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     

阿尔芬波加热研究的进展

本文概述了阿尔芬波加热的理论和实验情况。讨论了阿尔芬波加热的基本物理问题,并介绍了某些重要的实验结果。对在大托卡马克上采用阿尔芬波加热的可能性进行了全面论述。     

阿尔芬波加热低β托卡马克等离子体的数值分析

本文对托卡马克等离子体阿尔芬波加热的动力学问题提出了一种新的处理方法,该方法简便、直观,并适用于其他波加热动力学问题的数值分析。     

托卡马克理想磁流体不稳定性的统一描述 (I)

在与平衡磁面相联系的坐标系下，用剪切阿尔芬波近似给出了统一描述托卡马克等离子体理想磁流体线性运动的本征模方程。利用此方程，可以进一步给出大尺度扰动（扭曲模、低模数气球模、阿尔芬模）和小尺度扰动（高模数气球模、Mercier模）的本征模方程。本文详细讨论了小尺度扰动的本征模方程。     

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采用本征模式的数值打靶方法研究了离散阿尔芬本征模在DⅢ-D高性能运行条件下的物理特性,包括负磁剪切位形、高性能加热、正反中性束注入、内部输运垒以及高自举电流和甚高约束运行状态对这种阿尔芬模式的影响。在DⅢ-D托卡马克装置负磁剪切位形及先进运行状态实验参数下这些离散阿尔芬本征模存在于宽的径向区域,且具有广泛的本征频谱;高性能加热、同向中性束注入以及内部输运垒的存在有利于产生多个较深的气球模驱动势阱,由之得以很好地形成这种阿尔芬束缚态本征模;在高自举电流和甚高约束运行条件下这些离散阿尔芬本征模束缚态能够在更广的径向区域存在,且可具有较高的本征频率。另外,参照DⅢ-D装置放电实验数据的时间演变情况,这些离散阿尔芬本征模能在很宽的运行参数范围内出现,使之成为该类大型托卡马克实验中可能广泛存在的潜在不稳定性。     

阿尔芬高斯波包演化为阿尔芬孤波的条件及阿尔芬波的调制不稳定性判据

通过计算阿尔芬孤波的运动常数C1，发现消零孤波（vanishing soliton）均满足C1≤0，结合其他研究者关于阿尔芬波调制不稳定性的定性结论，提出阿尔芬波包演化为孤波的条件为C1≤0.数值计算结果支持了这个猜测.同时计算结果还表明,最终演化成的孤波数目既不完全依赖于积分常数C0，也不完全依赖于C1 .文献［1］和［2］所得的结论源于演化时间太短.通过与其他文献比较，发现C1≤0还可以作为阿尔芬波的调制不稳定性判据. 关键词： 阿尔芬波 derivative nonlinear Schrdinger方程 调制不稳定性判据 孤立波 高斯波包     

磁化热等离子体中短波漂移阿尔芬涡旋

本文研究低β磁化热等离子体中非线性短波漂移阿尔芬波。我们导出了描述磁化等离子体中短波漂移阿尔芬波的非线性方程组,求出了该方程组的偶极涡旋解,这种解属于Rossby型涡旋,涡旋的势在离涡旋中心远处的渐近行为是按指数衰减的。     

非均匀磁场中的剪切阿尔芬波涡旋

本文研究了非均匀磁场中非线性剪世阿尔芬波，研究表明，在非均匀磁场情况下，阿尔芬波通过自相互作用也可以形成避域涡旋结构。磁场的非均匀性将导致传播区的展宽。     

ICRF快波模转换及快波传播

本文通过分析离子回旋频段(ICRF)快波在模转换区传播的物理过程,导出了一个新的快波近似——完全快波近似二阶波方程。数值计算表明,它能给出与求解高阶方程非常一致的结果,尤其是在弱回旋阻尼(k_1较小)情况下,完全快波近似比快波近似有更满意的结果。最后讨论了二次谐波加热和少数成份离子加热的实例。     

阿尔芬波加热托卡马克等离子体的能量平衡问题

本文用“剖面不变性”确定等效电子热导系数,研究了TCA装置上阿尔芬波加热的能量平衡,结果与实验符合很好。证明本文所用的方法对不同装置、不同加热方式都适用。     

Theoretical study of two-element array of equilateral triangular patch microstrip antenna on ferrite substrate

