High frequency fast magnetoacoustic modes in the plasma core

Fast magnetoacoustic modes (FMM) [known also as compressional Alfvén eigenmodes (CAE) and magnetosonic modes] with frequencies exceeding or equal the ion gyrofrequency are considered. It is shown that edge-localized FMM, which presumably are responsible for the superthermal ion cyclotron emission (ICE) observed in many experiments on tokamaks and stellarators, represent a particular case of these modes. In general, FMMs with frequencies above/about the ion gyrofrequency have different radial locations and structures. They can extend over a large part of the plasma cross section and even can have maximum amplitudes at the magnetic axis. Modes with the same frequency and the same poloidal mode number are multiple, having different radial structures. These results are obtained in the approximation of cylindrical plasma with one-ion species.     

微波技术对ECR离子源性能的影响

The coupling between microwave generators and ECR ion sources(ECRIS)is a key point for the design of the new generation ECRIS as well as for the optimization of the existing ones.The electromagnetic characterization of the plasma chamber where the ionization phenomena take place is a fundamental starting point to understand and model such process.In such effort the complex structures of the injection and extraction flanges together with the large dimensions of the chamber and the high frequencies that are typically used make impossible an analytical solution and also create great difficulties in the modelling even with state-of- art electromagnetic simulators(CST,HFSS),In the following paper the results of some numerical calculations for the optimum plasma chamber excitation will be presented along with the experimental measurements carried out with the SERSE ion source at INFN-LNS.A campaign of measurements is also planned to further investigate the microwave coupling and the mode excitation,which determines the efficiency of the ECR plasma heating.     

电子注对谐振腔中TM模式谐振频率和电磁场分布的影响

将电子注视为等离子体柱,从填充等离子体柱的谐振腔的物理模型出发,推导了圆柱腔填充中心电子注时TM0m0模式的特征方程,并重点分析了填充电子注的圆柱腔中TM010模式和TM020模式的谐振频率和电磁场分布随等离子频率的变化情况。研究结果表明,随着电子注的等离子体频率不断增大,谐振频率也不断增大,谐振腔内电场和磁场的分布也随之发生改变。当电子注的等离子体频率超过谐振腔的谐振频率时,谐振腔内的电磁场分布将发生很大的变化,出现了电子注内外电场方向相反和趋肤效应等现象。     

TM610高次模圆柱谐振腔的模拟研究

 根据电磁场理论设计了S波段TM610高次模圆柱谐振腔。运用HFSS，ISFELD3D， CST-MS及MAFIA软件计算了该谐振腔中TM₆₁₀及其附近模式的电磁场分布、谐振频率及模式间隔。计算表明：TM₆₁₀模式的电磁场集中在漂移管头周围的区域，谐振腔中心处无电磁场分布。根据TM₆₁₀模式的特点，采取了在腔中心放置铁氧体微波吸收材料的方法来抑制杂模。HFSS模拟表明：腔内吸收材料可消除TM₅₁₀模式外大部分杂模的影响。采用了在主谐振腔外加耦合吸收腔的方法来抑制TM₅₁₀模式，该吸收腔基模TM₀₁₀的谐振频率等于TM₅₁₀的谐振频率。模拟表明：TM₅₁₀模式的大部分能量可以被吸收腔内的铁氧体材料衰减掉，Q值从15 604下降到571。     

Analysis for the new type long-pulsed and high efficient microwave amplifier—magnicon

This paper begins with the cylindrical cavity field expression of the rotating TM_n10 mode in magnicon, and obtains its dissipated power, cold quality formula and so on, which are different from those in the static state TM_n10. Furthermore starting from the dynamics equations, the passive deflect cavity electron velocity and position solution, as well as the interact instantaneous power solution between electron and wave have been solved. The cylindrical coordinate electron energy dynamics equation in the output cavity, and the modification of terminal parameter formula for relativity have also been discussed. This work is supported by the Sic. & Tech. Funds of CAEP.     

