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High proton conductivity and good chemical stability are keys to development of new electrolytes for PC-SOFCs as the next-future energy generation systems. However, the extensive use of new polycrystalline materials as solid electrolytes is still avoided, since the grain boundary response usually leads to a decrease in total conductivity due to electrical blocking effect. Here, we present our results on the space-charge modeling of impedance spectroscopy data obtained for Ba 3 Ca 1.18 Nb 1.82- x R x O 9-δ proton conducting ceramics, where x  = 0, 0.30 and R = Y 3+ , Gd 3+ , Sm 3+ , Nd 3+ are doping agents. Non-stoichiometric barium calcium niobate perovskites have received much attention as potential solid electrolytes for proton conducting solid oxide fuel cells. We show that despite their increased grain conductivity, the doped ceramics possess Schottky barriers that are higher than those observed for undoped Ba 3 Ca 1.18 Nb 1.82 O 9-δ . In view of the space-charge model, proton depletion at the space-charge layer is the reason for the reduction of grain boundary conductivity in the doped compositions. Our findings are important for the understanding of proton conduction mechanisms in polycrystalline materials, which may allow future optimization of new doped electrolytes based on barium calcium niobate perovskites. [ABSTRACT FROM AUTHOR]

Y-doped BaZrO 3 (BZY) can be deposited epitaxially on MgO (0 0 1) and the considered interface serves as a model system for studying heterointerface properties of protonic conductors. In this study, the defect chemistry of the interface between ZrO 2 -terminated BaZrO 3 (0 0 1) and MgO (0 0 1) was investigated by first-principles calculations and space-charge theory. Segregation energies from the BZY bulk to the interface ZrO 2 and MgO layers were calculated for effectively charged protons, oxygen vacancies, Y-acceptors as well as cation vacancies. Protons were found to exhibit a strong tendency for segregating to the interface, particularly to an oxide ion in the MgO layer, rendering a net positive charge of the interface. According to the applied thermodynamic space-charge models, the interface potential could reach more than 1 V under the Mott-Schottky approximation, with depletion regions extending up to 2 nm into BZY. With fully equilibrated Y-segregation profiles, the interface potential was significantly diminished to about 0.2 V at 573 K and 0.025 bar H 2 O. While the interface was found to be close to saturated by protons under most condition, it was concluded that proton conduction along the interface could not contribute significantly to the in-plane conductivity of BZY films deposited on MgO substrate. [ABSTRACT FROM AUTHOR]

This study demonstrates the hydrothermal treatment of core-shell polytetrafluoroethylene (PTFE) nanoparticles decorated with TiO 2 (h -PTFE@TiO 2); this material exhibits strain-induced local dipole enhancement of the space-charge piezopotential that improves the photocatalytic effect. Under acoustic cavitation, dielectric barrier discharge and electric dipole formation are initiated in voids within the PTFE nanoparticles and at the TiO 2 –PTFE interface. The h -PTFE@TiO 2 nanoparticles (NPs) have exceptionally high catalytic activity in organic dye degradation because of the local dipole enhancement of photoinduced charge separation with a carrier lifetime of 3.14 ns. The observed rate constant of the h- PTFE@TiO 2 NPs in the piezophototronic reaction reaches 0.1388 min−1, which is 17 times that of the photocatalytic reaction (0.0084 min−1) and 66 times that of the piezocatalytic reaction (0.0021 min−1). Computational simulation reveals that large strain-induced space charge piezoelectric polarization induces an internal electric field between the unsaturated PTFE (fluorine vacancies) and TiO 2 surface. The piezopotential has a critical role in band bending at PTFE-TiO 2 interfaces to enhance the electron-hole separation when PTFE is constrained in TiO 2 shells. Results of piezoresponse force microscopy reveal that the piezoelectric coefficient d 33 of PTFE is approximately 79.77 pCN−1. The findings provide insights into catalytic activity for environmental remediation. This study demonstrates the hydrothermal treatment of core-shell polytetrafluoroethylene (PTFE) nanoparticles decorated with TiO2; this material exhibits strain-induced local dipole enhancement of the space-charge piezopotential improves the photocatalytic effect. Computational simulation reveals that large strain-induced space charge piezoelectric polarization induces an internal electric field between the unsaturated PTFE (fluorine vacancies) and TiO2 surface. Considerable local dipole enhancement was observed in the fluorine vacancies of the PTFE, further enhancing the space-charge piezophototronic effect that benefits the performance of the material when used as a photocatalyst. [Display omitted] • Space charge piezoelectric polarization occurs between the fluorine vacancies of PTFE and TiO 2 surface. • The piezoelectric coefficient d 33 of PTFE is approximately 79.77 pCN−1. • A local dipole enhancement of PTFE@TiO 2 photoinduced charge separation with a carrier lifetime of 3.14ns. • Piezopotential modulates the band bending at PTFE-TiO 2 interfaces to enhance electron-hole separation. [ABSTRACT FROM AUTHOR]

