Optimized calculation of the synergy conditions between electron cyclotron current drive and lower hybrid current drive on EAST

The optimized synergy conditions between electron cyclotron current drive(ECCD) and lower hybrid current drive(LHCD) with normal parameters of the EAST tokamak are studied by using the C3PO/LUKE code based on the understanding of the synergy mechanisms so as to obtain a higher synergistic current and provide theoretical reference for the synergistic effect in the EAST experiment. The dependences of the synergistic effect on the parameters of two waves(lower hybrid wave(LHW) and electron cyclotron wave(ECW)), including the radial position of the power deposition, the power value of the LH and EC waves, and the parallel refractive indices of the LHW(N) are presented and discussed.     

On the Nonlinear Processes During Generation of Current Drive

The manifestations of the induced scattering effects in the generation process of current driven by lower-hybrid (LH) waves are studied taking into account the radiative-resonant interactions. The influence extent of the LH wave modulational instability on current drive is estimated. It is shown that the induced scattering of LH waves on plasma particles leads to a change of the LH waves spectrum and through this leads to an essential influence on fast electrons generation rate and the steady-state current drive. The modulational instability of LH waves can provide a “spectral gap” filling in the case of sufficiently strong LH wave pumping.     

离子迴旋共振加热对低杂波电流驱动的影响

离子迴旋共振频率(ICRF)波(ω=2Ω_D)和低杂(LH)波同时进入D-T聚变反应堆等离子体时,ICRF加热产生的高能D离子对LH波存在着较强的Landau阻尼吸收,影响了低杂波驱动电流(LHCD)的效率;提高LH波的频率,可降低加热离子对LH波的阻尼吸收。     

HL-2A装置的LHCD运行区域与驱动电流分布控制

讨论了低杂波电流驱动（LHCD）实验中电流驱动效率、电流分布控制与等离子体参数和入射波谱的关系,以及波的可近性对确定功率沉积分布的作用。讨论了控制电流密度分布的方法及在HL－2A装置上实现中心负剪切位形的可能性。     

Numerical simulation of electron cyclotron current drive characteristics on EAST

Electron cyclotron current drive （ECCD） will be applied in the EAST tokamak during its the new campaign. In order to provide theoretical predictions for relevant physical experiments, some numerical simulations of ECCD with the parameters of EAST have been can＇ied out by using TORAY-GA code based on the understanding of ECCD mechanisms. ECCD efficiencies achieved in different plasma and electron cyclotron （EC） wave parameters are given. The dependences of ECCD characteristics on EC wave injection angle, toroidal magnetic field, plasma density, and temperature are presented and discussed.     

Current drive by an HF electromagnetic wave in a magnetized plasma

The problem of current drive by an HF wave is analyzed in a one-particle model of a magnetized plasma. A general expression for the current drive is derived by an averaging method in the nonrelativistic case, in second order in the expansion parameter. The presence of a constant and strong magnetic field, the presence of a constant electric field, and the dynamic friction effect are all taken into account. For a monochromatic wave with an amplitude which varies slowly in time and space, expressions for the current drive are derived in closed form. The mechanism for the current drive is analyzed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 87–91, March, 1989.     

Investigation of lower hybrid current drive during H-mode in EAST tokamak

H-mode discharges with lower hybrid current drive (LHCD) alone are achieved in EAST divertor plasma over a wide parameter range. These H-mode discharges are characterized by a sudden drop in D_α emission and a spontaneous rise in main plasma density. Good lower hybrid (LH) coupling during H-mode is obtained by putting the plasma close to the antenna and by injecting D₂ gas from a pipe near the grill mouse. The analysis of lower hybrid current drive properties shows that the LH deposition profile shifts off axis during H-mode, and current drive (CD) efficiency decreases due to the increase in density. Modeling results of H-mode discharges with a general ray tracing code GENRAY are reported.     

