Abstract: The heating neutral beam injectors (HNBs) of ITER are designed to deliver 16.7 MW of 1 MeV D0 or 0.87 MeV H0 to the ITER plasma for up to 3600 s. They will be the most powerful neutral beam (NB) injectors ever, delivering higher energy NBs to the plasma in a tokamak for longer than any previous systems have done. The design of the HNBs is based on the acceleration and neutralisation of negative ions as the efficiency of conversion of accelerated positive ions is so low at the required energy that a realistic design is not possible, whereas the neutralisation of H− and D− remains acceptable (≈56%). The design of a long pulse negative ion based injector is inherently more complicated than that of short pulse positive ion based injectors because: • negative ions are harder to create so that they can be extracted and accelerated from the ion source; • electrons can be co-extracted from the ion source along with the negative ions, and their acceleration must be minimised to maintain an acceptable overall accelerator efficiency; • negative ions are easily lost by collisions with the background gas in the accelerator; • electrons created in the extractor and accelerator can impinge on the extraction and acceleration grids, leading to high power loads on the grids; • positive ions are created in the accelerator by ionisation of the background gas by the accelerated negative ions and the positive ions are back-accelerated into the ion source creating a massive power load to the ion source; • electrons that are co-accelerated with the negative ions can exit the accelerator and deposit power on various downstream beamline components. The design of the ITER HNBs is further complicated because ITER is a nuclear installation which will generate very large fluxes of neutrons and gamma rays. Consequently all the injector components have to survive in that harsh environment. Additionally the beamline components and the NB cell, where the beams are housed, will be activated and all maintenance will have to be performed remotely. This paper describes the design of the HNB injectors, but not the associated power supplies, cooling system, cryogenic system etc, or the high voltage bushing which separates the vacuum of the beamline from the high pressure SF6 of the high voltage (1 MV) transmission line, through which the power, gas and cooling water are supplied to the beam source. Also the magnetic field reduction system is not described.

Abstract: Ultrafast processes in matter, such as the electron emission after light absorption, can now be studied using ultrashort light pulses of attosecond duration (10 −18 seconds) in the extreme ultraviolet spectral range. The lack of spectral resolution due to the use of short light pulses has raised issues in the interpretation of the experimental results and the comparison with theoretical calculations. We determine photoionization time delays in neon atoms over a 40–electron volt energy range with an interferometric technique combining high temporal and spectral resolution. We spectrally disentangle direct ionization from ionization with shake-up, in which a second electron is left in an excited state, and obtain excellent agreement with theoretical calculations, thereby solving a puzzle raised by 7-year-old measurements.

Abstract: The elastic scattering of an atomic nucleus plays a central role in dark matter direct detection experiments. In those experiments, it is usually assumed that the atomic electrons around the nucleus of the target material immediately follow the motion of the recoil nucleus. In reality, however, it takes some time for the electrons to catch up, which results in ionization and excitation of the atoms. In previous studies, those effects are taken into account by using the so-called Migdal's approach, in which the final state ionization/excitation are treated separately from the nuclear recoil. In this paper, we reformulate the Migdal's approach so that the "atomic recoil" cross section is obtained coherently, where we make transparent the energy-momentum conservation and the probability conservation. We show that the final state ionization/excitation can enhance the detectability of rather light dark matter in the GeV mass range via the {\it nuclear} scattering. We also discuss the coherent neutrino-nucleus scattering, where the same effects are expected.

Abstract: The first hundred attoseconds of the electron dynamics during strong field tunneling ionization are investigated. We quantify theoretically how the electron's classical trajectories in the continuum emerge from the tunneling process and test the results with those achieved in parallel from attoclock measurements. An especially high sensitivity on the tunneling barrier is accomplished here by comparing the momentum distributions of two atomic species of slightly deviating atomic potentials (argon and krypton) being ionized under absolutely identical conditions with near-infrared laser pulses (1300 nm). The agreement between experiment and theory provides clear evidence for a nonzero tunneling time delay and a nonvanishing longitudinal momentum of the electron at the ``tunnel exit.''