We present theoretical and numerical studies of matching sub-femtosecond space-charge-dominated electron bunch into the Laser-plasma Wake Field Accelerator (LWFA) foreseen at the SINBAD facility. The longitudinal space-charge (SC) effect induced growths of the energy spread and longitudinal phase-space chirp are major issues in the matching section, which will result in bunch elongation, emittance growth and spot size dilution. In addition, the transverse SC effect would lead to a mismatch of the beam optics if it were not compensated for. Start-to-end simulations and preliminary optimizations were carried out in order to understand the achievable beam parameters at the entrance of the plasma accelerator. [ABSTRACT FROM AUTHOR]

Acceptor-doped cerium oxides are a promising solid electrolyte material for solid oxide fuel cells (SOFCs) due to their exceptionally high oxygen ion conductivity. Typical solid electrolytes are polycrystalline with a number of grain boundaries, and it is common for grain boundaries to block the motion of mobile oxygen ions as they migrate from one grain to the next. Accordingly, it is important precisely to measure the grain boundary conductivities of doped cerium oxides, particularly at the temperature of relevance (>500 °C). Here, we undertake a quantitative analysis of the transport properties of singly and doubly doped cerium oxides. So that we may precisely extract the grain boundary contribution out of the total conductivity at an elevated temperature (>500 °C), both epitaxial and polycrystalline thin films of the oxides are grown via pulsed layer deposition (PLD) on two different insulating, single-crystal substrates: Al 2 O 3 (0001) and SiO 2 (001), and these are then characterized by a range of analysis tools, in this case TEM, SEM, XRD, ICP-MS and AFM. These samples with controlled microstructures, in combination with in-plane ionic conductivity measurements by impedance spectroscopy as a function of the thickness, temperature and p O 2 , enable us precisely to measure the grain boundary conductivity of the doped ceria at temperatures ranging from 620 to 700 °C. The impact of the number and type of dopants on the transport properties are also explored. [ABSTRACT FROM AUTHOR]

Time-dependence of space-charge built-up at the ITO/organic semiconductor interface has been investigated for the first time using the charge extraction by linearly increasing voltage (CELIV) technique in the dark. It will be demonstrated that space-charge next to an ITO/P3HT interface is extracted during the initial CELIV ramp establishing a non-equilibrium situation whose temporal recovery can be probed by utilizing sequentially prolonged delay times for successive voltage ramps. It will be reported that the build-up time constant for space charge at the ITO/P3HT interface amounts to 230 μs. The dynamics of the relatively slow charge transfer at the interface of the transparent conducting oxide and the organic semiconductor as well as time-limiting processes will be discussed by considering tunneling, thermal detrapping and diffusion of the involved electrons and holes. It will be shown that thermal detrapping of electrons from molecules with their ground state close the center of the HOMO-DOS to vibronic states within the same molecule followed by tunneling to neighboring molecules with their not occupied ground state within the tail states of the DOS is the time limiting process and responsible for the long build-up time. [ABSTRACT FROM AUTHOR]

The influence of space-charge on ion cyclotron resonances and magnetron eigenfrequency in a gas-filled Penning ion trap has been investigated. Off-line measurements with K + 39 using the cooling trap of the WITCH retardation spectrometer-based setup at ISOLDE/CERN were performed. Experimental ion cyclotron resonances were compared with ab initio Coulomb simulations and found to be in agreement. As an important systematic effect of the WITCH experiment, the magnetron eigenfrequency of the ion cloud was studied under increasing space-charge conditions. Finally, the helium buffer gas pressure in the Penning trap was determined by comparing experimental cooling rates with simulations. [ABSTRACT FROM AUTHOR]

Abstract: The present LANSCE injector utilizes two 750-keV Cockcroft–Walton (CW) based injectors for simultaneous injection of H+ and H− beams into 800-MeV accelerator. To reduce long-term operational risks, the new project to replace the existing H+ CW injector with a Radio-Frequency Quadrupole (RFQ) accelerator is underway [1]. The new injector requires a Low-Energy Beam Transport (LEBT). An ion source and 2-solenoid magnetic LEBT have been designed and optimized to transport beams over a wide range of space-charge neutralization and transverse emittance, while allowing sufficient space for diagnostics and a beam deflector. The design layout minimizes the beam size in the LEBT and potential emittance growth due to solenoid aberrations and nonlinear space-charge forces. This paper describes the details of the LEBT design activity. [Copyright &y& Elsevier]

