Table of contents

The 17th edition of the International Conference on the Physics of Highly Charged Ions (HCI 2014) was held in San Carlos de Bariloche, in the southern region of Argentina known as Patagonia, from August 31 to September 5, 2014. This meeting corresponds to a series of HCI conferences, which has been held every other year since 1982 in cities in Europe, USA, Japan and China. This was the first time that the conference took place in Latin America. This edition was organized by a Local Committee made up of physicists mainly from the cities of Bariloche and Rosario and also from Buenos Aires and Bahía Blanca, all sites where research on Atomic Collisions is developed. The conference was attended by delegates coming from 18 countries, more that 23% of whom were women.

The field of highly charged ions has seen in recent years a promising evolution originating from bold progress in theory and significant advances in experimental techniques. The HCI conferences aim at bringing together experimentalists and theoreticians from as wide a range of fields as, for instance, Fundamental Aspects, Structure and Spectroscopy, Collisions with Electrons, Ions, Atoms and Molecules, Interaction with Clusters, Surfaces and Solids, Interactions with Photons and Plasmas, Strong Field Processes, and Production, Experimental Developments and Applications.

The Scientific Programme, selected by an International Advisory Board, included 5 Review Lectures, 11 Progress Reports, 1 Local Report and 24 Special Reports. In addition, the results of 132 contributed works were presented as poster communications and a Public Lecture on 'The wonders of the Southern Skies' was delivered by an Argentinean expert. Thus, a wide range of subjects comprising a balanced mix of topics was covered throughout the course of the conference.

The HCI 2014 was a resounding success for the international and local communities, from both the scientific and social aspects, considering that the attendees and accompanying persons had the opportunity to enjoy a comfortable and friendly ambiance as well as the beautiful landscapes of the region including big lakes and high mountains. During the conference vivid and interesting scientific discussions were maintained by the participants in a relaxed environment.

The Local Organizing Committee would like to recognize the generous contributions made by various institutions: International Pure and Applied Physics (IUPAP), Comisión Nacional de Energía Atómica (CNEA), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Investigación Aplicada S. E. (INVAP), Patagonia Norte Division of CONICET, Instituto Balseiro and NEC Corporation.

The Local Chairs would like to express their gratitude to all the other members of the Local Organizing Committee who collaborated with a great effort and in countless ways to the success of the conference. In particular, we thank Omar Fojón for the outstanding collaboration received, and Juan Manuel Monti, who worked hard for the production of the Book of Abstracts and other related activities. We also would like to thank Renata Della Picca, Juana Gervasoni and Silvina Seguí, for their generous work in printing the book of abstracts, bags, banners, etc. and for their continuous help at the Registration Desk. We extend our gratitude to the younger members of the Local Organizing Committee, Marcos Feole, Francisco Navarrete and Juan Martín Randazzo for their help with the poster logistics; and to Luis Rodríguez for ensuring that all the presentations were ready and on schedule. We thank María Silvia Gravielle, our colleague and liaison in Buenos Aires, for helping delegates to get their visas on time; Sebastián Otranto and Jocelyn Hanssen, for their early work collecting and sorting the talk's proposals and Carlos Stia, for helping with the revision of the style of the manuscripts. We also thank M. Galassi, P Focke and D. Fregenal. We recognize Sergio Suárez, for getting funding from private sources and Roberto Garibotti, for his help with the edition of the book of abstracts. We thank Lynn van Brook for her work as conference secretary, and Silvana Peralta and Natalia Mastrángelo, for the web development and graphic design.

Finally, we express our acknowledgements to the scientists that participated during the refereeing process of the present Proceedings.

Raúl Barrachina

Flavio Colavecchia

Roberto Rivarola

Local Chairs, HCI 2014

December 2014

A list of the Local Organizing Committee members can be found in the pdf.

A list of the International Advisory Board members can be found in the pdf.

All papers published in this volume of Journal of Physics: Conference Series have been peer reviewed through processes administered by the proceedings Editors. Reviews were conducted by expert referees to the professional and scientific standards expected of a proceedings journal published by IOP Publishing.