Abstract: The use of cold atmospheric pressure plasma jets for in vivotreatments implies most of the time plasma interaction with conductive targets. The effect of conductive target contact on the discharge behavior is here studied for a grounded metallic target and compared to the free jet configuration. In this work, realized with a Plasma Gun, we measured helium metastable HeM (23S1) concentration (by laser absorption spectroscopy) and electric field (EF) longitudinal and radial components (by electro-optic probe). Both diagnostics were temporally and spatially resolved. Mechanisms after ionization front impact on target surface have been identified. The remnant conductive ionized channel behind the ionization front electrically transiently connects the inner high voltage electrode to the target. Due to impedance mismatching between ionized channel and target, a secondary ionization front is initiated and rapidly propagates from the target surface to the inner electrode through this ionized channel. This leads to a greatly enhance HeM production inside the plasma plume and the capillary. Forward and reverse dynamics occur with further multi reflections of more or less damped ion ization fronts between the inner electrode and the target as long as ionized channel is persisting. This phenomenon is very sensitive to parameters such as target distance and ionized channel conductivity affecting electrical coupling between these two andevidenced using positive or negative voltage polarity and nitrogen admixture. In typical operating condition for the plasma gun used in this work, it has been found that after the secondary ionization front propagation, when the ionized channel is conductive enough, a glow like discharge occurs with strong conduction current. HeM production and all species excitation, especially reactive ones, are then driven by high voltage pulse evolution. The control of forward and reverse dynamics, impacting on the production of the glow like discharge, will be useful for biomedical applications on living tissues.

Abstract: Upon exposure to ultra-intense, hard X-ray pulses, polyatomic molecules containing one heavy atom reach a much higher degree of ionization than do individual heavy atoms, contrary to previous assumptions X-ray free-electron lasers offer many new applications such as the ability to structurally probe fast biological processes This requires the use of hard and intense X-ray pulses, but the behaviour of matter under such conditions has not been fully explored Artem Rudenko et al show that when exposing small polyatomic molecules that contain one heavy atom to hard X-ray pulses with ultra-high intensities, the response is qualitatively different from what is seen in experiments carried out under less extreme conditions The observed ionization of the molecule is considerably enhanced compared to that of an individual heavy atom under the same conditions, owing to ultrafast charge transfer within the molecule that replenishes the electrons removed from the heavy atom, enabling further ionization Being able to account for this effect will aid further use of X-ray free-electron lasers for studying biological systems X-ray free-electron lasers enable the investigation of the structure and dynamics of diverse systems, including atoms, molecules, nanocrystals and single bioparticles, under extreme conditions1,2,3,4,5,6,7 Many imaging applications that target biological systems and complex materials use hard X-ray pulses with extremely high peak intensities (exceeding 1020 watts per square centimetre)3,5 However, fundamental investigations have focused mainly on the individual response of atoms and small molecules using soft X-rays with much lower intensities8,9,10,11,12,13,14,15,16,17 Studies with intense X-ray pulses have shown that irradiated atoms reach a very high degree of ionization, owing to multiphoton absorption8,12,13,18, which in a heteronuclear molecular system occurs predominantly locally on a heavy atom (provided that the absorption cross-section of the heavy atom is considerably larger than those of its neighbours) and is followed by efficient redistribution of the induced charge14,15,16,17,19,20 In serial femtosecond crystallography of biological objects—an application of X-ray free-electron lasers that greatly enhances our ability to determine protein structure2,3—the ionization of heavy atoms increases the local radiation damage that is seen in the diffraction patterns of these objects21,22 and has been suggested as a way of phasing the diffraction data23,24 On the basis of experiments using either soft or less-intense hard X-rays14,15,16,17,18,19,25, it is thought that the induced charge and associated radiation damage of atoms in polyatomic molecules can be inferred from the charge that is induced in an isolated atom under otherwise comparable irradiation conditions Here we show that the femtosecond response of small polyatomic molecules that contain one heavy atom to ultra-intense (with intensities approaching 1020 watts per square centimetre), hard (with photon energies of 83 kiloelectronvolts) X-ray pulses is qualitatively different: our experimental and modelling results establish that, under these conditions, the ionization of a molecule is considerably enhanced compared to that of an individual heavy atom with the same absorption cross-section This enhancement is driven by ultrafast charge transfer within the molecule, which refills the core holes that are created in the heavy atom, providing further targets for inner-shell ionization and resulting in the emission of more than 50 electrons during the X-ray pulse Our results demonstrate that efficient modelling of X-ray-driven processes in complex systems at ultrahigh intensities is feasible

