Phase and frequency locked magnetron
A magnetron of improved performance capable of stabilizing the frequency and phase of magnetron output for use in particle accelerators and other applications. Thin variable-permeability blocks are attached inside the resonant anode structures of a standard magnetron design. A variable bias electromagnet, with field orthogonal in direction to the RF magnetic field, is used to vary the permeability of each block and therefore the resonant frequency of each anode structure. An electronic feedback control circuit adjusts the bias magnetic fields to lock in the frequency and phase of the magnetron output to an external low-level reference signal. Such devices may be used to provide synchronized high-power RF to many locations (e.g. the RF cavities of a particle accelerator), while requiring the distribution only of electrical power and an appropriate low-level RF reference signal.
1. A magnetron comprising:
an anode structure oriented about an axis, the anode structure defining an interior chamber and having a plurality of vanes extending radially into the interior chamber and terminating at a vane tip, with each pair of the plurality of vanes defining a cavity to form a plurality of cavities within the interior chamber and each of the plurality of cavities has a resonant frequency;
a cathode aligned substantially along the axis, the plurality of vanes and the cathode configured so as to define a first gap between the vane tips of the plurality of vanes and the cathode, wherein the cathode and anode are configured to create an RF field;
a conductive output terminal for receiving an output signal;
an output coupler disposed in communication with at least one of the plurality of vanes and in electrical communication with the conductive output terminal;
a magnetron magnet configured to create an axially aligned magnetic field within the interior chamber;
a plurality of variable-permeability blocks affixed in the anode structure, wherein each of the variable-permeability blocks is magnetic-field-dependent and orthogonally-biased with respect to the RF field, for changing the resonant frequency of each of the plurality of cavities of the anode structure;
a plurality of variable-strength, localized-field bias magnets, for changing the permeability of each of the plurality of variable-permeability blocks, magnetically connected to said variable-permeability blocks, each of the plurality of bias magnets having a coil;
a feedback control circuit in communication with the conductive output, an RF reference signal source generating an RF reference signal, and to the coils of the plurality of bias magnets; and
wherein the feedback control circuit is configured to detect an output signal at the conductive output terminal, to detect the reference signal, to compare the output signal to the reference signal, to calculate desired settings for a bias magnet current to be applied to the coils of the plurality of bias magnets based on the comparison, and to generate and apply the bias magnet current to the coils of the plurality of bias magnets.
2. The magnetron of claim 1 , wherein the feedback control circuit is configured to detect an output signal frequency, to detect a reference signal frequency, to compare the output signal frequency to the reference signal frequency, and to calculate desired settings for a bias magnet current to be applied to the coils of the plurality of bias magnets based on the comparison, and to generate and apply the bias magnet current to the coils of the plurality of bias magnets together to control the output signal frequency.
3. The magnetron of claim 1 , wherein the feedback control circuit is configured to detect an output signal phase, to detect a reference signal phase, to compare the output signal phase to the reference signal phase, and to calculate desired settings for a bias magnet current to be applied to the coils of the plurality of bias magnets based on the comparison, and to generate and apply the bias magnet current to the coils of the plurality of bias magnets individually to control the output signal phase.
4. The magnetron of claim 1 , wherein the feedback control circuit is configured to detect an output signal frequency, to detect an output signal phase, to detect a reference signal frequency, to detect a reference signal phase, to compare the output signal frequency to the reference signal frequency, to compare the output signal phase to the reference signal phase, to calculate desired settings for a bias magnet current to be generated and applied to the coils of the plurality of bias magnets based on the comparisons, and to apply the bias magnet current to the coils of the plurality of bias magnets together to control the output signal frequency and individually to control the output signal phase.
5. The magnetron of claim 1 , wherein each of the plurality of variable-permeability blocks are disposed within the cavity of each of the plurality of cavities.
6. The magnetron of claim 1 , wherein the variable-permeability blocks are ferrite.
7. The magnetron of claim 1 , wherein the variable-permeability blocks are yttrium iron garnet.