Xuesong Yuan

Two-beam magnetron injection guns for coaxial gyrotron with two electron beams

To verify the concept of a coaxial gyrotron with two electron beams (CGTB), an electron gun with two beams is needed. In this paper, two types of two-beam magnetron injection guns are proposed: a normal two-beam magnetron injection gun and a coaxial two-beam magnetron injection gun. The design models and space charge limiting current are given. The simulation results show that both types of guns could fulfill the requirement for a CGTB. Comparisons between the two types of injection guns are discussed.

A Fully-Sealed Carbon-Nanotube Cold-Cathode Terahertz Gyrotron.

Gigahertz to terahertz radiation sources based on cold-cathode vacuum electron technology are pursued, because its unique characteristics of instant switch-on and power saving are important to military and space applications. Gigahertz gyrotron was reported using carbon nanotube (CNT) cold-cathode. It is reported here in first time that a fully-sealed CNT cold-cathode 0.22 THz-gyrotron is realized, typically with output power of 500 mW. To achieve this, we have studied mechanisms responsible for CNTs growth on curved shape metal surface, field emission from the sidewall of a CNT, and crystallized interface junction between CNT and substrate material. We have obtained uniform growth of CNTs on and direct growth from cone-cylinder stainless-steel electrode surface, and field emission from both tips and sidewalls of CNTs. It is essential for the success of a CNT terahertz gyrotron to have such high quality, high emitting performance CNTs. Also, we have developed a magnetic injection electron gun using CNT cold-cathode to exploit the advantages of such a conventional gun design, so that a large area emitting surface is utilized to deliver large current for electron beam. The results indicate that higher output power and higher radiation frequency terahertz gyrotron may be made using CNT cold-cathode electron gun.

A Gridded High-Compression-Ratio Carbon Nanotube Cold Cathode Electron Gun

In order to develop field emission cold cathode radiation source devices, a gridded carbon nanotube (CNT) cold cathode electron gun is theoretically and experimentally investigated in this letter. The planar grid and annular CNT cold cathode are used and optimal parameters of a high-compression-ratio electron gun are obtained by particle in cell simulation software. A 4-mA/10-kV annular electron beam with an average radius of 1.75 mm is achieved based on a permanent magnet in the experiment. The area compression ratio of electron beam is ~10.

Design and Experiment of a 220/420-GHz Gyrotron for Nondestructive Evaluation

We report the design and experiment of a 220/420-GHz gyrotron oscillator for nondestructive evaluation which operates at the fundamental near 220 GHz and the second harmonic near 420 GHz of the electron cyclotron resonance frequency. Through optimizing electron gun for both operation modes, the TE26 mode at 423.1 GHz and the TE03 mode at 221 GHz are observed at output powers up to 8 and 6 kW, respectively, by only changing the beam voltage at a magnetic field of 8.2 T. The experimental results are in reasonable agreement with the design and simulation. In addition, the measurements of potential operation modes with peak output power are also presented in this paper.

Parametrically Optimized Carbon Nanotube-Coated Cold Cathode Spindt Arrays

Here, we investigate, through parametrically optimized macroscale simulations, the field electron emission from arrays of carbon nanotube (CNT)-coated Spindts towards the development of an emerging class of novel vacuum electron devices. The present study builds on empirical data gleaned from our recent experimental findings on the room temperature electron emission from large area CNT electron sources. We determine the field emission current of the present microstructures directly using particle in cell (PIC) software and present a new CNT cold cathode array variant which has been geometrically optimized to provide maximal emission current density, with current densities of up to 11.5 A/cm2 at low operational electric fields of 5.0 V/μm.

Theoretical study on a 0.6 THz third harmonic gyrotron

A theoretical study on a 0.6 THz third harmonic TE37 mode gyrotron oscillator is reported in this paper in order to develop a compact, reliable, and high power terahertz radiation source. An output power of 4 kW can be generated in the TE37 mode (0.6 THz) at a resonant magnetic field of 7.86 T by the gyrotron oscillator operating at 55 kV/2 A with an electron beam radius of 0.32 mm. A magnetron injection gun (MIG) with high compression ratio has been designed. The simulation results of MIG show that the velocity ratio α is 1.37, and the perpendicular velocity spread and parallel velocity spread are 6.1% and 8.9%, respectively.

Theoretical Research on a Multibeam-Modulated Electron Gun Based on Carbon Nanotube Cold Cathodes

Multi-beam modulation in a carbon nanotube (CNT) cold cathode electron gun is herein investigated in order to develop miniaturized and fully integrated vacuum electron devices. By exposing the electron source to a millimeter-wave signal, the steady-state field emission current density is efficiently modulated by the incident high-frequency (HF) electric field. Our simulation results of this multibeam electron gun show that the field emission current density can be efficiently modulated by different incident frequency millimeter waves. We find that the modulation depth is increased by enhancing the HF input power and anode operation voltage. The modulation frequency and phase of each electron beam can be controlled using a single millimeter-wave source and by simply adjusting the lateral distance between adjacent CNT cold cathodes.

Theoretical research on an 8mm traveling wave tube based on carbon nanotube cold cathode

An 8mm traveling wave tube (TWT) based on carbon nanotube (CNT) cold cathode is theoretically researched to develop millimeter-wave vacuum electron radiation source devices based on CNT cold cathode in this paper. A gridded sheet-beam CNT electron gun and staggered double vane slow-wave structure (SWS) is adopted in the 8mm TWT based on a periodic permanent magnetic system. Simulation results show that the maximum output power of the CNT TWT can reach 128 W at 32 GHz with an input power of 80 mW, corresponding to the maximum gain of 32 dB, when the operation voltage and beam current are 20 kV and 100 mA, respectively. And the 3-dB bandwidth of the CNT TWT is about 6 GHz.

Conjugated polyelectrolyte nano field emission adlayers

Here we report on a straightforward and rapid means of enhancing the field electron emission performance of nascent vertically aligned multi-walled carbon nanotubes by introducing a polar zwitterionic conjugated polyelectrolyte adlayer at the vacuum-emitter interface. We attribute the observed 66% decrease in turn-on electric field to the augmented emitter micro-morphology and shifted surface band structure. The composite emitters can be optically modulated by exploiting the absorption cross-section of the solution cast adlayer, which increases the local carrier concentration which broadens the effective electrostatic shape of the emitter during optical excitation. Assessment via scanning anode field emission microscopy reveals a 25% improvement in DC time stability, a significant reduction in long-term hysteresis shift, and a threefold increase in bandwidth during pulsed mode operation.

Experimental results of a 0.42 THz harmonic gyrotron

We report primarily results of a 0.42 THz second harmonic gyrotron. In microsecond pulse length operation at 52kV and 3A, 4.4kW output power have been observed at the TE2,6 mode at 0.423 THz. Modes at fundamental, including the TE0,3 at 0.221 THz and the TE2,3 at 0.216 THz, have output powers up to 20kW.