Real-Time Dynamic Spectrum Analysis for Plasma Electron Density and Faraday Rotation Angle Measurement on HL-2A

Electron density and Faraday rotation angle are important physical parameters in nuclear fusion research.To measure them simultaneously,the three-wave polarimeter/interferometer diagnostic system is applied.Both the final probe output signal and the reference signal contain three frequency components.The time-varying phase difference curve of each frequency component can be measured by the Real-time Dynamic Spectrum Analysis(RDSA)method based on Field-Programmable Gate Array(FPGA).The phase difference precision is better than 0.1° and the real-time feedback delay is less than 1 ms,which satisfy the requirements of HL-2A.     

Research on the real-time signal conditioning method for dispersion interferometer in HL-2M

A new CO₂ laser dispersion interferometer has been developed in the HL-2M tokamak to measure the electron density. In order to meet the needs of high-precision measurement, a data acquisition system with real-time signal conditioning (RSC) method is proposed. It can eliminate part of the impacts of environmental factors, such as mechanical vibration, light path changes, and plasma refraction effect during experiments. In harsh environments, the system can measure the line-integrated density with a high precision of 2 × 10¹⁸ m⁻² with the RSC method. The system has been tested in a recent HL-2A experimental campaign, and the results show that the RSC method plays an important role in the plasma electron density measurement.     

Reconstruction of the Density Profile for the EAST Tokamak Based on Polarimeter/Interferometer and Microwave Reflectometer Systems

A plasma density profile reconstruction procedure based on the Park matrix method has been developed for both circular and elongated plasma configuration on the Experimental Advanced Superconducting Tokamak(EAST).This method incorporates the line integrated electron density measured by the HCN interferometer and polarimeter/interferometer(POINT) system,the equilibrium fit(EFIT) based on magnetic measurements and the edge electron density profile provided by the microwave reflectometer.It is shown that when the magnetic flux surfaces are slightly corrected,the fitting error is less than 5% in comparison with the measurement data.     

Design of FPGA based high-speed data acquisition and real-time data processing system on J-TEXT tokamak

Tokamak experiment requires high-speed data acquisition and processing systems. In traditional data acquisition system, the sampling rate, channel numbers and processing speed are limited by bus throughput and CPU speed. This paper presents a data acquisition and processing system based on FPGA. The data can be processed in real-time before it is passed to the CPU. It provides processing ability for more channels with higher sampling rates than the traditional data acquisition system while ensuring deterministic real-time performance. A working prototype is developed for the newly built polarimeter–interferometer diagnostic system on the Joint Texas Experimental Tokamak (J-TEXT). It provides 16 channels with 120 MHz maximum sampling rate and 16 bit resolution. The onboard FPGA is able to calculate the plasma electron density and Faraday rotation angel. A RAID 5 storage device is adopted providing 700 MB/s read–write speed to buffer the data to the hard disk continuously for better performance.     

Recent progress on the J-TEXT three-wave polarimeter-interferometer

The J-TEXT three-wave polarimeter-interferometer system (POLARIS), which measures time-space distribution of electron density and current density, has been optimized with both the optical system and the equilibrium reconstruction method. The phase resolution of a Faraday rotation angle has been improved from 0.1 to 0.06 degree in chords from –0.18 to 0.18 m (plasma minor radius), and the sawtooth oscillation behavior has been detected by Faraday rotation angle measurement. By combining the POLARIS measured data and the equilibrium and fitting code (EFIT), an upgraded equilibrium reconstruction method has been developed, which provides a more accurate temporal and spatial distribution of current density and electron density. By means of the optimized POLARIS and improved equilibrium reconstruction, variations of profiles with increasing density have been carried out, under both Ohmic and electron cyclotron resonance heating discharges.     

Research on the phase adjustment method for dispersion interferometer on HL-2A tokamak

A synchronous demodulation system is proposed and deployed for CO_2 dispersion interferometer on HL-2 A,which aims at high plasma density measurements and real-time feedback control.In order to make sure that the demodulator and the interferometer signal are synchronous in phase,a phase adjustment(PA) method has been developed for the demodulation system.The method takes advantages of the field programmable gate array parallel and pipeline process capabilities to carry out high performance and low latency PA.Some experimental results presented show that the PA method is crucial to the synchronous demodulation system and reliable to follow the fast change of the electron density.The system can measure the lineintegrated density with a high precision of 2.0?×?10~(18)m~(-2).     

