Search

Physically realized electron gas systems usually reside in either the quantum non-degenerate or fully degenerate limit, where the average de Broglie wavelength of the thermal electrons becomes comparable with the interparticle distance between electrons. A few systems, such as young brown dwarfs and the cold dense fuels created in imploded cryogenic capsules at the National Ignition Facility, lie between these two limits and are partially degenerate. The National Ignition Facility has the unique capability of varying the electron quantum degeneracy by adjusting the laser drive used to implode the capsules. This allows experimental studies of the effects of the degeneracy level on plasma transport properties. By measuring rare nuclear reactions in these cold dense fuels, we show that the electron stopping power, which is the rate of energy loss per unit distance travelled by a charged particle, changes with increasing electron density. We observe a quantum-induced shift in the peak of the stopping power using diagnostics that measure above and below this peak. The observed changes in the stopping power are shown to be unique to the transition region between non-degenerate and degenerate plasmas. Our results support the screening models applied to partially degenerate astrophysical systems such as young brown dwarfs. Transitions between non-degenerate and degenerate plasma are observed in laser-driven implosions of cryogenic capsules at the National Ignition Facility. The observed partially degenerate regime is relevant to the physics of young brown dwarfs.

Neutron spectra from secondary ^{3}H(d,n)α reactions produced by an implosion of a deuterium-gas capsule at the National Ignition Facility have been measured with order-of-magnitude improvements in statistics and resolution over past experiments. These new data and their sensitivity to the energy loss of fast tritons emitted from thermal ^{2}H(d,p)^{3}H reactions enable the first statistically significant investigation of charged-particle stopping via the emitted neutron spectrum. Radiation-hydrodynamic simulations, constrained to match a number of observables from the implosion, were used to predict the neutron spectra while employing two different energy loss models. This analysis represents the first test of stopping models under inertial confinement fusion conditions, covering plasma temperatures of k_{B}T≈1-4 keV and particle densities of n≈(12-2)×10^{24} cm^{-3}. Under these conditions, we find significant deviations of our data from a theory employing classical collisions whereas the theory including quantum diffraction agrees with our data.

The National Ignition Facility (NIF) provides the opportunity to study nuclear reactions under controlled conditions at high temperatures and pressures at a level never before achieved. However, the timescale of the deuterium-tritium (DT) implosion is only a few nanoseconds, making data collection and diagnostics very challenging. One method that has been proposed for obtaining additional information about the conditions of the implosion is to activate a dopant material using the $\ensuremath{\alpha}$ particles produced from the DT fuel as a diagnostic. The yield of the activated material can give a measure of the mixing that occurs in the capsule. One of the reactions that has been proposed is $^{10}\mathrm{B}(\ensuremath{\alpha},n)\phantom{\rule{0.16em}{0ex}}^{13}\mathrm{N}$ as it produces a radioactive reactant product with a convenient half-life of $\ensuremath{\approx}10\phantom{\rule{0.16em}{0ex}}\mathrm{min}$. Although this reaction has several advantages for the application at hand, it has not seen much study in the present literature, resulting in large uncertainties in the cross section. Furthermore, for the current application, the cross section must be well characterized. With this motivation, the $^{10}\mathrm{B}(\ensuremath{\alpha},n)\phantom{\rule{0.16em}{0ex}}^{13}\mathrm{N}$ cross section has been remeasured for $2.2l{E}_{\ensuremath{\alpha}}l4.9\phantom{\rule{0.28em}{0ex}}\mathrm{MeV}$ with the angle-integrated ground-state cross section reported for the first time. The present results, combined with previous measurements, allow for a determination of the cross section to a significantly higher degree of accuracy and precision than obtained previously and are shown to be consistent with thick-target measurements. Preliminary calculations are performed to test the feasibility of this reaction as a diagnostic for a NIF implosion.

At the completion of the National Ignition Campaign (NIC), the National Ignition Facility (NIF) had about 36 different types of diagnostics. These were based on several decades of development on No...