The nuclear recoil effect to the g factor of boron-like ions is investigated. The one-photon-exchange correction to the nuclear recoil effect is calculated in the nonrelativistic approximation for the nuclear recoil operator and in the Breit approximation for the interelectronic-interaction operator. The screening potential is employed to estimate the higher-order contributions. The updated g-factor values are presented for the ground ²P_1/2 and first excited ²P_3/2 states of B-like argon ⁴⁰Ar¹³⁺, which are presently being measured by the ARTEMIS group at GSI.

The LIBELLE experiment performed at the experimental storage ring (ESR) at the GSI Helmholtz Center in Darmstadt aims for the determination of the ground state hyperfine (HFS) transitions and lifetimes in hydrogen-like (²⁰⁹Bi⁸²⁺) and lithium-like (²⁰⁹Bi⁸⁰⁺) bismuth. The study of HFS transitions in highly charged ions enables precision tests of QED in extreme electric and magnetic fields otherwise not attainable in laboratory experiments. While the HFS transition in H-like bismuth was already observed in earlier experiments at the ESR, the LIBELLE experiment succeeded for the first time to measure the HFS transition in Li-like bismuth in a laser spectroscopy experiment.

Energy levels, radiative rates, lifetimes, collision strengths and effective collision strengths are calculated for two important Al-like ions, namely Si II and Fe XIV. For Si II, the lowest 56 levels of the 3s²3p, 3s3p² 3p³ 3s²3d, 3s3p3d, 3s²4ℓ and 3s²5ℓ configurations are included, whereas for Fe XIV additional 80 levels of 3p²3d, 3s3d² and 3p3d² are considered, but not of 3s² 5ℓ. For the determination of atomic structure GRASP has been adopted and radiative rates are calculated for all E1, E2, Ml and M2 transitions. Electron impact excitation collision strengths are calculated with the DARC code, over a wide energy range, and resonances are resolved in a fine energy mesh to determine effective collision strengths over a wide range of temperatures. Extensive comparisons are made for all atomic parameters with available theoretical and experimental data, and the accuracy of the present results is assessed. Energy levels are estimated to be accurate to ~1% and all other parameters to be better than 20%.

The photon energy dependence of photoelectron spectra (PES) for two members of the polycyclic aromatic hydrocarbon (PAH) family namely pyrene and fluorene is studied in FUV regime (15 - 40 eV) using high-resolution synchrotron photoelectron spectrometer. The difference in outer (π dominated) and inner (σ dominated) valence relative photoelectron emission cross sections as a function of photon energy identifies the region of plasmon excitation (~ 15-27 eV). This excitation mode is present in the same region for both the molecule irrespective of the difference in their structure and symmetry. The feature is observed to be independent of the details of the molecular orbital associated with the outgoing electron. The results are in contradiction to the observed in benzene for inner valence bands. With the help of OVGF/cc-pVDZ calculations, the experimental bands are assigned as per their binding energy and symmetry. The first ionization potentials are estimated to be 7.436 ± 0.015 and 7.944 ± 0.055 eV for pyrene and fluorene, respectively.

Calculation of the differential cross section for the dielectronic recombination with one-electron uranium within the framework of QED is presented. The contribution of the QED corrections and the interfernce of the photon multipoles is investigated.

The thirteen times ionized tungsten is isoelectronic with PmI. Wavelengths and transition probabilities for the 5s-5p and 5p-5d transitions of WXIV, identifying the ground state as 4f¹³ 5s^{2 2}F_7/2 were calculated. Both, a relativistic Hartree Fock approach, including core-polarization effects, and a purely relativistic multiconfiguration Dirac-Fock method were used for the calculations. Particularly, 5s-5p transitions were compared with experimental results obtained with VUV electron beam ion trap (EBIT) spectroscopy.

We have observed extreme ultraviolet (EUV) spectra from terbium (Tb) ions in optically thin and thick plasmas for a comparative study. The experimental spectra are recorded in optically thin, magnetically confined torus plasmas and dense laser-produced plasmas (LPPs). The main feature of the spectra is quasicontinuum emission with a peak around 6.5-6.6 nm, the bandwidth of which is narrower in the torus plasmas than in the LPPs. A comparison between the two types of spectra also suggests strong opacity effects in the LPPs. A comparison with the calculated line strength distributions gives a qualitative interpretation of the observed spectra.