Equilibrium Reconstruction and Integration of EFIT with Diagnoses in J-TEXT Tokamak

The EFIT program is integrated with the high resolution laser polarimeter interferometer system(POLARIS), the soft X-ray imaging diagnostic system(SXR) and the electron cyclotron emission radiometer(ECE) in the J-TEXT tokamak. Then some internal information about Faraday angle and the position of safety factor q=1 can be obtained as a constraint to EFIT. The modified EFIT code is used to calculate the internal parameters such as flux function, safety factor q, pressure and current density.     

The Real-Time,High Precision Phase Difference Measurement of Electron Density in HL-2A Tokamak

This paper introduces a real-time high precision measurement of phase difference based on Field Programmable Gate Array (FPGA) technology, which has been successfully applied to laser grating interference measurement and real-time feedback of plasma electron density in HL-2A tokamak. It can track the changes of electron density while setting the starting point of the density curve to zero. In a laboratory test, the measuring accuracy of phase difference is less than 0.1?, the time resolution is 80 ns, and the feedback delay is 180 μs.     

Research on the Real-Time Phase Jump Process Method for Plasma Electron Density Measurement in HL-2A Tokamak

In the real-time plasma electron density measurement using far infrared(FIR) laser interferometry, the plasma electron density can be calculated by measuring the real time phase difference between the reference signal and the probe signal. A novel Real-time Phase Jump Process(RPJP) method is applied to the HL-2A tokamak. With this method, the phase difference precision is up to1/3600fringe(1 fringe is equal to a phase shift of 2π), and the dynamic measurement range is extensible 65536 fringes. The time resolution of the phase difference is 80 ns, while the feedback delay is 180 μs.     

北京同步辐射软X射线偏振测量装置及其应用

在北京同步辐射装置(BSRF)设计建造了-套基于多层膜偏振元件的软X射线偏振测量分析装置,可工作在双反、双透、前反后透和前透后反四种工作模式,既可作为偏振测量装置,用于同步辐射光束线和多层膜偏振元件偏振特性测量,也可作为通用反射率计,用于多层膜和薄膜的反射或透射率测量,又可用于磁性材料的磁光效应研究等.利用自行研制的装置和光学元件对BSRF的3W1B光束线的偏振特性进行了系统的测量.测量结果指出,在206 eV时,输出光的线偏振度从起偏前的O.585上升到起偏后的0.995,同步光的线偏振度得到极大改善.利用非周期宽带Mo/Si多层膜开展了铁磁性材料的磁光法拉第效应测量,获得了Ni薄膜3p边附近(60-70 eV)的法拉第旋转角度,最大偏转角度在65.5 eV和68 eV分别为1.85±0.19°和-0.75±0.09°.     

Radiation shielding design of the CFETR polarimeter interferometer and CO2 dispersion interferometer

A three-wave based laser polarimeter/interferometer and a CO₂ laser dispersion interferometer are used to determine the electron and current density profiles on a Chinese fusion engineering test reactor (CFETR). Radiation shielding is designed for the combination of polarimeter/interferometer and CO₂ dispersion interferometer. Furthermore, neutronics models of the two systems are developed based on the engineering-integrated design of CFETR polarimeter/interferometer and CO₂ dispersion interferometer and the major material components of CFETR. The polarimeter/interferometer and CO₂ dispersion interferometer's neutron and photon transport simulations were performed using the Monte Carlo neutral transport code to determine the energy deposition and neutron energy spectrum of the optical mirrors. The energy depositions of the first mirrors on the polarimeter/interferometer are reduced by three orders with the whole shielding. Since the mirrors of CO₂ dispersion interferometer are very close to the diagnostic first wall, shielding space is limited and the CO₂ dispersion interferometer energy deposition is higher than that of the polarimeter/interferometer. The dose rate after shutdown 10⁶ s in the back-drawer structure has been estimated to be 83 μSv h⁻¹ when the radiation shield is filled in the diagnostic shielding modules, which is below the design threshold of 100 μSv h⁻¹. Radiation shielding design plays a key role in successfully applying polarimeter/interferometer and CO₂ dispersive interferometer in CFETR.     