We determined fission yields of xenon (133mXe, 135Xe, 135mXe, 137Xe, 138Xe, and 139Xe) resulting from 14 MeV neutron induced fission of depleted uranium at the National Ignition Facility. Measurements begin approximately 20 s after shot time, and yields have been determined for nuclides with half-lives as short as tens of seconds. We determined the relative independent yields of 133mXe, 135Xe, and 135mXe to significantly higher precision than previously reported. The relative fission yields of all nuclides are statistically indistinguishable from values reported by England and Rider (ENDF-349. LA-UR-94-3106, 1994), with exception of the cumulative yield of 139Xe. Considerable differences exist between our measured yields and the JEFF-3.1 database values.

Journal of physics / Conference Series 875, 012008 (2017). doi:10.1088/1742-6596/875/2/012008, Published by IOP Publ., Bristol

The exploration of the unique properties of stored and cooled beams of highly-charged ions as provided by heavy-ion storage rings has opened novel and fascinating research opportunities in the realm of atomic and nuclear physics research. Since the late 1980s, pioneering work has been performed at the CRYRING at Stockholm (Abrahamsson et al. 1993) and at the Test Storage Ring (TSR) at Heidelberg (Baumann et al. 1988). For the heaviest ions in the highest charge-states, a real quantum jump was achieved in the early 1990s by the commissioning of the Experimental Storage Ring (ESR) at GSI Helmholtzzentrum fur Schwerionenforschung (GSI) in Darmstadt (Franzke 1987) where challenging experiments on the electron dynamics in the strong field regime as well as nuclear physics studies on exotic nuclei and at the borderline to atomic physics were performed. Meanwhile also at Lanzhou a heavy-ion storage ring has been taken in operation, exploiting the unique research opportunities in particular for medium-heavy ions and exotic nuclei (Xia et al. 2002).

Radiochemical diagnostic techniques such as solid- and gas-phase capsule debris analysis may prove to be successful methods for establishing the success or failure of ignition experiments at the National Ignition Facility (NIF). Samples in the gas phase offer the most direct method of collection by simply pumping out the large target chamber following a NIF shot. The target capsules will be prepared with dopants, which will produce radioactive noble-gas isotopes upon activation with neutrons or charged particles. We have designed and constructed the Radchem Apparatus for Gas Sampling (RAGS) in order to collect postshot gaseous samples for NIF capsule diagnostics. The design of RAGS incorporates multiple stages intended to cryogenically purify, transfer, and count the radioactive decays from gaseous products synthesized in NIF experiments. An implementation timeline at NIF is discussed.

The generation of dynamic high energy density plasmas (HEDP) in the pico- to nano-second time domain at high-energy laser facilities affords unprecedented nuclear science research possibilities. At the National Ignition Facility (NIF), the primary goal of Inertial Confinement Fusion research has led to the synergistic development of a unique high brightness neutron source, sophisticated nuclear diagnostic instrumentation, and versatile experimental platforms. These novel experimental capabilities provide a new path to investigate nuclear processes and structural effects in the time, mass and energy density domains relevant to astrophysical phenomena in a unique terrestrial environment. Some immediate applications include neutron capture cross-section evaluation, fission fragment production, and ion energy loss measurement in electron-degenerate plasmas. More generally, the NIF conditions provide a singular environment to investigate the interplay of atomic and nuclear processes such as plasma screening effects upon thermonuclear reactivity. Achieving enhanced understanding of many of these effects will also significantly advance fusion energy research and challenge existing theoretical models.

The paper describes a novel application of an electron beam ion trap as a plasma target facility for intense laser-plasma interaction studies. The low density plasma target (~;1013/cm3) is confined in a mobile cryogenic electromagnetic charged particle trap, with the magnetic confinement field of 1-3 T maintained by a superconducting magnet. Ion plasmas for a large variety of ion species and charge states are produced and maintained within the magnetic field and the space-charge of an energetic electron beam in the "electron beam ion trap" (EBIT) geometry. Intense laser beams (optical lasers, X-ray lasers and upcoming "X-ray free electron lasers" (XFEL)) provide strong time varying electromagnetic fields (>1012 V/cm in femto- to nano-second pulses) for interactions with electromagnetically confined neutral/non-neutral plasmas. Experimental scenarios with intense photon fields on ionization/excitation processes, the ionization balance, as well as photon polarization effects and tests with intense lasers that utilize the ion plasma target are outlined. A first test of the plasma target with the PHELIX high intensity laser at GSI is described.