Abstract: Photoelectron photoion coincidence (PEPICO) spectroscopy could become a powerful tool for the time-resolved study of multi-channel gas phase chemical reactions. Toward this goal, we have designed and tested electron and ion optics that form the core of a new PEPICO spectrometer, utilizing simultaneous velocity map imaging for both cations and electrons, while also achieving good cation mass resolution through space focusing. These optics are combined with a side-sampled, slow-flow chemical reactor for photolytic initiation of gas-phase chemical reactions. Together with a recent advance that dramatically increases the dynamic range in PEPICO spectroscopy [D. L. Osborn et al., J. Chem. Phys. 145, 164202 (2016)], the design described here demonstrates a complete prototype spectrometer and reactor interface to carry out time-resolved experiments. Combining dual velocity map imaging with cation space focusing yields tightly focused photoion images for translationally cold neutrals, while offering good mass resolution for thermal samples as well. The flexible optics design incorporates linear electric fields in the ionization region, surrounded by dual curved electric fields for velocity map imaging of ions and electrons. Furthermore, the design allows for a long extraction stage, which makes this the first PEPICO experiment to combine ion imaging with the unimolecular dissociation rate constant measurements of cations to detect and account for kinetic shifts. Four examples are shown to illustrate some capabilities of this new design. We recorded the threshold photoelectron spectrum of the propargyl and the iodomethyl radicals. While the former agrees well with a literature threshold photoelectron spectrum, we have succeeded in resolving the previously unobserved vibrational structure in the latter. We have also measured the bimolecular rate constant of the CH2I + O2 reaction and observed its product, the smallest Criegee intermediate, CH2OO. Finally, the second dissociative photoionization step of iodocyclohexane ions, the loss of ethylene from the cyclohexyl cation, is slow at threshold, as illustrated by the asymmetric threshold photoionization time-of-flight distributions.

Abstract: We perform first-principles calculations to investigate the electronic and vibrational spectra and the electron mobility of β-Ga2O3. We calculate the electron–phonon scattering rate of the polar optical phonon modes using the Vogl model in conjunction with Fermi's golden rule; this enables us to fully take the anisotropic phonon spectra of the monoclinic lattice of β-Ga2O3 into account. We also examine the scattering rate due to ionized impurities or defects using a Yukawa-potential-based model. We consider scattering due to donor impurities, as well as the possibility of compensation by acceptors such as Ga vacancies. We then calculate the room-temperature mobility of β-Ga2O3 using the Boltzmann transport equation within the relaxation time approximation, for carrier densities in the range from 1017 to 1020 cm−3. We find that the electron–phonon interaction dominates the mobility for carrier densities of up to 1019 cm−3. We also find that the intrinsic anisotropy in the mobility is small; experimental findings of large anisotropy must therefore be attributed to other factors. We attribute the experimentally observed reduction of the mobility with increasing carrier density to increasing levels of compensation, which significantly affect the mobility.

Abstract: Ions produced by cosmic rays have been thought to influence aerosols and clouds. In this study, the effect of ionization on the growth of aerosols into cloud condensation nuclei is investigated theoretically and experimentally. We show that the mass-flux of small ions can constitute an important addition to the growth caused by condensation of neutral molecules. Under atmospheric conditions the growth from ions can constitute several percent of the neutral growth. We performed experimental studies which quantify the effect of ions on the growth of aerosols between nucleation and sizes >20 nm and find good agreement with theory. Ion-induced condensation should be of importance not just in Earth's present day atmosphere for the growth of aerosols into cloud condensation nuclei under pristine marine conditions, but also under elevated atmospheric ionization caused by increased supernova activity.

