托卡马克中离子回旋频率范围内快波电流驱动的研究

在现在和未来的先进托卡马克装置中,离子回旋频率范围内的快波电流驱动都是一种不可或缺的非感应电流驱动方式。本文利用全波方程得到波电场和磁场分布,代入扩散系数并求解Fokker-Planck方程,采用自行编写的程序对快波在等离子体中的电子吸收功率和驱动电流等物理量进行数值求解。初步研究了快波频率和等离子体温度对电子吸收功率及电流驱动效率的影响,结果显示快波能传播到托卡马克等离子体的中心区域并被电子吸收;快波频率对电子吸收快波功率有显著的影响,在70～100 MHz波频率范围内电子对快波吸收效果较好,能有效驱动电流;另外在该频段内随着等离子体温度的升高,电子吸收效果变差。     

DⅢ—D托卡马克H模式等离子体中的快波电流驱动

在DⅢ-D托卡马克的H模式和VH模式等离子体中首次测量了由快阿尔芬波驱动的电流。对极向通量演变的分析表明，快波电流驱动分布是中心峰化的，但有时比理论预计的宽。尽管对于很少发生ELMs的等离子体，测得的电流驱动效率与理论一致，但是对于有快ELMs的等离子体，电流驱动效率为一个数量级，则太低了。功率调制实验表明，电流驱动随ELM频率的增大而降低是由于中心吸收的快速功率的份额降低引起的。当等离子体分界面外侧的电子密度上升到大于ELMs引起的快波截止密度时，吸收和电流驱动是最弱的，从而可能允许边缘损失机制耗散快波功率，因为对于脱离等离子体的快波，截止密度是一个障碍。     

ITER中的电子回旋波电流驱动模拟

通过将相对论Fokker-Planck方程与波迹方程联合求解,对ITER(国际热核实验反应堆)参数下的电子回旋波电流驱动进行了数值模拟。结果表明,当波的环向发射角度不太大时,波功率沉积将发生在ITER的强场侧。当环向发射角度为21°时,电子回旋波的能量在等离子体中心区域被吸收并驱动起等离子体中心区域的电流。当发射角度变大时,电子回旋波将在弱场侧沉积功率。当发射角度为20°～30°时,能够驱动归一化的径向位置(r/a)小于0.35区域内的等离子体电流,并有较高的电流驱动效率。     

EAST电子回旋波与低杂波双波协同的数值模拟

为在EAST装置中优化电子回旋波与低杂波双波协同的电流驱动效率,从而获得更大的协同驱动电流以维持长脉冲运行,本文以双波协同驱动电流的物理机制为基础,运用模拟程序C3PO/LUKE对EAST参数下电子回旋电流驱动与低杂波电流驱动的协同效果进行了数值模拟计算,给出了协同电流和协同因子。计算结果表明：当两波驱动电流密度峰值的位置一致时协同效果最佳;而电子密度和电子温度的增加可能导致两波重叠区域的变化进而影响协同效果。     

离子回旋频率范围的加热和电流驱动状态

在离子回旋频率范围（ＩＣＲＦ）发射的快声波是托卡马克等离子体的主要加热方案之一，这个加热和电流驱动方案可能有很大的灵活性，既可利用各种波－粒子相互作用机制，也可利用快波能经受到的模转换，如设计适当，ＩＣＲＦ系统能用于离子或电子加热的电流驱动，而且还有定域沉积分布的优点，几乎的有现在的托卡马克现都使用ＩＣＲＦ加热和电流驱动，而且正在为ＩＴＥＲ研究ＩＣＲＦ系统。     

电子回旋波Ohkawa机制电流驱动计算

从电子回旋波电流驱动的机制出发,理论推导出了Boozer-Fisch电流与Ohkawa电流的计算表达式,并给出了具体的计算方法。数值模拟结果表明:电子回旋波的波功率沉积在托卡马克高场侧的离轴位置时,Ohkawa电流较小,Boozer-Fisch电流能达到较大值;波功率沉积在低场侧的离轴位置时,通过调整波参数,有效抑制Boozer-Fisch电流,能充分利用Ohkawa电流的优势使离轴驱动电流同样能达到较大值。     

剩余电场在低混杂波电流驱动中的效应

本文考虑了在等离子体中的低混杂波的动力过程,对剩余电场在低混杂波电流驱动中的效应进行了研究,增大剩余电场,可使波驱动的电流增强,但波消耗的功率增大更多,因此电流驱动的效率是随着剩余电场的增大而减小的。     

