Ion heat transport in electron cyclotron resonance heated L-mode plasma on the T-10 tokamak

Anomalous ion heat transport is analyzed in the T-10 tokamak plasma heated with electron cyclotron resonance heating(ECRH) in second-harmonic extra-ordinary mode. Predictive modeling with empirical scaling for Ohmical heat conductivity shows that in ECRH plasmas the calculated ion temperature could be overestimated, so an increase of anomalous ion heat transport is required. To study this effect two scans are presented: over the EC resonance position and over the ECRH power. The EC resonance position varies from the high-field side to the low-field side by variation of the toroidal magnetic field. The scan over the heating power is presented with on-axis and mixed ECRH regimes. Discharges with high anomalous ion heat transport are obtained in all considered regimes. In these discharges the power balance ion heat conductivity exceeds the neoclassical level by up to 10 times. The high ion heat transport regimes are distinguished by three parameters: the ratio Te/Ti, the normalized electron density gradient R/■, and the ion–ion collisionality νii~*. The combination of high Te/Ti, high νii~*, and R/■=6-10 results in values of normalized anomalous ion heat fluxes up to 10 times higher than in the low transport scenario.

Suppression of the m/n=2/1 tearing mode by electron cyclotron resonance heating on J-TEXT

Stabilization of tearing modes and neoclassical tearing modes is of great importance for tokamak operation.Electron cyclotron waves(ECWs)have been extensively used to stabilize the tearing modes with the virtue of highly localized power deposition.Complete suppression of the m/n=2/1 tearing mode(TM)by electron cyclotron resonance heating(ECRH)has been achieved successfully on the J-TEXT tokamak.The effects of ECW deposition location and power amplitude on the 2/1 TM suppression have been investigated.It is found that the suppression is more effective when the ECW power is deposited closer to the rational surface.As the ECW power increases to approximately 230 k W,the 2/1 TM can be completely suppressed.The island rotation frequency is increased when the island width is reduced.The experimental results show that the local heating inside the magnetic island and the resulting temperature perturbation increase at the O-point of the island play dominant roles in TM suppression.As the ECW power increases,the 2/1 island is suppressed to smaller island width,and the flow shear also plays a stabilizing effect on small magnetic islands.With the stabilizing contribution of heating and flow shear,the 2/1 TM can be completely suppressed.

Investigating the occurrence and predictability of pitch angle scattering events at ADITYA-Upgrade tokamak with the electron cyclotron emission radiometer

This paper describes the experimental analysis and preliminary investigation of the predictability of pitch angle scattering(PAS) events through the electron cyclotron emission(ECE)radiometer signals at the ADITYA-Upgrade(ADITYA-U) tokamak. For low-density discharges at ADITYA-U, a sudden abnormal rise is observed in the ECE signature while other plasma parameters are unchanged. Investigations are done to understand this abrupt rise that is expected to occur due to PAS. The rise time is as fast as 100 μs with a single step and/or multiple step rise in ECE radiometer measurements. This event is known to limit the on-axis energy of runaway electrons. Being a repetitive event, the conditions of its repetitive occurrence can be investigated, thereby exploring the possibility of it being triggered and surveyed as an alternate runaway electron mitigation plan. Functional parameterization of such events with other discharge parameters is obtained and the possibility to trigger these events is discussed.PREDICT code is used to investigate the possible interpretations for the PAS occurrence through modeling and supporting the ECE observations. The trigger values so obtained experimentally are set as input criteria for PAS occurrence. Preliminary modeling investigations provide reliable consistency with the findings.

Study of runaway electron behaviour during electron cyclotron resonance heating in the HL-2A Tokamak

During the current flat-top phase of electron cyclotron resonance heating discharges in the HL-2A Tokamak, the behaviour of runaway electrons has been studied by means of hard x-ray detectors and neutron diagnostics. During electron cyclotron resonance heating, it can be found that both hard x-ray radiation intensity and neutron emission flux fall rapidly to a very low level, which suggests that runaway electrons have been suppressed by electron cyclotron resonance heating. From the set of discharges studied in the present experiments, it has also been observed that the efficiency of runaway suppression by electron cyclotron resonance heating was apparently affected by two factors： electroh cyclotron resonance heating power and duration. These results have been analysed by using a test particle model. The decrease of the toroidal electric field due to electron cyclotron resonance heating results in a rapid fall in the runaway electron energy that may lead to a suppression of runaway electrons. During electron cyclotron resonance heating with different powers and durations, the runaway electrons will experience different slowing down processes. These different decay processes are the major cause for influencing the efficiency of runaway suppression. This result is related to the safe operation of the Tokamak and may bring an effective control of runaway electrons.