We report on electron emission and defect formation in the interaction between slow ( ν ≈ 0.3 ν Bohr ) highly charged ions (SHCI) with insulating (type IIa) and semiconducting (type IIb) diamonds. Electron emission induced by 31 P q + ( q = 5–13) and 136 Xe q + ( q = 34–44) with kinetic energies of 9 kV × q increase linearly with the ion charge states, reaching over 100 electrons per ion for high xenon charge states without surface passivation of the diamond with hydrogen. Yields from both diamond types are up to a factor of two higher than from reference metal surfaces. Crater like defects with diameters of 25–40 nm are formed by the impact of single Xe 44+ ions. High secondary electron yields and single ion induced defects enable the formation of single dopant arrays on diamond surfaces.

Highly charged radioactive ions can be stored for extended periods of time in storage rings which allows for precision measurements of their decay modes. The straightforward motivation for performing such studies is that fully ionised nuclei or few-electron ions can be viewed as clean quantum-mechanical systems, in which the interactions of the many electrons can be either excluded or treated precisely. Thus, the influence of the electron shell on the decay probability can be investigated. Another important motivation is stellar nucleosynthesis, which proceeds at high temperatures and the involved atoms are therefore highly ionised. Presented here is a compact review of the relevant experiments conducted at heavy-ion storage rings. Furthermore, we outline the perspectives for future experiments at new-generation storage-ring facilities.

Deterministic doping by single ion implantation, the precise placement of individual dopant atoms into devices, is a path for the realization of quantum computer test structures where quantum bits (qubits) are based on electron and nuclear spins of donors or color centers. We present a donor - quantum dot type qubit architecture and discuss the use of medium and highly charged ions extracted from an Electron Beam Ion Trap/Source (EBIT/S) for deterministic doping. EBIT/S are attractive for the formation of qubit test structures due to the relatively low emittance of ion beams from an EBIT/S and due to the potential energy associated with the ions' charge state, which can aid single ion impact detection. Following ion implantation, dopant specific diffusion mechanisms during device processing affect the placement accuracy and coherence properties of donor spin qubits. For bismuth, range straggling is minimal but its relatively low solubility in silicon limits thermal budgets for the formation of qubit test structures.

Spins of electrons bound to donor electrons are attractive candidates for exploration of quantum information processing in silicon. We present results from our development of donor electron spin qubit structures. Donors are placed into isotopically enriched ^2^8Si by ion implantation. The coherence properties of donor implants in pre-device structures are probed by pulsed electron spin resonance (ESR). The spin de-coherence time, T"2, for ^1^2^1Sb donors implanted into a peak depth of 50nm from a thermal oxide interface is 0.3ms at 5K, increasing to 0.75ms when the silicon surface is passivated with hydrogen. A technique for formation of donor arrays by ion implantation with scanning force microscope alignment is presented, and we discuss coherence limiting factors with respect to the implementation of a single spin readout scheme.

The total electron emission yields following the interaction of “Slow (⩽2 keV/a.u.) Highly Charged Ions” (SHCI) (O 3+⋯7+ , Xe 12+⋯52+ , Au 54+⋯69+ ) with different target surfaces (highly-oriented pyrolytic graphite (HOPG), Au and SiO2) have been measured. The emission yields increase with charge state, and is found to be highest for carbon, the HOPG target, and lowest for the SiO 2 target. An empirical formula for the electron emission is including recent results from investigations of plasmon excitation following SHCI impact are used to interpret the results.