剩余电场在低混杂波电流驱动中的效应

本文考虑了在等离子体中的低混杂波的动力过程,对剩余电场在低混杂波电流驱动中的效应进行了研究,增大剩余电场,可使波驱动的电流增强,但波消耗的功率增大更多,因此电流驱动的效率是随着剩余电场的增大而减小的。     

SUNIST球形托卡马克的研究进展

球形托卡马克为聚变能的商业应用提供了一条可能的途径。中国联合球形托卡马克SUNIST以真空室的环向和极向都有绝缘隔缝为结构特征。该装置的主要任务是研究低环径比等离子体的基本特性和等离子体的非感应加热与电流驱动。包括同轴磁螺旋性注入电流启动、电极放电辅助电子回旋波电流启动、电子伯恩斯坦波以及离子高次谐波快波加热与电流驱动。装置已经顺利组装完毕,并安装了磁测量、静电探针和软X射线等基本的诊断系统。目前正处于系统联调阶段。     

HL-1托卡马克低混杂波电流驱动实验计算机模拟研究

在完整的Bonoli-Englade模拟模型基础上,编制了一组即适合用于稳态,又适用于准稳态低混杂波电流驱动(LHCD)的模拟计算代码。它包括平衡计算,环形射线追踪和福克-普朗克计算。其中采用了Shafranov平衡位形和热等离子体波色散关系。福克-普朗克计算考虑了由Pitch角散射引起高垂直温度造成的二维效应,同时还考虑了相对论效应。代码能重复以往文献显示的结果。结合阵列天线计算代码,完成了真实低混杂波功率注入时LHCD的静态模拟(未包括场演化、输运过程),获得波传播、功率沉积、驱动电流和电流驱动效     

Fully Implicit Iterative Solving Method for the Fokker-Planck Equation in Tokamak Plasmas

A three dimensional bounce-averaged Fokker-Planck (FP) numerical code has been newly developed based on fully implicit iterative solving method,and relativistic effect is also included in the code.The ...     

射频波电流驱动抑制双撕裂模不稳定性研究

采用不可压缩磁流体模型,在圆柱位形下研究了射频波电流驱动对双撕裂模不稳定性的影响。结果表明,托卡马克装置中沉积在有理面上的同向驱动电流能有效减缓3/1双撕裂模的发展。电流驱动幅值约占等离子体电流初始值的4%、驱动电流沉积宽度约为小环半径的7%时,抑制效果较好。此外,研究表明,在双撕裂模进入快速增长阶段前加入外部驱动电流,才能有效抑制撕裂模的磁爆发。     

Discharge instability in a plasma contactor

Like the hollow cathode, discharge instability also occurs during the operation of a plasma contactor.Voltage and current probes were employed to test the change of keeper voltage, keeper current,anode voltage, and anode current parameters with time under different working conditions. The anode current range corresponding to the discharge instability phenomenon is about 0.4 A to 1.2 A,and the emission characteristic curve in this area appears to bulge wherein the four parameters all produce different degrees of oscillation, the anode current oscillation being the greatest. Its waveform is considered to consist of a small-amplitude, high-frequency triangular wave and a large-amplitude,low-frequency sawtooth wave, and we have explained the shape of the wave. Each parameter shows hundreds of Hz in oscillation frequency and the phases of the four parameters appear to be regular.After fast Fourier transform processing, the frequency and amplitude of the main peak of the anode current oscillation tend to change with changes of the anode current, and there are differences in the trends under different keeper currents and xenon flows.     

Recent progress of the ECRH system and initial experimental results on the J-TEXT tokamak

In order to broaden the range of the plasma parameters and provide experimental conditions for physical research into high-performance plasma, the development of the electron cyclotron resonance heating (ECRH) system for the J-TEXT tokamak was initiated in 2017. For the first stage, the ECRH system operated successfully with one 105 GHz/500 kW/1 s gyrotron in 2019. More than 400 kW electron cyclotron (EC) wave power has been injected into the plasma successfully, raising the core electron temperature to 1.5 keV. In 2022, another 105 GHz/500 kW/1 s gyrotron completed commissioning tests which signifies that the ECRH system could generate an EC wave power of 1 MW in total. Under the support of the ECRH system, various physical experiments have been carried out on J-TEXT. The electron thermal transport in ECRH plasmas has been investigated. When ECRH is turned on, the electron thermal diffusivity significantly increases. The runaway current is elevated when a disruption occurs during ECRH heating. When the injected EC wave power is 400 kW, the conversion efficiency of runaway current increases from 35% to 75%. Fast electron behavior is observed in electron cyclotron current drive (ECCD) plasma by the fast electron bremsstrahlung diagnostic (FEB). The increase in the FEB intensity implies that ECCD could generate fast electrons. A successful startup with a 200 kW ECW is achieved. With the upgrade of the ECRH system, the J-TEXT operational range could be expanded and further relevant research could be conducted.     