基于宽度可调节的线缺陷平板型光子晶体的空气槽微腔

研究了一种空气槽光子晶体微腔,这种腔是由在平板型光子晶体上引入一条宽度可以调节的线缺陷空气槽形成的.腔模的电场被强烈局限在空气槽中,由于介电常量的不连续性,电场得到很大的提高,同时模体积被大大地降低.数值模拟与分析了微腔的能带结构和场分布,考虑到腔模的谐振频率和对称性,发现一阶偶膜同时具有较高的品质因子和较小的模体积;应用有限时域差分法,得到腔模的品质因子可以高达10⁶,模体积仅为0.02(λ/n)³.计算了一阶偶模谐振波长随空气槽宽度以及空气孔半径的变化,发现随着宽度的增加,波长越来越短.而随着空气孔半径的增加,波长近似线性地减小;当空气孔半径为170 nm时,可以获得最高的腔品质因子.     

Photonic-band-gap resonator gyrotron.

We report the design and experimental demonstration of a gyrotron oscillator using a photonic-band-gap (PBG) structure to eliminate mode competition in a highly overmoded resonator. The PBG cavity supports a TE(041)-like mode at 140 GHz and is designed to have no competing modes over a minimum frequency range delta omega/omega of 30% about the design mode. Experimental operation of a PBG gyrotron at 68 kV and 5 A produced 25 kW of peak power in the design mode. No other modes were observed over the full predicted operating range about the design mode. PBG cavities show great promise for applications in vacuum electron devices in the millimeter- and submillimeter-wave bands.     

Particle-in-cell simulation of generation of an HF sequence of short current pulses in the vircator with counter-propagating beams

We performed a particle-in-cell (PIC) simulation of a vircator with counter electron beams in a cylindrical cavity with metal walls. Two pairs of counter-propagating superlimiting electron beams with different energy and current in each pair are injected along the cylinder axis. It is found that the electron charge in the cavity is formed as a sequence of pulses corresponding to slow accumulation and fast discharge. It is shown that the pulses are related to the characteristic dynamics of the squeezed beam state, the distributed virtual cathode. This regime can be used to generate anHF sequence of ultrawideband electromagnetic pulses.     

Numerical Investigation of the Effects of the Injection Current on the SHB-Effects of VCSEL''s

A spatially independent model of vertical-cavity surface-emitting lasers (VCSEL's) is built up in this paper by integrating the spatially dependent rate equations over the cross section of the active reigon of VCSEL's. The LP cosine modes in a weakly guiding cylindrical waveguide are used to represent the transverse modes in the VCSEL's cavity. This model is performed numerically with the 4^th order Runge-Kutta method in a self-consistent way. The dynamic and steady state characteristics of the multi-transverse mode competitions are investigated in detail. Different kinds of injection currents such as a disk-contact and ring-contact injection current are employed in these numerically implementations. Some interesting results are obtained and analyzed detailedly.     

等离子体填充耦合腔链特性研究

 用严格的场匹配方法分析了填充等离子体的耦合腔链，研究了等离子体 腔混合模的形成以及“冷带宽”和“热带宽”的展宽效应。等离子体填充周期性耦合腔链后，形成周期性的截止频率为0的等离子体TG模式。当填充的等离子体密度较大，且腔模和TG模式发生部分重叠时，两者相互耦合，形成等离子体 腔混合模式。工作在混合模式下，其“冷带宽”和“热带宽”大大增宽，且耦合阻抗比真空时提高了近5倍，因此在填充等离子体后，耦合腔链的慢波特性得到了显著的改善。     

Eigenmodes for electromagnetic waves propagating in a toroidalcavity

A solution has been attempted by means of the Helmholtz equation for an electromagnetic wave propagating in an empty torus in a system of toroidal coordinates. The electromagnetic fields are expressed in terms of the Hertz vector to obtain a scalar Helmholtz equation. The latter has been solved by making use of an inverse aspect ratio expansion of the solution. Unlike most previous workers, the authors have obtained their solutions in terms of hypergeometric functions whose static limit is the toroidal harmonics. The cylindrical solutions in terms of Bessel functions can also be recovered by taking the appropriate large aspect ratio limit. The eigenmodes, with arbitrary toroidal and poloidal mode numbers, have been obtained by applying the boundary conditions on the metallic walls of infinite conductivity, and they cannot be distinguished as TE or TM modes. Eigenfrequencies for various toroidal and poloidal mode numbers are plotted against the inverse aspect ratio. First-order approximations to the fields in the toroidal cavity have also been derived     