High-resolution extreme ultraviolet spectra of ions in an electron beam ion trap are investigated as a laboratory complement of the moderate-resolution observation bands of the AIA experiment on board the Solar Dynamics Observatory (SDO) spacecraft. The latter observations depend on dominant iron lines of various charge states which in combination yield temperature information on the solar plasma. Our measurements suggest additions to the spectral models that are used in the SDO data interpretation. In the process, we also note a fair number of inconsistencies among the wavelength reference data bases.

We present spectroscopic measurements of the M-shell emission of highly charged europium performed at the Livermore SuperEBIT electron beam ion trap facility using the EBIT Calorimeter Spectrometer (ECS). There is significant blending among the emission lines from the different charge states but despite the complexity of the observed spectra we have successfully identified the ten brightest n = 4 → 3 transitions from sodium-like Eu⁵²⁺ utilizing the Flexible Atomic Code (FAC). We find that the difference between the calculated and measured transition energies for these ten Eu⁵²⁺ lines does not exceed 3 eV. In fact, for four of the identified lines we find agreement within the measured uncertainties. Additional comparison with semi-empirical transition-energy predictions for sodium-like ions from laser-generated plasmas is included and shows that overall the semi-empirical predicted values for the transition energies are slightly higher than the measured values, while the FAC values that didnt agree with the measured transition energies are almost 1 eV lower than the measured values.

In this work we theoretically study photonic spectra that follow charge exchange processes between highly charged ions and neutral argon and CO targets. The range of collision energies studied is 5 eV/amu-10 keV/amu, covering typical EBIT-traps and Solar Wind energies. Our studies are based on multiple electrons schemes within the classical trajectory Monte Carlo method. Electrons are sorted with the sequential binding energies for the target under consideration. The role played by the multiple electron capture process for the different collision systems under consideration is explicitly analyzed and its contribution separated as arising from double radiative decay and autoionizing multiple capture. Present studies are stimulated by the upcoming launch of the Astro-H mission in 2015, which will provide high resolution spectra in the 0.3 keV-12keV band.

We report experimental indications of chemical reactions inside clusters of pyrene (C₁₆H₁₀) molecules following collisions with 11.25 keV He+ - and 12.0 keV Ar²⁺ ions. It appears that bond-forming reactions are more likely with the heavier projectile. We have also performed classical molecular dynamics simulations of these processes where we treat the interaction between the projectiles and all atoms in the cluster as well as non-dispersive and dispersive forces between all atoms in the cluster before, during and after the collision. The time step is typically 10⁻¹⁷ s and the total simulation time 1 picosecond. The simulations were performed for a fixed cluster size with 36 pyrene molecules, although there is a broad range of cluster sizes in the experiment. Still, there is good qualitative agreement between the experimental and the simulated mass spectra exhibiting reaction products with masses between those of the C₁₆H₁₀- monomer and dimer in both cases. Additional studies of the influence of the projectile charge and mass is planned as well as simulations on longer time scales and as functions of cluster size.

We used a time-reolving high-resolution grating spectrometer to study extreme ultraviolet emission from plasmas in the National Spherical Tokamak Experiment (NSTX). The NSTX spectral range from 150-250 Å is typically dominated by emission from M-shell iron lines, L- shell transitions of oxygen, or K-shell lines of lithium. However, we also observed several intense emission lines, which we now attribute to transitions in C V and C VI. Collisional-radiative modeling shows that electron-impact excitation is far too weak to account for the features we observed. Instead, these lines appear to be produced by charge exchange with neutral hydrogen.

We present theoretical and experimental results for angular and energy distributions of electrons emitted in collisions of B²⁺ with He atoms. In particular, we analyze the cusp formed by projectile Electron Loss to Continuum (ELC) and Electron Capture to Continuum (ECC). The cusp shape dependence on the electronic initial state is discussed and compared with our previous measurements on Li⁺ + He. The projectile incident energy was about 414 keV/u and the electron detection angle was varied between 0° and 150°. The experimental data is compared with three-body quantum Continuum-Distorted-Wave calculations.

