A comparison is made between the experimental and theoretical behaviour of the H" beam in the TRIUMF central region cyclotron. The axial injection process and the first six accelerated turns are studied in detail. In order to optimize the cyclotron performance the phase space emittance of the beam at the injection line exit must be matched to the central region acceptances. To this end,a theoretical study was made of the ion optical properties of the injection elements: the magnet bore, the spiral electrostatic inflector, the electrostatic deflector and the first radio-frequency accelerating gap. In many cases these results were confirmed by experimental observations. It was also shown theoretically that by a suitable choice of the accelerating gap, under optimum conditions, 10% of the injected beam can be directed within the radial acceptance and 30% within the vertical acceptances. The effects of a chopper and buncher in the injection line were also measured. A minimum pulse length of approximately 2.5 nsec was obtained with a bunching factor of 3-0. To accelerate a beam to full radius, vertical steering had at first to be provided by means of asymmetrically-powered trim coils and electrostatic deflection plates for each turn. The steering required is known to be consistent with the effects of magnetic field asymmetries and dee misalignments measured later. The size and shape of the vertical beam envelopes were found to be consistent with theory. The vertical tune vz was estimated to be 0.17 ± 0.03 for 20 deg phase ions. This agreed with the predicted value of 0.17- The transition phase which separates the vertically-focused and defocused phases was estimated to be -3 ± 3 deg, while the predicted value was 0 deg. The radial beam diagnostic techniques used for determining proper centring and isochronous operating conditions are discussed. With these techniques it was possible to centre a 30 deg phase interval to within 0.15 in., which was the approximate uncertainty in our measurements. A simplified treatment of radia 1 - longitudinal coupling is given and used to explain qualitatively the behaviour of a small emittance beam. The effects of space charge on the first six accelerated turns are calculated. For a beam occupying a phase width of 30 deg, these effects are predicted to be negligible for average accelerated currents below 100 uA. The experimental observations made on high-current beams are described.; prior to the shutdown of the cyclotron beams of up to 1^0 uA average current were accelerated. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

In order to design a successful space system, the unique challenges of the space environment it will operate in must be considered during the design process. Atomic oxygen (AO) is a detrimental environmental effect found in Low Earth Orbit (LEO) that affects spacecraft surfaces by oxidizing and eroding material over time, particularly polymers. Carbon fiber/epoxy composites are a commonly used spacecraft material affected by AO exposure. Carbon composites are used as a structural material, such as on solar panels; their large surface area therefore is a potential contamination source to sensitive components. The Space Environments and Testing Lab at California Polytechnic State University, San Luis Obispo (Cal Poly SLO) includes an apparatus that can simulate AO in the LEO environment. This apparatus was used to expose carbon composite samples to AO before being tested for short beam strength to measure the effect on material properties. Results showed no significant difference in short beam strength for a 24-hour AO exposure compared to unexposed samples, but a 4% decrease for samples with a 48-hour exposure. Previous work at Cal Poly SLO found that AO-exposed composite generated particulate contaminants. Tape lift tests and mass measurements of samples were conducted before and after AO exposure to characterize the particulate contamination generated and percent mass loss. It was found that AO exposure increased the percent mass loss by 1.5% for 24-hour exposure and 3% for 48-hour exposure. The tape lift percent area coverage increased by 2.5% near sample ends and 0.35% in the middle after AO exposure.

The spectral phase of high harmonic and attosecond pulses is typically shaped by the interaction of the recollision electron with the strong field in the continuum. However, the phase of the transition moment coupling bound and continuum states can be significant in shaping the emitted radiation. The measurement of transition moment phase shifts can reveal information about attosecond electron dynamics and structure. Here, I demonstrate that all-optical approaches to attosecond measurement, based on perturbing recollision with a weak infrared field, are sensitive to transition moment phase shifts arising from electronic structure and multielectron interaction using analytical theory, ab initio simulation, and experiment. The insensitivity of all-optical approaches to transition moment phase shifts arising from ionic structure is found to be a result of a first-order cancellation of the effect of the perturbing field on the recollision electron wave packet and the transition moment. Prior to these findings, it was widely believed that all-optical methods were insensitive to the transition moment phase. The insensitivity of all-optical measurement to both ionic structure and propagation effects will permit for the unambiguous isolation of electron structure and multielectron interaction in attosecond measurement. These results will allow any laboratory capable of generating attosecond pulses to perform measurements of the transition moment phase without an additional experimental apparatus, even at wavelengths where the single photoionization cross-section becomes small.

