Design and preliminary test of a 105/140 GHz dual-frequency MW-level gyrotron

A dual-frequency(105/140 GHz)MW-level continuous-wave gyrotron was developed for fusion application at Institute of Applied Electronics,China Academy of Engineering Physics.This gyrotron employs a cylindrical cavity working in the TE18,7 mode at 105 GHz and the TE24,9 mode at 140 GHz.A triode magnetron injection gun and a built-in quasi-optical mode converter were designed to operate at these two frequencies.For the proof-test phase,the gyrotron was equipped with a single-disk boron nitride window to achieve radio frequency output with a power of~500 k W for a short-pulse duration.In the preliminary short-pulse proof-test in the first quarter of2021,the dual-frequency gyrotron achieved output powers of 300 k W at 105 GHz and 540 k W at140 GHz,respectively,under 5 Hz 1 ms continuous pulse-burst operations.Power upgrade and pulse-width extension were hampered by the limitation of the high-voltage power supply and output window.This gyrotron design was preliminarily validated.

A 0.33-THz second-harmonic frequency-tunable gyrotron

Dynamics of the axial mode transition process in a 0.33-THz second-harmonic gyrotron is investigated to reveal the physical mechanism of realizing broadband frequency tuning in an open cavity circuit. A new interaction mechanism about propagating waves, featured by wave competition and wave cooperation, is presented and provides a new insight into the beam-wave interaction. The two different features revealed in the two different operation regions of low-order axial modes （LOAMs） and high-order axial modes （HOAMs） respectively determine the characteristic of the overall performance of the device essentially. The device performance is obtained by the simulation based on the time-domain nonlinear theory and shows that using a 12-kV/150-mA electron beam and TE 3,4 mode, the second harmonic gyrotron can generate terahertz radiations with frequency-tuning ranges of about 0.85 GHz and 0.60 GHz via magnetic field and beam voltage tuning, respectively. Additionally, some non-stationary phenomena in the mode startup process are also analyzed. The investiga- tion in this paper presents guidance for future developing high-performance frequency-tunable gyrotrons toward terahertz applications.

Theoretical and numerical studies on a planar gyrotron with transverse energy extraction

In this paper, we study the planar gyrotron theoretically and numerically. Applying the large-signal theory to the planar gyrotron, the wave equation of electric field and the equation of motion of an electron are simultaneously solved to obtain some characteristic parameters, such as the phase-space plot of electrons, working frequency, startup time, electronic efficiency, and output power of the device. To verify the formulations used in this paper, three-dimensional particle simula- tions are performed on the same device, and the numerical results accord well with those obtained by using the large-signal theory. Theoretical and numerical results show that the electronic efficiency can reach 21% for the prototype of the planar gyrotron working at the frequency of 0.81 THz.

Three-dimensional particle-in-cell method of simulating high power terahertz gyrotrons with planar structure

Based on analyzing the large-signal theory of the planar gyrotron, it is suggested that a simplified structure of the device is used for simulating this kind of device, with the working characteristics of the device kept unchanged, i.e., the same as those of the device with the original structure. Thus, the computational burden can be significantly reduced. Using the proposed method, we simulate a planar gyrotron with its simplified parameters by using the UNIPIC-3D code. Numerical results show that the working frequency, output power, and electron efficiency are respectively about 0.813 THz, 14 kW, and 21%.

Design and experimental results of a 28 GHz,400 kW gyrotron for electron cyclotron resonance heating

A high-power 28 GHz gyrotron has been successfully developed at the Institute of Applied Electronics,China Academy of Engineering Physics.This gyrotron was designed for electron cyclotron resonance heating(ECRH)in the spherical tokamak XL-50.A diode magnetron injection gun was designed to produce the required gyrating electron beam.The gyrotron operates in the TE8,3mode in a cylindrical open cavity.An internal quasi-optical mode converter was designed to convert the operating mode into a fundamental Gaussian wave beam and separate the spent electron beam from the outgoing microwave power.A tube has been built and successfully tested.The operational frequency of the tube is 28.1 GHz.For beam parameters at an accelerating voltage of 71 kV and beam current of 16 A,the gyrotron has delivered an output power of 400 kW,with a pulse length of 5 s.The output efficiency is about 50%with a singlestage depressed collector.The gyrotron has been installed on the XL-50 and has played an important role in the ECRH experiments.

Study and Design of a High-Frequency Interaction Cavity for a 140 GHz Megawatts Gyrotron

The gyrotron is one of the most promising high-power millimeter-wave sources for electron cyclotron resonance heating（ECRH） in controlled thermal nuclear fusion experiments.In this paper,the design of a high-frequency interaction cavity of a 1 MW/140 GHz gyrotron is described in detail.The cavity is designed by using eigen mode analysis and radio frequency（RF） behavior calculation.Rounded transitions at the input and output tapers are designed for reducing mode conversion.With the obtained cavity structure,non-linear self-consistent equations are adopted to calculate its output power and efficiency.A particle-in-cell（PIC） method is used to simulate the beam-wave interaction process for obtaining the resonant frequency and output power of the cavity.The PIC simulation results match considerably well with the results obtained by the non-linear self-consistent calculation.The cavity is currently under construction and will be integrated with other components for overall testing.