The new research initiative APAPES (http://apapes.physics.uoc.gr/) has already established a new experimental station with a beam line dedicated for atomic collisions physics research, at the 5 MV TANDEM accelerator of the National Research Centre "Demokritos" in Athens, Greece. A complete zero-degree Auger projectile spectroscopy (ZAPS) apparatus has been put together to perform high resolution studies of electrons emitted in ion-atom collisions. A single stage hemispherical spectrometer with a 2-dimensional Position Sensitive Detector (PSD) combined with a doubly-differentially pumped gas target will be used to perform a systematic isoelectronic investigation of K-Auger spectra emitted from collisions of preexcited and ground state He-like ions with gas targets using novel techniques. Our intention is to provide a more thorough understanding of cascade feeding of the 1s2s2p ⁴P metastable states produced by electron capture in collisions of He-like ions with gas targets and further elucidate their role in the non-statistical production of excited three-electron 1s2s2p states by electron capture, recently a field of conflicting interpretations awaiting further resolution. At the moment, the apparatus is being completed and the spectrometer will soon be fully operational. Here we present the project progress and the recent high resolution spectrum obtained in collisions of 12 MeV C⁴⁺ on a Neon gas target.

Electron capture reactions for ³He²⁺ collisions on He at impact energies in the range 40 keV-300 keV have been studied using the Cold Target Recoil-Ion Momentum Spectroscopy setup which has recently became operational at the Centro Atomico Bariloche. State-selective charge exchange cross sections were obtained and in this work we present recoil-ion transverse momentum distributions. For targets with residual thermal motion, we show that the implementation of a back-projection algorithm based on the transverse momentum distribution component along a direction perpendicular to the jet direction provides results in agreement with those obtained by using previously cooled targets. Present results nicely fit the gaps in the datasets already published by other laboratories and are found to be in good agreement with classical trajectory Monte Carlo simulations.

An apparatus for low-energy collision of highly charged ions with molecules, comprising a position sensitive time-of-flight measurement devise for recoil ions and a charge state analyser for the scattered projectile, was newly constructed at a beam line of an electron cyclotron resonance ion source. Collision experiments of 120 keV Ar⁸⁺ with the target of nitrogen molecules were conducted as a test run of this apparatus. Focusing on the dissociation channels with asymmetric sharing of the charges by fragmentation, correlation between Auger electron emission of the projectile and Coulomb explosion of the target is discussed.

Monte Carlo simulation is performed under local density approximation for electronic energy loss distribution by intermediate velocity protons for several examples of polycyclic aromatic hydrocarbon (PAH) molecules as well as for some of naphthalene derivatives. The energy loss distribution was found to peak in the range of 50-70 eV for all the molecules except C₆₀. Apart from this, a strong orientation effect with respect to projectile for electronic stopping magnitude is observed for all molecules except C₆₀ due to its icosahedral symmetry. This work helps in estimation of the ionization and fragmentation cross sections using electronic stopping.

The energy threshold for the formation of highly charged ions is experimentally well-known and measured. For single ionization, it is the binding energy of the outermost electrons. For multiple ionization, the ionization begins at impact energies much larger than the theoretically expected ones. In this contribution we present a simple expression for the energy threshold for multiple ionization by electron or positron impact. It was obtained as the mean value of the energy transferred to each ionized electron by using Thompson classical approximation. Present results reproduce quite well the experimental thresholds. Moreover, the inclusion of these values in the theoretical multiple ionization cross sections allows describing rather well the experimental data for single up to sextuple ionization of rare gases.

We present emission spectra of highly charged Fe ions in the extreme ultraviolet range obtained with two electron beam ion traps. The intensity ratio between the 3s3p³P₂ - 3s3d³D₃ (233.9 Å) and 3s3p¹P₁ - 3s3d¹D₂ (243.8 Å) transitions in Fe XV is given for various electron beam parameters. The experimental ratios are compared with theoretical model calculation as well as our previous experiment, where significant discrepancy with theoretical model was found. The present result, which has been obtained with a higher resolution spectrometer to investigate possible line blending, confirms that the discrepancy is not due to line blending.