Abstract: This work is devoted to the study of the interaction between pulses of electromagnetic radiation and space-charge waves in laser-plasmas settings. We analyse modes depending only on the co-moving coordinate of the beam frame, but make no a priori assumption on the longitudinal-to-transverse aspect ratio of the pulses. The model thus constructed allows us to investigate regimes where transverse and longitudinal length scales of the pulses are comparable. Resonant and nonresonant excitations of space-charge modes are analyzed and the endurance of trains of solitons against transverse effects is clarified. [Copyright &y& Elsevier]

Abstract: The foremost challenge for Heavy-Ion Fusion (HIF) is achieving sufficiently low emittances and small energy spreads in the presence of intense space-charge, to achieve the high deposition densities necessary for pellet ignition. The University of Maryland Electron Ring (UMER) uses intense low-energy electron beams to access the scaled physics of HIF drivers. In particular, the long path-length propagation in UMER presents an opportunity to study, at realistic scales, the longitudinal beam dynamics and manipulations required for such a driver. With the use of induction modules, as in the ion machines such as NDCX-II, the resulting bunch dynamics show evidence of space-charge waves excited by an initial mismatch between the detailed initial beam distribution at the bunch ends and the applied focusing waveforms, persisting with multiple damped reflections propagating along the bunch flat-top. Using the induction module we are able to suppress space-charge waves with great accuracy, at amplitudes that include wave steepening prior to the formation of solitary wave trains. The longitudinal dynamics largely dominates when no containment fields are applied, coupling through the natural chromaticity of the ring even within the first turn. After subsequent turns, the bunch elongates and wraps the circumference of the machine multiple times; eventually reaching a point of instability that has also been shown through simulation, obtaining excellent agreement when the detailed longitudinal dynamics of the experiment are carefully incorporated into the model. [Copyright &y& Elsevier]

Abstract: NDCX-II, the second neutralized drift compression experiment, is a moderate energy, high current accelerator designed to drive targets for warm dense matter and IFE-relevant energy coupling studies, and to serve as a testbed for high current accelerator physics. As part of the design process, studies were carried out to assess the sensitivities of the accelerator to errors, and to further optimize the design in concert with the evolving pulsed power engineering. The Warp code was used to carry out detailed simulations in both axisymmetric and full 3-D geometry. Ensembles of simulations were carried out to characterize the effects of errors, such as timing jitter and noise on the accelerator waveforms, noise on the source waveform, and solenoid and source offsets. In some cases, the ensemble studies resulted in better designs, revealing operating points with improved performance and showing possible means for further improvement. These studies also revealed a new non-paraxial effect of the final focus solenoid on the beam, which must be taken into account in designing an optimal final focusing system. [Copyright &y& Elsevier]

Abstract: At the radioactive ion-beam facility REX-ISOLDE more than 60 different types of radionuclide ions have been post-accelerated to energies up to 3.15MeV/u within the last years. The transmission efficiency of the system has continually increased with gained operation experience. Apart from striving for the highest possible intensity, the beam purity is also of crucial importance for many experiments. For this reason isobaric contaminant suppression in the low energy stage of REX-ISOLDE has been investigated. Until now the Penning trap system REXTRAP was used solely as a device for bunching the incoming quasi-continuous radioactive ion-beam from ISOLDE and reducing the emittance for efficient injection into the REXEBIS charge breeder. The possibility of operating REXTRAP in a mass-resolving mode and injecting bunched beams from the recently installed radiofrequency quadrupole cooler and buncher ISCOOL has been studied in detail. Results related to transmission efficiency,achieved mass-resolving power, and limitations due to space-charge effects are presented. [ABSTRACT FROM AUTHOR]

Abstract: Pulse radiolysis, a stroboscopic method involving the use of an ultrashort electron bunch and ultrashort light, is essential for the observation of ultrafast reactions. The time resolution of pulse radiolysis depends on the electron bunch length. At Osaka University, a 98-fs electron bunch was generated using a photocathode RF gun linac for the development of femtosecond pulse radiolysis. In order to improve the time resolution of pulse radiolysis, the feasibility of sub-femtosecond electron bunch generation using a photocathode RF gun linac and a magnetic bunch compressor was studied in a simulation. Increase in bunch length due to higher-order effects and bunch charge was investigated using the simulation codes PARMELA and ELEGANT. [Copyright &y& Elsevier]

Abstract: The applicability of extremely thin non-electroneutral membranes for ion-selective electrodes (ISEs) is investigated. A theoretical treatment of potential and concentration profiles in space-charge membranes of ≪1μm thickness is presented. The theory is based on the Nernst–Planck equation for ion fluxes, which reduces to Boltzmann’s formula at equilibrium, and on the Poisson relationship between space-charge density and electric field gradient. A general solution in integral form is obtained for the potential function and the corresponding ion profiles at equilibrium. A series of explicit sub-solutions is derived for particular cases. Membrane systems with up to three different ion species are discussed, including trapped ionic sites and co-extracted ions. Solid-contacted thin membranes (without formation of aqueous films at the inner interface) are shown to exhibit a sub-Nernstian response. The theoretical results are confirmed by numerical simulations using a simplified finite-difference procedure based on the Nernst–Planck–Poisson model, which are shown to be in excellent agreement. [Copyright &y& Elsevier]