No description available.

No description available.

The absolute probabilities for low energy ion bombardment induced secondary emission of electrons and anions have been measured as a function of adsorbate coverage of the surface. The primary ion beams were incident at less than 500 eV on metallic, semiconducting and insulating surfaces. The adsorbate used was chiefly oxygen, and the coverage range studied was zero to about one monolayer. The presence of an adsorbate was observed to significantly enhance secondary emission of electrons and anions in the case of O - and Na+ impacting metallic (W, Al) and semiconducting (Si) substrates; the effect of the adsorbate was little to minimal in the case of N2+, Ar+, Ne+ and He+ impacting these substrates, however. No appreciable adsorbate-induced changes in the secondary emission probability were measured for any of the probe beams incident on the insulating (MgO) substrate.;Secondary electron and anion kinetic distributions were also measured, as functions of projectile impact energy and of adsorbate exposure. The most probable energy of the secondary products was in the 1--3 eV region; the form of the distributions had little to no dependence on the impact energy or adsorbate exposure, but varied with different projectile and substrate species. The identities of the secondary anions were determined through mass spectroscopic techniques; atomic ion forms of the adsorbate and simple adsorbate-substrate molecular ions are the predominantly emitted species.;The data are discussed in terms of a model in which a molecular anion residing on the surface is collisionally excited, its subsequent decay giving rise to both electron and negative ion emission into the vacuum. The results of N2+, Ar+, Ne+ and He+ bombardment, in which secondary emission does not appear to be adsorbate-mediated, suggest that there exists a condition of excitation energy resonance which projectiles having high ionization potentials do not satisfy; experimental evidence shows that incident O- and Na+ satisfy this condition to a greater degree than do the above projectiles. The concepts of this excitation model can be represented mathematically and made to fit the observations with careful parameter choice; the parameters can be shown to reflect properties of the interaction.

We examine the energy spectrum of hydrogen in weak near-perpendicular electric and magnetic fields using quantum computations and semiclassical analysis. The structure of the quantum spectrum is displayed in a lattice constructed by plotting the difference between total energy and first order energy versus first order energy, for all states of a given principal quantum number n. For some field parameters, the lattice structure is not regular, but has a lattice defect structure which may be characterized by the transport of lattice vectors. We find that in near-perpendicular fields the structure of the spectrum is divided into six distinct parameter regions, which we characterize by the presence and type of lattice defect. to explain this structure we examine a corresponding classical system which we have derived by classical perturbation theory. Starting from Kepler action and angle variables, we give a derivation of a classical Hamiltonian to second order in perturbation theory; the derivation is different from, but the final result agrees with previous work. We focus especially on the topological structure of the reduced phase space and on the resulting topological structure of the trajectories. We show that construction of action variables by the obvious methods leads to variables that have discontinuous derivatives. Smooth continuation of these "primitive" action variables leads to action variables that are multivalued. We show how these multivalued actions lead to lattice defects in the quantum spectrum. Finally we present a few correlation diagrams which show how quantum eigenvalues evolve from one region of near-perpendicular parameter space to another and show how the structure of the quantum correlations is related to structures in the classical phase space.

We report laser desorption from a Room Temperature Ionic Liquid (RTIL) as a novel source for time of flight mass spectrometry. We use the 2nd harmonic of an Nd:YAG laser to deposit intensities of 1-50 MW/cm2 via backside illumination onto our RTIL desorption sample. A microstructured metal grid situated on top of a glass microscope slide coated with RTIL serves as our desorption sample. The RTIL we use, 1-Butyl, 3-Methylimidazolium Hexafluorophosphate, remains liquid at pressures below 10-8 torr. The use of liquid desorption sample allows for improved surface conditions, homogeneity and sample life as compared to Matrix Assisted Laser Desorption Ionization (MALDI) techniques. Our desorption technique is also unique as it allows the study of both multiphoton and acoustic desorption processes within the same time of flight spectra. Our technique yields intrinsically high resolution, low noise data. We observe differences between ion species in their preference for desorption by a particular desorption method. Specifically, we observe desorption solely by acoustic means of an entire RTIL molecule adducted with an RTIL cation. Finally, we report the applicability of this technique for the desorption of biomolecules.

No description available.

No description available.