Xingjun Ge

An L-band coaxial relativistic backward wave oscillator with mechanical frequency tunability

The initial experimental results of an L-band coaxial relativistic backward wave oscillator with mechanical frequency tunability are presented. The key effects of the inner-conductor contributing to the mechanical frequency tunability are investigated theoretically and experimentally. In the experiments, the L-band microwave with frequency of 1.58 GHz is radiated when the inner-conductor radius is 1.5 cm. Meanwhile, the S-band microwave with frequency of 2.31 GHz is generated after removing the inner-conductor. In addition, the frequency tuning within 4% is realized by mechanically altering the radius of the inner-conductor at a half power level.

Asymmetric-mode competition in a relativistic backward wave oscillator with a coaxial slow-wave structure

The initial experimental results of an L-band relativistic backward wave oscillator with a coaxial slow-wave structure are presented. The asymmetric-mode-competition mechanism in the device is investigated theoretically and experimentally. It is shown that the diode voltage, guiding-magnetic field, and concentricity play a key role in the suppression and excitation of the asymmetric-mode (coaxial quasi-TE11 mode). In the experiments, the asymmetric-mode with a frequency of 2.05 GHz is suppressed and excited, which is in good agreement with the theoretical results.

Transversal and longitudinal mode selections in double-corrugation coaxial slow-wave devices

To reduce the dimensions of relativistic backward wave oscillators (RBWOs) operating in the low frequency regime of less than 2 GHz, the theory of transversal and longitudinal mode selections are introduced in this paper. The transversal mode selection is achieved using the property of “surface wave” of the coaxial slow-wave structure (SWS) to excite the quasi transverse electromagnetic (quasi-TEM) mode without the higher transverse magnetic (TM) modes and it is proved that the coaxial SWS may decrease the transversal dimension of the SWS sections. In addition, the S-parameter method is employed to investigate the longitudinal resonant characteristic of the finite-length SWS, and the scheme of longitudinal mode selection is put forward. It is proposed that the introduction of a well-designed coaxial extractor to slow-wave devices can help to achieve the longitudinal mode selection and reduce the period number of the SWS, which not only can make the devices more compact, but also can avoid the destructive ...

Dispersive characteristics and longitudinal resonance properties in a relativistic backward wave oscillator with the coaxial arbitrary-profile slow-wave structure

The method for calculating the dispersion relations of the slow-wave structures (SWSs) with arbitrary geometrical structures is studied in detail by using the Fourier series expansion. In addition, dispersive characteristics and longitudinal resonance properties of the SWSs with the cosinusoidal, trapezoidal, and rectangular corrugations are analyzed by numerical calculation. Based on the above discussion, a comparison on an L-band coaxial relativistic backward wave oscillator (BWO) and an L-band coaxial BWO with a coaxial extractor is investigated in detail with particle-in-cell KARAT code (V. P. Tarakanov, Berkeley Research Associates, Inc., 1992). Furthermore, experiments are carried out at the TORCH-01 accelerator under the low guiding magnetic field. At diode voltage of 647 kV, beam current of 9.3 kA, and guiding magnetic field strength of 0.75 T, the microwave is generated with power of 1.07 GW, mode of TM01, and frequency of 1.61 GHz. That is the first experimental report of the L-band BWO.

A compact relativistic backward-wave oscillator with metallized plastic components

This letter presents the mechanism and realization of a compact relativistic backward-wave oscillator with metallized plastic components. The physical idea, specific structure, and the main testing results are presented. The three periods slow-wave structures with both inner and outer ripples and the coaxial extractor are designed to reduce the volume and increase the efficiency of the device. The metallized plastic components replacing the stainless steel components in the high power microwave (HPM) sources are put forward to reduce the device weight. In the initial experiment, a microwave with frequency of 1.54 GHz, power of 1.97 GW, efficiency of 33.5%, and pulse duration above 47 ns is generated, which proves that this technical route is feasible. Undoubtedly, the technical route can provide a guide to design other types of HPM sources and be benefit to the practical application of the compact HPM systems.

A high efficient relativistic backward wave oscillator with coaxial nonuniform slow-wave structure and depth-tunable extractor

A high efficient relativistic backward wave oscillator with coaxial nonuniform slow-wave structures (SWSs) and depth-tunable extractor is presented. The physical mechanism to increase the power efficiency is investigated theoretically and experimentally. It is shown that the nonuniform SWSs, the guiding magnetic field distribution, and the coaxial extractor depth play key roles in the enhancement of the beam-wave power conversion efficiency. The experimental results show that a 1.609 GHz, 2.3 GW microwave can be generated when the diode voltage is 890 kV and the beam current is 7.7 kA. The corresponding power efficiency reaches 33.6%.