Investigation of electron cyclotron current drive efficiency on the J-TEXT tokamak

Electron cyclotron current drive (ECCD) efficiency research is of great importance for the neoclassical tearing mode (NTM) stabilization. Improving ECCD efficiency is beneficial for the NTM stabilization and the ECCD power threshold reduction. ECCD efficiency has been investigated on the J-TEXT tokamak. The electron cyclotron wave (ECW) power scan was performed to obtain the current drive efficiency. The current drive efficiency is derived to be approximately η₀ = (0.06–0.16) × 10¹⁹ A m⁻² W⁻¹ on the J-TEXT tokamak. The effect of the residual toroidal electric field has been included in the determination of the current drive efficiency, which will enhance the ECCD efficiency. At the plasma current of I_p = 100 kA and electron density of n_e = 1.5 × 10¹⁹ m⁻³, the ratio of Spitzer conductivity between omhic (OH) and ECCD phases is considered and the experimental data have been corrected. The correction results show that the current drive efficiency η1 caused by the fast electron hot conductivity decreases by approximately 79%. It can be estimated that the driven current is approximately 24 kA at 300 kW ECW power.     

Polarization and Mode Control of EAST 140 GHz ECRH&CD System

The 140 GHz electron cyclotron heating and current drive (ECRH&CD) project was launched in 2011 on EAST tokamak facility, which is designed to launch 4 MW of total power for the duration up to 1,000 s into the plasma. The heating and current drive efficiencies depend on the wave coupling mode in plasma and the coupling performance relies on polarization characteristics of injected beam, so polarization control is necessary for efficient plasma heating and current drive. Two polarizer miter bends will be used to control the wave polarization for each transmission line on EAST ECRH&CD system, any required wave polarization can be produced by adjusting the mirror rotation angle of each polarizer miter bend. This work mainly shows the calculated polarizer mirror settings as a function of the injection angles for pure second extraordinary harmonic mode coupling.     

Non-inductive start up of QUEST plasma by RF power

Both start-up and sustainment of plasma were successfully achieved by fully non-inductive current drive using microwave with a frequency of 8.2 GHz. Plasmas current of 15 kA was implemented for 1 s. Magnetic surface reconstruction exhibited a plasma shape with an aspect ratio of below 1.5. The plasma current was dependent significantly on the launchen microwave power and vertical magnetic field, whiile not affected by the mode of launched wave and the toroidal refractive index. Hard X-ray (HXR) emitted from energetic electrons accelerated by the microwave was observed, and the discharge with a plasma current over 4 kA followed the same trend as the number of photons of 10 to 12 keV. This suggests that the plasma current may be driven by energetic electrons. Based on the experimental conditions, alternative explanations of how the plasma current could be driven are discussed.     

Investigation of the fast magnetosonic wave excited by the Alfvén wave phase mixing by using the Hall–MHD model in inhomogeneous plasma

The inhomogeneity is introduced by a nonzero density gradient which separates the plasma into two different regions where plasma density are constant. The Alfvén waves, the phase mixing and the fast magnetosonic wave are excited by the boundary condition in inhomogeneous magnetized plasma. By using the Hall–magnetohydrodynamics(MHD) model, it is found that there are Alfvén waves in the homogeneous regions, while the phase mixing appears in the inhomogeneous region. The interesting result is that a fast magnetosonic wave is excited in a different direction which has a nonzero angle between the wave propagation direction and the direction of the background magnetic field. The dependence of the propagation direction of the excited fast magnetosonic wave and its strength of the magnetic field on the plasma parameters are given numerically. The results show that increasing both the driving frequency and the ratio of magnetic pressure to thermal pressure will increase the acceleration of the electrons. The electron acceleration also depends on the inhomogeneity parameters.