Thesis

Design and operation of a harmonic gyrotron based on a cusp electron gun

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Awarding institution
  • University of Strathclyde
Date of award
  • 2010
Thesis identifier
  • T13121
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Abstract
  • This thesis presents the results of successful operation of a 2nd harmonic gyrotron based on a cusp electron gun. The numerical and experimental results agreed well with the gyrotron design parameters. Two gyrotrons based on a cusp electron gun were designed: the first gyrotron operated at the 2nd harmonic and the second gyrotron was studied to look at the scaling of this concept for operation at the 7th harmonic at a frequency of 390 GHz. The cusp electron gun was used to produce the electron beam in the gyrotron which was annular in shape. The electron beam had a voltage of 40 kV, a current of 1.5A and a velocity ratio (perpendicular component to horizontal component) of 1.5. The experimental results from the first cusp electron gun and measurements of the high quality electron beam with ~8% velocity spread and ~10% alpha spread are presented. Analytical, numerical and experimental results of a DC harmonic gyrotron are presented. The 3D PIC code MAGIC was used to simulate the interaction of the harmonic gyrotron such as the TE71 mode at the 7th cyclotron harmonic with the large orbit electron beam with the beam thickness and beam spread introduced into the simulation. The interaction cavity of both gyrotrons was in the form of a smooth cylindrical waveguide. The relationship between the cavity dimensions and cavity Q values has been studied for optimized output at the design mode with the aim of suppressing other competing modes. A linear output taper was designed with low mode conversion at the gyrotron output. A Vector Network Analyzer with high frequency millmetre wave heads was used to measure the millimeter wave properties of the gyrotron cavity. Experiments were conducted using the electron gun for the harmonic gyrotron. The gyrotron and electron gun were built as well as the interlock and safety system, pulsed power supply and magnet, the cooling and vacuum system. Millimetre wave radiation was measured for the 2.6 mm diameter cavity gyrotron operating at the 2nd harmonic at a magnetic field of 2.08 T. Experiments demonstrated that the harmonic gyrotron was sensitive to the magnetic field and electron beam parameters. Millimetre wave radiation from 108GHz to 110GHz was measured with the use of a W-band rectifying crystal detector and high pass cut off filters. The frequency of the measured millimeter wave radiation agreed very well with the design and predictions of theory.
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  • Strathclyde theses - ask staff. Thesis no. : T13121
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Date Created
  • 2010
Former identifier
  • 946582

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