Recent and future upgrades to the DIII-D tokamak

Research on the DIII-D tokamak focuses on support for next-generation devices such as ITER by providing physics solutions to key issues and advancing the fundamental understanding of fusion plasmas. To support this goal, the DIII-D facility is planning a number of upgrades that will allow improved plasma heating, control, and diagnostic measurement capabilities. The neutral beam system has recently added an eighth ion source and one of the beamlines is currently being rebuilt to allow injection of 5 MW of off-axis power at an angle of up to 16.5° from the horizontal. The electron cyclotron heating (ECH) system is adding two additional gyrotrons and is using new launchers that can be aimed poloidally in real-time by an improved plasma control system. The fast wave heating system is being upgraded to allow two of the three launchers to inject up to 2 MW each in future experiments. Several diagnostics are being added or upgraded to more thoroughly study fluctuations, fast ions, heat flux to the walls, plasma flows, rotation, and details of the plasma density and temperature profiles.     

Application Study of Film Capacitor of DC Link Capacitor in EAST Vertical Stabilization Control Power Supply

A hydrogen cyanide laser interferometer is mostly used to measure the plasma electron density in many Tokamak devices. The real-time calculation system of the plasma electron density based on a field-programmable gate array is proposed in this work. An Altera EP4CE30F23C8 FPGA chip is selected as the master chip, and an AD9238 chip of 10 MSps is employed for analog-to-digital conversion. The FPGA-based adapted Fast Fourier Transform and the proposed processing algorithm are designed to obtain the plasma electron density. The calculated density is stored in the secure digital card and can also be transmitted to the plasma control system via Ethernet. The experimental results show that the proposed system can effectively obtain the plasma density. The maximum error range is from ? 1 to 1 degree and the time resolution is 0.025 ms which is better than that of the convention method 0.1 ms. Meanwhile, this system is highly flexible and reduces design costs to meet the demands of Tokamak devices.

     

Application of the Magnetic Surface Based PARK-Matrix Method in the HCOOH Laser Interferometry System on HL-2A

A new electron density profile reconstruction procedure based on the PARK-matrix method has been firstly exploited for the multi-chord formic acid(HCOOH, λ=432.5 μm) laser interferometry system on the HL-2A tokamak. According to the geometric coordinates of the magnetic surfaces reconstructed by the CF(current fitting) code and the assumption that the electron density between two adjacent magnetic surfaces is a constant, the local electron density is calculated layer by layer, and the electron density profile n_e(Z) can be determined, as well as the density profile n_e(R). The simulation result indicates that the error of the PARK-matrix method is acceptable for the four-chord HCOOH laser interferometer. In the applications, it shows that the reconstructed electron density profile agrees well with the microwave reflectometry measurement,and the sawtooth reversion radius is consistent with that deduced from the soft X-ray signals.Meanwhile, the electron density profiles with electron cyclotron resonance heating(ECRH) and supersonic molecular beam injection(SMBI) are also reconstructed and analyzed.     

The far-field plasma characteristics of LHT40 low-power Hall thruster for commercial aerospace applications

To achieve a better insight into the far-field plasma spatial distribution and evolution characteristics of the 300 W class low-power Hall thruster (LHT) for commercial aerospace applications,a dedicated and integrated plasma diagnostic system composed of seventeen Faraday cups (FC) and two triple Langmuir probes (TLP) is established to investigate the time-averaged in situ spatial distribution characteristics of far-field ions and electrons.The ion current density (ICD),plasma potential,plasma density,and electron temperature at 1000 mm downstream of 300 W class LHT for commercial aerospace applications in the azimuthal angle range of-90° to 90° were investigated under the conditions of different anode mass flow rates and discharge voltages.The results demonstrated that ICD,beam divergence angle,and mass utilization efficiency increased with increasing anode mass rate.The double-wings phenomenon was observed in the spatial distribution of ICD at large angles from the thruster axis,which is attributed to charge exchange collisions at increasing vacuum backpressure.The plasma electron temperature,electron density,and plasma potential parameters derived from the TLP decreased rapidly in the angle range from 0° to 30° and did not exhibit significant variations above 30°,which was also in good agreement with the results of the measured divergence angle of the FC.The discrepancy of average ion speed was calculated.The maximum error is better than 31.5％which checks the consistency between the TLP's results and that of FC to some extent.     

