Corrugated Horn Antenna for Low-Power Testing of the Quasioptical Transmission Lines at TJ-II Stellerator

This paper presents the design and characterisation of a millimetre-wave corrugated horn antenna to perform low power measurements of the main parameters of the quasioptical transmission lines of the Electron Cyclotron Resonance Heating (ECRH) at TJ-II stellerator experiment working in Madrid (E). The antenna generates a practically pure Gaussian Beam at 53.2 GHz that simulates the stellerator gyrotron output beam. Simulations of the designed corrugated horn, by using a specially developed computer code, are presented. The far field radiation pattern of the constructed prototype was measured at the ESTEC Compact Antenna Test Range (CATR). The measurement results are in excellent agreement with those obtained from simulations.     

Quasioptical Transmission Lines for ECRH at TJ-II Stellarator

Two mirror lines have been used to transmit the microwave power from the powerful microwave generators to the TJ-II plasmas. Both lines have been tested at nominal power level and they are in operation now. This paper deals with the final design of the transmission lines and their testing. Before starting operation at high power level, measurements of the wave beam parameters at low power level were performed. Two horn antennas were designed to simulate the gyrotron output. The results are presented in this paper. A computer code based on Huygens diffraction theory was developed to simulate the propagation of the beam along the mirror lines. A comparison of the theoretical and the experimental results is also shown here.     

High Power,Frequency Tunable,Submillimeter Wave ESR Device Using a Gyrotron as a Radiation Source

ESR device using a submillimeter wave gyrotron as a radiation source and a pulse magnet for high field up to 30 T has been constructed. Our gyrotrons (Gyrotron FU series) were developed as millimeter and submillimeter wave radiation sources and have attractive advantages for ESR spectroscopy, for example, high power and frequency tunability over broad range. The ESR device has been successfully applied to three cases of ESR measurements. In the first case, the temperature dependence of ESR was measured for a typical antiferromagnetic material MnO at the frequency of 301 GHz. In the second case, the dependence of the fine structure constant of the ruby on the magnetic field intensity was measured in the millimeter to submillimeter wave region. In these two cases, the gyrotron was operated by complete cw mode. In the final case, a pulse technique was applied to the ESR, the gyrotron was operated in pulse mode and the pulsed magnetic field was generated in the synchronized phase with the gyrotron operation.     

电子迴旋脉塞研究的现状和展望

电子迴旋脉塞作为开拓毫米波、亚毫米波波谱的高功率相干辐射源,近年来研究工作十分活跃,取得了不少鼓舞人心的新进展。本文综述了迴旋单腔振荡器、迴旋管放大器、高次谐波迴旋管和强流相对论迴旋管等电子迴旋脉塞各类器件的研究现状,指出了一些技术关键问题及其解决措施,并展望了它的发展前景。     

Gyrotron with quasi-optical cavity of special configuration†

A quasi-optical cavity of special configuration suitable for use in a high-power gyrotron operating at short millimetre and submillimetre wavelength has been developed. A gyrotron using this new type of cavity is under development. Both the linear and non-linear analyses are worked out. Digital calculation predicts efficiency of 37% at V ₀ = 50 kV.     

A submillimeter gyrotron with a pulsed magnetic field

Pulse solenoids seem promising for sumbillimeter wave generation in gyrotrons. In this paper a single-pulse submillimeter gyrotron with a pulsed magnetic field is described. At the wavelength 0.8 mm the output power 120 KW with the efficiency 15% has been obtained.     

Gyrotrons: relativistic case,E and H modes,output converter design

Self-consistent non-linear equations of a relativistic gyrotron with the operational mode E ₀₁ as well as the E ₀₁ and H ₀₁ modes interacting are presented. On their basis, we have optimized the efficiency of a number of gyrotron variants—with uniform and non-uniform magnetic field and regular or irregular waveguide systems. An analysis of the peculiarities of the interaction in such variants has been performed. It has been shown that the total electron efficiency of relativistic gyrotrons with E₀₁ working mode can reach 35-45%. The interaction of the E₀₁ and H₀₁ modes (at the E ₀₁ working mode) is of an interference nature and under optimal conditions the efficiency may increase by 10%. An algorithm has been suggested to optimize the profile of the gyrotron waveguide output converter based on the optimization parameters separation technique. Results are presented for the case of the H₀₁ working mode.     

