Youlei Pu

Design and Experiment of a Q-band Gyro-TWT Loaded With Lossy Dielectric

Distributed lossy dielectric is of considerable interest for high-power milli- and submillimeter radiation sources, particularly for gyrotron traveling wave tubes (gyro-TWTs). The analytical design and experiment of a Q-band gyro-TWT loaded with periodic lossy dielectric rings operating in the circular TE01 mode at the fundamental cyclotron harmonic are presented. The gyro-TWT is driven by a 70-kV 10-A helical electron beam with a velocity ratio of 1.0. Hot test performs maximum peak output power of 152 kW, 41-dB saturated gain, and 21.7% efficiency at 47.6 GHz. The measured bandwidth over 100 kW is at the range of 47-49 GHz. PIC simulation and large-signal prediction show excellent agreements to the hot test results. The potential backward wave oscillation interactions involving the spurious modes TE11, TE21, and TE02 are effectively suppressed by loading lossy dielectric rings periodically. The Q-band gyro-TWT is zero-drive stable at the operating points, which demonstrates that loading lossy dielectric is excellent to stabilize the spurious oscillations. Moreover, the designs of magnetron injection gun, interaction circuits, and input and output structures are also achieved to satisfy the requirements.

Simulation and Experiment of a Ku-Band Gyro-TWT

Design techniques and experimental results are presented on a Ku-band TE11 mode gyro-traveling wave tube. The hot test of this amplifier gives more than 153-kW output power, 2.3-GHz bandwidth (14%), 41-dB saturated gain, and 20% efficiency driven by a 63 kV, 12-A electron beam with a pitch angle (vtvz) of 1.2, and velocity spread of 5%. A linear polarized TE11 mode input coupler is used to introduce the input power. The stability of the amplifier from oscillation, including both the operating TE11 mode and the backward wave TE21 mode, has been investigated with linear codes, nonlinear selfconsistent theory, and 3-D PIC CHIPIC simulation. To suppress the potential gyro-backward wave oscillator interactions, the high frequency circuit is loaded with lossy ceramic rings. The lossy structure is optimized by nonlinear theory and 3-D PIC simulation. A low velocity spread magnetron injection gun is designed with a new structure.

Automatic Hot Test of Gyrotron-Traveling Wave Tubes by Adaptive PID Feedback Control

It is of great importance in many applications to provide a stable output power of a gyrotron-traveling wave tube (gyro-TWT) during a long operation time (over several hours). In order to achieve this goal, an automatic hot test platform of gyro-TWTs was set up and the power stabilization was obtained by an adaptive scheme of proportional integral derivative (PID) feedback by the beam current controlled by the filament heating power and cathode-anode beam voltage. With determined operating parameters, the PID controller can adaptively adjust the beam current and voltage, and then maintain the output power on a target. This PID controlling process can effectively eliminate the influence of the power supply voltage surge and cathode emission instability. Automatic hot test of the gyro-TWTs shows that the PID feedback controlling accuracy of the output power is better than 2%.

Design and experiment of a 34GHz TE01 gyro-TWT

The design and experimental study of a 34GHz gyro-TWT amplifier operating in the circular TE01 mode at the fundamental cyclotron harmonic are presented. The interaction circuit in this experiment consisted of periodic dielectric loaded circuits that provided the required loss for stable operation. The potential backward wave oscillation interactions involving the spurious modes TE11, TE21, and TE02 are effectively suppressed. The Ka-band gyro-TWT is zero-drive stable at the operating points. A saturated peak power of 160 kW was measured at 34GHz by hot test, corresponding to a saturated gain of 40 dB and an efficiency of 22.8%.The measured bandwidth over 120 kW is at the range of 33.5-35.5GHz. The large-signal prediction shows excellent agreement to the hot test results. Moreover, the designs of interaction circuits, and input coupler and output window are also achieved to satisfy the requirements.