Extensive research with low emittance, low energy (2 keV/u) highly charged ion beams up to U 90+ and their interaction with solid surfaces has been conducted over the past decade. The studies have revealed a variety of unique physical processes, which are characteristic for the interaction. These are based on the highly localized (nm) and fast (femo-seconds) high potential energy ( E pot ) release from individual highly charged ions (e.g. Au 69+ has E pot = 160 keV (equivalent to a power density of 10 14 W/cm 2 )). Subsequent material dependent high yields of (∼100) secondary electrons emitted per ion and increased secondary ion yields are observed. Until now sources of such low emittance, low energy, highly charged ions have required liquid He to cool the superconducting magnets necessary to compress an electron beam to current densities greater than 2000 A/cm 2 . With the advent of the physics and technology refrigerated (cryogenic) electron beam ion trap (REBIT-S) a system now exists that requires no liquid cooling gasses and provides such low emittance, low energy, highly charged ions in nearly any species at rates of many 10 6 ions/s. The operation, capabilities and specifications of this REBIT-S are discussed.

This report reviews the production of strongly-coupled, multi-component, non-neutral, highly-charged ion plasmas in a cryogenic Penning trap. A unique ion source–Penning trap system has been developed and used an Electron Beam Ion Trap-Source (EBIT-S), able to produce ions up to U92+, has been combined with a cold-bore Penning ion trap. The developed experimental techniques such as the ion production, extraction, bunching, multi-ion species trapping and storage (ions up to Th80+), detection, cooling, and imaging are presented. The produced mixed plasmas, consisting of several ion species [e.g. Be+, Xeq+ (charge q = 34 ... 44)], are cooled to a temperature of about 1 degree Kelvin and below. These low temperatures were obtained by applying a sypathetic cooling scheme, using laser cooled Be+ ions. The determination of the temperature and the density from the laser resonance width and the fluorescence imaging of the Be+ clouds respectively, yield a Coulomb coupling parameter for the xenon ion plasma of over 1000, large enough for crystallization. Crystallization can be achieved at these relatively high temperatures since the Coulomb coupling parameter scales with q2. Ion species with different mass to charge ratios centrifugally separate at low temperatures in the trap, and the plasma consists of concentric spheroidal shells of single component plasmas. But even in this case excellent thermal coupling between ion species takes place due to the long range Coulomb interactions. This is demonstrated by molecular dynamics simulations of the ion mixtures, which show ordered structures, indicating evidence for crystallization of the highly charged xenon ions. During the investigation of highly charged ion Coulomb crystallization in mixed strongly coupled plasmas, several enabling techniques were developed that are applicable to various areas of physics research Analogous thermodynamics (Coulomb matter) of white dwarf astrophysical plasmas can experimentally be investigated, high precision laser spectroscopy is made possible due to reduced Doppler broadening effects, cold ion sources can be developed and coherent quantum control experiments can be further explored.

Spins of single donor atoms are attractive candidates for large scale quantum information processing in silicon. Formation of devices with a few qubits is crucial for validation of basic ideas and development of a scalable architecture. We describe our development of a single ion implantation technique for placement of single atoms into device structures. Collimated highly charged ion beams are aligned with a scanning probe microscope. Enhanced secondary electron emission due tohigh ion charge states (e.g., 31P13+, or 126Te33+)allows efficient detection of single ion impacts. Studies of electrical activation of low dose, low energy implants of 31P in silicon show a drastic effect of dopant segregation to the SiO2/Si interface,while Si3N4/Si retards 31P segregation. We discuss resolution limiting factors in ion placement, and process challenges forintegration of single atom arrays with control gates and single electron transistors.

Spawned by the finding of efficient quantum algorithms, the development of a scalable quantum computer has emerged as a premiere challenge for nanoscience and nanotechnology in the last years. Spins of electrons and nuclei in 31P atoms embedded in silicon are promising quantum bit (qubit) candidates. In this article we describe single atom doping strategies and the status of our development of single atom qubit arrays integrated with control gates and readout structures in a “top down” approach. We discuss requirements for 31P qubit array formation by single ion implantation, and integration with semiconductor processing.