Abstract: For the first time, the electrospray ionization efficiency (IE) scales in positive and negative mode are united into a single system enabling direct comparison of IE values across ionization modes. This is made possible by the use of a reference compound that ionizes to a similar extent in both positive and negative modes. Thus, choosing the optimal (i.e., most sensitive) ionization conditions for a given set of analytes is enabled. Ionization efficiencies of 33 compounds ionizing in both modes demonstrate that, contrary to general practice, negative mode allows better sensitivity for 46% of such compounds whereas the positive mode is preferred for only 18%, and for 36%, the results for both modes are comparable.

Abstract: In this tutorial it is explained the procedure to analyze an optical emission-line spectrum produced by a nebula ionized by massive star formation. Particularly, it is described the methodology used to derive physical properties, such as electron density and temperature, and the ionic abundances of the most representative elements whose emission lines are present in the optical spectrum. The tutorial is focused on the direct method,based on the measurement of the electron temperature to derive the abundances, given that the ionization and thermal equilibrium of the ionized gas is dominated by the metallicity. The ionization correction factors used to obtain total abundances from the abundances of some of their ions are also given. Finally, some strong-line methods to derive abundances are described. These are used when no estimation of the temperature can be derived, but that can be consistent with the direct method if they are calibrated.

Abstract: A phase-controlled orthogonal two-color (OTC) femtosecond laser pulse is employed to probe the time delay of photoelectron emission in the strong-field ionization of atoms. The OTC field spatiotemporally steers the emission dynamics of the photoelectrons and meanwhile allows us to unambiguously distinguish the main and sideband peaks of the above-threshold ionization spectrum. The relative phase shift between the main and sideband peaks, retrieved from the phase-of-phase of the photoelectron spectrum as a function of the laser phase, gradually decreases with increasing electron energy, and becomes zero for the fast electron which is mainly produced by the rescattering process. Furthermore, a Freeman resonance delay of 140±40 attoseconds between photoelectrons emitted via the 4f and 5p Rydberg states of argon is observed.

Abstract: We review the presence and signatures of the non-equilibrium processes, both non-Maxwellian distributions and non-equilibrium ionization, in the solar transition region, corona, solar wind, and flares. Basic properties of the non-Maxwellian distributions are described together with their influence on the heat flux as well as on the rates of individual collisional processes and the resulting optically thin synthetic spectra. Constraints on the presence of high-energy electrons from observations are reviewed, including positive detection of non-Maxwellian distributions in the solar corona, transition region, flares, and wind. Occurrence of non-equilibrium ionization is reviewed as well, especially in connection to hydrodynamic and generalized collisional-radiative modeling. Predicted spectroscopic signatures of non-equilibrium ionization depending on the assumed plasma conditions are summarized. Finally, we discuss the future remote-sensing instrumentation that can be used for the detection of these non-equilibrium phenomena in various spectral ranges.

Abstract: The plasma chemical splitting of carbon dioxide (CO2) to produce carbon monoxide (CO) in a pulsed corona discharge was investigated from both an experimental and a numerical standpoint. High voltage nanosecond pulses were applied to a stream of pure CO2 and its mixture with argon, and the gaseous products were identified using Fourier transform infrared spectroscopy. Due to the shape of pulses, the process of CO2 splitting was found to proceed in two phases. The first phase is dominated by ionization, which generates a high electron density. Then, during the second phase, direct electron impact dissociation of CO2 contributes to a large portion of CO production. Conversion and energy efficiency were calculated for the tested conditions. The conversions achieved are comparable to those obtained using other high pressure non-thermal discharges, such as dielectric barrier discharge. However, the energy efficiencies were considerably higher, which are favorable to industrial applications that require atmospheric conditions and elevated gas flow rates.