The 5.8 T Cryogen-Free Gyrotron Superconducting Magnet System on HL-2A

A 5.8 T cryogen-free superconducting magnet （SCM） system with a warm bore hole of 160 mm in diameter, used for gyrotrons operating in the frequency range from 68 GHz to 140 GHz, is installed on the site of the HL-2A tokamak. The SCM consists of two separate solenoidal magnetic coils connected in series, a 4.2 K Gifford-McMahon （GM） refrigerator, a com- pressor, a coil power supply and two temperature monitors. The performance, test and preliminary experimental results of this SCM system are described in this paper. The magnetic field distribu- tion was measured along the axis, and a dummy tube was used for adjusting the magnet system. Finally, the magnet was used for the operation of a 68 GHz/500 kW gyrotron, which is part of an electron cyclotron resonance heating （ECRH） system. With an additional auxiliary coil and after adjusting tile magnet system, a maximum output power for the ECRH system of up to 400 kW was achieved.

PHASE-LOCKING OF HIGH POWER GYROTRON OSCILLATOR

The phase-locking process is studied for high-power gyrotron oscillator driven by an external signal. The phase-locking nonlinear differential equations are derived, and the condition of phase-locking is shown and analyzed. The phase-locking signal can be introduced after gyrotron oscillates into saturation or before it. Two different ways of inputting signal make markable influence on the phase-locking process, this phenomenon is discussed. In this paper, the numerical calculations and analysis are given for gyrotron TE13 mode.

STUDY OF CROSSED FIELD GYROTRON OPERATING ON WHISPERING-GALLERY MODE

A linear and nonlinear analysis of crossed-field gyrotron operating on whispering-gallery mode TEm11 is presented. The detailed discussions are given for the starting oscillationcondition, the effect of the internal conductor in coaxial cavity on the cut-off frequency of modeand the spacing between adjacent modes as well as the effect of the applied voltage on thecyclotron frequency of electron, the starting oscillation beam power and the electron efficiency.It is shown that the efficiency of 41% can be attained for m=2. A comparison of these resultswith those in cylindrical cavity is made. The analyses are helpful for the engineering design.

Rocket Propulsion Powered Using a Gyrotron

Abstract： This paper presents a review of a beamed energy propulsion rocket, the Microwave Rocket, WlllCn proauces propmslve thrust from millimeter-wave beams transferred from the ground. The thrust is generated through millimeter-wave discharge driven in a cylindrical thruster. As a high-power millimeter-wave generator, a Gyrotron is promising as the beam source. The salient benefit of Microwave Rockets is the resultant drastic cost reduction of mass transportation into space. We have already conducted launch experiments and have achieved continuous thrust generation under multi-pulse operation. Recently, a long-distance beam transfer system has been developed. Ignition tests have been conducted. The physics of the millimeter-wave discharge remain unclear. Additional studies using exoerimentation and calculations must be conducted to optimize the thrust generation.

Denisov-type quasi-optical mode converter forhigher-order asymmetric volume mode gyrotron

The principle and design method of Denisov-type quasi-optical mode converter is investigated indetail. The operation process of the Denisov-type launcher is analyzed by applying the geometrical optics, andthe Gaussian-like field distribution achieved on the waveguide wall is also derived. The method for designing arippled-wall launcher is proposed on the basis of coupled mode theory. A simulation code for Denisov-type qua-si-optical mode converter GQOMC-D is developed based on coupled mode theory, vector diffraction integrationand physical optics, which is compared to the design parameters and experimental results reported in literaturefor its validity. According to this code, a Denisov-type quasi-optical mode converter used in 110 GHz TE22.6mode gyrotron oscillators is designed. Simulation results indicate that a Gaussian-like beam is obtained at theoutput window with a scalar content of 98.4 % and a conversion efficiency of 94.7 %.

Investigation of gyrotron-based collective Thomson scattering for fast ion diagnostics in a compact high-field tokamak

As a promising method for fast ion diagnostics,collective Thomson scattering(CTS)can measure the one-dimensional velocity distribution of fast ions with high spatial and temporal resolution.The feasibility of diagnosing fast ions in a compact high-field tokamak by CTS was studied in this work,and the results showed that a wide range of probing frequencies could be applied.A high-frequency case and a low-frequency case were mainly considered for fast ion diagnostics in a compact high-field tokamak.The use of a high probing frequency could effectively avoid the refraction effect of the beams,while the application of a low probing frequency allows greater flexibility in the selection of scattering angle which may help to improve the spatial resolution.Based on typical plasma conditions(B_(0)=12.2 T,n_(e0)=4.3×10^(20)m^(-3),T_(e0)=22.2 keV,T_(i0)=19.8 keV)for a compact high-field tokamak,a220 GHz CTS diagnostic that utilizes a small scattering angle ofθ=30°and a 160 GHz CTS diagnostic that utilizes an orthogonal geometry were proposed.Further study showed that the high-frequency case could operate in a wider range of plasma conditions and provide more information on fast ions while the low-frequency case could achieve higher spatial resolution of the poloidal direction.