The intense, ultra-fast electronic excitation of clean silicon (100)–(2×1) surfaces leads to the formation of silicon nanostructures embedded in silicon, which photoluminesce in the yellow-green (∼2-eV band gap). The silicon surfaces were irradiated with slow, highly charged ions (e.g. Xe44+ and Au53+) to produce the ultra-fast electronic excitation. The observation of excitonic features in the luminescence from these nanostructures has recently been reported. In this paper we report the dispersion of the excitonic features with laser excitation energy. A phonon-scattering process is proposed to explain the observed dispersion.

We describe results from highly charged ion extraction experiments at the Electron Beam Ion Trap (EBIT) facility which is now operated at Lawrence Berkeley National Laboratory after transfer from Lawrence Livermore National Laboratory. Requirements on ion source performance for the application of highly charged ions (e.g., Xe44+) in surface analysis and materials science are discussed.

The extraction of high-Z high-charge-state ions up to U90+ from a high-energy electron-beam ion trap, the SuperEBIT at Lawrence Livermore National Laboratory, is reported. The SuperEBIT provides a 240 mA electron beam with up to 200 keV of energy. Depending on the operating conditions (pulsed, continuous) and charge state, the number of ions extracted from the SuperEBIT varies between 102 and 105 ions per second under the tested conditions. The ions produced in SuperEBIT are extracted at potentials ranging from 0.5 to 20 keV (continuously variable) to provide highly charged low-emittance ion beams with energies between a few keV and several MeV. The performance of the SuperEBIT as an ion source is described and aspects for future developments and potential applications are discussed.

We present the first measurements of reaction-in-flight (RIF) neutrons in an inertial confinement fusion system. The experiments were carried out at the National Ignition Facility, using both Low Foot and High Foot drives and cryogenic plastic capsules. In both cases, the high-energy RIF ($E_n>$ 15 MeV) component of the neutron spectrum was found to be about $10^{-4}$ of the total. The majority of the RIF neutrons were produced in the dense cold fuel surrounding the burning hotspot of the capsule and the data are consistent with a compressed cold fuel that is moderately to strongly coupled $(\Gamma\sim$0.6) and electron degenerate $(\theta_\mathrm{Fermi}/\theta_e\sim$4). The production of RIF neutrons is controlled by the stopping power in the plasma. Thus, the current RIF measurements provide a unique test of stopping power models in an experimentally unexplored plasma regime. We find that the measured RIF data strongly constrain stopping models in warm dense plasma conditions and some models are ruled out by our analysis of these experiments.

We describe a radiochemical measurement of the ratio of isotope concentrations produced in a gold hohlraum surrounding an Inertial Confinement Fusion capsule at the National Ignition Facility (NIF). We relate the ratio of the concentrations of (n,γ) and (n,2n) products in the gold hohlraum matrix to the down-scatter of neutrons in the compressed fuel and, consequently, to the fuel's areal density. The observed ratio of the concentrations of (198m+g)Au and (196g)Au is a performance signature of ablator areal density and the fuel assembly confinement time. We identify the measurement of nuclear cross sections of astrophysical importance as a potential application of the neutrons generated at the NIF.

Molecular dynamics simulations of the cooling of highly-charged ions captured into a Penning ion trap (RETRAP) along with Be+ ions are described. Experimentally, the Be+ ions were directly cooled continuously using a laser, and collisional coupling to these laser-cooled ions cooled the highly-charged ions. The simulation is described as a tool for experimental interpretation and refinement. Under conditions closely related to the experimental parameters, the highly charged ions were found to form ordered structures, and to exhibit characteristics of a magnetized non-neutral plasma.

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 have measured the deposition of potential energy of slow $(\ensuremath{\sim}6\ifmmode\times\else\texttimes\fi{}{10}^{5}\mathrm{m}/\mathrm{s})$, highly charged ions in solids with an ion implanted silicon detector. A large fraction (about $35%$ or 60 keV) of the potential energy dissipated by ${\mathrm{Au}}^{69+}$ ions can be traced in electronic excitations deep $(g50\mathrm{nm})$ inside the solid. In contrast, only about $10%$ of the potential energy has been accounted for in measurements of emitted secondary particles.