Abstract: We introduce a fully stand-alone version of the Quantum Chemistry Electron Ionization Mass Spectra (QCEIMS) program [S. Grimme, Angew. Chem. Int. Ed., 2013, 52, 6306] allowing efficient simulations for molecules composed of elements with atomic numbers up to Z = 86. The recently developed extended tight-binding semi-empirical method GFN-xTB has been combined with QCEIMS, thereby eliminating dependencies on third-party electronic structure software. Furthermore, for reasonable calculations of ionization potentials, as required by the method, a second tight-binding variant, IPEA-xTB, is introduced here. This novel combination of methods allows the automatic, fast and reasonably accurate computation of electron ionization mass spectra for structurally different molecules across the periodic table. In order to validate and inspect the transferability of the method, we perform large-scale simulations for some representative organic, organometallic, and main-group inorganic systems. Theoretical spectra for 23 molecules are compared directly to experimental data taken from standard databases. For the first time, realistic quantum chemistry based EI-MS for organometallic systems like ferrocene or copper(II)acetylacetonate are presented. Compared to previously used semiempirical methods, GFN-xTB is faster, more robust, and yields overall higher quality spectra. The partially analysed theoretical reaction and fragmentation mechanisms are chemically reasonable and reveal in unprecedented detail the extreme complexity of high energy gas phase ion chemistry including complicated rearrangement reactions prior to dissociation.

Abstract: The definition of ambient ionization is updated from “no sample preparation” to sample preparation proximal and in real time with the ionization and analysis step We differentiate between ambient ionization methods and the direct and hyphenated techniques Ambient ionization has been reviewed many times and we summarise some of the approaches that reviews have taken to categorize the many ambient ionization methods Due to the large number of permutations, frequent redundancy and complexity of the 80+ techniques developed so far, none of the review classifications is successful in classifying all the ambient ionization methods based on the chosen scheme Likewise our classification based on major sample preparation method also fails at finding a good category for every method, but it does highlight the central role that real-time, proximal sample preparation plays in ambient analysis

Abstract: We investigate the ability of time-dependent density functional theory (TDDFT) to capture attosecond valence electron dynamics resulting from sudden X-ray ionization of a core electron. In this special case the initial state can be constructed unambiguously, allowing for a simple test of the accuracy of the dynamics. The response following nitrogen K-edge ionization in nitrosobenzene shows excellent agreement with fourth-order algebraic diagrammatic construction (ADC(4)) results, suggesting that a properly chosen initial state allows TDDFT to adequately capture attosecond charge migration. Visualizing hole motion using an electron localization picture (ELF), we provide an intuitive chemical interpretation of the charge migration as a superposition of Lewis dot resonance structures.

Abstract: Matrix-assisted laser desorption/ionization (MALDI), a soft ionization method, coupling with time-of-flight mass spectrometry (TOF MS) has become an indispensible tool for analyzing macromolecules, such as peptides, proteins, nucleic acids and polymers. However, the application of MALDI for the analysis of small molecules (<700 Da) has become the great challenge because of the interference from the conventional matrix in low mass region. To overcome this drawback, more attention has been paid to explore interference-free methods in the past decade. The technique of applying nanomaterials as matrix of laser desorption/ionization (LDI), also called nanomaterial-assisted laser desorption/ionization (nanomaterial-assisted LDI), has attracted considerable attention in the analysis of low-molecular weight compounds in TOF MS. This review mainly summarized the applications of different types of nanomaterials including carbon-based, metal-based and metal-organic frameworks as assisted matrices for LDI in the analysis of small biological molecules, environmental pollutants and other low-molecular weight compounds.

Abstract: The density normalized effective ionization coefficients and critical breakdown electric field of the Heptafluoro-iso-butyronitrile (Fluoronitriles), and Fluoronitriles-CO2 mixture are investigated using the steady state Townsend (SST) experimental setup, over a range of the density normalized critical electric field (E/N) from 200–1066 Td (E is the electric field and N the gas density). Breakdown voltage measurements are also performed to plot the Paschen curves for small product values (N×d) (d being the electrode gap), to identify the Paschen minimum, and to validate the density normalized critical electric field (E/N)0 when α=η (α and η are the ionization and attachment coefficients, respectively). The influence of electrode surface roughness is also analyzed.

