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HL-2A装置电子回旋共振加热系统的主要指标是2MW/1s/68GHz,系统由4个单元组成,每个单元包括一只回旋管,微波传输系统,控制保护测量和冷却等子系统。通过对ECRH系统和回旋管的调试,每只管子微波输出功率500kW,脉冲宽度1s,四管并联运行时总输出功率达到1.63MW,系统使用效率高于80%。     

Phase-locking of a second-harmonic gyrotron oscillator using aquasi-optical circulator to separate injection and output signals

Phase-locking in a 34.5-GHz special complex cavity gyrotron oscillator operating at the second harmonic of the electron cyclotron frequency was studied. Injection of the locking power was made via a quasi-optical circulator connected to the gyrotron output. Locking bandwidth was measured by comparing the phase of the injection signal and output signal using a balanced mixer. Locking was observed with input power level as low as 40 dB below the gyrotron output power. The locking bandwidth is, however, narrower than in gyrotrons operating at the fundamental cyclotron frequency which may be attributed to the longer resonant cavity in the second harmonic gyrotron and the corresponding larger value of external quality factor. The measurements are roughly in agreement with predictions of Adler's phase-locking equation which is given for our system in terms of powers propagating in the output waveguide toward and away from the gyrotron cavity     

Experimental study of a continuous-wave high-stability second-harmonic gyrotron for spectroscopy of dynamically polarized nuclei

We present the results of the experiments on a continuous-wave gyrotron with an output frequency of about 260 GHz, which has been developed for dynamic polarization of nuclei and is operated at the second cyclotron-frequency harmonic. For an accelerating voltage of 16 kV and a beam current of 0.3 A, a maximum continuous-wave radiation power of about 200 W has been obtained. Measurements of the thermal load on the resonator cavity allow evaluating its actual ohmic Q-factor. Gyrotron radiation is also observed at other frequencies and modes. Their generation zones and the structure of the output radiation have been studied. Long-term stability of gyrotron parameters has been determined.     

Continuous-Wave Operation of a 460-GHz Second Harmonic Gyrotron Oscillator

We report the regulated continuous-wave (CW) operation of a second harmonic gyrotron oscillator at output power levels of over 8 W (12.4 kV and 135 mA beam voltage and current) in the TE(0,6,1) mode near 460 GHz. The gyrotron also operates in the second harmonic TE(2,6,1) mode at 456 GHz and in the TE(2,3,1) fundamental mode at 233 GHz. CW operation was demonstrated for a one-hour period in the TE(0,6,1) mode with better than 1% power stability, where the power was regulated using feedback control. Nonlinear simulations of the gyrotron operation agree with the experimentally measured output power and radio-frequency (RF) efficiency when cavity ohmic losses are included in the analysis. The output radiation pattern was measured using a pyroelectric camera and is highly Gaussian, with an ellipticity of 4%. The 460-GHz gyrotron will serve as a millimeter-wave source for sensitivity-enhanced nuclear magnetic resonance (dynamic nuclear polarization) experiments at a magnetic field of 16.4 T.     

High-power oscillator of continuous electromagnetic radiation with a frequency of 300 GHz

We consider a general concept of construction, the possible versions, and specific features of a gyrotron, whose output power in CW oscillation regime can reach a few kilowatts at a frequency of 300 GHz. The gyrotron is designed for work in a high-frequency facility in combination with a “dry” cryomagnet, which ensures a magnetic field of up to 12 T, required for the gyrotron operation. The basic results of numerical simulation and optimization of the electron gun, the resonant cavity, and other subsystems of the gyrotron are presented. The designs used for the gyrotron development are justified. Preliminary experiments showed the efficiency of the pilotproduction gyrotron with an output power of about 2 kW, which is record-breaking in this frequency range. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 50, No. 6, pp. 461–470, June 2007.     

D-band frequency step-tuning of A 1 MW gyrotron using a brewster output window

In order to demonstrate the usability of gyrotron oscillators as frequency step tunable high power millimeter-wave sources, experiments on a 1 MW, 140 GHz TE_22,6 gyrotron with a built-in quasi-optical (q. o.) mode converter have been performed. By varying the operating parameters of the tube, a series of oscillations in the frequency range from 114 GHz to 166 GHz were excited. To avoid reflections, caused by the required vacuum barrier window, the gyrotron was equipped with a Brewster window. The achieved output power levels between 0.85 and 1.05 MW are compared to measurements carried out with the same tube using a conventional single-disk window. These experiments showed that even by using a q. o. mode converter, the influence of window reflections on the gyrotron oscillatory behavior cannot be removed completely.     

Observations of Phase Locking in a Single-Cavity Gyrotron Oscillator

Observations of phase locking in a single-cavity gyrotron oscillator operating at 35 GHz are reported. Injection of the locking power was made via a circulator into the gyrotron output guide. Locking was observed with input power levels as low as 35 dB below the gyrotron power. For low input powers, good agreement is found with theory based on lumped-element circuit modeling and a new distributed oscillator model.     