Single- and double-electron transfer from He to the Ne8+(ls(2))S-0(1) ion has been studied at 80 keV by extreme ultraviolet (EUV) spectroscopy and zero-degree electron spectroscopy. Signals originating from the stabilization after two-electron capture are

We report observations of nonequilibrium charge state distributions of slow, highly charged (33+{le} q{le}75+) ions after transmission of thin carbon foils. Charge equilibration times are determined directly from the dependencies of exit charge states on projectile velocity (0.5{times}10{sup 6}{lt}v{lt}10{sup 6} m/s) and foil thickness (5{endash}10thinspthinspnm). Ions like Xe{sup 44+} and Au{sup 68+} are found to equilibrate inside of solid matter in a time of only 7thinspthinspfs. {copyright} {ital 1999} {ital The American Physical Society}

The present article reviews recent advances in the studies of the interaction of slow (v < vBohr), very highly charged ions (such as Xe 52+ and Au 69+ ) with surfaces of metals, semiconductors, and insulators (including biological materials). After a brief summary of past developments, we describe key experimental techniques for studies of secondary particle emission and the de-excitation dynamics of the highly charged ions. Recent progress in measurement and determination of the mechanisms leading to secondary electron yields, secondary ion yields and total sputtering yields will be discussed. The deexcitation dynamics are addressed in experiments on projectile neutralization and energy loss in thin films of material. We review the theoretical concepts briefly and introduce theoretical models in the discussion of experimental results. Following the presentation of fundamental studies we will address emerging applications of slow, very highly charged ions in surface analysis and surface modification. # 1999 Published by Elsevier Science Ltd. All rights reserved.

In light of recent progress in the fabrication and diagnostics of nanostructures and surfaces, more advanced spectroscopic and imaging methods are necessary in order to elucidate the detailed structure, nature and creation of such microsystems. We present here one especially promising method, namely highly charged ion surface interaction using an electron beam ion trap (EBIT) facility. Specifically we focus on the microspectroscopy, nano- and subnanostructure modification of surfaces and generation of x-rays involving heavy highly charged ion-structure interaction. In this process a large amount of potential energy is deposited by single ions at the surface leading to localized surface defects of subnanosize. In particular, we present new results on highly charged (q = 50-71) ions interacting with gold surfaces. A detailed experimental and theoretical analysis is provided for the x-ray spectra from the gold surface. These data have been measured at the Lawrence Livermore National Laboratory EBIT highly charged ion facility. The comparison of our computer simulation with experimental x-ray spectra provides evidence for the formation of subsurface hollow atoms. A striking orbital (n) and angular momentum (l) dependence for hollow atoms formation has been found shedding more light on the dynamics of complex ion-surface and ion-solid interaction processes. Finally, new developments in imaging on nano- and angstrom-scale using heavy highly charged ions are discussed.

Energy levels, radiative transition probabilities and autoionization rates for Fe XVI including the 1s 2 2s 2 2p 5 3 l n l ′ (n=3–8, l ′≤(n−1) ) and 1s 2 2s2p 6 3 l n l ′ (n=3–4, l ′≤(n−1)) doubly excited states were calculated by using the multi-configurational Hartree–Fock (Cowan code) method. The contribution of relativistic effects is studied in comparison with the data obtained using the multi-configurational Dirac–Fock (YODA code) method. The comparison of the theoretical data with experimental spectra obtained by double-electron capture in slow ion-atom collisions is discussed.

We have measured total ablation rates and secondary ion yields from undoped GaAs(100) interacting with slow $(v\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}6.6\ifmmode\times\else\texttimes\fi{}{10}^{5}\mathrm{m}/\mathrm{s})$, very highly charged ions. Ablation rates increase strongly as a function of projectile charge. Some 1400 target atoms are removed when a single ${\mathrm{Th}}^{70+}$ ion deposits a potential energy of 152.6 keV within a few femtoseconds into a nanometer-sized target volume. We discuss models for ablation of semiconductors by intense, ultrafast electronic excitation.

We present first results of experiments on the fragmentation of biomolecules using highly charged heavy ions. Fragmentation and modification of oligopeptides, such as dimerization and attachment of ionic salt components, have been observed by means of mass spectrometry. Plasmid DNA molecules were imaged with an atomic force microscope after ion irradiation and profound molecular damage was found.

