In this paper, a quasi-optical (QO) output coupler, consisting of a tapered waveguide coupling to WR-10 waveguide, was designed to serve as the multigap output cavity of a 50-kW peak-power W-band sheet-beam klystron. In this structure, TE10 mode radiation from the gap ports is superimposed in the tapered waveguide coupling out to the external waveguide. In our numerical design, the circuit dimensions were systematically optimized by parametric finite-difference time-domain simulations; the 2 pi mode of the optimized QO output cavities (three, five, and seven gaps) have an external Q(Qe) of 650, an ohmic Q(Q 0) of 1650, and a total Q(Qt) of 460 at 95.4 GHz. The measured transmission coefficient (S 21) through the two QO external waveguide ports is in reasonable agreement with the transmission predicted from simulation. MAGIC3-D particle-in-cell simulation predicts that the QO output cavity stably produces more than 50-kW output power from a 70-kV and 3.6-A electron beam in the eight-cavity klystron circuit.

Quasi-Optical Output-Cavity Design for a 50-kW Multicavity W-Band Sheet-Beam Klystron

This paper reports the research work of an X-band sheet beam klystron with the aim of principle verification, which is fulfilled at the Institute of Electronics, Chinese Academy of Sciences. This paper includes two phases. The first phase is planned to build the sheet beam electron optics prototype tube using the closed periodically cusped magnetic focusing. The measured data shows that the rectangular beam with the cross section of 50 mm × 4 mm can propagate through ~ 300 mm from the cathode surface to the collector with the transmission of 92.4% at the voltage of 110 kV. This foregoing work successfully solves the beam formation and transportation and becomes the basis for developing the sheet beam klystron. In the second phase, the high-frequency interaction structure is designed and cold tested. The X-band sheet beam klystron is constructed and hot tested in the full voltage. The amplification characteristic can be observed near the voltage of 125 kV. For the drive power of 0.71 kW and the working frequency of 11.69 GHz, the output power of 2.8 MW is achieved with the 3 dB bandwidth of 30 MHz, and, correspondingly, the gain and the efficiency are 35.96 dB and 32.52%, respectively. At the same time, the beam transmission is 73.3%. An over 93% transmission is realized at the voltage of 135 kV, whereas the oscillation occurs in the tube. This research exhibits that the sheet beam klystron is a promising device for the high-power applications, whereas seeking the measures to overcome the oscillation is still an arduous task in the future.

Researches on an $X$ -Band Sheet Beam Klystron

Development of high frequency, high-average power linear beam devices is hindered by the slow progress in advancement of suitable mechanical design and manufacturing techniques. To compliment the significant progress in electromagnetic modeling and design of high-frequency electronics, the mechanical design and manufacturing approach employed for the development of a 10 kW continuous wave W-band sheet beam klystron is reported. The reported design enabled demonstration of 10-kW, 20-ms duration pulses with 17-dB gain and 97% (hot) beam transmission. This high-average power design was based on the demonstration of a 56 kW short pulse ( $1~\mu \text{s}$ ) device with 54 dB of gain. The high-average power design features a multilayer strengthened material structure with hybrid microcooling and macrocooling circuits for enhanced heat flux handling. Microcooling channels fit between circuit cavities providing heat removal as well as thermal-stress relief for reduced cavity deformation. The design achieves a 1.5-safety factor on yield and less than 2- $\mu \text{m}$ deformation at the cavities. The presented design and manufacturing approach can be applied to the development of other high-average power high-frequency linear beam devices.

Mechanical Design and Manufacturing of W-Band Sheet Beam Klystron

In this paper, the dumbbell resonant cavity frequency tuning method and beam wave interaction system of W band sheet beam Klystron (WSBK) has been studied. Under the designed value of beam voltage 75kV, beam current 3.8A, and beam size of 10*0.5 mm2, the structures and high frequency parameters of single gap and multi-gap cavities are tested and discussed to achieve the higher output power in detail. With the tuning system proposed, the bandwidth of 100MHz can be obtained. Then, the output power is calculated by both 2-dimensional software SBK2D and the 3D PIC program, and the results agree very well.

Design of resonant cavity and beam wave interaction system for a W-band sheet beam Klystron

A sheet-beam Extended Interaction Klystron (SBEIK) is an attractive MMW amplifier because of its high gain per unit length and compact configuration. The output cavity is an important part of the whole tube, which is used for RF power extraction. In this paper, multi-gap extended output cavity designs of SBEIK are presented by 3D simulations, RF parameters have been calculated. Beam wave interaction process of the output circuit has been studied.

Design of multi-gap extended output cavity for W band Sheet beam EIK

At millimeter wavelengths, there is a growing need for a small size and weight, high average power RF source. The sheet beam klystron (SBK) is ideally suited to many of these needs. The SBK is characterized by a large rectangular drift tube, which allows the use of a high current, low voltage beam, resulting in a low beam current density, and hence high efficiency and the possibility of PPM focusing.

W-band sheet beam klystron design

In this paper, the development of W-band sheet beam klystron has been introduced with high transmission rate beam and a 2-dimensional code SBK2D calculation. The ellipse cathode and electrode structure is used to form the sheet electron beam with the beam aspect ratio about 25:1. And the uniform magnetic system is used to transport the sheet electron beam with the drift tube length about 100mm. After the sheet beam tube is manufactured, the transmission rate and cross-section experiment are performed. With the beam voltage of 20–82 kV, and beam current of 0.5–4.2A, the transmission rate is more than 98%, and the beam cross-section is about 10×0.5mm2. Then the sheet electron beam wave interaction process with 4 single-gap and 4 multi-gap cavities are calculated using the 2-dimensional code SBK2D based on the rod shape macro-particle model, the 55kW high frequency output with the efficiency of 20% and gain of 40 dB are observed at the frequency of 94.5 GHz.

Development of W-band sheet beam klystron with high transmission rate electron optics system

The sheet beam klystron (SBK) is characterized by a large rectangular drift tube, which allows the use of a high current, low voltage beam, resulting in a low beam current density, and hence high efficiency and the possibility of Periodic Permanent Magnet (PPM) focusing. Our research group has designed a 5-Cavity X-Band SBK recently. In this paper, we discusses the general design of this X-Band SBK and presents the transfer characteristic of it predicted by a large signal code we developed.

Wang Ruan

Papers

W-band sheet beam klystron design

Development of W-band sheet beam klystron with high transmission rate electron optics system

Design of resonant cavity and beam wave interaction system for a W-band sheet beam Klystron

X-Band sheet beam klystron design

Study of the Sheet Beam Transmission Based on 2D Macroparticle Model: Study of the Sheet Beam Transmission Based on 2D Macroparticle Model