Mechanical Analysis and Measurements of a Multicomponent NbTi/Cu Superconducting Magnets Structure for the Fully Superconducting Electron Cyclotron Resonance Ion Source

A fully superconducting electron cyclotron resonance （ECR） ion source （SECRAL ID is currently being built in the Institute of Modern Physics, Chinese Academy of Sciences. Its key components are three superconducting solenoids （Nb-Ti/Cu） and six superconducting sextupoles （Nb-Ti/Cu）. Different from the conventional supercon- ducting ECR magnetic structure, the SEC17AL Ⅱ includes three superconducting solenoid coils＇ that are located inside the superconducting sextupoles. The SECRAL Ⅱ can significantly reduce the interaction forces between the sextupole and the solenoids, and the magnets can also be more compact in size. For this multi-component SECRAL Ⅱ generating its self field of -8 T and being often exposed to the high self field, the mechanical analysis has become the main issue to keep their stress at 〈200 MPa on coils. The analytical and experimental results in mechanics are presented in the SECRAL Ⅱ structure. To improve the accuracy and efficiency of analysis, according to the composite rule of micromechanics, the equivalent uniform windings are used to simulate the epoxy-impregnated Nb-Ti/Cu coils. In addition, using low temperature strain gauges and a wireless fast strain acquisition system, a fundamental experiment on the based on our analysis, the stresses and deformations optimized. strains developments of a sextupole is reported. Finally, for its assembly of each SECRAL Ⅱ coil will be further

A Polarizer with Sinusoidal Grooves in the Electron Cyclotron Resonance Heating System of the HL-2A Tokamak

Theoretical calculation and experimental results for a polarizer with sinusoidal grooves used in the electron cyclotron resonance heating （ECRH） system of the HL-2A tokamak are presented. The calculation is based on an integral method developed in the vector theory of diffraction gratings, and the polarization characteristics obtained with a low-power test are in good agreement with the numerical calculated results. With the polarizer assembled in a miter bend in the ECRH transmission line, pure ordinary mode （O-mode） and extraordinary mode （X-mode） polarized waves are also expected in the high-power experiment, depending on the polarizer rotation angle and the toroidal injection angle of the electron cyclotron （EC） wave beam. Second-harmonic X-mode experiments were successfully explored in HL-2A. Experimental result revealed that the electron temperature increased from 0.8 keV （Ohmic heating phase） to 1.5 keV （second X-mode heating phase）.

On the heating mechanism of electron cyclotron resonance thruster immerged in a non-uniform magnetic field

To study the heating mechanism of electron cyclotron resonance thruster(ECRT)immersed in a non-uniform magnetic field,experiments and simulations are performed based on an electron cyclotron resonance plasma source at ASIPP.It is found that the first harmonic of electron cyclotron resonance is essential for plasma ignition at high magnetic field(0.0875 T),while the plasma can sustain without the first and second harmonics of electron cyclotron resonance at low magnetic field(till 0.0170 T).Evidence of radial hollow density profile indicates that upper hybrid resonance,which has strong edge heating effect,is the heating mechanism of low-field ECRT.The heating mode transition from electron cyclotron resonance to upper hybrid resonance is also revealed.Interestingly,the evolutions of electron temperature and electron density with input power experience a‘delayed’jump,which may be correlated with the different power levels required for cyclotron and ionization.Moreover,when the field strength decreased,the variation of electron density behaves in an opposite trend with that of electron temperature,implying a possible competition of power deposition between them.The present work is of great interest for understanding the plasma discharge in ECRT especially immersed in a non-uniform magnetic field,and designing efficient ECRT using low magnetic field for economic space applications.