Ions with charge states as high as 80+, produced in the Lawrence Livermore National Laboratory electron beam ion trap were extracted and transferred to a Penning ion trap (RETRAP). RETRAP was operated at cryogenic temperature in the field of a superconducting magnet. The stored low-energy ions collided occasionally with H{sub 2} molecules in the ultrahigh-vacuum environment of the trap, capturing one or two electrons and reducing the charge state of the ions. The number of ions was monitored nondestructively by ramping the axial oscillation frequencies of the ions through resonance with a tuned circuit composed in part of trap capacitance and an external inductor. This produced resonance signals whose square is proportional to the number of ions in each charge state. These signals were recorded vs storage time to determine the electron-capture rates. From these rates the relative electron-capture cross sections were obtained using estimates of the mean ion energies based on modeling the ion storage, and with the aid of a density calibration measurement using Ar{sup 11+}. The measured total electron-capture cross sections are consistent with a linear increase with charge state q. The cross-section data for the highest charge states lie above the predictions of the absorbing spheremore » model, but agree within uncertainties in both experiment and theory. The true double-capture cross-section fraction for q{gt}35 is near 25{percent}. The results are discussed with relation to measurements on lower charge states, and with theory. {copyright} {ital 1998} {ital The American Physical Society}« less

The emission of secondary ions and neutrals from uranium oxide has been measured for impact of highly charged, heavy ions. Total ablation rates and secondary ion yields increase strongly with projectile charge. The dependencies on projectile charge $(16lql70)$, impact energy $(10\mathrm{keV}l{E}_{\mathrm{kin}}l1\mathrm{MeV})$, and projectile mass of secondary ion yields demonstrate the presence of an interaction regime where electronic excitation by charge neutralization and elastic collision spikes combine synergistically.

B–SiO2 films formed by chemical vapor deposition on silicon substrates were analyzed by time-of-flight secondary ion mass spectrometry using slow Xe44+ and Th70+ as primary ions. Boron concentrations of 2×1021 cm−3 determined directly from positive secondary ion spectra agree with results from elastic recoil detection measurements, indicating strong decoupling of positive secondary ion production probabilities from elemental ionization potentials in the intense electronic sputtering induced by highly charged ions. Results demonstrate advantages of highly charged ions for quantitative analysis of surface near layers of materials.

Cluster ion emission from a variety of surfaces upon impact of highly charged ions is investigated by time-of-flight secondary ion mass spectrometry. The yield of cluster ions as a function of cluster size for and surface follow a power law decline with exponent approaching the -2 limit of the ”equilibrium” and ”shock wave” cluster emission models. While the decline of the cluster ion emission with cluster size is an exponential decay for highly oriented pyrolytic graphite upon impact, the decline is more gradual than for impact, such that at the relative cluster yield is 1000 times higher.

Energy levels, radiative transition probabilities and autoionization rates for CuXIX including the 1s22s22p53lnl' (n = 3 ÷ 8, l' ≤ n – 1) and 1s22s2p63lnl' (n = 3 ÷ 4, l' ≤ n – 1) doubly excited states were calculated using the multi-configurational Hartree–Fock method (Cowan code). Contributions of relativistic effects were discussed in comparison with data obtained by the multi-configurational Dirac–Fock method (YODA code). Application of the theoretical data for interpretation of experimental spectra obtained by double-electron capture in slow ion-atom collisions is discussed.

Recombination of slow highly charged ions at the surface of a target foil can be used as a source of x rays for a projection x-ray microscope. In a first test of this concept, a low emittance beam of Ar18+ and Ar17+ ions from an electron beam ion trap was focused with einzel lenses to a 20 μm full width at half maximum spot on a beryllium target foil. The 3 keV x rays from radiative deexcitation of the ions were used to obtain a magnified image of an electroformed nickel mesh with 20 μm resolution by projection onto a CCD camera. Prospects for substantial improvements in resolution and intensity are discussed.

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.

