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

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.

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.

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.

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.

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.

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}

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.

RETrap is a cryogenic Penning ion trap system, capable of the capture and cooling of highest charge high Z ions from external low-energy ion sources such as the Electron Beam Ion Trap (EBIT) or Electron Cyclotron Resonance Ion Sources (ECRIS). Recently RETrap has been moved from Lawrence Livermore National Laboratory (LLNL) to Lawrence Berkeley National Laboratory (LBNL), where its operation for sophisticated research is currently being re-established.

At the FAIR facility for antiproton and ion research, the new ESR + CRYRING combination of storage rings CRYRING@ESR opens up a wealth of opportunities for in-ring atomic physics experiments on few-body quantum dynamics. The low-energy storage ring CRYRING will serve in its new location at FAIR/ESR for experiments with decelerated antiprotons and highly charged ions. We will discuss selected new experiments in the field of quantum dynamics of high-Z ions, for example for adiabatic superheavy quasi-molecules transiently formed with bare and H-like projectiles. Such experiments will be for the first time possible at the future CRYRING at ESR.

The Electron Beam Ion Trap (EBIT) produces ions, confined within the electron beam, with charges ranging up to U92+ at near rest energies. This allows to study the interaction of a monoenergetic electron beam with any trapped ion to a high degree of precision via X-ray spectroscopy. The development of the EBIT into an ion (trap) source enables the possibility to perform for the first time studies of the interaction dynamics in strong fields of ions with matter where the ions carry hundreds of keV potential energy at very low kinetic energies (eV).

Charge-exchange cross sections for collisions between ${\mathrm{H}}_{2}$ and ions with unusually low center-of-mass energies (\ensuremath{\approx}6 eV) and high-charge states (${\mathrm{Xe}}^{q+}:35, 43\ensuremath{\le}q\ensuremath{\le}46$, ${\mathrm{Th}}^{q+}:73\ensuremath{\le}q\ensuremath{\le}80$) have been measured using a Penning ion trap. A nondestructive measurement technique permitted both primary and product ion analysis. The data, averaged over the charge states indicated above, are consistent with a total cross section that scales linearly with ion charge $q$. The true double-capture cross section is found to be about 25% of the total cross section at high $q$. The results are compared to predictions of the absorbing-sphere model.

The interaction of Ar{sup (17,18)+} ions with C{sub 60} has been studied by observing coincidences between Ar {ital K} x rays and the fullerene ions and fragments. At large distances the capture of electrons from C{sub 60} into excited states of the ion has been observed and compared to the interaction of the same ions with surfaces. Most of the observed events correspond to the capture of many electrons by the ion and the loss of all but one. These results show clearly the characteristic behavior of ions flying over a surface without any contact. {copyright} {ital 1996 The American Physical Society.}

Experimental results from a series of investigations, the aim of which is to provide an exploratory overview of the wide range of phenomenon associated with the interaction of slow very highly charged ions with solids and solid surfaces, are reported. Incident charge state dependencies of secondary electron, x-ray and secondary ion emission are measured. In addition, microscopic studies are performed using an Atomic Force Microscope to investigate highly charged ion induced surface defects. The ions, used for these studies, range from O7+ to Th80+ and U82+ with low incident kinetic energies (~2 eV/amu to 3 keV/amu). As an overall result, enhancements for the low energy secondary electron, sputter ion and photon emission are observed with increasing charge states. X-ray emission spectra are found to be consistent with the formation of so called hollow atoms above and at the surface as part of the neutralization processes. Small angle scattering behaviour, under specular reflection conditions, indicate very fast decay processes for the hollow atom, outside the solid surface. The microscopic studies reveal interesting nano-size surface defects caused by single highly charged ion incidence.

We studied the molecular dynamics of vanadyl−chelate complexes covalently attached to the surface of cascade polymers, dendrimers. The rotational correlation times of the ion−chelate complex were determined from computer simulations of their EPR spectra. The chelate 2-(4-isothiocyanatobenzyl)-6-methyldiethylenetriaminepentaacetic acid was covalently attached to ammonia core poly(amidoamine) (PAMAM) cascade polymers via a thiourea (TU) linkage, resulting in PAMAM−TU−DTPA cascade polymers. X-band EPR spectra of their vanadyl complexes were taken, and the A and g matrices were determined from the rigid limit spectra using the SIMPOW program. Spectra were fitted with modification of the slow-motional line-shape theory. Our results indicate that the rotational correlation times of the surface chelate increase with molecular weight and resemble those of “internal” segmental motions found in PAMAMs. For this macromolecular system, the rotational correlation times alone cannot account for differences in the relax...

Reductive methylation of nearly all lysine groups of myosin subfragment-1 (S1) was required for crystallization and solution of its structure at atomic resolution. Possible effects of such methylation on the radius of gyration of chicken skeletal muscle myosin S1 have been investigated by using small-angle neutron scattering. In addition, we have investigated the effect of MgADP.Vi, which is thought to produce an analog of the S1.ADP.Pi state, on the S1 radius of gyration. We find that although methylation of S1, with or without SO42- ion addition, does not significantly alter the structure, addition of ADP plus vanadate does decrease the radius of gyration significantly. The S1 crystal structure predicts a radius of gyration close to that measured here by neutron scattering. These results suggest that the overall shape by crystallography resembles nucleotide-free S1 in solution. In order to estimate the effect of residues missing from the crystal structure, the structure of missing loops was estimated by secondary-structure prediction methods. Calculations using the complete crystal structure show that a simple closure of the nucleotide cleft by a rigid-body torsional rotation of residues (172–180 to 670) around an axis running along the base of the cleft alone does not produce changes as large as seen here and in x-ray scattering results. On the other hand, a rigid body rotation of either the light-chain binding domain (767 to 843 plus light chains) or of a portion of 20-kDa peptide plus this domain (706 to 843 plus light chains) is more readily capable of producing such changes.