The radiation characteristics of a two-element array of equilateral triangular patch microstrip antenna on a ferrite substrate are studied theoretically by considering the presence of bias magnetic field in the direction of propagation of electromagnetic waves. It is found that the natural modes of propagation in the direction of magnetic field are left- and right-circularly polarized waves and these modes have different propagation constants. In loss-less isotropic warm plasma, this array antenna geometry excites both electromagnetic (EM) and electroacoustic plasma (P) waves in addition to a nonradiating surface wave. In the absence of an external magnetic field, the EM- and P-waves can be decoupled into two independent modes, the electroacoustic mode is longitudinal while the electromagnetic mode is transverse. The far-zone EM-mode and P-mode radiation fields are derived using vector wave function techniques and pattern multiplication approaches. The results are obtained in both plasma medium and free space. Some important antenna parameters such as radiation conductance, directivity and quality factor are plotted for different values of plasma-to-source frequency.     

A NEW LEAKY WAVE ANTENNA BASED ON CHANNEL GUIDE FILLED WITH LEFT-HAND MATERIAL FOR MILLIMETER-WAVE APPLICATIONS

A new leaky wave antenna based on channel guide filled with left-handed material (LHM), operating in evanescent surface mode of TM polarization, is presented for millimeter wave applications. A transverse equivalent network that yields a dispersion relation in closed form is employed to analyze the leakage characteristics of the antenna. Numerical results are presented for the phase and leakage constants of the antenna in terms of different geometric parameters and dielectric distributions. Besides, the frequency dependences of the leaky characteristics for the present antenna are given, from which the backward radiation is clearly demonstrated.     

Nanoparticle using parallel split rings and implementation of chain for creating Fano resonance with polarization independence for energy harvesting in mid-infrared

In optical devices, the polarization of the incident wave affects the Nano particle characteristics. Therefore, designing a polarization-independent device is significant in the process of designing optical structures. On the other hand, the concept of Fano resonance and dark mode has been utilized for achieving more energy enhancement. In this paper, we have developed a symmetrical Nano antenna by employing Fano resonance, which is independent of the incident wave polarization. The proposed Nano antenna is modified in mid infrared regime for biosensing and energy harvesting applications. The designed metamaterial antenna is made by Nano split ring resonators with etched capacitive gaps, which are utilized for concentrating energy. The introduced Nano antenna has a bright and dark mode with a weak enhancement of electric field. The effect of the incident wave polarization is investigated at wave incident angles between 0° and 45° to illustrate the independency of the polarization due to the symmetrical shape of the Nano antenna. In order to trigger the dark mode and enhance the electric field, a Nano chain is incorporated in the final structure. This arrangement has led to increasing of electric field drastically. Furthermore, the figure of merit has been calculated as an advantageous factor in sensing the surrounding materials with various refractive indices. Our findings illustrated that the chain arrangement has caused a peak in the linear form of the extinction cross section of the Nano antenna. This in turn has resulted in the appearance of Fano resonance with no impact on the resonance frequency that has been originally adjusted by capacitive gaps and inductive strips.     

Strip dielectric wave guide antenna-for the measurement of dielectric constant of low-loss materials

The value of dielectric constant are the most important parameters in material science technology. In micro-wave and millimeter wave circuits using dielectric materials the values of this parameters should be known accurately. It is observed that the number of methods are reported in litrature, however these methods impose difficulties in experimentation and are not very accurate. In this paper a novel approach to the measurement of the dielectric constant of low loss materials at micro-wave and millimeter wave frequencies has been discussed. In this method by using antenna theory, a metallic strip dielectric guide is taken in to constideration and band reject phenomenon of dielectric antenna is used. Frequency response of an antenna in band reject mode is a function of the dimensional parameters, such as the metallic strip period, the profile of the metallic strip and the dielectric constant of the material used. Hence if one measure the frequency responce of the antenna in band reject mode, the dielectric constant of the material is determined provided all other parameters are known. This method gives a direct measure of dielectric constant and is quite accurate as computer techniques are used for evaluating the dielectric constant. This method verified experimentally also.     