The mechanism and realization of a band-agile coaxial relativistic backward-wave oscillator

The mechanism and realization of a band-agile coaxial relativistic backward-wave oscillator (RBWO) are presented. The operation frequency tuning can be easily achieved by merely altering the inner-conductor length. The key effects of the inner-conductor length contributing to the mechanical frequency tunability are investigated theoretically and experimentally. There is a specific inner-conductor length where the operation frequency can jump from one mode to another mode, which belongs to a different operation band. In addition, the operation frequency is tunable within each operation band. During simulation, the L-band microwave with a frequency of 1.61 GHz is radiated when the inner-conductor length is 39 cm. Meanwhile, the S-band microwave with a frequency of 2.32 GHz is radiated when the inner-conductor length is 5 cm. The frequency adjustment bandwidths of L-band and S-band are about 8.5% and 2%, respectively. Moreover, the online mechanical tunability process is described in detail. In the initial experiment, the generated microwave frequencies remain approximately 1.59 GHz and 2.35 GHz when the inner-conductor lengths are 39 cm and 5 cm. In brief, this technical route of the band-agile coaxial RBWO is feasible and provides a guide to design other types of band-agile high power microwaves sources.

A relativistic backward-wave oscillator with frequency-selectable across X- and Ku-bands

The mechanism and realization of a relativistic backward-wave oscillator (RBWO) with frequency-selectable across X- and Ku-bands are presented. Both the transverse and the longitudinal mode selections contribute to the frequency-selectable across different bands. The transverse mode selection is achieved using the property of “surface wave” of the slow-wave structures to excite the coaxial TM01 mode (Ku-band) or the hollow TM01 mode (X-band) without exciting the higher TM modes. The longitudinal mode selection is achieved by the introduction of a coaxial extractor, which contributes to the compact structure and the restraints of the longitudinal mode competitions. In simulation, a Ku-band microwave with a frequency of 12.6 GHz and an X-band microwave with a frequency of 10.6 GHz are radiated when the inner-conductor length is 10.2 cm and 0 cm, respectively. The output power of both bands is above 2 GW. This technical route of RBWO with frequency-selectable across different bands is feasible and provide a ...

Research activities on high-power microwave sources in National University of Defense Technology of China

Research activities on High-power microwave (HPM) sources in National University of Defense Technology (NUDT) of China are presented. The research issues are focused on following aspects. (1) Suppression of pulse-shortening phenomenon in O-type Cerenkov HPM devices. (2) Enhancement of the power efficiency in M-Type HPM tubes without guiding magnetic field. (3) Enhancement of the power efficiency in Space-charge device with multi-cavity. (4) Development of the compact coaxial relativistic backward-wave oscillator (RBWO) at low bands. (5) Enhancement of the power capacity and power efficiency in triaxial klystron amplifier (TKA) at higher frequencies. (6) Enhancement of the power capacity and power efficiency in relativistic transit-time oscillator (TTO) at higher frequencies. In experiments, some exciting results were obtained. The X-band source generated 2GW microwave power with pulse duration of 110ns in 30Hz repetition mode. A 1.755GHz MILO produced 3.1GW microwave power with power efficiency of 10.4%. Furthermore, the experimental waveforms for a 10 pulse, 2Hz shot series are obtained. A 4.1GHz multi-cavity VCO produced 1GW microwave power with power efficiency of 6.6%. Both L- and P-band compact RBWOs generated over 2GW microwave power with power efficiency of over 30%. There is approximately a 75% decline of the volume compared with that of conventional RBWO under the same power level. A 9.37GHz RKA produced the 240MW microwave power with the gain of 34dB. A 14.3GHz TTO produced 1GW microwave power with power efficiency of 20%.

Particle simulation of a sinusoidal corrugation compact L-band coaxial backward wave oscillator

In this paper, a sinusoidal corrugation compact L-band coaxial relativistic backward wave oscillator (BWO) is investigated using the 2.5 D particle simulation code. A field- matching method is presented to obtain the dispersive characteristics of TM01 electromagnetic modes in the sinusoidal corrugation slow wave structure (SWS). Detail physical interaction pictures of the oscillator are presented. Simulation results show that for an electron beam of 700keV and 10kA, a microwave of coaxial TM01 mode is generated with power of 2.2GW and frequency of 1.6GHz when the external guiding magnetic field is about IT. The beam to microwave efficiency is about 30% . The optimized electromagnetic structure of the device is only phi100mmtimes520mm.