Huarong Gong

High-Power Millimeter-Wave BWO Driven by Sheet Electron Beam

The sheet beam vacuum electron device is an attractive choice for generating high-power high-frequency microwave radiation. A millimeter-wave sheet beam backward wave oscillator (BWO) is presented in this paper. The rectangular waveguide grating structure is used as its slow wave structure. The BWO is driven by a sheet beam with a cross-sectional area of 30 mm × 1 mm which is generated by a thin cathode. For a beam voltage of 167 kV and a beam current of 1.4 kA, the output power is 40 MW at 36.6 GHz. The beam-wave interaction efficiency is about 17%, which is higher than that of conventional hollow beam BWO. It is clear from the results presented in this paper that the sheet beam device is promising for producing high-efficiency high-power millimeter-wave radiation.

Experimental Investigation of a High-Power Ka-Band Folded Waveguide Traveling-Wave Tube

A Ka-band traveling-wave tube (TWT) was fabricated with a folded waveguide (FWG) as its slow-wave structure. The TWT demonstrates more than 700-W radio-frequency peak output power within a 2.5-GHz bandwidth. Because this type of TWT can be manufactured and assembled in an easy and cheap way, the FWG TWT will be a competing high-power millimeter wave source, compared to helix and coupled-cavity TWTs in Ka-band.

Study on Wideband Sheet Beam Traveling Wave Tube Based on Staggered Double Vane Slow Wave Structure

In this paper, a wideband 220-GHz sheet-beam traveling-wave tube (TWT) based on staggered double vane slow-wave structure (SWS) is investigated. A novel method of loading the attenuator into the SWS for suppressing backward wave oscillation is proposed. In addition, a novel focusing electrode of the sheet beam gun is carried out in this paper, which is a whole structure but divided into two parts artificially, one is used to compress the electron beam in X-direction and the other is used to compress the electron beam in Y-direction. In addition, a novel anode is redesigned to reduce the defocusing effect caused by the equipotential surfaces. A nonuniform periodically cusped magnet is used for focusing the sheet electron beam, which is predicted to exhibit 100% beam transmission efficiency in a 75-mm length drift tube. The high-frequency characteristics of the SWS and the beam-wave interaction are also studied. The results reveal that the designed TWT is expected to generate over 78.125-W average power at 214 GHz, and the 3-dB bandwidth is 31.5 GHz, ranging from 203 to 234.5 GHz.

Stable Sheet-Beam Transport in Periodic Nonsymmetric Quadrupole Field

Stable sheet electron-beam transport is critical for sheet-beam microwave device which is attractive for high-power millimeter wave to terahertz-regime radiation. This paper studies the stable sheet-beam transport in periodic nonsymmetric quadrupole field. First, the conditions for stable round- and sheet-beam transport in periodic magnetic quadrupole field are deduced. In the deduction, we find that the symmetric quadrupole field and the space-charge field of sheet beam are not well matched. In order to settle this problem, we use periodic nonsymmetric quadrupole field instead of periodic symmetric quadrupole field to transport sheet beam. Finally, 3-D PIC simulations verify the conditions for stable sheet-beam transport and show that periodic nonsymmetric quadrupole field is intrinsically well suited for sheet-beam transport.

High-Power Tunable Terahertz Radiation by High-Order Harmonic Generation

We propose a new type of terahertz (THz) radiation source based on the electron beam-wave interaction. A high-order harmonic-generation process was introduced to a traveling-wave tube (TWT)-like device-the high-harmonic TWT or HHTWT. The scheme is configured as a frequency multiplier and amplifier with W-band (millimeter wave) input signals and THz output power. Simulations show that operation at the seventh harmonic is possible and other order harmonic waves were suppressed. The output frequency can be tuned continuously over a 30-GHz bandwidth with more than 20-dBm output power. The peak output power is about 30 dBm at 707 GHz. The output frequency is insensitive to beam voltage jitter.

A 1-kW 32–34-GHz Folded Waveguide Traveling Wave Tube

Folded waveguide (FWG) traveling wave tubes (TWTs) are potential sources of wideband, high-power millimeter and terahertz wave radiation. However, low efficiency limits its application. In this paper, we discuss a design strategy to improve efficiency of the FWG TWT meanwhile how to avoid instability is also discussed. The critical factors for the slow-wave structure design and the sever design are analyzed. A phase velocity taper profile incorporating a positive period followed by a negative period is introduced into the design to improve the efficiency. A Ka-band FWG TWT was developed, which demonstrated the output power up to in 2-GHz bandwidth and electronic efficiency up to .

The design of Ka-band High Power Folded Waveguide Traveling-Wave Tube

A Ka-band High Power Traveling-Wave Tube was designed with folded waveguide as its slow wave structure. The simulation result show it can output 1000 Watte and the bandwidth is more than 1 GHz. It maybe an ideal driving source for Gyroklystrons and Gyro-TWT.

Dispersion Equations of a Rectangular Tape Helix Slow-Wave Structure

A rectangular tape helix slow-wave structure with infinitesimal thickness and finite width in free space is investigated. With the expansion of surface currents in the helix and the applications of the modified Marcatilis method, as well as average power flow matching method at the boundaries, the dispersion properties and the interaction impedance for transverse antisymmetric modes in a rectangular tape helix immersed in free space are obtained. It is shown that, compared with the results of the simplified sheath model by previous researchers, higher accuracy has been obtained between the calculation results of the present theory and the data obtained from HFSS, and the validity of the present theory is further demonstrated by comparison with experiments. The improved characteristic equations hold scientific and practical significance in the design and performance evaluation of such plane slow-wave structure in the application of compact traveling-wave tubes. The distribution characteristics on the cross section of the longitudinal electric field fundamental component are also discussed based on this theory.

Theoretical and Experimental Research on a Novel Small Tunable PCM System in Staggered Double Vane TWT

In this paper, a novel small tunable periodic cusped magnet (NSTPCM) system is proposed for the purpose of realizing low voltage, big current sheet electron beam propagation in a long distance in engineering, which is composed of a series of position-fixed magnet blocks in alignment and freely sliding staggered pole pieces. This kind of NSTPCM not only generates higher magnetic field in the axial direction but also realizes more convenient adjustment of magnetic field in the transverse direction. This NSTPCM system has been successfully applied in a Ka-band sheet electron beam staggered double vane traveling wave tube. The tested sheet beam transmission efficiency is >93 % in a 112.7-mm-length slow-wave structure under the condition of beam voltage 24.3 kV and beam current 0.8 A. Moreover, the measured output power is >75 W in the range from 33 to 37.5 GHz, and the maximum output power is 128 W at 34 GHz. This paper provides the foundation for the development of sheet electron beam vacuum devices.

Producing high current sheet electron beam with compact, repetitive Tesla generator

Sheet electron beam device has the potential for high-power millimeter wave to terahertz regime radiation. A key part of this system is a high current sheet electron beam source. This paper introduces our currently ongoing program on producing high current, high aspect ratio sheet electron beam with compact, repetitive 160KV generator. In our experimental, a cathode which looks like a blade and a slit anode is fabricated. High current sheet electron beam is transported in a solenoid. Here we report the experimental demonstration.