Development of the Highly Homogeneous Magnetic Field for Simulative Gyrotron by HTS

The low temperature superconducting magnet system, with the highly homogeneous magnetic field, has been applied extensively, and has had important effects on many domains. With the development of the cryogenic and superconducting techniques, it is possible that high temperature superconducting magnet with highly homogeneous magnetic field is manufactured by high temperature superconductor（HTS）. Therefore, a simulative gyrotron applied into war, with highly homogeneous magnetic field, is designed and manufactured by high temperature superconducting material.

The Analysis of the Phenomenon for ECRH Gyrotrons Test

in HL-2A tokamak the system of ECRH has been consisted of two gyrotrons that each is 500 kW of the microwave output power, the frequency is 68 ±0.1 GHz and the duration is 1 s. A set of appropriate parameters of the power supply and the control procedure are very important during the test of gyrotrons. Basing on analysis of the phenomenon observed, we conside that the troubles came from mainly the stability of the power supply, the sequence of control, the overcurrent protection and the grounding of the system. The solutions have been put forward and the system have been improved partly. The gyrotron has been adjusted one by one. This paper introduces the analysis of power supply for gyrotrons.

Measurement of the Distribution of Magnetic Field in Gyrotron of ECRH System on HL-2A Tokamak

In ECRH system of HL-2A tokamak, we chose a new type of gyrotron imported from Russia. We finished the installation and testing last year with the help of Russian experts. We got a lot of useful data and satisfying results after our experiments with the operating of gyrotron.

Self-consistent Nonlinear Theory of High-power Gyrotron Pump for EMW-FEL

Some theoretic problems of gyrotron pump for free electron laser with electro- magnetic wiggler(EMW-FEL)are studied,such as the azimuthal polarization of EMW,and the relation between the transient properties of gyrotron and the working conditions.These prob- lems make a remarkable influence on EMW-FEL system.In this paper,the numerical calcula- tions and analysis are given for TE_13 mode.

Preliminary design of 1MW, Ku-band gyrotron traveling-wave amplifier

The preliminary design results of a 1-MW,Kuband gyrotron traveling wave amplifier(gyro-TWA)are presented.Operating at the second cyclotron harmonic of the TE11 mode,the amplifier characterizes good stability even in the case of no distributed losses loaded,which could potentially allow it to be operated at high average power.Large signal simulation shows that the amplifier can generate a saturated peak power of about 1MW with efficiency of 26.6%,gain of 31 dB,and 3-dB bandwidth of about 1 GHz when driven by a 100 kV,40 A electron beam with 5%axial velocity spread.

Design and demonstration of a 0.22 THz gyrotron oscillator

Gyrotrons are the most powerful terahertz sources and have potential applications in many areas. A terahertz gyrotron oscillator with a pulsed solenoid producing up to an 8 T magnetic field has been designed, constructed and tested. In a 7.96 T magnetic field, 3 kW output power radiations at 0.22 THz frequency have been generated.

Generating 0.42 THz radiation from a second harmonic gyrotron

Gyrotrons are high powered coherent electromagnetic radiation sources, and are considered to be available powerful sources that have the potential to bridge the so-called terahertz gap. In the University of Electronic Science and Technology of China, a second harmonic gyrotron has been designed, manufactured, and tested. The gyrotron generated radiation at a 0.423 THz frequency in 5μs pulses with an 8.1 Tesla magnetic field, with a power per pulse of about 4.4 kW. To date this is the highest frequency recorded for vacuum electronic devices in China. The gyrotron design, operation and measurements are presented.

自研28 GHz/50 kW回旋管实现长时间连续运行

介绍了中国工程物理研究院应用电子学研究所针对磁约束聚变装置电子回旋共振加热(ECRH)系统、重离子加速器电子回旋共振(ECR)离子源以及前沿科技探索应用研制的28 GHz/50 kW连续波回旋管最新实验结果。研究团队在2019年该回旋管实现50 kW/30 s运行的基础上,通过结构优化和稳定性设计验证,最终实现了在10~50 kW功率范围多个功率水平的稳定长时间连续运行,典型运行结果为16 kW/3000 s、26 kW/900 s、46 kW/1800 s、50 kW/300 s,特别在输出功率32 kW连续稳定工作了400 min。这是国内首次研制出小时级连续工作的中等功率回旋管。