Abstract: The FEBIAD (“forced electron beam induced arc discharge”) ion sources are used for the production of radioactive ion beams for a wide range of chemical elements. Their small volume and high operating temperature provide good confinement times and ionization efficiencies. The extracted ion current from a FEBIAD ion source depends on the parameters of the plasma created inside (density, temperature, potential), parameters which are themselves dependent on the input gas pressure and composition. Within the framework of the HIGHINT Marie Curie and the EURISOL DS programs, investigations are ongoing for high power direct targets, which can accommodate up to 100kW incoming proton beam power. For such systems, the quantity of impurities entering the ion source will increase, thus leading to a change of the plasma characteristics. The gas flow coming from the target will exceed the buffer gas flow, and the ionization of the trace elements will be controlled by the gas composition released from the target. An insight on the complex phenomena taking place in the ion source can be achieved using a Particle-In-Cell code (VORPAL, “versatile, object-oriented, relativistic, plasma analysis code with lasers”), which can simulate the dynamics of neutral and charged particles inside the plasma: ionization, recombination and charge exchange phenomena, secondary emissions and sputtering. [Copyright &y& Elsevier]

Abstract: We propose a technique for timing an X-ray free-electron laser (XFEL) to a high-power conventional laser with femtosecond accuracy, yielding the relative jitter between pump and X-ray probe, and allowing sorting of experimental results over a certain time window. The same electron bunch is used to produce both an XFEL pulse and an ultrashort optical pulse by means of an optical radiator downstream of the X-ray undulator. Being produced by the same electron bunch, these pulses are perfectly synchronized. Cross-correlation techniques will allow to determine relative jitter between the optical pulse (and, thus, the XFEL pulse) and a pulse from an external pump-laser. Technical realization of the proposed timing scheme uses an optical-replica synthesizer setup to be installed after the final bunch-compression stage of the XFEL for electron bunch diagnostics purposes. A number of critical issues are quantitatively analyzed. [Copyright &y& Elsevier]

Abstract: Some interfaces in semiconductors or insulators structurally cause a valence mismatch, which leads to a two-dimensional space charge that must be balanced by localised or mobile charge carriers. Screening by mobile electrons presents a lot of theoretical as well as practical interests. However it is extremely rare, so that we are aware of only one case, on which we focus here: the (001) interface between LaAlO3 and TiO2-terminated SrTiO3. Theoretically, this interface between two insulators is positively charged. Electron conductivity is observed in this system, but whether it is associated with the interface screening or an extrinsic unintended doping is not yet settled. Here, we use the literature and our own numerical and practical experiments to discuss the physics of this system. [Copyright &y& Elsevier]

Abstract: A radiofrequency electron gun joined to a compressor can generate trains of THz sub-picosecond electron pulses by illuminating the photocathode with trains of laser pulses. Assuming a prompt electron emission, each laser pulse generates an electron disk at the cathode. The disk train evolves toward a slightly modulated slug having a peculiar sawtooth energy modulation. This kind of energy modulation is transformed into a density modulation within a velocity-bunching compressor recovering at a good extent the initial multi-disk profile. The electron beam evolution is analyzed through simulations looking at its features as function of pulse and frequency characteristics of the laser and of the accelerator parameters. [Copyright &y& Elsevier]

Abstract: The deposition of unipolarly charged aerosol particles by simultaneous Brownian diffusion and electrostatic dispersion (space-charge) in laminar flow tubes has been modelled in two different ways. In the first approach, the rigorous transport equation has been solved numerically under the restriction of negligible axial components of the particle Brownian motion and of the space-charge electric field. The thus calculated theoretical penetrations agree satisfactorily with the experimental results obtained for air ions. Second, the system has also been modelled from a phenomenological point of view, based on the fact that deposition by diffusion and space-charge follows first- and second-order kinetics, respectively. The latter approach yields a simple and practical equation correlating particle penetration with tube geometry, aerosol flow rate, and particle mobility and concentration. [Copyright &y& Elsevier]

