Power microwave tubes use magnetic flux to emit microwave radiation. The invention has application in magnets for an electron cyclotron maser (also referred to as a gyrotron), a peniotron tube and other types of high frequency microwave tubes that require very high magnetic fields, such as millimeter and submillimeter wave traveling-wave tubes, backward wave oscillators, carcinotrons, and others.
In this application, reference to “power microwave tubes” is intended to be broadly defined to include: (1) high frequency microwave tubes of varying types and interactions; and, (2) microwave generators, especially those that would benefit from higher magnetic fields without using superconducting coils. Gyrotrons and peniotrons, with their microwave cavities, are used as examples herein, but it should be understood that principles discussed apply the larger spectrum of power microwave tubes as defined above.
A gyrotron gyrates the path of a stream of electrons flowing through a microwave cavity in a strong magnetic field and, by doing so, imparts electrons with cyclotron motion while emitting a millimeter wave beam. Essentially, microwaves are generated by maser effects of cyclotron resonance. A peniotron uses the energy exchange between gyrating electrons and a high frequency electromagnetic field structure to generate microwaves. Gyrotrons and peniotrons are high powered electron tubes that convert electron kinetic energy to microwave radiation using a magnetic field.
The present invention encompasses improvements to applicant's prior invention described in U.S. Pat. No. 7,764,020, which is incorporated herein by reference in its entirety. The '020 patent teaches the use of a solid permanent magnet having a through-bore where its magnetic flux density is combined with flux density delivered by an internal electromagnet placed within a cavity of the permanent magnet.
The combination of an electromagnet (interchangeably referred to herein as a solenoid, a coil, a torus-like coil and a solenoid coil) and a permanent magnet in the specified configuration is termed as a “compact magnet system,” a “magnet,” and alternatively as an “electropermagnet.” The electropermagnet may include high-permeability materials (e.g. iron) for added performance improvements.
It is noted that a “toroidal” coil is not used herein because even though a toroidal coil and a “solenoid coil” have the same external shape they are wound differently and have different magnetic fields. A toroidal coil primarily has a high azimuthal magnetic field within the core of the winding, and zero axial (on axis) field. A toroidal coil is commonly used for inductors and transformers. In contrast, a solenoid coil has zero azimuthal field and a maximum axial field (i.e. Bz is maximum on axis at r=0), see FIG. 6.