D形截面环流器中的磁面及LHCD的研究

本文利用环形系统的Ｇｒａｄ－Ｓｈａｆｒａｎｏｖ方程得到了Ｄ形截面的托卡马克磁面位形，并利用射线追踪技术研究了Ｄ形磁面位形下低杂波的运动形态。定性地研究了Ｄ形磁面位形下利用低杂波驱动电流的可行性，优化地给出了驱动电流的最佳方式。     

分布式电流刺激抑制心肌组织中螺旋波

利用两种恒定电信号刺激介质不同区域来产生分布式电流, 外界分布式电流内化为跨膜电流后在介质中形成稳定的梯度力可抑制螺旋波的传播. 当螺旋波被消除后系统进一步演化为均匀态且对应的膜片电位采样序列逐渐趋于一个稳定值. 在考虑噪声情况下, 该方法仍然能消除螺旋波, 对其采样序列分析也验证了方法的可靠性. 关键词： 螺旋波 分布式电流 激发介质     

捕获电子对低杂波与电子回旋波的协同效应的影响

电子回旋波和低杂波的协同效应可有效地提高两只波的电流驱动效率.本文数值研究了捕获电子效应对电子回旋波和低杂波协同的影响.结果显示,随着捕获角的增大,双波协同驱动电流会减小,且协同因子也会明显减小,即捕获角对两只波协同驱动流的影响要比其对单独驱动电流的影响更加敏感.通过加宽低杂波共振区可减弱电子回旋波电流驱动对捕获角的依赖,同时发现随着电子回旋波功率的增加,捕获角对电子回旋波电流驱动的影响也会变小.     

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The synergy current drive by combining electron cyclotron wave (ECW) with lower hybrid wave (LHW) can be used to either increase the noninductive current drive efficiency or shape the plasma current profile. In this paper, the synergy current drive by ECW and LHW is studied with numerical simulation. The nonlinear relationship between the wave powers and the synergy current of ECW and LHW is revealed. When the LHW power is small, the synergy current reduces as the ECW power increases, and the synergy current is even reduced to lower than zero, which is referred as negative synergy in the this context. Research shows that the mechanism of the negative synergy is the peaking effect of LHW power profile and the trapped electrons effect. The present research is helpful for understanding the physics of synergy between electron cyclotron current drive and lower hybrid current drive, it can also instruct the design of experiments.     

High density current drive by high frequency radiation

A self-consistent theory is developed for current drive by intense radiation in the presence of the ion-acoustic instability. The spectrum of ion-acoustic turbulent noise generated by the driven current and concentrated in a limited cone of angles along the propagation direction of the wave is found. Excitation of the instability is accompanied by the establishment of an electron drift that is excited by the electromagnetic wave and has a velocity on the order of the ion acoustic speed. This current drive regime is realized over a wide range of intensities, as long as the region of turbulence in the angles of the acoustic wave vector is expanding. At yet higher intensities, the driven current increases in proportion to the intensity of the fundamental wave. Similar behavior is found for driven heat fluxes. Zh. éksp. Teor. Fiz. 111, 107–119 (January 1997)     

The Introduction to the ECRH System of the HL-2A Tokamak

The 1 MW/68 GHz/1 s ECRH system of HL-2A device is being designed or fabricated. The O mode wave beams are injected into plasma from low field side of the HL-2A tokomak. Because the EC wave can heat plasma locally, it is a very versatile scheme which has been employed to heating, current drive, profile control, confinement improvement. Up to now, the basic physical and engineering parameters of the whole system have been fixed and the subsystems are being designed or fabricated.     