Abstract: We propose a theoretical investigation of a new principle of bi-stable MEMS based on the remnant electrostatic force generated by the space-charge density that builds up when two semiconductors, having different doping densities, are brought into contact. Following a physical description of the device, a complete analytical formulation of some key parameters such as the pull-in and pull-out voltages could be obtained. The model reveals that both closed and open configurations of the switch MEMS can be stable states at zero applied voltage. The impact of the different technological parameters is also discussed in details, supporting that the so-called junction-MEMS might be an interesting alternative to address bi-stability in MEMS, still remaining fully compatible with the standard microelectronics technologies. [Copyright &y& Elsevier]

Abstract: The modulation of the betatron tune by the space-charge force as a result of synchrotron oscillation is studied. A one-turn-map model is devised and is applied to the various designs of the International Linear Collider damping ring. [Copyright &y& Elsevier]

Abstract: Much of the theory and experimentation concerning creation of a high-brightness electron beam from a photocathode, and then applying emittance compensation techniques, assumes that one must strive for a uniform density electron beam, having a cylindrical shape. On the other hand, this shape has large nonlinearities in the space-charge field profiles near the beam''s longitudinal extrema. These nonlinearities are known to produce both transverse and longitudinal emittance growth. On the other hand, it has recently been shown by Luiten that by illuminating the cathode with an ultra-short laser pulse of appropriate transverse profile, a uniform density, ellipsoidally shaped bunch is dynamically formed, which then has linear space-charge fields in all dimensions inside of the bunch. We study here this process, and its marriage to the standard emittance compensation scenario that is implemented in most recent photoinjectors. It is seen that the two processes are compatible, with simulations indicating a very high brightness beam can be obtained. The robustness of this scheme to systematic errors is examined. Prospects for experimental tests of this scheme are discussed. [Copyright &y& Elsevier]

Abstract: We developed an exact analytical treatment for space-charge waves within a relativistic electron beam in terms of (self-reproducing) propagating eigenmodes. This result is of obvious theoretical relevance as it constitutes one of the few exact solution for the evolution of charged particles under the action of self-interactions. It also has clear numerical applications in particle accelerator physics where it can be used as the first self-consistent benchmark for space-charge simulation programs. Today our work is of practical relevance in FEL technology in relation with all those schemes where an optically modulated electron beam is needed and with the study of longitudinal space-charge instabilities in magnetic bunch compressors. [Copyright &y& Elsevier]

Abstract: A magnetic alloy (MA)-loaded cavity has been installed in Heavy Ion Medical Accelerator in Chiba (HIMAC). A beam study with a new Direct Digital Synthesis (DDS) system has been performed. The DDS system can generate multi-harmonic RF that includes up to 3 different RF frequencies. The multi-harmonic RF is amplified by a solid state and final amplifiers. These harmonic frequencies are in the band width of the MA RF system. Beam acceleration was performed by the system, and the acceleration efficiency was improved by both dual and triple harmonic RF. [Copyright &y& Elsevier]

Abstract: The High-Current Experiment (HCX) at Lawrence Berkeley National Laboratory is part of the US program to explore heavy-ion beam transport at a scale representative of the low-energy end of an induction linac driver for fusion energy production. Four pulsed magnetic quadrupoles are being used to study gas and electron effects with a 0.2A, 1-MeV K+ beam. The magnets, originally designed and built for a prototype pulsed magnetic quadrupole array, have an elliptical beam tube (6×10cm) and iron yoke. The magnet coil and field length are ≈31cm, and operating gradients are 10–40T/m. To establish that the field quality of the prototype quadrupoles is satisfactory for the experiments, a 1-cm pickup loop was used to measure the flux B r(θ) at the magnet mid-plane and also at the lead and return ends. A longer probe was used to measure the integrated flux of Bθ (θ) along the magnet. The field quality appears satisfactory for the short transport experiments through these quadrupoles. [Copyright &y& Elsevier]

Abstract: The transport of intense beams for heavy-ion inertial fusion demands tight control of beam characteristics from the source to the target. The University of Maryland Electron Ring (UMER), which uses a low-energy (10keV), high-current electron beam to model the transport physics of a future recirculator driver, employs real-time beam characterization and control in order to optimize beam quality throughout the strong focusing lattice. We describe the main components and operation of the diagnostics/control system in UMER. It employs phosphor screens, real-time image analysis, quadrupole scans and electronic skew correctors. The procedure is not only indispensable for optimum transport over a long distance, but also provides important insights into the beam physics involved. We discuss control/optimization issues related to beam steering, quadrupole rotation errors and rms envelope matching. [Copyright &y& Elsevier]

Abstract: The need to reach high temperatures in an inertial fusion energy (IFE) target (or a target for the study of High Energy Density Physics, HEDP) requires the ability to focus ion beams down to a small spot. System models indicate that within the accelerator, the beam radius will be of the order of centimeters, whereas at the final focal spot on the target, a beam radius of the order of millimeters is required, so radial compression factors of order ten are required. The IFE target gain (and hence the overall cost of electricity) and the HEDP target temperature are sensitive functions of the final spot radius on target. Because of this sensitivity, careful attention needs to be paid to the spot radius calculation. We review our current understanding of the elements that enter into a systems model (such as emittance growth from chromatic, geometric, and non-linear space charge forces) for the final focus based on a quadrupolar magnet system. [Copyright &y& Elsevier]

