HIGH PERFORMANCE GYROKLYSTRON AMPLIFIER

Objectives

Sources for high power microwave and millimeter-wave applications.

Approach

The gyroklystron (see schematic) is a high power source which can be configured as a phase-locked oscillator or amplifier.

Accomplishments

A gyroklystron design has been designed at 33 GHz with 50 dB saturated gain, 250 kW output power and 40% efficiency. The experiment is under construction.

Gyrotron Schematic

Some applications for high frequency microwaves are radar, communications, particle accelerators and plasma heating. These applications can require peak and average power levels ranging from tens of kilowatts to several megawatts per source. A deep space radar system upgrade has been proposed which would require ground-based sources at 35 GHz producing 400 kW of cw power.

The gyroklystron is an innovative rf source capable of these high power levels in the microwave and millimeter wave regions. The device consists of an magnetically confined electron beam with a high percentage of transverse energy that traverses a relatively simple circuit composed of two or more waveguide cavities separated by drift regions.

A proof of principle experiment has been designed at 33 GHz. The 80 kV, 8 A electron beam with a transverse to axial velocity ratio of 1.5 and a predicted axial velocity spread of 7% is produced by a gyrotron MIG (magnetron injection gun). In order to achieve approximately 50 dB gain, three circular waveguide cavities are necessary. The input and penultimate cavites operate in TE011 modes and have Q=300. The output cavity operates in the TE021 mode and Q=500. These low loss modes along with the diffraction coupled output cavity make the device cw relevant. The circuit length is 11 cm. Simulations of the device using a partially self-consistent code which includes linear and non-linear theories predict a saturated output power of 250 kW with 40% efficiency.

Simulation Results Showing Gain Transfer Curves of the Three-Cavity, 33 GHz Gyroklystron for Several Axial Velocity Spreads

35 GHz Gyro-Klystron Amplifier


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