First- and second-harmonic radiations from a near-millimeter-wave gyromonotron

First- and second-harmonic radiations in frequency regions centered around 120 and 240 GHz, respectively, have been observed from a gyromonotron employing magnetic fields between 34 and 54 kG and a magnetron injection gun preducing a 30-kV, 1- to 2-A electron beam. Extensive redesign of the cavity, electron beam tunnel holders, and vacuum envelope resulted in greatly improved tube performance over that obtained previously. Nine first-harmonic modes and three second-harmonic modes were identified with specific TE cavity modes. These identifications were based on agreement between the measured frequency of a radiation and the calculated resonant frequency of a TE mode, and one or both of the following: (a) the agreement between the magnetic field at which the radiation occurred and that predicted by linear theory calculations of threshold current versus magnetic field for that mode; and (b) the similarity between the far-field antenna pattern measured with calibrated, waveguide-mounted detectors and that predicted for that mode. Output power was measured with a Scientech 362 Calorimeter and also estimated by integrating the far-field antenna patterns measured with the calibrated detectors. The power ranged from a fraction of a watt to 200 W for second-harmonic modes, and from tens of watts to 2 kW for first-harmonic modes.     

光子带隙谐振腔回旋管振荡器的自洽非线性理论

定义了光子带隙谐振腔(photonic-band-gap cavity, PBGC)的等效半径,论证了使用该半径将PBGC等效为具有模式选择性的金属圆柱谐振腔的有效性,揭示了其在PBGC设计过程中的指导性作用.基于等效半径的运用,建立起光子带隙谐振腔回旋管振荡器(PBG回旋管)的自洽非线性理论,并对工作于TE₃₂模的PBG回旋管作了理论分析和数值计算.目前的研究表明:高频电磁场沿角向呈行波或驻波的不同极化形式对PBG回旋管的注-波互作用过程具有较大的影响;较之电子回旋基波,该器件中二 关键词： 光子带隙谐振腔 等效半径 回旋管 自洽非线性理论     

回旋管光子带隙谐振腔冷腔电磁模式分析

利用二维三角格子金属光子带隙谐振腔代替回旋管的传统柱形谐振腔,并对腔体进行了TE波模式的计算与分析.综合考虑腔体内外的结构特征,给出了光子带隙谐振腔冷腔模式理论的研究方法,发现腔内存在单模工作的可能与条件以及非角对称情况下的电磁模式分布特征.研究结果表明,利用光子带隙谐振腔代替回旋管的传统腔体,可使回旋管在不受腔体横向尺度限制的条件下实现单模工作.这对于提高回旋管的功率容量、有效实现高次单模与高次回旋谐波耦合条件下的注-波互作用、降低工作磁场并从物理上根本改变回旋管的工作状态提供了理论依据. 关键词： 回旋管 金属光子带隙 谐振腔     

Wave growth rate in a cylindrical metal waveguide with ion-channel guiding of a relativistic electron beam

This paper addresses the formulae and numerical issues related to the possibility that fast wave may be grown when a relativistic electron beam through an ion channel in a cylindrical metal waveguide.To derive the dispersion equations of the beam-wave interaction,it solves relativistic Lorentz equation and Maxwell’s equations for appropriate boundary conditions.It has been found in this waveguide structure that the TM 0m modes are the rational operating modes of coupling between the electromagnetic modes and the betatron modes.The interaction of the dispersion curves of the electromagnetic TM 0m modes and the upper betatron modes is studied.The growth rates of the wave are obtained,and the effects of the beam radius,the beam energy,the plasma frequency,and the beam plasma frequency on the wave growth rate are numerically calculated and discussed.     