Perturbation Analysis of Dielectric Grating Antenna with LHM Substrate

A dielectric grating leaky wave antenna with a substrate consisted of left handed material (LHM) is presented in this paper, the case where the n = −1 space harmonic of TM mode radiating into the space is carefully investigated through the improved perturbation analysis, which tremendously simplifies the analysis procedure with good calculation accuracy and brings considerable physical insight into the overall behavior of the dielectric grating antenna. It has been found that the new leaky wave antenna is of larger leakage constant than that of the traditional antenna with substrate of the right handed material (RHM). As a result the dimension of the antenna could be largely reduced, which is of practical significance for some applications. Extensive numerical results of the radiation characteristics are given to establish useful guidelines for the design of the new grating antenna.     

An asymmetric feeding X-band active frequency-scanning leaky-wave antenna

An asymmetric feeding X-band active leaky-wave antennas is developed, to excite the first high order mode of the microstrip leaky wave antenna. One is the asymmetric feeding leaky-wave antenna which integrated with a HEMT oscillator, and the other is the frequency-tuned leaky-wave antenna which integrated with a varactortuned HEMT VCO. The microstrip leaky-wave antenna is operated in the first higher mode. To excite the first higher mode, the microstrip leaky-wave antenna is fed asymmetrically. The dominant mode excitation has been successfully suppressed by adding a sequence of covered wire in the center of the microstrip leaky wave antenna. The design of these active leaky-wave antennas is discussed and the beam scanning phenomena of the antenna is presented. The HEMT oscillator frequency is controlled by tuning the varactor DC bias and the beam scanning is demonstrated. The measured scanning angle agree with prediction, it is close to 30° as the VCO frequency tuned from 8.06 GHz to 9GHz.     

A Gunn-Diode Active Leaky-Wave Frequency Scanning Antenna

A frequency tunable active leaky-wave scanning antenna using Gunn-diode voltage control oscillator (VCO) as source is developed. The frequency tuning controlled by changing either the varactor diode dc bias or the Gunn diode dc bias is demonstrated. The measured scanning angle of active antenna is close to 15 degree as the Gunn VCO frequency tuned from 12.58GHz to 12.98GHz. To excite the first higher order mode of the microstrip leaky-wave antenna is fed asymmetrically. The dominant mode excitation has been successfully suppressed by adding a sequence of covered wire in the middle line of the microstrip leaky wave antenna. This is a prototype of frequency scanning antenna using two terminal device, which can be easily scaled up to millimeter wave frequency region.     

准光激励毫米波圆波导旋转TE6 2模式产生器

 介绍了采用准光方法激励圆波导产生旋转TE_{6 2}模式的设计原理、测试方法和实验结果。该模式产生器由毫米波光学系统和开放同轴波导谐振腔系统组成:毫米波光学系统由角锥喇叭天线、双曲面反射镜、抛物面反射镜、修正抛物面反射镜等部件组成;开放同轴波导谐振腔系统由开放同轴波导谐振腔、圆波导、测试辐射喇叭天线组成。通过网络分析仪和毫米波近场自动测试系统测试表明:该模式产生器在频率为96.4 GHz附近产生的圆波导旋转TE_{6 2}模式的纯度达到97%。     

Brewster angle effect on the performance of omni-directional circular dielectric grating antenna-improved perturbation analysis

The radiation characteristics of the omni-directional periodic leaky wave antenna operating in TMol mode is investigated by the improved perturbation method with a particular attention directed to the Brewster angle effect on the performance of the antenna, and some interesting results are given.     

雪崩倍增GaAs光电导太赫兹辐射源研究进展

在飞秒激光激励下用GaAs光电导开关作为太赫兹(THz)辐射天线, 已经广泛用于太赫兹时域光谱系统, 但目前国际上都是使用GaAs光电导开关的线性工作模式, 而GaAs光电导开关的雪崩倍增工作模式所输出的超快电脉冲功率容量远大于其线性工作模式, 迄今为止, 还没有人提出用雪崩倍增机理的GaAs 光电导开关作为辐射源产生THz电磁辐射. 本文探讨了用 雪崩倍增工作模式的GaAs光电导开关作为光电导天线产生THz电磁波的可能性及研究进展. 通过理论分析及实验研究, 在实验上实现了: 1) 利用nJ量级飞秒激光触发GaAs光电导天线, 可以进入雪崩倍增工作模式; 2) 利用光激发电荷畴的猝灭模式, 可以使GaAs光电导天线载流子雪崩倍增模式的延续时间(lock-on 时间)变短. 这为利用具有雪崩倍增机理的GaAs光电导天线产生强THz辐射奠定了基础.