Sheet-beam Extended Interaction Klystron Research Articles

High-order mode interaction structure for a W-band CW sheet beam extended interaction klystron

To solve the problem of mode competition in high-order working modes, this paper presents a fast design method based on the TM31-2π mode for the dumbbell shaped extended interaction cavity. Based on the equivalent circuit theory, the high-frequency characteristics of the structure are studied. In addition, we propose a W-band continuous wave sheet beam extended interaction klystron high-frequency circuit. The circuit was driven by a 20 kV and 0.85 A sheet electron beam, with a 3.2 × 0.3 mm2 section. The beam was focused by a 0.8 T permanent magnet system. The high-frequency system adopts five dumbbell shaped five-gap cavities, and the output system adopts a symmetrical output waveguide. The 3D particle-in-cell simulation shows that more than 1.5 kW power can be obtained at an input power of 0.12 W, and the electron efficiency and gain are 9.2% and 41.2 dB, respectively.

A G-Band High Output Power and Wide Bandwidth Sheet Beam Extended Interaction Klystron Design Operating at TM31 with 2π Mode

In this paper, we propose a high-order mode sheet beam extended interaction klystron (EIK) operating at G-band. Through the study of electric field distribution, we choose TM31 2π mode as the operating mode. The eigenmode simulation shows that the resonant frequency of the modes adjacent to the operating mode is far away from the central frequency, so there is almost no mode competition in our high mode EIK. In addition, by studying the sensitivity of the related geometry parameters, we conclude that the height of the coupling cavity has a great influence on the effective characteristic impedance, and the width of the gap mainly affects the working frequency. Therefore, it is necessary to strictly control the fabrication tolerance within 2 μm. Finally, the RF circuit using six barbell multi-gap cavities is determined, with five gaps for the input cavity and idler cavities and seven gaps for the output cavity. To expand the bandwidth, the stagger tuning method is adopted. Under the conditions of a voltage of 16.5 kV, current of 0.5 A and input power of 0.2 W, the peak output power of 650 W and a 3-dB bandwidth of 700 MHz are achieved without any self-oscillation.

Design of G-band 500 W sheet beam extended-interaction klystron

High power generation in terahertz frequency band is limited by physical mechanism. A G-band sheet beam extended-interaction klystron was designed to demonstrate the power level and the physical factors that affect the performance of the klystron. An elliptical electron beam with a voltage of 24.5 kV, a current of 0.6 A and the dimension of 1 mm×0.15 mm was used. To match the size of the sheet beam and obtain high efficiency and high gain, the transverse-oversized barbell type multi-gap resonant cavity was used as the interaction circuit. The 3D PIC simulation results show that more than 500 W of power output can be obtained with the actual cavity loss considered, and the electron efficiency and gain are 3.65% and 38.2 dB respectively. It is found that the power and efficiency are largely restricted by the mode stability of the multi-gap cavity as well as the ohmic loss. The ohmic loss of the output cavity has a significant effect on the final output power which should be given special consideration in engineering design. The research in this paper has laid a good foundation for the development of high frequency sheet beam extended-interaction devices.

Theoretical analysis and simulation of W-band sheet beam extended interaction klystron amplifier