Experimental investigation of a 110 GHz/1 MW gyrotron with the one-step depressed collector

The results of experimental investigation of high power gyrotron with depressed collector are given. Total efficiency of a gyrotron with one-step energy recovery of 0.65 at the level of output power about 1 MW was achieved experimentally.     

Particle Simulation of a 35-GHz Third-Harmonic Low-Voltage Complex Cavity Gyrotron

A self-consistent particle simulation code has been developed for the research of a 35-GHz third-harmonic Low-voltage complex cavity gyrotron. Aided with microcomputer we use FORTRAN to simulate the process of interaction between electron beam and electromagnetic field. About 7000 macro particles are included at the same time. In the program many useful physical graphs are accessible for the further research of this kind of gyrotron such as the field profile, electrons distribution in various spaces, output power, efficiency and et al. Such simulation results may be helpful to the optimization of devices operation parameters     

Experimental investigation of a 140-GHz coaxial gyrotron oscillator

We report experimental results on a megawatt power level, 140-GHz coaxial gyrotron oscillator. The gyrotron has an inverted magnetron injection gun (IMIG) designed for operation at up to 95 kV and 88 A. The IMIG has an inner grounded anode which extends from the center of the gun down through the entire length of the tube including the cavity and collector. The IMIG was tested at up to 105 kV and 93 A in 3 μs pulses, achieving an electron beam power of 10 MW. The output power from the coaxial gyrotron cavity was transported to an internal mode converter and a single mirror that coupled the power out transversely from the tube axis. A maximum output power of up to 1 MW was obtained in the TE_27,11 mode at 142 GHz at an efficiency of 16%, about one half of the design efficiency. The reduced efficiency was attributed to nonuniformity of the cathode emission and the sensitivity to the relative alignment of the electron gun, coaxial insert, and cavity. The cathode emission over the azimuthal angle was measured for two cathodes and was shown to be nonuniform due to both temperature and emitter work function nonuniformity. The gyrotron was also tested in two alternate configurations: 1) with the internal mode converter removed (axial output), and 2) with both the internal converter and the coaxial insert removed (empty cavity). In operation in the empty cavity configuration, which is equivalent to a conventional gyrotron oscillator, output power of up to 0.9 MW was observed     

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 simulations 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.     

全三维110GHz和220GHz同轴腔双注回旋管数值模拟研究

为了打破传统单注回旋管只能产生较低功率的局限性, 本文基于自主研发的PIC粒子模拟软件CHIPIC 对110 GHz和220 GHz同轴腔双注回旋管进行全三维数值模拟研究. 在理论分析同轴双电子注电子枪设计模型和初始参数的基础上通过CHIPIC对其进行优化设计, 得到了具有横纵速度比为1.0, 最大速度零散约为5.4%的高性能电子束; 并将此优化后的双阳极双注电子枪取代传统回旋管数值模拟时采用的回旋 发射进行110 GHz和220 GHz双注回旋管整管的数值模拟, 并采用MPI四进程并行计算, 最终获得了具有双频分别为110 GHz和220 GHz、模式为TE₀₂模、平均输出功率约在70 kW、 效率达到8.75%的高性能双注回旋振荡管. 关键词： 同轴腔双注回旋管 同轴双电子注电子枪 横纵速度比 速度零散     

Continuous-Wave Operation of a Frequency-Tunable 460-GHz Second-Harmonic Gyrotron for Enhanced Nuclear Magnetic Resonance

The design, operation, and characterization of a continuous-wave (CW) tunable second-harmonic 460-GHz gyrotron are reported. The gyrotron is intended to be used as a submillimeter-wave source for 700-MHz nuclear magnetic resonance experiments with sensitivity enhanced by dynamic nuclear polarization. The gyrotron operates in the whispering-gallery mode TE(11,2) and has generated 16 W of output power with a 13-kV 100-mA electron beam. The start oscillation current measured over a range of magnetic field values is in good agreement with theoretical start currents obtained from linear theory for successive high-order axial modes TE(11,2,q). The minimum start current is 27 mA. Power and frequency tuning measurements as a function of the electron cyclotron frequency have also been carried out. A smooth frequency tuning range of 1 GHz was obtained for the operating second-harmonic mode either by magnetic field tuning or beam voltage tuning. Long-term CW operation was evaluated during an uninterrupted period of 48 h, where the gyrotron output power and frequency were kept stable to within ±0.7% and ±6 ppm, respectively, by a computerized control system. Proper operation of an internal quasi-optical mode converter implemented to transform the operating whispering-gallery mode to a Gaussian-like beam was also verified. Based on the images of the gyrotron output beam taken with a pyroelectric camera, the Gaussian-like mode content of the output beam was computed to be 92% with an ellipticity of 12%.     