俘获电子效应对低杂波电流驱动的影响

利用的程序是基于FASTFP开发的RFP准线性Fokker-Planck程序，该程序适用于各种辅助加热和电流驱动的动力学计算.利用开发的编码对低杂波在托卡马克等离子体中的吸收和驱动效率进行了Fokker-Planck计算，考查了环形托卡马克装置的纵横比对波功率沉积和电流驱动效率产生的作用.研究表明，俘获电子效应对低杂波电流驱动的影响与波驱动的功率谱结构有关.俘获电子的平行速度较低，优化的功率谱可以在共振的电子数和俘获电子之间取得折中.俘获电子效应可以使低杂波电流驱动效率减小30%. 关键词： Fokker-Planck方程 俘获电子效应 低杂波电流驱动     

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在EAST上通过分析剩余环电压与低杂波功率之间的关系,计算得到了低杂波电流驱动效率。采用归一化功率,即功率对等离子体电流、电子密度、等离子体大半径以及有效电荷数归一化,将所有数据绘制在同一曲线中,这样可以得到不同等离子体参数下的低杂波电流驱动效率。实验得到低杂波电流驱动效率η0=(0.5~1.3)×1019 A.m-2.W-1,在等离子体电流Ip=277kA、低杂波功率PLH=681kW条件下,实验得到长达3s的低杂波全波驱动。     

Simulation on effect of poloidal power spectrum on lower hybrid wave propagation

The coupling of lower hybrid wave to the plasma is a crucial issue for efficient current drive in tokamaks. This paper establishes a new coupling model which assumes the antenna to be a curved face and the plasma to be a cylinder. Power spectrum considering the coupling between wave-guides in both poloidal and toroidal direction is simply estimated and discussed. The effect of the poloidal wave vector on wave propagation, power deposition and driven current is also investigated with the help of lower hybrid current drive code. Results show that the poloidal wave vector affects the ray tracing, and also has effect on power deposition and driven current. The effect of the poloidal wave vector on power deposition and driven current profile depends on plasma parameters. Preliminary studies suggest that it seems possible to control the current profile by adjusting the poloidal phase difference between the waveguide in poloidal direction.     

Modeling of a lower-hybrid current drive by including spectral broadening induced by parametric instability in tokamak plasmas

By incorporating parametric instabilities of lower hybrid (LH) waves into a ray-tracing Fokker-Planck code, accurate simulations of the LH deposition profiles are provided, which are useful for interpreting the long-lasting internal transport barriers (ITBs) sustained by lower hybrid current drive (LHCD) on JET (Joint European Torus). Utilizing the new model, the simulation of the q-profile evolution results in agreement with that provided by the motional Stark effect reconstructed equilibria. Low magnetic shear (s approximately equal to 0) is produced by LHCD in a layer close to the ITB radial foot.     

EAST装置低杂波电流驱动效率分析

在EAST上通过分析剩余环电压与低杂波功率之间的关系,计算得到了低杂波电流驱动效率。采用归一化功率,即功率对等离子体电流、电子密度、等离子体大半径以及有效电荷数归一化,将所有数据绘制在同一曲线中,这样可以得到不同等离子体参数下的低杂波电流驱动效率。实验得到低杂波电流驱动效率η₀=(0.5~1.3)×10¹⁹ A.m^-2.W^-1,在等离子体电流I_p=277kA、低杂波功率P_LH=681kW条件下,实验得到长达3s的低杂波全波驱动。     

Enhancement of Resonant Activation by Constant Bias Current for Superconducting Junction

We consider a superconducting(Josephson) junction driven by the thermal noise with an ac drive current and a dc constant bias current in the overdamped case and in the underdamped case,respectively,and investigate the effect of the constant bias current on the evolution of the net voltage versus the driving frequency.It is shown that,with some suitably selected values of the system's parameters,suitably increasing the absolute value of the constant bias current can lead to the enhancement of resonant activation of the net voltage versus the driving frequency.This result can benefit the investigation for the Josephson junction subjected to the constant bias current(or voltage).     

CFETR低杂波电流驱动数值模拟研究

利用射线追踪和福克-普朗克方程,研究了CFETR上驱动电流和功率沉积对低杂波注入位置和耦合波谱的依赖关系,讨论了边界非线性效应对电流驱动与功率沉积的影响,给出了低杂波平行折射率和低杂波注入位置的一个优化值。初步数值计算表明：边界非线性效应会导致驱动电流降低;不考虑低杂波非线性效应时,驱动电流的差异约为6%左右,小于考虑该效应时的差异(~25%)。