Single ionization from ammonia and methane molecules by impact of protons is analysed. Double differential cross sections are calculated, within the post- and prior-versions of the continuum distorted wave-eikonal initial state (CDW-EIS) model, considering two different representations of the initial bound state of the active electron. A comparison between both set of results shows a very little sensitivity of the double differential cross sections to the initial state representation in the case of ammonia molecules. On the other hand, discrepancies are found when CH₄ molecular target is considered, showing that in this case the description of the corresponding molecular orbitals influences the cross section calculations.

We study the projectile charge state dependence of doubly differential electron emission cross section (DDCS) in ionization of Ne under the impact of dressed and bare oxygen ions. Experimental DDCS results measured at different angles are compared with the calculations based on a CDW-EIS approximation using the GSZ model potential to describe projectile active-electron interaction. This prescription gives an overall very good agreement. In general a deviation from the q²-law was observed in the DDCS. The observations crudely identify the dominance of different projectile electron loss mechanisms at certain electron energy range.

We have been measuring the L-shell x-ray emission produced by dielectronic recombination of neonlike Fe¹⁶⁺ ions populating doubly excitated levels of the form 1s²2l⁷3ℓn'ℓ' in Fe¹⁵⁺. The measurements are carried out at the Livermore electron beam ion trap facility, where we isolate dielectronic resonances by choice of the electron beam energy. We utilize crystal spectrometers to record the x-ray lines generated in the radiative deexcitation of the 1s²2l⁷3ℓn'ℓ' upper levels. The measurements aim to support the identification of such lines in low-density astrophysical plasmas.

We study the ionization of water molecules in liquid phase by fast electron impact. We use our previous first-order model within an independent electron approximation that allows the reduction of the multielectronic problem into a monoelectronic one. The initial molecular states of the liquid water are represented in a realistic way through a Wannier orbital formalism. We complete our previous study by taking into account approximately the influence of the passive electrons of the target by means of different model potentials. We compute multiple differential cross sections for the most external orbital 1B₁ and compare them with other results.

In this work, a theoretical study of the double ionization of He by ion impact at the fully differential level is presented. Emphasis is made in the role played by the projectile in the double emission process depending on its charge and the amount of momentum transferred to the target. A Born-CDW model including a second-order term in the projectile charge is introduced and evaluated within an on-shell treatment. We find that emission geometries for which the second-order term dominates lead to asymmetric structures around the momentum transfer direction, a typical characteristic of higher order transitions.

A hybrid CDW-CDW-EIS model is developed in order to include the dynamic screening in the post CDW approximation for single ionization. Doubly differential cross sections for single ionization of water molecules are calculated and comparison with available experimental data and other theories are shown.

After being overlooked for decades, the presence of quantum vortices in atomic ionization processes was recently uncovered both theoretically and experimentally. On the other hand, the electron capture to the continuum cusp is one of the most conspicuous and well-studied features of the multiple differential cross section in the ionization of atoms by the impact of positively charged projectiles. Here we analyze the conditions for these two structures to approach each other in the configuration space of the transition matrix element, and the effects that this encounter might produce.

The striking observation of interference structures produced by grazing impact of fast atoms on crystal surfaces reported a few years ago [1,2] has given rise to the development of a powerful surface analysis technique. This article gives a brief account of the main features of the process, using the Surface Eikonal (SE) approximation as a theoretical tool to analyze the different mechanisms responsible for the quantum interference. The SE approach is a semiclassical method based on the use of the eikonal wave function, which takes into account the coherent superposition of transition amplitudes for different axially channeled trajectories. It has proved to provide a quite good description of experimental diffraction patterns for different collision systems.

In this work we analyze the production of bulk and surface plasmons by fast ions entering or leaving a material at different incidence angles. In the framework of a semi classical dielectric formulation, we study the different contributions to the induced potential, mainly in the vicinity of the surface, analyzing the differences and similarities that arise when in and out trajectories are compared. In particular, we find some novel oscillatory structures for both perpendicular and oblique trajectories.