A Theory of the Self-Consistent and Space-Charge Effect in Hybrid-Magnicon Amplifier

A novel axially modulated, annular electron beam cusp-injected, slowly varied section opened cavity, hybrid-magnicon amplifier had been proposed I once. The hybrid-magnicon has wavelength up to millimeter wave bend. The while its non-self-consistent non-space-charge nonlinear numerical calculation method was discussed. But due to bunch effect is changing uniform distribution state of the annular electron beam in the driver cavity, and then dynamic force balances of the beam is changing. Therefore, besides the interaction force between electron beam and the rotating TM_n10 mode electromagnetic field also must consider the electromagnetic force of current density and the action force between the space-charges and the action force of the charge density grade, et al. effect. For some problems of theory, this report try discuss from Maxwell Equations.     

光声池径向共振模式耦合系数理论分析

光声光谱法是基于红外吸收光谱原理的一种高灵敏度的微量气体探测技术。它使用声共振腔来实现微弱声信号的共振放大。通过调节激光的调制频率,当它等于腔的某个共振频率时,在腔内形成声驻波,而腔本身的作用相当于一声放大器。共振腔的放大作用取决于当前被激活的共振模式、腔的品质因素、声传感器的状态以及电磁辐射与腔共振模式的耦合作用。值得关注的是,红外激光相对于声共振腔的入射方位不同则激励产生的光声信号幅值也不同。采用理论推导与数值计算相结合的方法,以圆柱形光声池为例,研究了径向共振模式下耦合系数受激光入射方位的影响。研究表明,激光入射角在0～π/2范围变化时耦合系数存在2个零点和2个极大值：入射角为0或tan-1(0.859 2×2R/L)时,耦合系数为零而径向共振失效;入射角为tan-1(0.556 8×2R/L)或tan-1(2R/L)时,耦合系数极大而径向共振最强。此处R为池径而L为池长。结果可用于指导光声池结构优化设计与安装调试,增强光声法检测微量气体的信号幅值,提高检测灵敏度。     

Electromagnetic wave chaos in gradient refractive index optical cavities.

Electromagnetic wave chaos is investigated using two-dimensional optical cavities formed in a cylindrical gradient refractive index lens with reflective surfaces. When the planar ends of the lens are cut at an angle to its axis, the geometrical ray paths are chaotic. In this regime, the electromagnetic mode spectrum of the cavity is modulated by both real and ghost periodic ray paths, which also "scar" the electric field intensity distributions of many modes. When the cavity is coupled to waveguides, the eigenmodes generate complex series of resonant peaks in the electromagnetic transmission spectrum.     

同轴虚阴极谐振效应研究

中国工程物理研究院应用电子学研究所的一些实验表明由阳极反射板、阳极网和阴极发射的电子束形成的环状虚阴极围成的准谐振腔是决定同轴虚阴极输出微波功率和传输模式的关键所在. 在二极管电压350kV，电流23kA条件下，获得了500MW的微波输出功率，能量转换效率约6.2％，工作频率3.3GHz，输出微波主要由TM₀₁模式和TE₁₁模式组成. 对同轴虚阴极的谐振效应进行了分析. 关键词： 高功率微波 同轴虚阴极 谐振腔 模式竞争     

Analytic theory of a tapered gyrotron resonator

An analytic theory has been derived for determining the eigenfrequencies, RF-field distribution and Q of the TE_mpq modes of a gyrotron resonator consisting of a circular cylinder joined to a slowly tapered section. Explicit results are obtained for a linear taper. The cavity modes are found to have an RF-field distribution which is useful for prebunching the electron beam and enhancing efficiency. For high Q cavities, the cavity Q depends on axial mode number q as q^–2, which is important for mode discrimination. Proper selection of taper length is found to reduce the Q of high q modes, also aiding in mode discrimination. The present approach may be applied to other forms of weakly irregular cavities, such as cavities with nonlinear tapers.Work supported by U.S.D.O.E. Contract DE-AC02-78ET-51013Supported by U.S. Department of Energy