托卡马克超声分子束注入加料的进展

超声分子束注入作为一种新的托卡马克加料方法由作者在1992年首次提出并于当年在中国环流器一号(HL-1)装置演示成功,随后相继应用于中国环流器新一号(HL-1M)和中国科学院超导托卡马克HT-7装置。超声分子束注入等离子体呈现出电子密度峰化和温度中空分布的特征;等离子体流极向旋转速度提高,边缘扰动被抑制,等离子体能量约束得到改善。加料效率较常规脉冲送气提高一倍,而滞留器壁的粒子大为减少。近期开展的高气压氢超分子束注入实验,在束流中发现团簇流,可注入等离子体中心区域。多脉冲分子束注入形成电子密度的阶跃上升,如同冰弹丸注入效果。近年来该项技术已陆续应用于国外大型托卡马克和仿星器,是核聚变装置稳态运行的一种有效的加料方法。     

Development of a combined interferometer using millimeter wave solid state source and a far infrared laser on ENN's XuanLong-50 (EXL-50)

A millimeter wave solid state source—far infrared laser combined interferometer system (MFCI) consisting of a three-channel 890 GHz hydrogen cyanide (HCN) laser interferometer and a three-channel 340 GHz solid state source interferometer (SSI) is developed for real-time line-integrated electron density feedback and electron density profile of the EXL-50 spherical tokamak device. The interferometer system is a Mach–Zehnder type, with all probe-channels measured vertically, covering the plasma magnetic axis to the outermost closed magnetic plane. The HCN laser interferometer uses an HCN laser with a frequency of 890 GHz as a light source and modulates a 100 kHz beat signal by a rotating grating, giving a temporal resolution of 10 μs. The SSI uses two independent 340 GHz solid-state diode sources as the light source, the frequency of the two sources is adjustable, and the temporal resolution of SSI can reach 1 μs by setting the frequency difference of the two lasers at 1 MHz. The main optical path of the two interferometers is compactly installed on a set of double-layer optical platform directly below EXL-50. Dual optical path design using corner cube reflectors avoids the large support structures. Collinear the probe-beams of two wavelengths, then the phase error caused by vibration can be compensated. At present, the phase noise of the HCN Interferometer is 0.08 rad, corresponding to a line-integrated electron density of 0.88 × 10¹⁷ m⁻², one channel of measuring result was obtained by the MFCI system, and the highest density measured is about 0.7 × 1019 m⁻².     

Multichannel Microwave Interferometer for Simultaneous Measurement of Electron Density and its Fluctuation on HL-2A Tokamak

A multichannel microwave interferometer system has been developed on the HL-2A tokomak. Its working frequency is well designed to avoid the fringe jump effect. Taking the structure of HL-2A into account, its antennas are installed in the horizontal direction, i.e.one launcher in high field side(HFS) and four receivers in low field side(LFS). The fan-shaped measurement area covers those regions where the magnetohydrodynamics(MHD) instabilities are active. The heterodyne technique contributes to its high temporal resolution(1 μs). It is possible for the multichannel system to realize simultaneous measurements of density and its fluctuation. The quadrature phase detection based on the zero-crossing method is introduced to density measurement. With this system, reliable line-averaged densities and density profiles are obtained. The location of the saturated internal kink mode can be figured out from the mode showing different intensities on four channels, and the result agrees well with that measured by electron cyclotron emission imaging(ECEI).     

Experimental Observation of the Pulsed High Pressure Gas Puffing on HL-2A Tokamak

The pulse propagations of both the electron temperature and the electron density have been observed during pulse-modulated molecular beam injection experiments on HL-2A. The propagation depth of the cold pulse in the low field side is much longer than that in the high field side. The cold pulses cannot propagate to the plasma center from either the low field side or the high field side. The electron temperature in the plasma center does not change during MBI, but the electron density pulse perturbations can be observed in the plasma center.     

Faraday angle of Linearly Polarized Waves along Magnetic Field in Magnetized Collisional Plasmas

In magnetized collisional plasmas, owing to the differences between attenuations of left- and right-handed polarized waves, the Faraday rotation angle differs from that in collisionaless plasmas. In this paper, the attenuation rates of left- and right-handed polarized waves are analyzed, and the Faraday angle is expressed by the real and imaginary parts of refractive index of the magnetized plasma, with clear physics meaning. Furthermore, the dependence of Faraday angle on collision frequency is calculated and discussed.