Electron Cyclotron Resonance Deposition of Wide Bandgap a-SiC:H Films Using Acetylene under High Hydrogen Dilution

The deposition of hydrogenated amorphous silicon carbide (a-SiC.H) films from a mixture of silane, acetylene and hydrogen gas using the electron cyclotron resonance chemical vapour deposition (ECR-CVD) process is reported. The variation of the deposition and film characteristics such as the deposition rate- optical bandgap, photoluminescence and the infra-red (IR) absorption as a function of the hydrogen dilution is investigated. The deposition rate increases to a maximum value of ~25 nm/min at a moderate hydrogen diIution ratio of ~20 [hydrogenflow (sccm)/acetylene+silane flow (sccm)], and decreases in response to a further increase in the hydrogen dilution. There is no strong dependence of the optical bandgap on the hydrogen dilution within the dilution range investigated (10 to 60), and the optical bandgap calculated from the E04 method varied marginally from ~2.85 eV to ~3.17 eV. The room temperaturephotoluminescence (PL) peak energy and intensity shows a prominent shift to a maximum value of ~2.17 eV corresponding to maximum PL intensity at a moderate hydrogen diIution of ~30.The PL intensity shows a strong dependence on the hydrogen dilution variation. IR absorption results show that films deposited at higher hydrogen dilution have more Si-C bonding.

Relative Irradiance Measurement and Bonding Configurations of Amorphous Fluorinated Carbon Films Deposited by Electron Cyclotron Resonance Plasma

a-C:F films are deposited by microwave electron cyclotron resonance (ECR)plasma chemical vapor deposition (CVD) using trifluoromethane (CHF3) and benzene (C6H6) as source gases at different microwave powers. The radicals in plasma originating from source gases dissociation are analyzed by relative irradiance measurement. The bonding configurations and binding state of a-C:F films are measured with Fourier-transformed infrared spectrometer (FTIR) and x-ray photoelectron spectroscopy (XPS). The results show that a-C:F films are mainly composed of CF radical at lower powers but of CF2 radical at higher powers. The deposition of films is related to the radicals generated in plasma and the main bonding configurations are dependent on the ratio of CF to CF2 radicals in films.

Simulation of nonlinear behavior in an electron cyclotron resonance plasma

Some nonlinear behavior in electron cyclotron resonance plasma was investigated using a two-dimension hybrid-mode with self-consistent microwave absorption. The saturation,oscillations of plasma parameters (plasma density, potential, electron temperature) versus operating conditions (pressure, power) are discussed. Our simulation results are consistent qualitatively with many experimental measurements.

Correlation ofⅢ/Ⅴsemiconductor etch results with physical parameters of high-density reactive plasmas excited by electron cyclotron resonance

Reactive ion etching is the interaction of reactive plasmas with surfaces. To obtain a detailed understanding of this process, significant properties of reactive composite low-pressure plasmas driven by electron cyclotron resonance（ECR） were investigated and compared with the radial uniformity of the etch rate. The determination of the electronic properties of chlorine-and hydrogen-containing plasmas enabled the understanding of the pressure-dependent behavior of the plasma density and provided better insights into the electronic parameters of reactive etch gases. From the electrical evaluation of I（V） characteristics obtained using a Langmuir probe,plasmas of different compositions were investigated. The standard method of Druyvesteyn to derive the electron energy distribution functions by the second derivative of the I（V）characteristics was replaced by a mathematical model which has been evolved to be more robust against noise, mainly, because the first derivative of the I（V） characteristics is used. Special attention was given to the power of the energy dependence in the exponent. In particular, for plasmas that are generated by ECR with EM modes, the existence of Maxwellian distribution functions is not to be taken as a self-evident fact, but the bi-Maxwellian distribution was proven for Ar-and Kr-stabilized plasmas. In addition to the electron temperature, the global uniform discharge model has been shown to be useful for calculating the neutral gas temperature. To what extent the invasive method of using a Langmuir probe could be replaced with the noninvasive optical method of emission spectroscopy, particularly actinometry, was investigated,and the resulting data exhibited the same relative behavior as the Langmuir data. The correlation with etchrate data reveals the large chemical part of the removal process—most striking when the data is compared with etching in pure argon. Although the relative amount of the radial variation of plasma density and etch rate is approximately ？5%, the etch rate shows a slightly concave shape in contrast to the plasma density.

