[en] This thesis concerns the formation, sintering and humidity dependent electrical behaviour of the spinel ceramic material nickel germanate, Ni₂GeO₄. Ni₂GeO₄ has been prepared via the solid state reaction between NiO and GeO₂ over a range of temperatures, and characterised using a number of techniques. The sintering behaviour of pressed pellets of Ni₂GeO₄ has also been investigated, together with a characterisation of the microstructure of the sintered bodies. Substitutional doping of Ni₂GeO₄ with Li as a replacement for Ni is found to promote a high degree of shrinkage in the sintering process, probably due to the formation of a liquid phase. XRD revealed that even when 10 % of the Ni atoms were replaced with Li, no change in the crystal structure could be detected. A.C. impedance spectroscopy of Ni₂GeO₄ samples was used to investigate the humidity sensitivity of this material. Equivalent circuit analysis, based on a network of resistors and constant phase elements, shows that the humidity sensitivity is due to conduction in a surface layer of water, in agreement with the models currently popular in the literature. Measurement of the water adsorption isotherm of Ni₂GeO₄ in pellet form indicates that a single monolayer of water is formed at around 20 %R_H, with an approximately linear increase in water layer thickness up to around 80 %R_H, after which capillary condensation causes a large increase in the volume of adsorbed water. The information gained on the thickness of this layer of water has been correlated with the resistance of the layer measured by impedance spectroscopy, and subsequently used to provide evidence for a model of the humidity sensitive conduction. The conduction in the surface layer is thought to be due to dissociation of the water, where the amount of dissociation is exponentially dependent on the humidity. (author)

[en] The authors report the use of a simple microwave discharge ion source for producing ions from a non-gaseous material, without the complication of a magnetic field. The source is simple in design and easily constructed. Discharges which were initiated in argon produced Na⁺ ions from both sodium iodide and pure sodium. The absolute and relative rates of production of Na⁺ ions were found to vary greatly with the discharge pressure and incident microwave power. Operating conditions ranging from 0.016 to 0.064 mbar (1.6-6.4 Pa) and from 20 to 60 W were tested. The percentage of all the ions which were Na⁺ ions in discharges with sodium iodide was as high as 17% while with pure sodium it was as high as 89%. (author)

[en] Photocathode rf guns depend on mode locked laser systems to produce an electron beam at a given phase of the rf. In general, the laser pulse is less than σ_z = 10^o of rf phase in length and the required stability is on the order of Δφ = 1^o. At 90 GHz (W-band), these requirements correspond to σ_z = 333 fsec and Δφ = 33 fsec. Laser system with pulse lengths in the fsec regime are commercially available, the timing stability is a major concern. We propose a multi-cell W-band photoinjector that does not require a mode locked laser system. Thereby eliminating the stability requirements at W-band. The laser pulse is allowed to be many rf periods long. In principle, the photoinjector can now be considered as a thermionic rf gun. Instead of using an alpha magnet to compress the electron bunch, which would have a detrimental effect on the transverse phase space quality due to longitudinal phase space mixing, we propose to use long pulse laser system and a pair of undulators to produce a low emittance, high current, ultra-short electron bunch for beam dynamics experiments in the 90 GHz regime

[en] The gun test facility (GTF) at SSRL was started in 1996 to develop an appropriate injector for the proposed linac coherent light source (LCLS) at SLAC. The LCLS design requires the injector to produce a beam with at least 1 nC of charge in a 10 ps or shorter pulse with no greater than 1π mm mrad normalized rms emittance. The photoinjector at the GTF is 1.6 cell S-band symmetrized gun and emittance compensation solenoid. Emittance measurements, reported here, were made as function of laser pulse width using Gaussian longitudinal pulses. The lowest achieved emittance to date with 1 nC of charge is 5.6π mm mrad and was obtained with a pulse width of 5 ps (FWHM) and is in agreement with simulation. There are indications that the accelerator settings for these results may not have been optimal. Simulations also indicate that a normalized emittance meeting the LCLS requirement can be obtained using appropriately shaped transverse and temporal laser/electron beam pulses. Work has begun on producing temporal flat top laser pulses which combined with transverse clipping of the laser is expected to lower the emittance to approximately 1π mm mrad for 1 nC with optimal accelerator settings

[en] Monte Carlo simulation calculations on a supercomputer have been made of the mobility of K⁺ ions drifting in pure He and Kr gases respectively under the action of a uniform electric field. Typical errors of 1% or less are achieved. By making direct comparisons with other theoretical and experimental data, these calculations have helped to verify both the three-temperature theory used to derive the theoretical mobility as well as the validity of various interaction potentials proposed. Results of these comparisons together with an earlier one for the K⁺-Ar system provide evidence that the three-temperature theory is generally applicable for the three different ion-neutral mass ratios studied, but yields a slight overestimation of the mobility around the peak mobility region. It is also found that the recent universal scaling law potential represents fairly well the collision interaction between the alkali ion and rare-gas atoms studied. (author)

[en] Measurements are made of the velocity distributions of He⁺, Ne⁺ and Ar⁺ ions drifting in their respective parent gas under the action of a uniform electric field at room temperature (297-300 K). Experimental results for E/N ranging from 60 to 320 Td are compared with both the Wannier equation for the RMS ion velocity and the corresponding Maxwellian distribution. The typical experimental curve is found to possess only a single maximum with its peak displaced towards the low velocity end and an enhanced high velocity tail in comparison with the Maxwellian. (author)

[en] Emittance growth is an important issue for plasma wakefield accelerators (PWFAs). Multiple Coulomb scattering (MCS) is one factor that contributes to this growth. Here, the MCS emittance growth of an electron beam traveling through a PWFA in the blow out regime is calculated. The calculation uses well established formulas for angular scatter in a neutral vapor and then extends the range of Coulomb interaction to include the effects of traveling through an ion column. Emittance growth is negligible for low Z materials; however, becomes important for high Z materials

[en] Coherent transition radiation is used to measure the length of the ultra-short electron bunches available at the Stanford Linear Accelerator Center. The results and the limitations of the method are described

[en] The creation of ultra-high current, ultra-short pulse beams Q=3 nC, σ_z = 20(micro)m at the SLAC FFTB has opened the way for very high gradient plasma wakefield acceleration experiments. We study here the use of these beams in a proposed Cherenkov wakefield experiment, where one may excite electromagnetic wakes in a simple dielectric tube with inner diameter of few 100 microns that exceed the GV/m level. We discuss the scaling of the fields with design geometric design parameters, and choice of dielectric. We also examine measurable aspects of the experiment, such as the total coherent Cerenkov radiation energy one may collect, and the expected aspects of dielectric breakdown at high fields

[en] Meningococcemia is a life-threatening infection which produces purpura fulminans and extremity gangrene in its most severe form. In patients with gangrene, amputation is usually necessary. The amputations frequently need revision as ischemic changes in the underlying soft tissues and bone are difficult to evaluate at the time of surgery. These ischemic changes often have non-vascular distributions and progress over time. We present two patients in whom MR imaging and MR angiography were performed prior to planned amputation. These cases demonstrate the potential utility of MR imaging in this setting, and compare the MR angiographic results to conventional arteriography in one of these patients. (orig.)