Ionization and successive evaporation of C₇₀^r+ is studied as a function of the internal energy using collision induced dissociation under energy control. Multicharged ions C₇₀^r+ are prepared in F⁺ (3 keV) + C₇₀ → F⁻ + C₇₀^r+ + ne collisions. Up to seven successive evaporation of C₂ are observed in an excitation energy range from 40 to 100eV. The dissociation energies of C_70-2m²⁺ (m=1-7) are determined using a statistical cascade model to reproduce the excitation energy distribution of C₇₀²⁺ parent ions for each dissociation channel. Results are in good agreement with previous theoretical calculations.

We study the fluctuations of the electronic density due to plasmon field associated to the wake potential generated by a dimer formed by two identical charged particles (such as two nuclei of the ionized hydrogen molecule) traveling through a semi-infinite dielectric medium. We use coherent states to describe plasmons as wave packets that raise fluctuations in the electronic density of the material. We analyze different configurations of interest, regarding the geometry of the surface and the orientation of the dimer.

We put forward an alternative mechanism to understand the physics underlying the electron emission and exciton formation occurring during grazing collision of neutral hydrogen on LiF(001) surfaces. Instead of visualizing the negative ion formation as the precursor, we propose the formation of excited H(n=2) as a catalyzer to produce excitons and electrons.

Charged particles, in particular slow highly charged ions, can be guided through nanocapillaries in various insulating materials by self-organized charge patches. We present a technique for observing directly the formation of these patches in glass capillaries. It is based on imaging the emitted visible photons. We report here on tests with 4.5 keV Ar⁺-ions transmitted through straight and tapered borosilicate capillaries, using a highly sensitive digital camera. Simultaneously, the ions transmitted through the capillaries were detected. The number of emitted photons decreases by increasing the tilt angle of the capillary. The time evolution of emitted photons revealed a change of location of the charge patches during charging-up the capillary walls.

We analyze the angular distribution of electrons in the laser-assisted photoionization of HeH²⁺ molecular targets. By means of a simple model, we obtain the observables for the reaction and we compare them with previous results obtained with more elaborated ones. The two-center interference effect and the asymmetric emission in the monochromatic ionization persist in the presence of a near infrared laser bath leading to a characteristic spectrum.

In this work, we analytically evaluate the exact matrix element for a non-relativistic Continuum-Bound radiative transition in a Coulomb potential. We apply this result to the photoionization (and radiative recombination) process, and calculate the total cross sections giving an analytical expression for the transition from the ground state. To our best knowledge the exact solution to this problem has never been addressed even though the analytical calculation is quite simple, and the final result is not more complicated than any of its approximations. We compare our result with the well-known plane wave and Coulombian dipolar approximations, in a wide range of energies.

In this work we investigate the ionization by proton impact, and photo ionization, involving highly charged ions of W, in particular the Ne-like W⁶⁴⁺ and Na-like W⁶³⁺ which are more likely to appear in ITER plasma. Total cross sections are calculated in the continuum-distorted-wave-eikonal-initial-state (CDW-EIS) approximation for ion-impact, while two completely different methods are used for photoionization: a perturbative dipolar aproach and the recently introduced Sturmian model.

Modeled within the Collisional-Radiative approach, for parameters relevant to plasmas in the centre of JET, the M X-ray line structures for tungsten and L X-ray line structures for molybdenum both occur in the wave length range 5.0-5.35 Å; and, their strengths are comparable. Therefore, the spectra obtained with the upgraded high-resolution X-ray spectrometer KX1 on JET should include both tungsten and molybdenum in their interpretation. The same will be true for the high-resolution X- ray diagnostic on tokamaks such as WEST and ITER, where tungsten plasma-facing components will be implemented.

We investigate different atomic processes that might occur in the interior of plasmas. In particular we apply the Final-State Interaction theory in order to study the behavior of the corresponding cross sections when the relative energy of a pair of charged particles in the initial or final states vanishes. Through this analysis we uncover the presence of zero - energy resonances for particular configurations of density and temperature. For fusion plasmas, these effects might have an important impact on the working conditions and performance of the reactor.

