A spectral system with the spatial resolution for plasma motion detection in the GOL-3 multi-mirror trap

A spectral system with the spatial resolution intended for diagnosing rotation of the plasma in the GOL-3 facility is described. The system is capable of measuring the radial dependences of the Doppler shift and broadening of spectral lines emitted by the plasma from various points in it. A DFS-24 double focusing spectrometer with a reciprocal linear dispersion of 0.45 nm/mm is the basis for the spectral system. If a radiation source is axially symmetric and extended, it is possible to obtain the intensity of spectral lines on the surface of the photosensitive area of a CCD array with the spatial resolution across the plasma by forming an image of the plasma in the sagittal focal plane of the entrance collimation lens, though the spectrometer astigmatism is strong. As a result, a spatial resolution of 0.8 mm has been attained in the developed system at a 55-mm field of view.     

A new control system for the capacitive energy storage of the GOL-3 multiple-mirror trap

A new control system for capacitive energy storage with a rated energy content as high as 16 MJ is described. Capacitive energy storage has been used since 1987 to supply power for the pulsed magnetic system of the GOL-3 multiple-mirror trap. It has an operating voltage of 6 kV and consists of 6000 IK-6-150 capacitors that are located in six remote rooms together with the necessary infrastructure. The system for control and data acquisition was built using Arduino microcontroller boards operating as a distributed network of remote servers. The client part of the control system uses a personal computer with a standard configuration; communication with remote servers is effected by the TCP/IP protocol. The control system was put into regular operation at devices of the GOL-3 facility in the early 2016.     

Spectral Diagnostics for Plasma Research at the GOL-3 Facility

A complex of visible-region spectral diagnostics for studying high-temperature plasma at the GOL-3 facility is described. The complex includes three spectral instruments with different spectral resolutions, apertures of optics, and spatial resolutions. These instruments are equipped with digital recording units that make it possible, depending on the task being performed, to obtain highly resolved plasma-radiation spectra with either temporal or spatial resolution. The technique for measuring the electron density, ion temperature, and magnetic field are presented, along with the corresponding results.     

A microwave detector based on an MCT photodiode for subthermonuclear plasma research

A microwave detector including a single-element infrared (IR) photodiode mounted in a cooled Dewar and a preamplifier is developed. An IR photodiode of the n ⁺-p type is created on the basis of mercury-cadmium telluride (HgCdTe or MCT) heteroepitaxial structures grown by means of molecular beam epitaxy. A special profile of MCT structures throughout the MCT layer thickness ensures a low series resistance of less than 10 Ω and a high quantum efficiency at a level of 0.65 without any antireflection coating. For the spectral range of 8 to 12 μm, IR photodiodes are characterized by a low threshold power of 3.8·10^?13 W·Hz^?1/2 and 10^?19 W·Hz^?1 in the direct and heterodyne regimes, respectively. The cooled Dewar maintains the operating temperature of the IR photodiode in the interval of 77 to 80 K for 8. The preamplifier operates in a frequency range up to 1 GHz. With the use of this microwave detector, a method is developed for detection of intensity of a CO₂ laser beam on plasma fluctuations caused by heating by a relativistic electron beam (REB). At high REB intensities, dips of the turbulence signal with a duration of several nanoseconds are observed, which is interpreted as a collapse of Langmuir waves.     

The Data-Acquisition System of the GOL-3 Facility

Using the upgrading of the measuring system of the GOL-3 plasma facility as an example, the structure of hardware and software environment developed for data-acquisition systems of large pulse electrophysical plants is considered. The equipment is built into 3U-size 19-inch subracks. The control computers are connected to the measuring equipment via standard network facilities (Ethernet-10/100 interface and TCP/IP protocol). At present, we have begun making basic diagnostic measurements using the ADC1250/32 multichannel synchronous data-acquisition systems.     

