Browsing by Author "Haynes, William Brian"
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Item Development of a 500 MW, one-microsecond, multi-kiloampere relativistic klystron amplifier(1996) Haynes, William Brian; Wilson, William L., Jr.This work presents research on the one-microsecond, L-band relativistic klystron amplifier (RKA) project conducted at Los Alamos National Laboratory. A collection of theoretical analyses is presented for rf cavities, intense electron beams, beam-cavity interactions, and small-signal klystron bunching. Electromagnetic field simulations were done for three dimensional cavity structures using HFSS with very accurate results. Particle-in-cell simulations of the complete RKA were done using the two dimensional code ISIS. Extraction efficiency for intense modulated beams is discussed and verified in simulations. Designs for input and idler cavities are reviewed. Extremely low-Q, single-gap, output cavities are investigated for coupling rf power from very low-impedance, modulated, electron beams. Output cavities with a Q less than 4 have been designed, measured, and tested. Methods were implemented for designing 2D equivalent output cavity structures to model 3D structures in 2D codes. A technique for ex-situ rf conditioning of the output cavity gap pieces is presented. A beam-pipe center conductor, intended to reduce the space-charge potential depression of the beam, is discussed. Diagnostics for intense-beam and high-power rf measurements are presented. A coaxial directional coupler and load, capable of handling more than 500 MW at 1300 MHz, were designed. Mode conversion from coax to waveguide is discussed for $>$100 MW power levels. Methods for determining the gap voltage in an operating cavity are presented. Pulse-shortening of the rf in the RKA is also discussed. A 650 kV, 5 kA, one-microsecond, annular beam has been produced from a stainless-steel, explosive-field-emission cathode. The beam current was modulated up to 70% $(I\sb1 /I\sb0$ = 70%) using a two-cavity bunching section operating at 1300 MHz. RKA structures simulated in ISIS have extracted up to 250 MW. This number was consistent with the extracted power actually measured in the equivalent experiment. Overall energy extraction was as high as 160 J per pulse. The average rf output power coupled into the 6-inch-diameter coax transmission line was approximately: 300 MW for 300 ns, 250 MW for 500 ns, and 100 MW for 1 $\mu$s. Peak power levels as high as 475 MW have also been produced.Item Methods of electrically characterizing zinc selenide epitaxial layers on gallium arsenide substrates(1994) Haynes, William Brian; Wilson, William L., Jr.A number of different methods for electrically characterizing ZnSe thin films are presented. These include the Hall effect, current-voltage profiling, and capacitance-voltage profiling. The planar Schottky technique is used to analyze p-type ZnSe. The conductance method of Nicollian and Brews is applied for the first time to the ZnSe/GaAs MIS system to find the surface state density profile and the time constants associated with particular states. A novel photowash technique is used to make the GaAs surface gallium rich before ZnSe growth. Electron Paramagnetic Resonance is discussed in the context of probing thin film semiconductors. Room temperature mobilities for undoped, 1 $\rm\mu m,$ ZnSe films grown by Laser-assisted Metal Organic Chemical Vapor Deposition are as high as 309 $\rm cm\sp2/V$-s. Measured mobilities at 77 K are low due to hole conduction in p-type GaAs at the interface. Heterojunction barrier heights are found to be in the range of 0.6-0.9 eV and are most likely due to interface traps. Schottky diode n-values are found to be high ($>$30) because of the heterojunction barrier. P-type conduction in the nitrogen-doped samples has not been found. Undoped ZnSe is n-type and is typically depleted of carriers. Surface state densities for both untreated and Ga-rich ZnSe/p-GaAs interfaces are found to be in the range of $10\sp{12}$ $\rm cm\sp{-2}$-$\rm eV\sp{-1}.$