Xinjian Niu

A 35-GHz low-voltage third-harmonic gyrotron with a permanent magnet system

A systematic theoretical and experimental study on a 35-GHz 45-kV third-harmonic gyrotron with a permanent magnet system is presented in this paper. A complex cavity with gradual transition and a diode magnetron injection gun (MIG) are employed in the gyrotron. A self-consistent field nonlinear theoretical investigation and numerical simulation for electron beam interaction with RF fields are given. The diode MIG is simulated numerically utilizing our code in detail. The permanent magnet system provided the maximum axial magnetic field of about 4.5 kG in the cavity region of the gyrotron. The Ka band third-harmonic complex cavity gyrotron with a permanent magnet system has been designed, constructed, and tested. A pulse output power of 147.3 kW was obtained at a beam voltage of 45 kV with beam current of 32.2 A, corresponding to an efficiency of 10.2%.

A study on the high-order mode oscillation in a four-cavity intense relativistic klystron amplifier

The high-order mode oscillation is studied in designing a four-cavity intense relativistic klystron amplifier. The reason for the oscillation caused by high-order modes and a method to suppress these kinds of spurious modes are found through theoretical analyses and the study on the influence of major parameters of a high frequency structure (such as the oscillation frequency of cavities, the cavity Q value, the length of drift tube section, and the characteristic impedance). Based on much simulation, a four-cavity intense relativistic klystron amplifier with a superior performance has been designed, built, and tested. An output power of 2.22 GW corresponding to 27.4% efficiency and 61 dB gain has been obtained. Moreover, the high-order mode oscillation is suppressed effectively, and an output power of 1.95 GW corresponding to 26% efficiency and 62 dB gain has been obtained in our laboratory.

Theoretical Investigation on a Multifrequency Multimode Gyrotron at Ka -Band

In this paper, a multifrequency, multimode gyrotron has been designed, which can operate at 28, 29, 31, and 32 GHz with corresponding modes TE0.3, TE+5.2, TE−3.3, and TE+6.2, respectively. For all operating status, the mode competitions have been investigated carefully with the help of a new time-dependent, multimode, self-consistent code, which is built on the trajectory approach. For the operating at 28 GHz, it also has been simulated by CST Particle Studio. They have similar results when comparing two results. For the operating at other status, the changes of electron parameters caused by the changed dc-magnetic field have been analyzed in detail. In the analyzes, the guiding center radius and Larmor radius would not be influenced severely, but the velocity ratio would be influenced seriously, such as, the velocity ratio of operating at 32 GHz would be reduced to about 0.9787, which caused a severe reduction in the efficiency. In order to alleviate the influences, a compensation magnetic coil (CMC) has been used in the magnetron injection gun region, in which the changes of electron parameters have been analyzed too. The simulation results show that the electron efficiency of operating at 32 GHz can be increased from 24.6% to 31% by applying CMC. The multimode multifrequency gyrotron operated at ka-band gyrotron has been investigated in theory, which can provide new possibilities in high-power millimeter source development.

Design of a 94 GHz transition section with cosinusoidal profile

Up to now, many transition sections have been designed and applied successfully. But a transition section with cosinusoidal profile, its operation principle and how to design it have not been found in available literature until now. In this study, a transition section with a cosinusoidal profile and the method to design it are proposed based on the operational principles of mode converters with similar profiles. A 94 GHz transition section used to transmit TE01 mode efficiently is designed using the method. The calculations by our codes and simulations on a high-frequency structure simulator indicate that the section can transmit TE01 mode with transmission efficiency over 0.987 (within a bandwidth of 7.6 GHz) and reflection below −40 dB. Experimental results show our design is successful. Comparison between the section and the linear one shows that the former is much shorter than the latter when they are used to transmit TE01 mode at the same characteristics above. Such a strong point of shorter length is very helpful for the construction of a compact microwave device.

Investigation on heat transfer analysis and its effect on a multi-mode, beam-wave interaction for a 140 GHz, MW-class gyrotron

