Gyrotron Performance Research Articles

Expansion of a frequency tuning band in a gyrotron with coupled cavities

An electron frequency tuning band of a conventional high-Q cavity gyrotron approximately coincides with the unloaded cavity bandpass which usually does not exceed 0.1%. To expand the frequency tuning band we introduce a gyrotron with an RF circuit that consists of two coupled circular cavities separated by a thin iris. A nonlinear self-consistent gyrotron theory predicts a saturated efficiency of 18% and a tuning band of 1.1%. An experimental study of an X-band tube operating in the TE011 mode was carried out to test the gyrotron with the coupled cavities concept. Measurements of gyrotron performance showed a 0.96% tuning band—a tenfold increase over that of an ordinary gyrotron. Simulation results are in a good agreement with the experimental data.

Rieke diagrams for gyrotrons

Rieke diagrams provide a useful way of estimating the effect of reflections from the window on gyrotron performance. In some cases, a small change in the reflection coefficient can have a large effect on the output power and on the resonator wall losses. Rieke diagrams can also be useful in determining whether or not a mode will oscillate at all for a given set of parameters and reflection coefficieat.

Status of gyrotron development

This discussion briefly reviews the usual scaling law for predicting higher-power gyrotron performance from existing data, proposes another way of charting improvement progress, perhaps more applicable than the scaling laws, and shows the number of actual experimental vehicles that were required to achieve various high-power CW gyrotron goals. It also briefly touches on some of the key elements and design factors considered for CW gyrotron design. Ongoing megawatt-gyrotron experiments at Varian Associates are presented and gyrotron applications in accelerators, weapons, ceramic sintering, and fusion are assessed.

Improved oscillator phase locking by use of a modulated electron beam in a gyrotron.

A new method of microwave oscillator phase locking, exploiting the extended nature of the gyroklystron configuration, is accomplished by modulation of the electron beam before it reaches the cavity oscillator. The amount of power required to give phase locking in a gyrotron is decreased by more than an order of magnitude from that predicted by Adler's theory. In addition, oscillator priming is observed at drive powers far below all other systems tested to date. These new methods provide the coherence required of rf sources for linear accelerators and may enhance gyrotron performance for fusion heating.

An investigation of a magnetron injection gun suitable for use in cyclotron resonance masers

The requirements of an electron-beam source suitable for use in cyclotron resonance masers are discussed. The beam source of preference, a magnetron injection gun with its emission temperature limited, is studied by use of a numerical simulation code. This computer code includes the effect of external magnetic fields, the beam's azimuthal self-magnetic field, and space charge in a self-consistent manner. By use of this program, a prediction of gun operation, particularly as it affects gyrotron performance, can be made. Of particular interest are the effects of varying such control parameters as the magnitude of the electric and magnetic fields, the shape of the electric and magnetic fields, and the current. It is demonstrated that, for a particular optimized gun design, the gun operation is very sensitive to both the applied electric and magnetic fields at the cathode. However, the gun shows no strong dependence on other factors such as the temperature-limited beam current or the magnetic-field taper used to compress the beam.