THE FIRST EXPERIMENT OF A THz GYROTRON WITH A PULSE MAGNET

A THz gyrotron with a pulse magnet has been designed, constructed and operated in FIR FU. It is developed as one of high frequency gyrotrons included in Gyrotron FU Series. The gyrotron has already achieved the first experimental result for high frequency operations whose radiation frequency exceeds 1 THz. In this paper, the design detail and the operation test results for sub-terahertz to terahertz range are described. The second harmonic operation is confirmed experimentally at the expected frequency of 1.005 THz due to TE_6,11 cavity mode at the magnetic field intensity of 19.0 T.     

The Gyrotron

This paper describes the genealogical tree of the gyrotron, stimulated emission of cyclotron radiation in microwave electronics from magnetron to gyrotron, and arrangement of the gyrotron. The structure of the alternating field in the gyrotron is also given, along with motion and bunching of electrons near cyclotron resonance, equations of the gyrotron, and varieties of the gyrotron. A review of experimental studies is discussed, with problems of utilization of stimulated emission cyclotron radiation.     

Experimental study of velocity spread in a cycloiding electron beam

The paper describes briefly the effect of electron velocity spread on the principal operating parameters of a gyrotron. A method of reducing velocity spread is discussed, and a new method of measuring electron velocity spread in a cycloiding electron beam is presented. By use of a high precision radial-gauge and multilobe collector, the distribution of the beam transverse velocity of a gyrotron is accurately measured. Compared with other methods conventionally used in this country and abroad such as those using retarding-field, pin-hole collector, this method is characterized by the fact that the space charge effect would not modify the experimental results, and the beam velocity spread of a gyrotron under real operating conditions can be measured. In order to characterize the beam in an overall manner, a new concept of relative density velocity spread is introduced in this paper. The experimental work has been performed on a special electron beam analyser with advanced design.     

Experimental study of a high efficiency quasi-optical mode converter for whispering gallery mode gyrotrons

A mode converter for whispering gallery mode gyrotrons has been designed and experimentally demonstrated. Experiments were performed on a megawatt power level, 3μs pulsed gyrotron operating in the TE_16,2,1 whispering gallery mode at 146 GHz. The gyrotron cavity employs a non-linear uptaper to minimize radial mode conversion. About 99% of the output power is in the TE_16,2 mode. The quasi-optical converter consists of a helically cut Vlasov-type waveguide launcher and a reflector. The doubly curved reflector, designed using geometric optics and vector diffraction theory, was built to focus the full radiation pattern to a small, gaussian-like focal spot. Of the power incident in the TE_16,2 mode, 96% is directed by the launcher and reflector to a gaussian-like focal spot in the far field. Small fractions of other modes were found to form distinct focal spots in the far field. Analysis of the power in the other focal spots allows for a good quantitative measurement of gyrotron output mode content, potentially on a single shot basis.     

A W-band Third Harmonic Gyrotron with an Iris Cavity

The design and experimental results of a W-band gyrotron operating at the third cyclotron harmonic are presented. The gyrotron is designed to operate at the TE₆₁ mode, which is significantly distinct from competing modes. An iris cavity is employed for the purpose of trapping the third harmonic mode more effectively and lowering its start current. In the experiment, the gyrotron is drived by a triode magnetron injection gun (MIG) which can produce a 45 kV, 3 A electron beam. When maximum axial magnetic field is 1.22 T, a single mode third harmonic gyrotron radiation is observed with the frequency of 94.86 GHz. The maximum output power is 5.5 kW, corresponding to an efficiency of 4%. Another third harmonic mode TE₀₂ is also detected at 88.8 GHz, with maximum output power of 1.5 kW.     

Determination of gyrotron wave beam parameters

The output radiation of a gyrotron has the form close to the Gaussian beam. Knowing parameters of the wave beam along its way from a gyrotron to an object permits one to optimize the transmission losses. By this, the structure of the wave beam can be recorded with an infrared camera in several cross-sections of the beam. Real gyrotron wave beam is approximated with high precision by the Gaussian beam.     

