Muon studies of Li+ diffusion in LiFePO4 nanoparticles of different polymorphs

The lithium diffusion in nanostructured olivine LiFePO4 has been investigated for the first time using muon spectroscopy (μSR). A microwave-assisted approach has been employed for nanoparticle preparation, where the choice of solvent is shown to play an important role in determining particle morphology and crystal chemistry. Two phases have been obtained: Pnma LiFePO4 and the high pressure Cmcm phase. The Li+ diffusion behaviour is strikingly different in both phases, with DLi of 6.25 × 10−10 cm2 s−1 obtained for Pnma LiFePO4 in good agreement with measurements of bulk materials. In contrast, Li+ diffusion is impeded with the addition of the high pressure Cmcm phase, with a lower DLi of 3.96 × 10−10 cm2 s−1 noted. We have demonstrated an efficient microwave route to nanoparticle synthesis of positive electrode materials and we have also shown μSR measurements to be a powerful probe of Li+ diffusion behaviour in nanoparticles

Results from the Scaled Final Focus Experiment

Vacuum ballistic focusing is the straightforward method to obtain a heavy ion beam spot size necessary to drive an inertial confinement fusion target. The beam is first expanded then focused to obtain the desired convergence angles at the exit of the last element. This is done in an attempt to achieve a focal spot size in which emittance is the limiting factor; however, aberrations and space charge will influence the spot radius. Proper scaling of particle energy, mass, beam current, beam emittance, and magnetic field replicates the dynamics of a full driver beam at the focus in a small laboratory experiment. By scaling the beam current to ~;100 mu A, 160 keV Cs+ has been used to study experimentally a proposed driver design at one-tenth scale. Once a nominal focal spot is achieved, the magnet strengths are deliberately de-tuned to simulate the effect of an off-momentum slice of the beam. Additionally, several methods will be used to inject electrons into beam following the last focusing element in order to study the neutralization of space charge and its effect on the focus. Transverse phase space and beam current density measurements at various stages of the focus will be presented as well spot size measurements from the various trials. This data will be compared to the results of a PIC model of the experiment

Results from the Scaled Final Focus Experiment

Vacuum ballistic focusing is the straightforward method to obtain a heavy ion beam spot size necessary to drive an inertial confinement fusion target. The beam is first expanded then focused to obtain the desired convergence angles at the exit of the last element. This is done in an attempt to achieve a focal spot size in which emittance is the limiting factor; however, aberrations and space charge will influence the spot radius. Proper scaling of particle energy, mass, beam current, beam emittance, and magnetic field replicates the dynamics of a full driver beam at the focus in a small laboratory experiment. By scaling the beam current to ~;100 mu A, 160 keV Cs+ has been used to study experimentally a proposed driver design at one-tenth scale. Once a nominal focal spot is achieved, the magnet strengths are deliberately de-tuned to simulate the effect of an off-momentum slice of the beam. Additionally, several methods will be used to inject electrons into beam following the last focusing element in order to study the neutralization of space charge and its effect on the focus. Transverse phase space and beam current density measurements at various stages of the focus will be presented as well spot size measurements from the various trials. This data will be compared to the results of a PIC model of the experiment

The Adiabatic Matching Section Solution for the Source Injector

Typical designs for a Heavy Ion Fusion Power Plant require the source injector to deliver 100 beams, packed into an array with a spacing of 7 cm. When designing source injectors using a single large aperture source for each beam, the emitter surfaces are packed into an array with a spacing of 30 cm. Thus, the matching section of the source injector must not only prepare the beam for transport in a FODO lattice, but also funnel the beams together. This can be accomplished by an ESQ matching section in which each beam travels on average at a slight angle to the axis of the quadrupoles and uses the focussing effect of the FODO lattice to maintain the angle. At the end of the matching section, doublet steering is used to bring the beams parallel to each other for injection into the main accelerator. A specific solution of this type for an 84-beam source injector is presented. PACS: 41.75.Ak,41.85.Ar, 41.85.J

The Adiabatic Matching Section Solution for the Source Injector

Typical designs for a Heavy Ion Fusion Power Plant require the source injector to deliver 100 beams, packed into an array with a spacing of 7 cm. When designing source injectors using a single large aperture source for each beam, the emitter surfaces are packed into an array with a spacing of 30 cm. Thus, the matching section of the source injector must not only prepare the beam for transport in a FODO lattice, but also funnel the beams together. This can be accomplished by an ESQ matching section in which each beam travels on average at a slight angle to the axis of the quadrupoles and uses the focussing effect of the FODO lattice to maintain the angle. At the end of the matching section, doublet steering is used to bring the beams parallel to each other for injection into the main accelerator. A specific solution of this type for an 84-beam source injector is presented. PACS: 41.75.Ak,41.85.Ar, 41.85.J

Multiple scattering in scanning helium microscopy

Using atom beams to image the surface of samples in real space is an emerging technique that delivers unique contrast from delicate samples. Here, we explore the contrast that arises from multiple scattering of helium atoms, a specific process that plays an important role in forming topographic contrast in scanning helium microscopy (SHeM) images. A test sample consisting of a series of trenches of varying depths was prepared by ion beam milling. SHeM images of shallow trenches (depth/width 1) exhibited an enhanced intensity. The scattered helium signal was modeled analytically and simulated numerically using Monte Carlo ray tracing. Both approaches gave excellent agreement with the experimental data and confirmed that the enhancement was due to localization of scattered helium atoms due to multiple scattering. The results were used to interpret SHeM images of a bio-technologically relevant sample with a deep porous structure, highlighting the relevance of multiple scattering in SHeM image interpretation

Experiments at The Virtual National Laboratory for Heavy Ion Fusion

An overview of experiments is presented, in which the physical dimensions, emittance and perveance are scaled to explore driver-relevant beam dynamics. Among these are beam merging, focusing to a small spot, and bending and recirculating beams. The Virtual National Laboratory for Heavy Ion Fusion (VNL) is also developing two driver-scale beam experiments involving heavy-ion beams with I(sub beam) ~; 1 Ampere to provide guidance for the design of an Integrated Research Experiment (IRE) for driver system studies within the next 5 years. Multiple-beam sources and injectors are being designed and a one-beam module will be built and tested. Another experimental effort will be the transport of such a beam through ~;100 magnetic quadrupoles. The experiment will determine transport limits at high aperture fill factors, beam halo formation, and the influence on beam properties of secondary electron Research into driver technology will be briefly presented, including the development of ferromagnetic core materials, induction core pulsers, multiple-beam quadrupole arrays and plasma channel formation experiments for pinched transport in reactor chambers

Experiments at The Virtual National Laboratory for Heavy Ion Fusion

An overview of experiments is presented, in which the physical dimensions, emittance and perveance are scaled to explore driver-relevant beam dynamics. Among these are beam merging, focusing to a small spot, and bending and recirculating beams. The Virtual National Laboratory for Heavy Ion Fusion (VNL) is also developing two driver-scale beam experiments involving heavy-ion beams with I(sub beam) ~; 1 Ampere to provide guidance for the design of an Integrated Research Experiment (IRE) for driver system studies within the next 5 years. Multiple-beam sources and injectors are being designed and a one-beam module will be built and tested. Another experimental effort will be the transport of such a beam through ~;100 magnetic quadrupoles. The experiment will determine transport limits at high aperture fill factors, beam halo formation, and the influence on beam properties of secondary electron Research into driver technology will be briefly presented, including the development of ferromagnetic core materials, induction core pulsers, multiple-beam quadrupole arrays and plasma channel formation experiments for pinched transport in reactor chambers