a Study of Fluxon - Traveling Wave Interactions.
Interactions between fluxons moving on a long Josephson junction and a traveling electromagnetic wave were investigated. Energy transfer similar to a traveling wave amplifier tube was expected. Gain and power estimates indicated large gain at low power levels. Requirements include unidirectional motion of individual fluxons or bundles of them and a wave propagation velocity lower than that of the fluxons. It is demonstrated that both conditions can be met. Impedance matching to low phase velocity, low characteristic impedance lines was pursued. Antipodal finlines and dielectric thickness tapers were evaluated. Small area Josephson junctions as high sensitivity, high frequency detectors could solve the problem of observing the low expected power levels. Analysis of their properties when driven by sources with finite internal impedances revealed limited usefulness when more than one signal is present. This was confirmed by simulations with an electronic Josephson junction analog. Devices allowing for efficient coupling between a long Josephson junction and a slow wave transmission line were fabricated. The required coupling was demonstrated. It was also discovered that a modification of the transmission line properties resulted. This property change occurred upon bias current application to the junction and altered phase velocity and characteristic impedance of the line. The latter was found to affect the amplitude of transmitted signals masked fluxon-wave interactions. The former was demonstrated to be useful as a phase shifter. A resistively heated line replacing the Josephson junction allowed for localized heating of the slow wave structure. Through this mechanism, phase velocity adjustments exceeding a factor of two were shown possible. Device fabrication necessitated the development of multilayer thin film deposition techniques. A novel process was introduced which allowed fabrication of Josephson junctions without breaking vacuum of the deposition system. Electrochemical conversion of niobium into niobium oxide proved invaluable. This provided a thin, high quality oxide with a high dielectric constant and also was used for film patterning. Finally, high quality niobium thin films and Josephson junctions on them were developed and characterized.
- Pub Date:
- Engineering: Electronics and Electrical; Physics: Electricity and Magnetism