Abstract: This study is focused on the streamer-to-spark transition generated by an overvoltage nanosecond pulsed discharge under atmospheric pressure air in order to provide a quantitative insight into plasma-assisted ignition. The discharge is generated in atmospheric pressure air by the application of a positive high voltage pulse of 35 kV to pin-to-pin electrodes and a rise time of 5 ns. The generated discharge consists of a streamer phase with high voltage and high current followed by a spark phase characterized by a low voltage and a decreasing current in several hundreds of nanosecond. During the streamer phase, the gas temperature measured by optical emission spectroscopy related to the second positive system of nitrogen shows an ultra-fast gas heating up to 1200 K at 15 ns after the current rise. This ultra-fast gas heating, due to the quenching of electronically excited species by oxygen molecules, is followed by a quick dissociation of molecules and then the discharge transition to a spark. At this transition, the discharge contracts toward the channel axis and evolves into a highly conducting thin column. The spark phase is characterized by a high degree of ionization of nitrogen and oxygen atoms shown by the electron number density and temperature measured from optical emission spectroscopy measurements of N+ lines. Schlieren imaging and optical emission spectroscopy techniques provide the time evolution of the spark radius, from which the initial pressure in the spark is estimated. The expansion of the plasma is adiabatic in the early phase. The electronic temperature and density during this phase allows the determination of the isentropic coefficient. The value around 1.2-1.3 is coherent with the high ionization rate of the plasma in the early phase. The results obtained in this study provide a database and the initial conditions for the validation of numerical simulations of the ignition by plasma discharge. © 2017 IOP Publishing Ltd.

Abstract: The effects of electron induced secondary electron (SE) emission from SiO2 electrodes in single-frequency capacitively coupled plasmas (CCPs) are studied by particle-in-cell/Monte Carlo collisions (PIC/MCC) simulations in argon gas at 0.5 Pa for different voltage amplitudes. Unlike conventional simulations, we use a realistic model for the description of electron-surface interactions, which takes into account the elastic reflection and the inelastic backscattering of electrons, as well as the emission of electron induced SEs (δ-electrons). The emission coefficients corresponding to these elementary processes are determined as a function of the electron energy and angle of incidence, taking the properties of the surface into account. Compared to the results obtained by using a simplified model for the electron-surface interaction, widely used in PIC/MCC simulations of CCPs, which includes only elastic electron reflection at a constant probability of 0.2, strongly different electron power absorption and ionization dynamics are observed. We find that ion induced SEs (γ-electrons) emitted at one electrode and accelerated to high energies by the local sheath electric field propagate through the plasma almost collisionlessly and impinge on the opposing sheath within a few nanoseconds. Depending on the instantaneous local sheath voltage these energetic electrons are either reflected by the sheath electric field or they hit the electrode surface, where each γ-electron can generate multiple δ-electrons upon impact. These electron induced SEs are accelerated back into the plasma by the momentary sheath electric field and can again generate δ-electrons at the opposite electrode after propagating through the plasma bulk. Overall, a complex dynamics of γ- and δ-electrons is observed including multiple reflections between the boundary sheaths. At high voltages, the electron induced SE emission is found to strongly affect the plasma density and the ionization dynamics and, thus, it represents an important plasma-surface interaction that should be included in PIC/MCC simulations of CCPs under such conditions.

Abstract: Using movable emissive and floating probes, we determined the plasma and floating potentials of an ionization zone (spoke) in a direct current magnetron sputtering discharge. Measurements were recorded in a space and time resolved manner, which allowed us to make a three-dimensional representation of the plasma potential. From this information we could derive the related electric field, space charge, and the related spatial distribution of electron heating. The data reveal the existence of strong electric fields parallel and perpendicular to the target surface. The largest E-fields result from a double layer structure at the leading edge of the ionization zone. We suggest that the double layer plays a crucial role in the energization of electrons since electrons can gain several 10 eV of energy when crossing the double layer. We find sustained coupling between the potential structure, electron heating, and excitation and ionization processes as electrons drift over the magnetron target. The brightest region of an ionization zone is present right after the potential jump, where drifting electrons arrive and where most local electron heating occurs. The ionization zone intensity decays as electrons continue to drift in the Ez × B direction, losing energy by inelastic collisions; electrons become energized again as they cross the potential jump. This results in the elongated, arrowhead-like shape of the ionization zone. The ionization zone moves in the –Ez × B direction from which the to-be-heated electrons arrive and into which the heating region expands; the zone motion is dictated by the force of the local electric field on the ions at the leading edge of the ionization zone. We hypothesize that electron heating caused by the potential jump and physical processes associated with the double layer also apply to magnetrons at higher discharge power, including high power impulse magnetron sputtering.