Design of a CW 1 THz Gyrotron (Gyrotron Fu Cw III) Using a 20 T Superconducting Magnet

Design of a CW 1 THz gyrotron at second harmonic operation using a 20 T superconducting magnet has been described. The mode competition analysis is employed to investigate operation conditions of second harmonic mode, which is being excited at the frequency ranging from 920 GHz to 1014 GHz. The output power up to 250 watt corresponding to the efficiency of 4.16 percent could be achieved by using an electron beam with accelerating voltage 30 kV and current 200 mA. The important advantage of this gyrotron is that the single mode excitation at second harmonic, and extremely high frequency of the radiation, could be maintained even at high currents. It opens possibility to realize a high power radiation source at 1 THz. Such gyrotron is under construction at FIR Center, University of Fukui.     

Nondestructive Gyrotron Cold-Cavity Q Measurements

A novel method for cold testing a gyrotron resonator to determine its total Q is presented. Probing radiation is coupled into the resonator through its radiation pattern. A sensitive heterodyne receiver is used in the far field to detect the reradiated cavity resonances. Good agreement between measurement and calculated total Q is found for several 140-GHz gyrotron resonators in the TE/sub 031, TE/sub 032/, TE/sub 231/, and TE/sub 611/ modes.     

Axisymmetric optical system for quasi-optical gyrotron

An analysis is carried out with a profile of hollow Gaussian radiation beam propagating in an optical system composed of coaxial annular curved mirrors. The result will be a useful tool in designing an axisymmetric quasi-optical gyrotron oscillator (ASQUOTRON).     

An improved design for quasi-optical mode conversion of whispering gallery mode gyrotron radiation

Results are reported of a theoretical and experimental investigation of a quasi-optical mode converter for the transformation of whispering gallery mode gyrotron output into a linearly polarized Gaussian like beam. The mode converter consists of a helically cut waveguide launcher, similar to that originally proposed by Vlasovet al, followed by a focusing mirror. Theoretical results using aperture field methods indicate that the length of the waveguide launcher is of critical importance in providing a confined radiation pattern. Experimental results on the radiation pattern were obtained for several launcher lengths using a 0.6 MW, 149 GHz pulsed gyrotron operating in the TE_16,2 mode. Radiation pattern results for the optimum launcher length agree well with theoretical calculations using the Stratton-Chu aperture radiation theory for unperturbed waveguide modes. A mirror focusing in the azimuthal direction was designed by a geometrical optics approach to focus the radiation coming from the launcher. Good focusing with 91.4% efficiency (power in the focused beam divided by gyrotron power) was found experimentally using the combined launcher and mirror with the pulsed gyrotron. These results indicate that quasi-optical antennas are useful for transforming high order, high frequency gyrotron modes into directed beams in free space.     

Efficient generation of picosecond coherent tunable radiation between 190 and 212 nm by sum-frequency mixing from Raman and optical parametric radiations

An efficient sum-frequency mixing of optical parametric radiation and stimulated Raman radiation has been used to generate picosecond continuously tunable coherent radiation ranging from 190 to 212 nm with energies of20-40 muJ. An ordinary KDP crystal was phase-matched by using a combination of long and short wavelength incident waves.     

Synthesis of Gyrotron Phase-Correcting Mirrors Using Irradiance Moments

A new approach using the moments of field amplitudes has been applied for phase-correcting mirror synthesis of a 110-GHz gyrotron internal mode converter. The synthesized mirrors have smooth profiles in contrast to the mirrors synthesized using the previously employed iteration method. The design has been checked using a physical optics propagation code with the result of a Gaussian output amplitude at the gyrotron window position.     

0.6 THz三次谐波回旋管的研究

 太赫兹回旋管是一类基于电子回旋受激辐射机理的快波器件,同时也是目前最具发展前景的高功率太赫兹辐射源.本文根据回旋管的线性理论和自洽非线性理论对三次谐波、工作频率0.6 THz的回旋管进行了研究,重点讨论了引导中心分别为0mm的实心回旋电子注和0.315mm的空心回旋电子注的模式竞争.通过分析比较,发现工作在0.6THz 、三次谐波的众多模式中TE37模是一比较理想的工作模式,它不仅有相对较高的功率输出,而且还有相对较少的模式竞争.本文中的设计采用55kV/1.0A,电子注的速度横纵比为1.5,在工作磁场7.86T下,数值计算结果表明输出功率达4.73kW.