34 GHz Second-harmonic Peniotron Oscillator
Author | : Lawrence Jude Dressman |
Publisher | : |
Total Pages | : |
Release | : 2010 |
ISBN-10 | : 1124509631 |
ISBN-13 | : 9781124509631 |
Rating | : 4/5 (31 Downloads) |
Book excerpt: There is a prevalent need for millimeter-wave sources, especially at frequencies in the atmospheric transmission window centered at 94 GHz. However, gyrotron oscillators, the technology of choice, have a significant drawback in that they require superconducting magnets which are costly and require long periods of time to bring to operational temperature. This makes application of gyrotrons outside of laboratory environments difficult and expensive. Harmonic operation has been proposed as a way to lower the magnetic field requirement to a level feasible with non-superconducting magnets. However, gyrotron efficiency drops dramatically at harmonics greater than two. An alternative, the peniotron, is capable of high conversion efficiency and harmonic operation. Though the principles of the device have been experimentally verified, demonstration of characteristics consistent with a practical device has been elusive. This is the goal of this dissertation - specifically, to experimentally demonstrate high device efficiency in a second-harmonic peniotron operating in the low millimeter-wave band. The design, including the key elements of the axis-encircling electron beam (produced by a compact cusp electron gun), four-vane slotted cavity, and magnet are described. Initial calculations and simulation predicted 47% device efficiency and 100 kW output power. Selection of the operating mode and beam current to achieve immunity from competing interactions are discussed and experimental results presented. An extensive discussion of start oscillation current is included. During operation, mode competition did prevent the second-harmonic peniotron mode from operating over its entire magnetic tuning range and arcing prevented the gun from operating at its full rated voltage. Consequently, the device produced a maximum 35 kW output power and 18% device efficiency at 34 GHz. However, this is unprecedented operation in a second-harmonic peniotron. Analysis of the experiment is presented which identifies the mode competition and reduced power output as resulting from an error in the original cavity design. The characteristics of the slotted cavity are described and a solution which will eliminate the design error proposed for a future device. The device is intended as a first step toward higher harmonic operation at higher frequencies.