Abstract: Context. Deuterium fractionation has been used to study the thermal history of prestellar environments. Their formation pathways trace different regions of the disk and may shed light into the physical structure of the disk, including locations of important features for planetary formation. Aims. We aim to constrain the radial extent of the main deuterated species; we are particularly interested in spatially characterizing the high and low temperature pathways for enhancing deuteration of these species. Methods. We observed the disk surrounding the Herbig Ae star HD 163296 using ALMA in Band 6 and obtained resolved spectral imaging data of DCO+ (J = 3 − 2), DCN (J = 3 − 2) and N2 D+ (J = 3 − 2) with synthesized beam sizes of 0.53 × 0.42, 0.53 × 0.42, and 0.50 × 0.39, respectively. We adopted a physical model of the disk from the literature and use the 3D radiative transfer code LIME to estimate an excitation temperature profile for our detected lines. We modeled the radial emission profiles of DCO+ , DCN, and N2 D+ , assuming their emission is optically thin, using a parametric model of their abundances and our excitation temperature estimates.Results. DCO+ can be described by a three-region model with constant-abundance rings centered at 70 AU, 150 AU, and 260 AU. The DCN radial profile peaks at about 60 AU and N2 D+ is seen in a ring at 160 AU. Simple models of both molecules using constant abundances reproduce the data. Assuming reasonable average excitation temperatures for the whole disk, their disk-averaged column densities (and deuterium fractionation ratios) are 1.6–2.6×1012 cm-2 (0.04–0.07), 2.9–5.2×1012 cm-2 (~0.02), and 1.6–2.5×1011 cm-2 (0.34–0.45) for DCO+ , DCN, and N2 D+ , respectively.Conclusions. Our simple best-fit models show a correlation between the radial location of the first two rings in DCO+ and the DCN and N2 D+ abundance distributions that can be interpreted as the high and low temperature deuteration pathways regimes. The origin of the third DCO+ ring at 260 AU is unknown but may be due to a local decrease of ultraviolet opacity allowing the photodesorption of CO or due to thermal desorption of CO as a consequence of radial drift and settlement of dust grains. The derived D f values agree with previous estimates of 0.05 for DCO+ /HCO+ and 0.02 for DCN/HCN in HD 163296, and 0.3−0.5 for N2 D+ /N2 H+ in AS 209, a T Tauri disk. The high N2 D+ /N2 H+ confirms N2 D+ as a good candidate for tracing ionization in the cold outer disk.

Abstract: We show the first experimental demonstration that electrons being accelerated in a laser wakefield accelerator operating in the forced or blowout regimes gain significant energy from both the direct laser acceleration (DLA) and the laser wakefield acceleration mechanisms. Supporting full-scale 3D particle-in-cell simulations elucidate the role of the DLA of electrons in a laser wakefield accelerator when ionization injection of electrons is employed. An explanation is given for how electrons can maintain the DLA resonance condition in a laser wakefield accelerator despite the evolving properties of both the drive laser and the electrons. The produced electron beams exhibit characteristic features that are indicative of DLA as an additional acceleration mechanism.

Abstract: The formation process of a microdischarge (MD) in both μm- and nm-sized catalyst pores is simulated by a two-dimensional particle-in-cell/Monte Carlo collision model. A parallel-plate dielectric barrier discharge configuration in filamentary mode is considered in ambient air. The discharge is powered by a high voltage pulse. Our calculations reveal that a streamer can penetrate into the surface features of a porous catalyst and MDs can be formed inside both μm- and nm-sized pores, yielding ionization inside the pore. For the μm-sized pores, the ionization mainly occurs inside the pore, while for the nm-sized pores the ionization is strongest near and inside the pore. Thus, enhanced discharges near and inside the mesoporous catalyst are observed. Indeed, the maximum values of the electric field, ionization rate and electron density occur near and inside the pore. The maximum electric field and electron density inside the pore first increase when the pore size rises from 4 nm to 10 nm, and then they decrease for the 100 nm pore, due to a more pronounced surface discharge for the smaller pores. However, the ionization rate is highest for the 100 nm pore due to the largest effective ionization region.