The loss of kinetic energy of slow $({v\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.3v}_{\mathrm{Bohr}})$ ions transmitted through thin carbon foils has been measured as a function of projectile charge state in the range from $q\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}3+$ for oxygen to $q\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}69+$ for gold ions. For the first time, charge state dependent energy loss enhancements have been observed for ${\mathrm{Xe}}^{q+}$ and ${\mathrm{Au}}^{q+}$ at $q\ensuremath{\ge}40+$, indicating strong preequilibrium contributions to the energy loss of slow, highly charged ions in solids.

The loss of kinetic energy of highly charged, heavy ions (Ar{sup 18+}, Xe{sup 44+}, and Au{sup 69+}) in thin carbon foils has been measured as a function projectile velocity in the range from 6{times}10{sup 5} to 11{times}10{sup 5}m/s. Evidence for strong pre-equilibrium energy-loss enhancements is observed for highly charged xenon and gold ions. {copyright} {ital 1997} {ital The American Physical Society}

We present in this paper some experiments on the interaction of slow ${\mathrm{N}}^{6+}$, ${\mathrm{O}}^{7+}$, and ${\mathrm{Ne}}^{9+}$ ions below C or Si surfaces carried out by looking at the projectile and target x rays. The study of the x rays emitted by the ions, in contrast with studies of Auger electrons, allows the observation of a much larger part of the decay, not yet explored, below the surface. Moreover, the x rays emitted by the target atoms may identify the shell from which the electrons are captured. It is shown that the electron promotion mechanism, previously observed, which transfers, e.g., K electrons of C targets into the L shell of these ions, represents only a very small part of the interactions occurring at the first atomic layer and that the neutralization takes place, below the surface, mainly via Auger neutralization.

The emission of secondary electrons and ions from clean Au, CxHyAu and SiO2 surfaces at impact of slow (v ≈ 0.3 vBohr) ions has been measured as a function of incident ion charge for 1 + ≤ q ≤ 75 +. Electron yields from thermal silicon dioxide films (150 nm on Si) are found to be lower than those from Au and CxHyAu for q > 3 +. Yields of negative secondary ions from SiO2 and CxHyAu were recorded in parallel with electron emission data and exhibit a qn, n ≈ 4, dependency on incident ion charge. A direct comparison of collisional and electronic contributions to secondary ion production from SiO2 films using a beam of charge state equilibrated Xeq=qeq (at 2.75 keV/u) shows positive and negative secondary ion yield increases with incident ion charge of > 400. Results are discussed in relation to key signatures of electronic sputtering by Coulomb explosions.

Charge states of slow (v{approx}0.3v{sub Bohr}) highly charged ions (O{sup 7+}, Ar{sup 16,18+}, Kr{sup 33+}, Th{sup 65+}) have been determined after transmission through 10nm thick amorphous carbon foils. Up to the highest charge states, ions reach charge state equilibrium in the foils within less than 21fs. High yields of secondary ions are emitted from the foils as a result of the dissipation of tens to hundreds of keV of potential energy during ion neutralization. Positive secondary carbon ion yields increase strongly for q{gt}25+. Our results demonstrate, for the first time, the occurrence of electronic sputtering in the interaction of slow ions with thin conductors. {copyright} {ital 1997} {ital The American Physical Society}

We have applied a new, more efficient diagnostic technique for studies of extreme ultraviolet (EUV) radiation from multicharged ions interacting with He gas. Following single and double electron capture and one electron capture plus target-ion excitation in He2++He and Ar8++He collisions, the subsequent emitted EUV photons are analyzed with a high-resolution 2.2 m grazing incidence monochromator in conjunction with a new type of glass capillary converter (GCC) specifically designed for the EUV wavelength region. This new optical device images a horizontal cylindrical ion beam segment onto the vertical entrance slit of the monochromator. With this new imaging technique a spectral intensity enhancement of about 10 has been achieved over a distance of about 60 cm. By further optimizing this method an enhancement of the flux density of EUV radiation of about 20–30 is expected. As prototype examples, new advanced EUV spectra arising from He2++He and Ar8++He collisions are presented and discussed.