氮气工质10厘米ECRIT中和器实验研究

10厘米电子回旋共振离子推力器(ECRIT)可以多类型气体工作,应用于吸气式电推进系统具有可行性,研究氮气工质ECRIT的ECR中和器是研究氮氧工质ECRIT的基础.当传统氙气工质10厘米ECRIT的ECR中和器以氮气为工质工作时,由于氮气分子量较低,离子容易漂移出中和器,引出电子电流减小,已不适合以氮气为工质工作.本文基于10厘米传统ECR中和器,以抑制离子漂移出中和器、提升电子引出性能为目的,实验研究适用于氮气工质工作的双极ECR中和器.结果表明,在气体质量流率0.04 mg/s、输入功率10W的条件下,以氮气为工质工作,引出电子电流134 mA时,传统ECR中和器所需的阳极电压为150 V,而双极ECR中和器仅需50 V的阳极电压,下降了约67%;阳极电压40 V时,传统ECR中和器的功率损耗为1204.82 W/A,而双极ECR中和器的功率损耗为95.23 W/A,约为前者的8.3%.氮气工质双极ECR中和器的离子屏蔽效果显著,电子引出性能得到改善.

Gap formation around Ω_e/2 and generation of low-band whistler waves by Landau-resonant electrons in the magnetosphere: Predictions from dispersion theory

In this paper we show that two significant phenomena of magnetospheric chorus emission can be explained by the participation of beam-like electron structures,created by Landau-resonant interaction with growing oblique whistler waves.The first concerns the widely observed spectral gap near half the electron cyclotron frequency Ωe;the second is related to the observation of very obliquely propagating lower-band waves that cannot be directly generated by temperature anisotropy.Concerning the gap,kinetic dispersion theory reveals that interference of the beam-related cyclotron mode ω~Ωe-kVb with the conventional whistler mode leads to mode splitting and the appearance of a ’forbidden’ area in the ω-k space.Thereby the beam velocity appears as an essential parameter.It is directly related to the phase velocity of the most unstable whistler wave mode,which is close to VAe/2 for sufficiently hot electrons(VAe is the electron Alfven velocity).To clarify the second point,we show that Landau-resonant beams with Vb Vb<VAe/2,which arise in cold plasmas from unstable upper-band waves,are able to generate lower-band whistler mode waves at very oblique propagation(θ≥60°).Our studies demonstrate the important role of Landau-resonant electrons in nonlinear whistler wave generation in the magnetosphere.

Electron Cyclotron Harmonic Wave Heating in Tokamak Plasmas with Different Polarization Modes

Electron cyclotron heating on HL-2A has been simulated by TORAY-GA with a second harmonic extraordinary wave and a fundamental ordinary wave. The results show that the wave absorption of the second harmonic extraordinary wave is better than that of the fundamental ordinary wave. In order to understand the interaction mechanism between electrons and the two different polarization modes, the energy exchange between electrons and the two modes are theoretically analyzed, and it is found that the coupling intensity described by the Bessel function and different polarizations of the two modes are the main reasons leading to the above phenomenon. The theoretical results of this study fit well with the simulated and numerical results.

自研28 GHz/50 kW回旋管实现长时间连续运行

介绍了中国工程物理研究院应用电子学研究所针对磁约束聚变装置电子回旋共振加热(ECRH)系统、重离子加速器电子回旋共振(ECR)离子源以及前沿科技探索应用研制的28 GHz/50 kW连续波回旋管最新实验结果。研究团队在2019年该回旋管实现50 kW/30 s运行的基础上,通过结构优化和稳定性设计验证,最终实现了在10~50 kW功率范围多个功率水平的稳定长时间连续运行,典型运行结果为16 kW/3000 s、26 kW/900 s、46 kW/1800 s、50 kW/300 s,特别在输出功率32 kW连续稳定工作了400 min。这是国内首次研制出小时级连续工作的中等功率回旋管。

磁场对电子回旋共振中和器等离子体与电子引出影响的数值模拟

10 cm电子回旋共振离子推力器(ECRIT)的ECR中和器是关键部件,其内部磁场是影响中和器性能的重要因素.磁场的均匀性和磁阱位置是磁场特征的重要表现,制约等离子体与电势的分布规律、电子引出过程及中和器性能.本文分别建立磁场均匀性低、磁阱位于电子引出孔上游和磁场均匀性高、磁阱位于电子引出孔下游的ECR中和器PIC/MCC模型,在给定参数条件下,开展等离子体和电势分布规律及电子引出过程的数值模拟研究并分析其对中和器性能的影响.结果表明,磁场均匀性高、磁阱位于电子引出孔下游时,中和器内整体电势分布较均匀,电子容易朝磁阱区迁移,低引出电势引出高电子束流,其性能高于磁场均匀性低、磁阱内置的中和器.研究工作将为发展高性能的ECR中和器奠定重要基础.

