天线阻抗特性对开关振荡器输出脉冲的影响

以单锥天线和螺旋天线作为开关振荡器辐射天线为例,采用等效电路模型和商业电磁仿真软件,分别对天线末端电压振荡信号和辐射电场脉冲进行了研究。研究结果表明:采用行波天线或者电长度与振荡器一致的振子天线作为辐射天线,都能够产生中心频率与振荡器本征频率一致的电磁脉冲信号;但采用振子天线时,振荡信号持续时间较短(Q值较低),频谱上能量较分散,带宽较宽,而采用行波天线则脉冲持续时间较长(Q值较高),频谱上能量较集中,带宽较窄。     

HL—1M装置等离子体软X射线的锯齿和模行为

用高灵敏、高时空分辨的软Ｘ射线诊断系统，诊断ＨＬ－１Ｍ装置中等离子体的锯齿振荡。对观测到的四种主要锯齿作了介绍，对出现最多的有模经典锯齿和有模非经典锯齿作了详细描述和分析。结果表明，后者（主要在低ｑａ放电中出现）具有比前者低的中心ｑ（０）值，在物理机制上与前者不同，属湍流模型范畴。     

Study of Power Coupling through an Electrostatic Shield on a Loop Antenna for ICRF Heating of EBT-S

The effects of electrostatic shields around the antenna used for ICRF heating in the EBT-S fusion experiment on the efficiency of power transfer from the antenna to the plasma were studied in bench tests using resonant coupling loops placed near the antenna to simulate plasma behavior. For the frequency range of interest in these experiments, the length of the antenna was much shorter than the free-space wavelength. Coupling efficiencies in excess of 90 percent were obtained under best conditions. There was a reduction in coupling efficiency due to the presence of the shield, which was found to be dependent on the proximity of the loop to the antenna and on the Q of the loop. The change in coupling efficiency of the antenna with the shield compared to the antenna without a shield was greater the farther the loop was removed from the antenna and the lower the Q of the loop. In general, the reduction in coupling efficiency due to the shield is probably tolerable, with the advantages of having an electrostatic shield outweighing the disadvantage of a lower power coupling efficiency.     

Application of the Gyrotron FU II Submillimeter Wave Radiation Source to Plasma Scattering Measurements

Gyrotron FU II has been successfully applied as a submillimeter wave radiation source to plasma scattering measurements on the Compact Helical System (CHS) in National Institute for Fusion Science (NIFS) in Japan. The gyrotron operates in a long pulse mode (the pulse width is about 600 ms) at a frequency of about 350 GHz (the corresponding wavelength is 0.85 mm). The output power is about 110 W. The output power is transmitted along a circular waveguide system and converted to a Gaussian-like beam by a quasi-optical antenna. After that, the beam is directed onto the CHS plasma and the scattered signal is detected by a homodyne detection system. The frequency and the wave number of the scattered signal are analyzed. The results suggest that a broad band low frequency (several tens to several hundreds kHz) density fluctuation is excited in the CHS plasma only during neutral beam injection (NBI) or ion cyclotron resonance (ICR) heating.     

快波加热的天线设计

托卡马克中离子回旋频段的天线耦合效率主要取决于天线的体制和天线的尺寸。根据等离子体对不同谱分量的吸收性能差别,以及天线激励电流的谱应与等离子体对射频波吸收谱相匹配,对快波加热天线设计问题进行了细致地探讨。     

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采用等离子体分层模型,利用WKB近似研究了离子回旋共振加热(ICRH)天线发射谱n||对离子回旋波在托卡马克等离子体的表面功率反射系数、吸收衰减的影响,数值模拟了不同天线发射谱n||条件下快波少数离子加热的效果.模拟结果表明,当其它实验参数一定时,ICRH天线发射合适的n||能提高天线与等离子体的耦合效率,增强少数离子加热的效果.     

Design of the Upgraded TJ-II Quasi-optical Transmission Line

TJ-II plasma start-up and heating are made by electron cyclotron resonance waves at the second harmonic of the electron cyclotron frequency. Two quasi-optical transmission lines transmit the microwave power of the gyrotrons to the vacuum vessel. The first line launches the microwave power under fixed injection geometry, i.e. there is no possibility to change the launching angle and the wave polarization. The second line has a moveable mirror installed inside the TJ-II vessel. To get high absorption efficiency and a narrow energy deposition profile the internal mirror focuses the wave beam at plasma center.To get more flexibility in the experiments on heating and current drive the first transmission line needs to be upgraded. The design is presented in this paper. The new launching antenna includes an internal mirror to focus the beam and to change the injection angle. Both launchers are then symmetrical. A polarizer consisting of two corrugated mirrors is used to get any wave polarization. Two mirrors with an array of coupling holes and calorimetric measurements of the energy absorbed in the barrier window allow the estimation of the microwave power launched into the TJ-II.     