The sheet beam extended interaction klystron is an important kind of millimeter-wave and sub-millimeter-wave vacuum electron device, which has extensive applications such as in high resolution radar, imaging system, satellite communication and precision guided missiles. Compared with conventional pencil beam klystron, the sheet beam extended interaction klystron, in which a thin rectangular sheet beam is used, can generate higher power by obtaining higher current and reducing space-charge-effect of electron beam. Kinematical theory and space charge wave theory are extensively used to analyze the bunching process of electrons. Kinematical theory is precise when electron beam is especially small because the influence of space charge effect is ignored, while space charge wave theory is accurate when the modulation of electron beam is small since it is based on the premise of small amplitude. Electron flow oscillatory theory is a compromise between kinematical theory and space charge wave theory, which adapts to the bigger modulation of electron beam than space charge wave theory, while it is inaccurate in the case of big bunching parameter. Based on electron flow oscillatory theory under the small signal condition, the influence of electron beam on standing wave electric field of 2π mode in a three-gap cavity is analyzed, and the expressions of beam loading conductance and beam loading susceptance in a three-gap cavity are obtained. The influences of plasma frequency, transit angle of single gap and transit angle of drift on the interaction of beam and wave in a three-gap cavity are discussed. The results show that space-charge-effect of beam is unbeneficial to the interaction between beam and wave, otherwise beam loading conductance and beam loading susceptance fluctuate with the increasing of transit angle of single gap and transit angle of drift. A W-band sheet beam extended interaction klystron is designed by theoretical analysis and 3D PIC software. The output power of 5773 W at 94.47 GHz is obtained with an efficiency of 8.46%, a gain of 37.6 dB and a 3 dB bandwith of about 140 MHz, when beam voltage is 19.5 kV, current is 3.5 A and focus magnetic field is 0.85 T. This research is important for the engineering of the W-band sheet beam extended interaction klystron amplifier.

RF characteristics of multiple-gap resonant cavity for sheet beam extended interaction klystron

The sheet beam extended interaction klystron( SBEIK) has the typical and attractive characteristics with the plan structural multiple-gap cavity and extended beam-wave interaction system. A type of novel miniaturization strong-coupling five-gap extended resonant cavity was investigated combined with the design of W-band SBEIK,which was compared with the traditional weak-coupling five-gap resonant and output cavity. The obtained characteristics shows that the strong-coupling five-gap cavity may have many advantages of resonant mode separation,radio frequency( RF) fields coupling in the gap and RF energy exporting,etc.Then,the degeneracy mode competition for the strong-coupling five-gap cavity was studied due to its axial period structures. The result shows that the frequency interval between the work mode and vicinal non-working mode is above 600 MHz,which is higher enough than the required 100 MHz bandwidth for the SBEIK. Finally,the 3D particle in cell( PIC) simulation software was used to calculate the beam-wave interaction for the strong-coupling five-gap extended output cavity,the expected high output power was observed with the corresponding performance and favorable stability. Thus,the research is very important for the physical design and engineering development of the SBEIK in the millimeter-wave and terahertz band with high power output radiation later.

Research on equivalent circuit of multi-gap output cavity for sheet beam extended-interaction klystron

Sheet beam extended interaction klystron, which has both the advantages of sheet beam klystron and extended-interaction klystron (EIK), has become a key technique for developing high power microwave and millimeter-wave vacuum electron devices. An equivalent circuit of the five-gap output cavity for sheet beam EIK is proposed in this paper. The mode, resonant frequency, and the cavity impedance can be calculated by using the method of equivalent circuit efficiently. The bandwidth could be estimated by the curve of cavity impedance versus frequency. The influences of coupling coefficient (k) and external Q (Qe) on mode frequency interval and bandwidth are discussed. In order to test and verify the method of equivalent circuit, the 3D-PIC simulation of output cavity is conducted. The bandwidths under different values of external Q are calculated in two ways. The results accord well with each other. It is confirmed that the method of equivalent circuit for sheet beam EIK is accurate and credible. This is useful for the design of the whole tube.

Particle-in-Cell Simulation and Optimization of Multigap Extended Output Cavity for a W-Band Sheet-Beam EIK

In this paper, a multigap extended output cavity was designed by 3-D simulations, which served as the output cavity for a W-band sheet-beam extended interaction klystron (SBEIK). In our numerical design, the circuit dimensions were systematically optimized by parametric finite-difference time-domain simulations, and the equivalent circuit for the output cavity was also analyzed. The proper external loading was selected by using a region of loss in 3-D, and the output power was optimized. The results were verified by using the coupler and the waveguide. The 2π mode of the optimized five-gap extended output cavities had an ohmic Q (Q0) of 1343.5, an external Q (Qe) of 501.6, and a loaded Q (QL) of 365.2 at 94.5 GHz. The 3-D particle-in-cell simulations predict that the output cavity of the SBEIK (75 kV and 4 A) can stably produce more than 50 kW of output power using a prebunched beam.