|dc.description.abstract||This thesis covers the design and development of a modulated Pierce electron gun
used in the construction of experimental travelling wave tube (TWT) amplifiers. The
gun incorporated an open aperture switching electrode, positioned mid-way between
anode and cathode, to pulse the beam. This method of modulation did not have the
same adverse effects on electron trajectories as in the case of a conventional mesh
grid, but rather the electrode could be used to alter the focus conditions within the
gun and subsequently improve certain beam characteristics. Ion focusing effects
could also be eliminated with the electrode, allowing dual mode operation of the guns
without the complications normally associated with such a practice.
The switching electrode was simulated to ascertain its effect on electron trajectories
within the gun, using finite element analysis as well as an electron optics design
program. A test gun was constructed in a glass envelope in order to investigate the
performance of the new design. The glass gun allowed a beam analysis to be
performed, as well as thermal measurements to be made. Results from this gun
compared favourably with earlier simulations. The results of two metal/ceramic
construction TWTs are presented, showing the beneficial effects of the switching
electrode on the performance of the tubes as a whole, and the electrode's potential
to compensate for constructional anomalies.
The joining of metals to ceramic using active brazing techniques is also an important
aspect tackled by the thesis, with several innovative ideas being implemented in the
construction of the devices. A simple yet reliable electrical feed-through was
developed for those guns having a ceramic envelope.
Extensive work was also performed on the manufacture of impregnated tungsten
cathodes for use in the electron guns. Several test diodes, including a water-cooled
demountable test vehicle, were constructed to test the performance of the cathodes.
An analysis was performed on the patchy behaviour of some of the initial cathodes
to improve the preparation methods used in the laboratory. The emission results
obtained from the cathodes are documented, as is the successful incorporation of
several of them into the new modulated gun design.||en