Tests of an ICRH Resonant Cavity Launcher with Faraday Shield

A resonant cavity antenna designed to be suitable for ion cyclotron heating in a tokamak has been bench tested. This antenna is a "discrete element" circuit designed to launch the fast magnetosonic wave in a magnetized plasma. The resonant autotransformer design allows matching to the transmission-line impedance. The tuning and matching properties of this antenna have been compared with a simple computer model. The effective transmission of various Faraday shields has been determined by measuring the change in Q of the antenna system with and without the shield. The test results show that the antenna behaves as predicted by a simple computer model and that coolable Faraday shields with high RF transmission can be designed.     

Toroidal Effect on Lower Hybrid Current Drive in Tokamak

In the review paper of N. J. Fish, the topics concerning the basic theory of lower hybrid wave heating and current drive are presented. In the consideration of radio-frequency heating and current drive of tokamak plasma near the lower hybrid frequency, the parallel wave length is imposed by the coupling device parallel to the magnetic field and is modified by gradients along the field. The important effects are found on wave penetration and damping when the toroidal aspect ratio is low. It may be possible to change the plasma current via electron Landau damping with a coupler rf power spectrum.     

Spectral Broadening of Ion Bernstein Wave Due to Parametric Decay Instabilities

The parametric decay instabilities(PDIs)of ion Bernstein wave with different input power levels are investigated via particie-in-cell simulation.It is found that the number of decay channels increases with the input power.Resonant mode-mode couplings dominate for a low input power.With increasing the input power,the nonresonant PDIs appear to dissipate the energy of the injected wave and give rise to edge ion heating.The generated child waves coupie with each other as well as the injected wave and/or act as a pump wave to excite new decay channels.As a result,the frequency spectrum is broadened with the increase of the input power.     

高通鸟笼线圈激发螺旋波等离子体特性研究

研制了高通鸟笼线圈,使用氩气作为工质气体对射频天线的工作性能进行了初步评估。利用COMSOL5.4模拟出了鸟笼天线在13.56MHz的工作频率下,电场和磁场呈线性极化分布。对鸟笼线圈进行了电路结构解剖,推导出了其谐振频率计算公式。利用热耦合红外测温仪测试了正常工作状态下的鸟笼线圈外表温度明显低于传统射频天线,电容器最高温度仅65.8°。使用光谱仪对螺旋波等离子体放电光谱特性进行诊断。通过朗缪尔探针诊断了不同压强和磁场强度下螺旋波等离子体密度,在1.0Pa、600Gs、射频功率700W条件下等离子体密度达到1.62×10¹⁸m^-3。诊断了正向功率和反向功率对应的等离子体密度,其与磁滞现象变化趋势雷同。测试了螺旋波等离子体的径向密度分布,其在轴心处密度达到最高。探究了无磁场条件下等离子体特性,其密度值不会发生大幅度跃迁,纵向磁场是引发螺旋波等离子体放电的关键因素,低压条件下有利于得到更低的电子温度,最低达到2.67eV。表明鸟笼线圈低热耗、高馈入的特性使其在激发大体积的高密度螺旋波等离子体方面具有明显优势,可以投入到下一阶段氢气螺旋波等离子体的激...     

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采用三支节液态调配器使离子回旋加热(ICRH)天线系统达到阻抗匹配,在阻抗匹配的条件下结合频率调制技术来减小由天线输入阻抗变化所引起的反射功率。数值模拟了频率调制前后天线负载与反射系数的变化关系,用来验证频率调制对ICRH天线中阻抗匹配装置的影响。模拟结果表明:三支节液态调配器结合频率调制方法,能更好地降低天线传输系统的反射系数,使得发射机的功率通过天线辐射更加有效地耦合到等离子体中去。     

频率调制对ICRH 天线阻抗匹配的影响研究

采用三支节液态调配器使离子回旋加热(ICRH)天线系统达到阻抗匹配,在阻抗匹配的条件下结合频率调制技术来减小由天线输入阻抗变化所引起的反射功率。数值模拟了频率调制前后天线负载与反射系数的变化关系,用来验证频率调制对ICRH 天线中阻抗匹配装置的影响。模拟结果表明：三支节液态调配器结合频率调制方法,能更好地降低天线传输系统的反射系数,使得发射机的功率通过天线辐射更加有效地耦合到等离子体中去。     