The interaction cavity of a 140 GHz, 1 MW continuous wave gyrotron developed in UESTC will be loaded with a very large heat load in the inner surface during operation. In order to reduce the heat, the axial wedge grooves of the outside surface of the cavity are considered and employed as the heat radiation structure. Thermoanalysis and structural analysis were discussed in detail to obtain the effects of heat on the cavity. In thermoanalysis, the external coolant-flow rates ranging from 20 L/min to 50 L/min were considered, and the distribution of wall loading was loaded as the heat flux source. In structural analysis, the cavitys deformation caused by the loads of heat and pressure was calculated. Compared with a non-deformed cavity, the effects of deformation on the performance of a cavity were discussed. For a cold-cavity, the results show that the quality factor would be reduced by 72, 89, 99 and 171 at the flow rates of 50 L/min, 40 L/min, 30 L/min and 20 L/min, respectively. Correspondingly, the cold-cavity frequencies would be decreased by 0.13 GHz, 0.15 GHz, 0.19 GHz and 0.38 GHz, respectively. For a hot-cavity, the results demonstrate that the output port frequencies would be dropped down, but the offset would be gradually decreased with increasing coolant-flow rate. Meanwhile, the output powers would be reduced dramatically with decreasing coolant-flow rate. In addition, when the coolant-flow rate reaches 40 L/min, the output power and the frequency are just reduced by 30 kW and 0.151 GHz, respectively.The interaction cavity of a 140 GHz, 1 MW continuous wave gyrotron developed in UESTC will be loaded with a very large heat load in the inner surface during operation. In order to reduce the heat, the axial wedge grooves of the outside surface of the cavity are considered and employed as the heat radiation structure. Thermoanalysis and structural analysis were discussed in detail to obtain the effects of heat on the cavity. In thermoanalysis, the external coolant-flow rates ranging from 20 L/min to 50 L/min were considered, and the distribution of wall loading was loaded as the heat flux source. In structural analysis, the cavitys deformation caused by the loads of heat and pressure was calculated. Compared with a non-deformed cavity, the effects of deformation on the performance of a cavity were discussed. For a cold-cavity, the results show that the quality factor would be reduced by 72, 89, 99 and 171 at the flow rates of 50 L/min, 40 L/min, 30 L/min and 20 L/min, respectively. Correspondingly, the co...

Investigation of a large power water-cooled microwave resonance window for application with the ECR ion source

A large power water-cooled microwave resonance window used for the electron cyclotron resonance (ECR) ion source is investigated in this paper. The microwave characteristic simulation, thermal analysis, and structure design are deeply and successively carried out before fabrication. After the machining and welding of the components, the window is cold and hot tested. The application results demonstrate that when the input power is 2000 W, the reflected power is only 5 W. The vacuum is below 10−10 Pa, and the high power microwave operation can last 30 h continuously and reliably, which indicates that the design and assembling can achieve the high efficiency of the microwave transmission. Finally, the performance of the ECR ion source is enhanced by the improvement of the injected microwave power to the ECR plasma.

Large power microwave nonlinear effects on multifunction amplifier chip for Ka-band T/R module of phased array radar

Nonlinear effects of large power millimeter wave on critical chips for the T/R module of phased array radar is experimental studied and analyzed in this paper. A multifunction amplifier chip is selected for our experiments. A solid continuous wave (CW) source and a large power pulsed magnetron are both employed to generate the Ka-band microwave. The input-output characteristics, the degradation and destroy threshold of the chips are obtained through a series of experimental tests. At last, the results are given by figures and analyzed theoretically.

Design of the resonator in a 110-GHz Gyrotron

On the basis of electron cyclotron resonance maser theory and generalized transmission line theory, we compiled programs to analyze the resonant cavity in a 110 GHz gyrotron. By calculating and studying different gradual-varying and line-joint resonant cavities, we designed a gradually tapered resonator for a 110 GHz Gyrotron, which is good at suppressing the parasitic modes, improving the purity of the operating mode and the efficiency of the beam-wave interaction.

Design and simulation of a magnetron injected electronic gun for 0.4 THz gyrotron

A double anode magnetron injected gun (MIG) for a terahertz (THz) band cyclotron oscillation tube has been presented in this paper. Through design, simulation and optimization by the particle-in-cell (PIC) code, a double-anode electron gun with trans-velocity spread of 3.19% is obtained, and the ratio of the transverse velocity to the axial velocity is equal to 1.4. The designed electron gun well satisfies the requirement of the 0.4 THz gyrotron.

Design and simulation of 94GHz Magnetron Injection Gun

This paper reports the results about a Magnetron Injection Gun(MIG) designed recently. This gun can work at frequency 94GHz for gyrostron. After lots of optimizings and simulations about the structure, at the coefficient of magnetic field 0.8313(3.5755T), beam voltage 24KV, and beam current 2A, it was observed that the electron ratio 1.4, the maximum transverse velocity spread less than 2.7%, the longitudinal velocity about 5.7%. The gun was used for a 94GHz gyrotron, it was obtained that the output power of about 25KW with efficiency 53%(SDC).