NSLS) are ideally suited for high-efficiency ionization of atomic-shell electrons. Given the high fluxes of photons available on a wiggler beam line, multiple photoionization in an ion trap can be easily achieved within times short compared to typical ion storage times in the trap. Measurements of the time evolution of ion population in such a trap can yield ionic photoionization cross sections and charge-exchange interaction rates for ion-atom or ion-ion collisions. The various processes governing this time evolution are discussed and model calculations illustrating the relative importance of these processes under different conditions are presented.