Abstract: Modern diagnostic techniques provide detailed information on beam conditions in injector, transport, and final focus experiments in the HIF-VNL. Parameters of interest include beam current, beam energy, transverse and longitudinal distributions, emittance, and space charge neutralization. Imaging techniques, based on kapton films and optical scintillators, complement and, in some cases, may replace conventional techniques based on slit scans. Time-resolved optical diagnostics that provide 4-D transverse information on the experimental beams are in operation on the existing experiments. Current work includes a compact optical diagnostic suitable for insertion in transport lines, improved algorithms for optical data analysis and interpretation, a high-resolution electrostatic energy analyzer, and an electron beam probe. A longitudinal diagnostic kicker generates longitudinal space-charge waves that travel on the beam. Time of flight of the space-charge waves and an electrostatic energy analyzer provide an absolute measure of the beam energy. Special diagnostics to detect secondary electrons and gases desorbed from the wall have been developed. [Copyright &y& Elsevier]

Abstract: The High Current Experiment (HCX) at Lawrence Berkeley National Laboratory is part of the US program to explore heavy-ion beam transport at a scale representative of the low-energy end of an induction linac driver for fusion energy production. The primary mission of this experiment is to investigate aperture fill factors acceptable for the transport of space-charge-dominated heavy-ion beams at high space-charge intensity (line charge density up to ∼0.2μC/m) over long pulse durations (4μs) in alternating gradient focusing lattices of electrostatic or magnetic quadrupoles. The experiment also contributes to the practical baseline knowledge of intense beam manipulations necessary for the design, construction and operation of a heavy ion driver for inertial fusion. This experiment tests transport issues resulting from nonlinear space-charge effects and collective modes, beam centroid alignment and beam steering, matching, image charges, halo, electron cloud effects, and longitudinal bunch control. We first present the results for a coasting 1MeV K+ ion beam transported through the first ten electrostatic transport quadrupoles, measured with optical beam-imaging and double-slit phase-space diagnostics. This includes studies at two different radial fill factors (60% and 80%), for which the beam transverse distribution was characterized in detail. Additionally, beam energy measurements will be shown. We then discuss the first results of beam transport through four pulsed room-temperature magnetic quadrupoles (located downstream of the electrostatic quadrupoles), where the beam dynamics become more sensitive to the presence of secondary electrons. [Copyright &y& Elsevier]

A technique is described of simulating thermionic cathodes in the Boundary Element Method by replacing the space charges in the cathode region by a set of thin sheets of charge. These sheets are subdivided into segments in the same way that the cathode itself is subdivided. This technique has been applied to cathodes that have zero and non-zero temperature T. It is shown that for T>0 the potential and position of the virtual cathode is well reproduced. Planar and non-planar cathodes are considered as well as unsaturated cathodes. [Copyright &y& Elsevier]

We present a simple experimental setup and an associated method enabling both the non-destructive diagnosis and the calculation of the beam evolution in a low energy medium current electron beam channel, where the space-charge and emittance effects are comparable. The diagnosis makes use of an axially symmetric magnetic lens while a second lens is added to increase the flexibility in the beam processing. The paper emphasizes the three steps involved in the method: the evaluation of the lenses'' magnetic field by numerical simulation, the beam diagnosis, and the computation of the beam envelope. The calculation of the magnetic field is based on the finite element method. Subsequently, the beam parameters at the electron source exit – emittance and cross-over radius and position – are found with the modified three gradient method. Finally, the beam dynamics are modeled with the K–V equation adapted for the particular case of axial symmetry. The results obtained in this paper can be used to optimize technological processes, such as welding, hardening, cladding, and surface alloying. [Copyright &y& Elsevier]

We report on the results of beam transport experiments at the University of Maryland Electron Ring (UMER) over a distance of approximately 4 m. The experiments involve a 10 keV, 25–100 mA, 100 ns electron beam in a lattice consisting of one short solenoid, 24 printed-circuit magnetic quadrupole lenses, and a number of bending and steering dipole magnets. The diagnostics include capacitive beam-position monitors, phosphor screens, slit-wire emittance meters and others. We discuss the conditions required for matching the space-charge-dominated beam into the UMER lattice, as well as emittance measurements and initial studies of longitudinal dynamics in the ring. [Copyright &y& Elsevier]