Electrical characteristics of helicon wave plasmas

The external electrical characteristics of helicon wave plasmas have been studied over a wide range of magnetic fields, radio frequency (RF) power, frequencies, and Ar gas pressures. External parameters, such as antenna voltage, current, and phase shifts, and internal parameters, such as electron density, are measured. The equivalent discharge resistance, reactance, and power transfer efficiency are calculated through these measurements. The characteristics of helicon mode is compared with inductively coupled plasma (ICP) and low mode. The power efficiency of the helicon mode is better than that of other modes. Consequently, electron density of helicon mode is much higher than that of other modes. This means the existence of a mechanism where electrons are very efficiently accelerated by the electric field of the antenna in the helicon mode. The power efficiency of helicon mode is higher at lower RF frequency and at optimum gas pressure than that of other modes     

Fabrication of the high power input coupler for BEPCⅡ superconducting cavities

The BEPCII storage ring adopts two 500 MHz superconducting cavities (SCC). Each one is equipped with a 500 MHz input power coupler. The coupler is to feed 150 kW power in continuous wave (CW) mode with both standing and traveling wave modes. Due to high power feeding and high frequency of the coupler, its fabrication is a big challenge. The fabrication started with two key components, the window and the antenna. Up to now, two sets including windows and antennas have beam made by IHEP. And a 270 kW RF power in CW has passed through the coupler during the high power test. The fabrication details are presented in this paper.     

Fabrication of the high power input coupler for BEPCⅡ superconducting cavities

The BEPCII storage ring adopts two 500 MHz superconducting cavities (SCC). Each one is equipped with a 500 MHz input power coupler. The coupler is to feed 150 kW power in continuous wave (CW) mode with both standing and traveling wave modes. Due to high power feeding and high frequency of the coupler, its fabrication is a big challenge. The fabrication started with two key components,the window and the antenna. Up to now, two sets including windows and antennas have been made by IHEP. And a 270 kW RF power in CW has passed through the coupler during the high power test. The fabrication details are presented in this paper.     

Predicting high harmonic ion cyclotron heating efficiency in Tokamak plasmas

Observations of improved radio frequency (rf) heating efficiency in ITER relevant high-confinement (H-)mode plasmas on the National Spherical Tokamak Experiment are investigated by whole-device linear simulation. The steady-state rf electric field is calculated for various antenna spectra and the results examined for characteristics that correlate with observations of improved or reduced rf heating efficiency. We find that launching toroidal wave numbers that give fast-wave propagation in the scrape-off plasma excites large amplitude (～kV?m(-1)) coaxial standing modes between the confined plasma density pedestal and conducting vessel wall. Qualitative comparison with measurements of the stored plasma energy suggests that these modes are a probable cause of degraded heating efficiency.     

Ku/K波段双频涡旋电磁阵列天线设计

涡旋电磁波具有携带轨道角动量的特性,利用这一特性,采用涡旋电磁波作为信号的载体,可以实现同一时间、同一频段的多路信号传输,极大地提高系统容量和频带利用率。以同轴馈电的半圆型开槽微带天线为单元,设计出了一种能工作在Ku波段和K波段的涡旋电磁阵列天线。使用三维电磁场仿真软件建模并且优化参数,最终得到在中心频率分别为17.1 GHz和19.7 GHz时,阵列天线产生的电磁波携带有轨道角动量。结论表明:该阵列天线能够产生双频涡旋电磁波。     

Optical scattering noise in high Q fiber ring resonators and its effect on optoelectronic oscillator phase noise

Nonlinear phenomena occurring in an optical fiber ring resonator featuring ultrahigh Q factor are experimentally studied. The laser is locked onto the resonator, and the optical power induced in the resonator is controlled. The onset of the first stimulated Brillouin scattering wave occurs at an optical input power as low as -9 dBm in these resonators. When the resonator is used as the frequency reference device in an optoelectronic oscillator (OEO), it has been found that these parasitic signals mix with the OEO signal and degrade its phase noise. More than 20 dB improvement of the OEO phase noise has been demonstrated by limiting these nonlinear optical effects.     

KT—5B托卡马克上阿尔芬波加热实验中天线阻抗的测量

一、引 言 托卡马克等离子体中的阿尔芬波加热实验研究自80年代初以来取得了许多有价值的实验结果。在阿尔芬波加热实验中,天线辐射阻抗的测量是十分重要的。天线辐射阻抗的变化不仅直接反映了阿尔芬波与等离子体之间的能量耦合情况,而且也反映了波在等离子体中传播过程的某些物理特性。例如,出现离散阿尔芬波(DAW模)或表面静电波(SEW模)便会使阻抗出现较大的峰值。因此,探索一种简便易行又能反映阻抗随放电时间变化的细微