Complex amplitudes and their dependence upon the projectile scattering angle have been measured for {vert_bar}{ital L},{ital M}{r_angle} substates of doubly excited 1{ital s}[2{ital s}2{ital p} {sup 1}{ital P}]{sup 2}{ital P} and the 1{ital s}2{ital p}{sup 22}{ital D} terms of C{sup 3+} formed in double electron capture by 25 keV C{sup 5+} ions from He atoms. These are extracted from Auger electron anisotropy measured with respect to the incident beam and scattering plane by a coincident electron--scattered ion technique. The results are the most complete experimental description of a low energy double capture collision.

High-resolution autoionization spectra of multiply charged Na-like states in silicon are presented. These states have been populated in collisions of Si{sup 5+} ions with 50 keV impact energy on two gas targets: He and Ar. The electron emission following the decay of core-excited 2{ital p}{sup 5}3{ital lnl}{prime} ({ital n}=3--6) levels in Si IV has been measured. The comparison of electron spectra obtained after collisions with He and Ar is given. Theoretical Auger energies due to core-excited (2{ital p}{sup 5}3{ital s}{sup 2}), (2{ital p}{sup 5}3{ital s}3{ital p}), (2{ital p}{sup 5}3{ital p}3{ital d}), (2{ital p}{sup 5}3{ital s}4{ital s}), and (2{ital p}{sup 5}3{ital s}4{ital f}) states have been calculated relative to the (2{ital p}{sup 6}){sup 1}{ital S} limit by using the multiconfiguration Hartree-Fock method. Additional theoretical estimates of Auger transition energies originating from (2{ital p}{sup 5}3{ital p}{sup 2}), (2{ital p}{sup 5}3{ital d}{sup 2}), (2{ital p}{sup 5}3{ital s}4{ital d}), (2{ital p}{sup 5}3{ital s}5{ital p}), (2{ital p}{sup 5}3{ital s}6{ital s}), (2{ital p}{sup 5}3{ital s}6{ital p}), and (2{ital p}{sup 5}3{ital s}6{ital g}) are also presented.

Radiation induced defects on mica caused by the impact of slow very highly charged ions (SVHCI) have been investigated with an atomic force microscope (AFM). Freshly cleaved surfaces of different types of muscovite were irradiated with SVHCI extracted from the LLNL electron beam ion trap (EBIT) at velocities of about 2 keV/amu. Atomic force microscopy of the surface reveals the formation of blisterlike defects associated with single ion impact. The determined defect volume which appears to increase linearly with the incident charge state and exhibits a threshold incident charge state has been determined using the AFM. These results indicate that target atoms are subjected to mutual electrostatic repulsion due to ionization through potential electron emission upon approach of the ion. If the repulsion leads to permanent atomic displacement, surface defects are formed.

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.

A single-detector technique for the measurement of negative ion time-of-flight spectra is introduced in this work. Spectra are presented for 390 keV Xe 44f ions at normal incidence on different samples. Mass distributions for C, and Si,O, clusters indicate that highly charged ions lead to a statistical off-surface formation of heavy clusters, whereas low-energy singly-charged ions may directly produce heavy carbon clusters. The detection technique has proven to be very efficient and might even be used as a nearly non-destructive surface-analysis method for investigations of time dependent surface modifications.

A high resolution, broad band X-ray microcalorimeter has been used for the first time to investigate the radiative deexcitation of highly charged 7 keV/q Ar 17+ ions as they interact with a beryllium surface at normal incidence. The 20 eV energy resolution of this instrument made it possible to clearly distinguish the argon K α and K β, γ complex simultaneously. The intensity ratio of the K β, γ to K α emission is 31%, compared to the 8% found in the neutral argon atom. There is strong evidence that the relative intensities of the KL n ( n = 1–8) transitions do not agree with those obtained with crystal spectrometers.

Cryogenically cooled inertial confinement fusion capsule designs are suitable for studies of reaction-in-flight (RIF) neutrons. RIF neutrons occur when energetically up-scattered ions undergo DT reactions with a thermal ion in the plasma, producing neutrons in the energy range 9-30 MeV. The knock-on ions lose energy as they traverse the plasma, which directly affects the spectrum of the produced RIF neutrons. Here we present measurements from the National Ignition Facility (NIF) of RIF neutrons produced in cryogenic capsules, with energies above 15 MeV. We show that the measured RIFs probe stopping under previously unexplored degenerate plasma conditions and constrain stopping models in warm dense plasma conditions.

We have performed high-resolution measurements of photon excitation functions for radiative recombination and dielectronic recombination in highly charged uranium ions. The data show evidence for quantum interference between the two processes in the vicinity of the [ital KLL] resonances.

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 studies is to cool the trapped very highly charged ions to low temperatures (