Abstract: We analyze the dynamics of fast electrons in plasmas containing partially ionized impurity atoms, where the screening effect of bound electrons must be included We derive analytical expressions for the deflection and slowing-down frequencies, and show that they are increased significantly compared to the results obtained with complete screening, already at sub-relativistic electron energies Furthermore, we show that the modifications to the deflection and slowing down frequencies are of equal importance in describing the runaway current evolution Our results greatly affect fast-electron dynamics and have important implications, eg for the efficacy of mitigation strategies for runaway electrons in tokamak devices, and energy loss during relativistic breakdown in atmospheric discharges

Abstract: Over the past ten years or so, great advances in our understanding of the dynamics of elementary (bimolecular) polyatomic reactions in the gas-phase have occurred. This has been made possible by critical improvements (a) in crossed molecular beam (CMB) instruments with rotating mass spectrometric detection and time-of-flight analysis, especially following the implementation of soft ionization (by tunable low energy electrons or vacuum-ultraviolet synchrotron radiation) for product detection with increased sensitivity and universal detection power, and (b) in REMPI-slice velocity map ion imaging (VMI) detection techniques in pulsed CMB experiments for obtaining product pair-correlated information through high-resolution measurements directly in the center of mass system. The improved universal CMB method is permitting us to identify all primary reaction products, characterize their formation dynamics, and determine the branching ratios (BRs) for multichannel non-adiabatic reactions, such as those of ground state oxygen atoms, O(3P), with unsaturated hydrocarbons (alkynes, alkenes, dienes). The improved slice VMI CMB technique is permitting us to explore at an unprecedented level of detail, through pair-correlated measurements, the reaction dynamics of a prototype polyatomic molecule such as CH4 (and isotopologues) in its ground state with a variety of important X radicals such as F, Cl, O, and OH. In this review, we highlight this recent progress in the field of CMB reaction dynamics, with an emphasis on the experimental side, but with the related theoretical work, at the level of state-of-the-art calculations of both the underlying potential energy surfaces and the reaction dynamics, noted throughout. In particular, the focus is (a) on the effect of molecular complexity and structure on product distributions, branching ratios and role of intersystem crossing for the multichannel, addition–elimination reactions of unsaturated hydrocarbons with O atoms, and (b) on the very detailed dynamics of the abstraction reactions of ground-state methane (and isotopologues) with atoms (F, Cl, O) and diatoms (OH), with inclusion of also rotational mode specificity in the vibrationally excited methane reactions.

Abstract: Author(s): Muller, A; Bernhardt, D; Borovik, A; Buhr, T; Hellhund, J; Holste, K; Kilcoyne, ALD; Klumpp, S; Martins, M; Ricz, S; Seltmann, J; Viefhaus, J; Schippers, S | Abstract: Single, double, and triple photoionization of Ne+ ions by single photons have been investigated at the synchrotron radiation source PETRA III in Hamburg, Germany. Absolute cross-sections were measured by employing the photon-ion merged-beams technique. Photon energies were between about 840 and 930 eV, covering the range from the lowest-energy resonances associated with the excitation of one single K-shell electron up to double excitations involving one K- and one L-shell electron, well beyond the K-shell ionization threshold. Also, photoionization of neutral Ne was investigated just below the K edge. The chosen photon energy bandwidths were between 32 and 500 meV, facilitating the determination of natural line widths. The uncertainty of the energy scale is estimated to be 0.2 eV. For comparison with existing theoretical calculations, astrophysically relevant photoabsorption cross-sections were inferred by summing the measured partial ionization channels. Discussion of the observed resonances in the different final ionization channels reveals the presence of complex Auger-decay mechanisms. The ejection of three electrons from the lowest K-shell-excited Ne+() level, for example, requires cooperative interaction of at least four electrons.