Fast population decay of naphthalene cations (C₁₀H₈⁺) has been observed in a compact electrostatic storage ring, the Mini-Ring, up to 5 ms. Laser induced dissociation due to single-photon absorption was used to probe the internal energy distribution (IED) of the stored molecular ions as a function of the storage time. To determine the energy distribution of naphthalene cations, the experimental neutral decay curve was analysed with a model including the competition between dissociation and radiative cooling. Fast cooling rates from about 70 s⁻¹ at the internal energy 5.6 eV to 140 s⁻¹ at 6.2 eV were measured and compared with the data in the literature. This fast cooling mechanism is attributed to the fluorescence from thermally excited electrons and may have important implications in astrophysics for the lifetime and the critical size of Polycyclic Aromatic Hydrocarbons (PAH) in the interstellar medium.

Measurements of hyperfine splittings in highly charged ions are sensitive to details of the nuclear structure and the nuclear magnetic field distribution, but the proper interpretation of the measurements requires that the atomic structure is understood in sufficient detail. We discuss the reasoning behind various recent experiments and what advantage is offered by the study of the Li-like ion of a mid-Z element such as praseodymium.

We analyse theoretically the Argon photoelectron spectra produced by strong and extreme ultraviolet radiation of six colors: from the 11th to the 16th harmonics of ω₀ (800nm). In particular we concentrate in the range of the spectra where absorption of two photons occurs. The combination of photons of different frequencies results in eleven peaks that are separated by ω₀. We point out that their relative intensities are very sensitive to the laser pulse parameters and target description. We also compare the theoretical description with experimental results finding good qualitative agreement.

Hard x-ray polarimetry of radiation emitted in collisions of heavy ions, electrons or photons with matter provides detailed information on the collision dynamics as well as of the atomic structure in the presence of extreme field strengths. Moreover, it also opens a route for polarization diagnosis of spin-polarized ion and electron beams which, for example, might be useful in future parity non-conservation studies. Owing to recent progress in the development of highly segmented solid-state detectors, a novel type of polarimeter for the hard x-ray regime has become available. Applied as Compton polarimeters, two-dimensional position-sensitive x-ray detectors now allow for precise and efficient measurements of x-ray linear polarization properties. In this report recent polarimetry studies using such detector systems are reviewed.

Radiative cooling of polycyclic aromatic hydrocarbon (PAH) cations has been studied using a compact electrostatic ion storage ring, the Mini-Ring, in a time range up to 8 ms. The time evolution of the internal energy distribution of the ensemble of stored ions shows evidences of fast cooling which is attributed to the fluorescence from thermally excited electronic states. The internal energy distribution was probed by inducing unimolecular dissociation with single-photon absorption at given storage times. Information on the fragmentation kinematics and the dissociation channels were obtained by analyzing the image of the emitted neutrals detected with a time and position sensitive detector.

The response of a double-sided segmented Si(Li) detector system has been investigated. The detector has been irradiated with a collimated, highly linearly polarized beam of 53.2 keV photons from the synchrotron radiation source PETRA III at DESY. The detector was mounted on a platform that could be moved with μm precision thus allowing for a defined beam position on the detector surface. In this paper, the effects of the isolation gaps (gap width = 50 μm) between adjacent segments (strips) were studied, in particular with respect to the effect of charge sharing. The fraction of such charge sharing events increases from about 5% (beam hits center of a strip) to over 50% when the beam is focused just on a gap. The fraction of reconstructed Compton scattering events, which is interesting for Compton polarimetry, amounts to about 3% with the beam impinging at a strip center and 2.8% on average. It can therefore be concluded that events related to charge sharing do not critically degrade the performance of the detector as a Compton polarimter.