Supported by analytical considerations and experimental verification, we demonstrate that thermionic electron current under partial space-charge condition follows the three-halves power Child–Langmuir law with a proportionality coefficient, j, that is material dependent and characterizes the emitter unambiguously. Such a partial space-charge regime has been assessed through experiments on parallel plane diodes with boron-doped diamond films (with four different B/C ratios) as electron emitters at temperature of 1000 K. All current measurements have indicated a 3/2-power relationship on voltage but with distinct, material dependent coefficients j that were found to decrease with the work function of the samples tested. [Copyright &y& Elsevier]

Synthetic polymers are demonstrated to be very useful probes for the characterization of a newly constructed external ion source matrix-assisted laser desorption and ionization quadrupole ion trap mass spectrometer (MALDI-ITMS). Mass discrimination effects and space-charge-induced mass shifts can readily be identified and quantified with these synthetic polymer probes. Mass dependencies in the trapping efficiency were evaluated by comparison of measurements of poly(methyl methacrylate) (PMMA) standards in the mass range m/z 400–3400 with MALDI-TOF-MS measurements of the same samples. This established the optimal experimental conditions for the analysis of mass ranges smaller than 1000 u with negligible mass discrimination. This is demonstrated on the basis of measurements on a tri-block copolymer of poly(ethylene oxide) poly(propylene oxide). As expected, mass measurements were highly influenced by the magnitude of the trapped ion population. Using poly(ethylene glycol) standards we were able to quantify these mass shifts as a function of the total ion load. Consequently, reproducible results can only be obtained by reproducing the total space-charge in the trap. In MALDI experiments, this can be achieved by tuning the laser power just above threshold. This approach allowed the mass determination of three different end groups in a complex Jeffamine D2000 sample with an accuracy of better than 0.1 u. [Copyright &y& Elsevier]

The piezoelectric (PZ) effect in strained semiconductor heterostructures can be used as an additional degree of freedom in designing novel heterostructures with desired optoelectronic properties. After a short review of previous work in the field, we discuss two examples in which the presence of the PZ field is either beneficial or unwelcome. First, we present a wavelength-tunable laser diode whose tuning mechanism is based on the quantum confined Stark effect and we show that the tuning range of the device can be significantly enhanced if the active quantum well contains a PZ field. Next, we discuss the case of nitride heterostructures where unwanted polarization-induced electric fields limit seriously their performance in optoelectronic applications. We show that the use of quaternary nitrides can help circumvent this problem. [Copyright &y& Elsevier]

This paper shows that In13Se87 and In20Se80 thin films can be prepared by thermal evaporation technique. Current density–voltage (J–V) characteristics and thermally stimulated currents have been obtained. Coplanar silver electrodes were used. At low voltages, the current density behavior suggests ohmic conductivity, while at higher voltages, a region of space-charge-limited current conduction was observed. The analysis of the temperature dependence of J–V curves yields the following parameters: barrier height ϕb, energy of activation trap Et, trapping factor θ, trap density Nt, and concentration of the free carriers, n0. The transition from ohmic to square law behavior was used to calculate all of these parameters. It was found that by increasing the In at% the trap density increased from 1.62×1015 to 3.12×1017 cm−3 and the trap activation energy Et, increases from 0.062 to 0.087 eV.The optical absorption of these films was studied in the UV-VIS spectral range and the value of the optical energy gap was determined. The results of changes in the J–V characteristics and optical energy gap are discussed using a simple consideration, based on average coordination numbers, cohesive energy and bond energies. [Copyright &y& Elsevier]

The effects of high density electric current pulses (103–106 A cm−2) on the flow stress of metals at low homologous temperatures and of a modest external electric field on the flow stress of fine-grained oxides at high temperatures is presented. The results in both cases are evaluated in terms of thermally-activated plastic deformation processes. In the case of the metals, the influence of an electron wind on each of the parameters in the equation for the thermally-activated motion of dislocations was determined, the largest effect being on the pre-exponential. The derived electron wind push coefficient was one or more orders of magnitude larger than the value normally accepted for the electron drag coefficient. In the case of the oxides, the substantial effect of an applied electric field on the flow stress was evaluated in terms of its influence on the electrochemical potential of vacancies in the space-charge cloud adjacent to the grain boundaries. Both the derived space-charge cloud width and the electric potential/stress parameter Δ∅/Δσ are in reasonable accord with theoretical predictions. [Copyright &y& Elsevier]