磁阵列微波放电中和器的电子引出机制

微波放电中和器作为微波离子推力器系统的重要组成部分,在维持航天器电位平衡、中和羽流方面发挥着重要作用,其电子引出性能直接关系到电推力器系统的工作状态.在磁阵列微波放电中和器的磁场结构定型实验中,发现调转磁阵列朝向后引出电流的伏安特性曲线差异极大.由于磁阵列微波放电中和器的放电室直径仅10 mm,介入式探针诊断对等离子体干扰大,本文采用了一体化粒子模拟方法对中和器的工作过程进行仿真,仿真结果与实验现象相符合.通过对比不同磁场结构、工作电压下的等离子体参数分布,发现引出孔附近的电势分布决定着中和器的电子引出能力;并进一步揭示了离子在中和器电子引出过程中发挥的关键作用,阐明了磁场结构对中和器电子引出能力的影响机制.最后,本文总结了微波放电中和器有效引出电子的两个必要条件:1)磁场梯度指向引出孔,引导等离子体迁移;2)引出孔附近有足够的离子抬升电势,降低或打破电势阱.

微波离子推力器中磁场发散区电子加热模式研究

在微波离子推力器的磁场结构设计中,一般认为增大磁镜区的面积能够约束更多电子,有利于提高能量利用率;减小发散区面积能够减少电子在壁面的损失,有利于降低放电损耗.随着一体化仿真研究深入,发现利用Child-Langmuir鞘层的特性可约束电子,使其在鞘层与磁镜间往复运动获能.对此,本文设计了适用于1 cm磁阵列微波离子推力器的磁场结构,并对其初始放电和束流引出过程进行了一体化仿真,对比阐明了电子在磁场发散区受Child-Langmuir鞘层、天线表面鞘层和磁镜共同约束下的获能模式.该获能模式可提升磁场发散区的电子温度,促进电离,提升栅极前等离子体密度,进而提升束流密度.仿真结果表明,在氙气流量0.3 sccm(1 sccm=1 mL/min),微波功率为1 W,栅极电压φ_(sc)/φ_(ac)=300 V/–50 V条件下,磁阵列微波离子推力器的电流密度较2 cm微波离子推力器提升57.9%.本文从理论上对磁场发散区电子加热模式进行了验证,研究结果将为微波离子推力器优化设计提供理论依据,促进微波离子推力器性能提升.

双放电腔微波-ECR等离子体源增强磁控溅射沉积技术

因其设备简单、沉积速率高等特点 ,磁控溅射沉积技术被广泛地用于各种薄膜制备中 .但用反应磁控溅射制备化合物薄膜如氧化物、氮化物膜时 ,为了得到化学配比的膜层 ,薄膜生长表面的反应激活基团、离子等的密度必须足够大 .为此对原有的微波 -ECR等离子体源进行了改造 .研究了双放电腔微波 -ECR等离子体源增强磁控溅射的放电特性 ,并用该方法制备了氮化碳膜 .结果表明 :该方法是一种有效的制备化合物薄膜的技术 ;用该方法制备的氮化碳膜 。

氩气和氪气作为ECR中和器工质的性能比较

为比较使用不同气体工质的电子回旋共振(ECR)中和器的性能,在真空环境下,用一个电子收集板模拟离子的作用,将电子电流从ECR中和器中引出,实验研究了以氩气和氪气为工质时,ECR中和器引出电子电流的大小以及中和器的性能。实验结果表明:以氩气为工质,ECR中和器在体积流量0.8 m L/min时,88.6 V电压可引出103.8 m A的电子电流,工质利用效率和电子损耗分别为1.278 9 W/A和194.573 W/A;以氪气为工质,ECR中和器在体积流量0.6 m L/min时,75 V电压可引出108 m A电子电流,工质利用效率和电子产生损耗分别为1.783 2W/A和176.7 W/A。以氪气为工质的中和器性能明显优于氩气,但2种工质都可以满足ECR离子源中和离子束流的需要。