A room-temperature miniature electron beam ion trap (EBIT) is being developed for the production of charge states with a relatively low ionization threshold. A unitary Penning trap is modified slightly to provide the magnetic field and electric potential necessary for ion production via electron impact in this compact EBIT. This design allows radial access for in- EBIT spectroscopy as well as extraction of highly-charged ions for isolation at low energy to investigate proposed experiments. A fast micro-channel plate is used as a time-of-flight detector to study the initial production of helium and neon ions. Planned work would also involve the use of a Wien filter to select a single charge state to be isolated in a secondary ion trap for various studies. For instance, fully stripped ions can be captured for recombination experiments to form one-electron ions in high-angular momentum Rydberg states.

To prepare the upcoming experiment of laser cooling of relativistic ¹²C³⁺ ion beams at the experimental cooler storage ring (CSRe), a test experiment was performed with ¹²C³⁺ ion beams at an energy of 122 MeV/u on the CSRe, at the Institute of Modern Physics, Lanzhou, China. In this experiment, the main storage ring of CSRm was employed to accumulate and accelerate the ion beam which was injected into the CSRe for the experiments. The number of ¹²C³⁺ ions at the CSRe reached 5×10⁸ for every injection, which satisfied the experimental requirement. To fulfil the laser cooling experiment, the ¹²C³⁺ ion beams were bunched by sinusoidal waveforms with fixed and sweeping frequencies, respectively. A resonant Schottky pick-up was employed to record the Schottky spectra of these ion beams. The test experimental results demonstrated that the RF-buncher and diagnostic systems at the CSRe worked well and the CSRe was very stable with ¹²C³⁺ ion beams, hereby the CSRe is suitable for laser cooling experiment.

Recent developments at Clemson University have established the need to model the production of x-rays using a highly charged ion beam generated by the Clemson University Electron Beam Ion Trap (CUEBIT). A Geant4 modeling environment has been developed on Clemson University's Palmetto2 supercomputing cluster to simulate the interaction of these x- rays with biological material. Preliminary results of the model have been obtained after performing initial simulations on the computing cluster. Future experiments using the CUEBIT as well as refinements to the Geant4 model are discussed.

The stopping power of α particles in thin films of decalcified sheep femur, in the range of 1.5 to 5.0 MeV incident energy, was measured by transmission of a backscattered beam from a heavy target. Additionally, the film elemental composition was determined by Rutherford Backscattering Spectrometry (RBS). These data will be used to measure boron concentration in thin films of bone using a spectrometry technique developed by the University of Pavia, since the concentration ratio between healthy tissue and tumor is of fundamental importance in Boron Neutron Capture Therapy (BNCT). The present experimental data are compared with numerical simulation results and with tabulated stopping power data of non-decalcified human bone.

Because of the importance of x-ray interactions in modern medicine, efforts must be made to combine the fields of biology and physics. This paper reviews the development of an x-ray irradiation port that allows us to study the interaction of x-rays generated by highly charged ions with biological material, such as stem and cancer cells. Our goal is to better understand these interactions in order to improve the techniques of x-ray therapy by narrowing and specifically selecting the range of radiation energies applied. Using the Clemson University Electron Beam Ion Trap (CUEBIT), the generation of quasi-monochromatic x- rays from highly charged ions is possible. In order to maintain the integrity of the cells being studied, the cell culture needs to be oriented horizontally during the irradiation process. This poses a problem, as the highly charged ion beam generated at the CUEBIT is also oriented horizontally. Therefore, we have designed a system that employs a quadrupole bender that directs the ion beam vertically, which allows for the production of x-rays directly under the cell culture. The experimental station consists of a vacuum chamber that attaches to the end of the beam line. This chamber houses the quadrupole bender, a beryllium window for generating x-rays, and the interface between the beryllium window and the cell culture. X-rays must transmit through the bottom of a flask before they interact with the cells. Hence, we implement a procedure to replace the bottom of the flask with a thin layer of Mylar, allowing x-rays to penetrate through easily. We will use this system to study the effects of monochromatic x- rays on stem cells, cancer cells, and their associated proteins.

Several numerical codes for proton and electron transport in water - a commonly used surrogate of the living matter - have been reported in the literature. In the current work, we report on a home-made step-by-step Monte Carlo code, called TILDA-V, based on a complete set of multiple-differential and total cross sections for describing all the inelastic processes occurring throughout the slowing-down of protons in water and DNA.