• Comprehensive theoretical framework to analyze microgap thermionic power generation. • Gap-dependent space-charge, image-charge, and near-field radiation are considered. • The optimum gap distance demonstrated to strongly depend on the heat input. • Interestingly, high-power output observed at retarding region for high heat inputs. • Electron reflection caused noticeable drop in performance of wide-gap TECs. We present a comprehensive model to fully characterize the behavior of thermionic energy conversion devices subject to constant heat flux inputs. Thermionic energy converters (TECs) have recently gained enormous attention mainly due to technological advances enabling the fabrication of converters with micro/nanometer interelectrode gaps. The reduced gap appeared to solve the long-lasting issue of negative space-charge build-up within TECs. However, the decrease in gap distance leads to the appearance of new physics in the energy interactions between the two electrodes, such as the image-charge effect and near-field thermal radiation. The intertwined energy exchange mechanisms require a deeper look and a systematic approach for accurately modeling the performance of TECs in the micro/nanoscales, especially in practical applications where the device is exposed to external energy sources such as concentrated solar power. We conducted a steady-state energy balance analysis to calculate the operating temperatures of the electrodes by considering constant heat flux inputs (such as concentrated solar energy) to the emitter and various cooling rates of the collector. The potential barrier profile within the interelectrode gap, the net current density, and the power output are subsequently calculated for a TEC with electrodes made of tungsten with and without electron reflection. The optimal values of the gap distance are also reported for various input scenarios revealing considerable deviation from the previously reported ones. An overall efficiency of 38.3 % with a power output of 19.2 kW/m2 can be reached for a TEC with perfectly absorbing electrodes at the gap distance of 6 μ m operating under a heat flux input of 50 kW/m2 and convective heat transfer coefficient of 500 W/m2K. We believe that the present work provides an unabridged framework for the rigorous analysis of thermionic power generation with (sub) micrometer interelectrode distances and offers substantial insight into the design and characterization of TECs. [ABSTRACT FROM AUTHOR]

In a LIGHT project experiment at GSI, the effect of space–charge on the quality of proton beam profile and focal line of permanent magnet quadrupole (PMQ) was investigated experimentally and numerically. In our experiment, the tracking of the real beam (electrons and protons) and pure proton beam (electrons blocked close to the source by a Cu foil) were compared in two schemes: with a mere pinhole collimation and with an additional PMQ. A generated beam distribution close to the experimental results was implemented in TraceWin simulations. In PMQ scheme, a generated field region divided into finite cubic grids with 10 μ m each side length was used to track the co-propagating electrons. The space–charge effect of the multispecies (protons and electrons) beam was calculated using an electrostatic model. The beam profile expansion in free space and at PMQ focal line was confirmed by simulation. [ABSTRACT FROM AUTHOR]

Schottky-pn diodes (SPNDs) have been proposed as a novel solution allowing high current density in the lightly-doped drift regions of diamond and other semiconductors where shallow doping is difficult. Here we show, using simulations, that while SPNDs may have applications in low voltage diamond devices, development of high voltage devices is precluded by space-charge limited conduction physics inherent to the SPND structure at high current densities. For designed blocking voltages above 1000 V, simulations indicate that SPNDs are dramatically outperformed by properly designed conventional Schottky diodes. Unlabelled Image • Standard diamond Schottky p-n diode designs will not scale to high voltages. • Mott-Gurney Law for space-charge limited current predicts high on-state voltage drops for high voltage designs. • Hybrid devices incorporating SPND concepts may be feasible at high voltages. [ABSTRACT FROM AUTHOR]

We developed a model to calculate the stability of Gaussian beam distributions with non-linear space-charge forces in the presence of random and skew-quadrupole errors. The effect of the space-charge force on the beam matrix is calculated analytically including full cross-plane coupling in 4D phase space, which allows us to perform fast parameter studies. For stability analysis, we find the fixed points of the beam including the space-charge forces and construct a Jacobi-matrix by slightly perturbing the periodic solution. The stability of envelope oscillations is inferred by eigenvalue analysis. Furthermore, we employ envelope tracking as a complementary method and compare the results of the eigenvalue analysis with FFT data from the tracked envelope. The non-linearity of the space-charge force in combination with lattice errors and beam coupling opens up for envelope-lattice resonances and envelope coupling resonances. Hitting these resonances leads to envelope blow-up, causing an effective beam mismatch. Therefore, we finally examine the effect of beam mismatch on the envelope tune-shift and its stability. [ABSTRACT FROM AUTHOR]

Tracking capabilities in Time Projection Chambers (TPCs) are strongly dictated by the homogeneity of the drift field. Ion back-flow in various gas detectors, mainly induced by the secondary ionization processes during amplification, has long been known as a source of drift field distortion. Here, we report on beam-induced space-charge effects from the primary ionization process in the drift region in low-energy nuclear physics experiment with Active Target Time Projection Chamber (AT-TPC). A qualitative explanation of the observed effects is provided using detailed electron transport simulations. As ion mobility is a crucial factor in the space-charge effects, the need for a careful optimization of gas properties is highlighted. The impact of track distortion on tracking algorithm performance is also discussed. [ABSTRACT FROM AUTHOR]