A one-megawatt gyrotron with radial electron beam extractio

In the past decade there has been much activity in the development of gyrotron tubes for efficient generation of high-power millimeter wave radiation. The primary impetus for this development has been the need for plasma heating in magnetic confinement fusion experiments. Next generation fusion experiments will require sources which are capable of operating continuously at power levels of one megawatt or greater. Successful development of these high-average power sources could also find applications in other areas such as space communications, high-resolution radar, high-directivity communications and next-generation linear accelerators.;Current conventional gyrotron designs do not appear capable of reaching these power levels at continuous operation. The present limitation in power handling capability in conventional gyrotrons comes from the coaxial transmission of the electron beam and rf in the same waveguide. This arrangement requires the spent electron beam to be dissipated in waveguides of insufficient area to achieve save power densities. In this thesis, the analysis, design and construction of a gyrotron with a novel new method of beam collection are presented. The technique developed involves separation of the electron and rf beam by a radial diversion of the electron beam through a gap in the output rf waveguide.;We begin the design with a multimode analysis of the rf transmission across a radial gap. A computer code implementation using this analysis is developed and verified via comparisons with computer calculations and measurements. Using the multimode analysis, a new method of reducing the rf leakage into the gap from 10% to 2% is shown. A sensitivity analysis of the design to thermal, mechanical and electrical variations is performed.;The design for the beam magnetics and collection is developed as two separate problems. The first aspect of the design is the separation of the electron beam and rf by a radial diversion of the electron beam. The design that accomplishes this is presented and then followed by the design for the manipulation of the separated beam to achieve a suitable power density distribution on the collector surface.;A prototype 1 MW cw tube at 110 GHz was constructed. The experimental results showed excellent agreement with the design predictions. The electron beam was successfully diverted through the gap in the rf waveguide wall and spread in the collection region with power densities well below maximum allowable amounts. RF leakage into the gap was very close to the predicted value. The design achieved the desired goals and resulted in a successful prototype for future gyrotron designs for cw megawatt power levels.