HL-2A装置ECRH系统的微波功率测量

新研制的微波功率测量系统主要由温度传感器、功率标定电源、电子学处理单元、数据采集和数据处理单元等几部分组成,通过测量EC系统MOU部件冷却水回路进水口和出水口的温度变化,得到MOU吸收的杂模功率。根据回旋管输出功率中的杂模含量比,计算得到回旋管的输出功率。在回旋管调试和ECRH实验期间,測量了4路回旋管的输出功率。从测量结果可知,HL-2A装置ECRH系统可提供大于1.6MW的总输出功率。     

Operation of a stable 200-kW second-harmonic gyro-TWT amplifier

The experimental results are reported for a stable second-harmonic gyrotron traveling wave amplifier, which generated a record-breaking 207-kW output power based on the principle that the weaker harmonic interactions are more stable to spontaneous oscillations than at the fundamental, and therefore, capable of generating higher output power. The high-power amplifier was kept completely (zero-drive) stable by employing a mode-selective interaction circuit and web-matched directional input and output couplers, and choosing an amplifier interaction length shorter than the start-oscillation length for gyrotron backward-wave oscillations. The single-stage Ku-band amplifier utilized an 80-kV 20-A υ_⊥/υ_∥=1.1 electron beam from a magnetron injection gun and yielded an efficiency of 12.9%, an output phase variation of 10°/kV, a saturated bandwidth of 2.1%, a large-signal gain of 16 dB, and a detuned small-signal gain of 38 dB     

Recent results of the 1-MW, 140-GHz, TE22,6-modegyrotron

The TE_22,6-mode gyrotron operated at Forschungszentrum Karlsruhe at a frequency of 140 GHz has been investigated with respect to the behavior of different emitter materials, step tunability and reflections of the output beam. Two different materials of an emitter ring, LaB₆ and a coated dispenser cathode, were used to test the features of the gyrotron. The output power was found to be independent from the cathode material, as long as a new emitter ring was used. Aging of the emitter led to a slightly decreased output power. The gyrotron also was operated with a Brewster window. The broad-band characteristics of this window made it possible to measure the neighboring frequencies in a frequency range extending from 114 to 166 GHz. Only a slight dependence of the output power has been found over the whole frequency range. The Brewster window also allows us to investigate the influence of reflections on the output power. A strong decrease of the output power was found even for very small reflections. Tilting the power calorimeter (the reflections were measured to be less than 1%) increased the output power by about 20% to 1.6 MW at an efficiency of 36.2%. With a collector depression voltage of 35 kV for energy recovery, efficiencies of 60% at the above-mentioned output power were obtained     

Parasitic oscillation in and suppression of a gyrotron backwardwave mode in a low-Q 8 GHz gyrotron

The parasitic oscillation of the TE°₂₁ gyrotron backward-wave (gyro BW) mode is observed in a low-Q, 8 GHz TE°₀₁₁, gyrotron. At low power (P_BW<5 kW), the oscillation of the gyro BW mode, simultaneously with the gyrotron mode, results in a maximum TE°₀₁₁, mode efficiency of less than 0.25. The parasitic oscillation is suppressed by operating the gyrotron with a negative magnetic field gradient along the electron beam, which allows the maximum efficiency to reach 0.40 and the output power to be multiplied by a factor varying from 1.4 to 1.7. The optimum efficiency curve of the TE°₀₁₁ mode indicates that the low-Q cavity behaves as a much higher Q_diff cavity. Excessive values of magnetic field gradient and α favor the TE°₀₁₂ , longitudinal mode, which oscillates in place of the TE°₀₁₁ mode and limits its maximum output power. This competitive process is responsible for the high-Q-like behavior of the optimum efficiency curve     

Long-pulse operation of a 0.5 MW TE10.4 gyrotron at 140GHz

The operation features of a TE_10.4-mode gyrotron oscillator with a quasi-optical mode converter and a single-stage depressed collector at 140 GHz with an output power of 500 kW in long pulses of 0.2 s are presented. Measurements on long-pulse operation of the tube are described in detail, and the significant differences between short- and long-pulse operation concerning efficiency and output power are pointed out. The variation of frequency during a pulse and an irreversible frequency shift during long-pulse operation were measured and are discussed with respect to gyrotron design     

A 100 kW, 140 GHz pulsed gyrotron

The design and operation of a 100 kW, 140 GHz pulsed gyrotron are reported. To our knowledge, this is the highest frequency at which high gyrotron output power (>-100 kW) has been achieved. Results are presented for gyrotron operation in the range of magnetic field from 4 to 7 T, voltage from 23 to 80 kV and current up to 7.5 A. Near a value of magnetic field of 5.4 T, and output power of 100 kW was obtained at 140.4 GHz in single mode operation in the TE₀₃₁ resonator mode.     

165 GHz, 1.5 MW-coaxial cavity gyrotron with depressed collector

A further step in the development of a coaxial-cavity gyrotron operated in the transverse electric TE_-31,17 mode at 165 GHz is presented. The gyrotron has been equipped with a quasi-optical output system consisting of a Vlasov launcher with a single cut and two mirrors, one with a quasi-elliptic and the other with a nonquadratic phase correcting surface. The radio frequency (RF) power is transmitted through a single output window. A maximum output power of 1.7 MW has been achieved. At the nominal operational parameters an RF power of 1.3 MW with an efficiency of 27.3% has been measured. The efficiency increases to 41% in operation with a single-stage depressed collector