Spectroscopic studies of the interaction of a high-power plasma stream with a solid on the GOL-3 facility

Experiments involving irradiation of carbon targets with a hot electron plasma stream performed on the GOL-3 facility were aimed at the simulation of the effect of hot plasma of a thermonuclear reactor on plasma collectors in regimes close to those expected in the ITER. In these experiments, the emphasis was on the study of the surface-erosion processes exposed to the plasma stream. The graphite evaporation and chemical-erosion processes were studied with absolutely calibrated spectroscopic systems of the visible region. Spectroscopic experiments yielded data on the flow of carbon atoms from the surface of a plasma collector and on the contribution of chemical erosion to the surface-damage process. The obtained values are compared with the results of direct measurements of the erosion depth and the results of numerical calculations.     

Novel interferometer for the measurement of plasma density

This report describes an interferometer recently developed and tested in prototype form. The device combines certain features of predecessor interometers but in a module which, subject to limitations on path-length and bandwidth, is simpler to use.     

A microwave two-wave interferometer for plasma diagnostics

The scheme and the main elements of an interferometer simultaneously operating at frequencies of the 8-and 4-mm ranges are presented. To combin e two radiations in a common waveguide section and separate them by sending to the corresponding receivers, a special separation filter has been developed. A homo-dyne technique for transferring phase measurements to an intermediate frequency is employed in the interferometer. The range of unambiguously measured phase shifts is 1.5°—360°, and the phase-shift measurement error is within 5%.     

A microwave interferometer for steady-state plasma density measurements

An interferometer for a wavelength of 8 mm, capable of homodyne frequency conversion for measuring the electron density of a steady-state plasma from a high-frequency ion source, is described. An original method for generating a reference intermediate-frequency signal using a cavity resonator is applied in the interferometer. The unambiguously measured phase shifts range from 1.5° to 360°, and the error in measuring the phase shift is 5%.__________Translated from Pribory i Tekhnika Eksperimenta, No. 2, 2005, pp. 98–100.Original Russian Text Copyright © 2005 by D. Nagornyi, A. Nagornyi, Voznyi.     

Quasi-quadrature interferometer for plasma density radial profile measurements

A cw Mach Zehnder multichannel interferometer has been developed to measure time-dependent fractional fringe shifts with an accuracy of one-fortieth fringe. The design is quasi-quadrature in that known phase shifts, introduced in the reference beam, are time multiplexed with the normal reference beam. This technique requires only one detector per interferometer channel as compared to two detectors for most quadrature designs. The quadrature information makes the sense of density changes unambiguous, it automatically calibrates the instrument during the plasma event, and it makes fringe shift measurements virtually independent of fringe contrast fluctuations caused by plasma refractive and/or absorptive effects. The interferometer optical design is novel in that the electro-optic crystal used to introduce the 90 degrees phase shifts is located in the common 2-mm-diam HeNe entrance beam to the interferometer, by exploiting polarization techniques, rather than in the expanded 1-2-cm reference beam itself. This arrangement greatly reduces the size, cost, and high-voltage requirements for the phase modulating crystal.     

An interferometer for measuring surveyor's pillars in the open air

Electronic distance meters are performance tested on a 650 m long baseline at the National Measurement Laboratory, Sydney, Australia. The distances between the pillars which make up the baseline must be measured in a way which is traceable to the international definition of the metre. A laser interferometer has been developed to measure one of the intervals in a very accurate manner. It has some novel features to allow the use of a simple carriage-way to transport the reflector and has demonstrated a measurement accuracy of 0.2 ppm over a distance of 80 m in the open air.     

Optoelectronic modulation of a laser interferometer in the infrared for accurate electron density variation measurements

An improved method for high-electron-density (10(17) cm(-3)) measurement in a shock-generated plasma is described. A laser interferometer operated at 3.39 mum is regularly modulated (1 MHz) by a LiNbO(3) electro-optical crystal. Thus electron-density variations of 8x10(15) cm(-3) mus(-1) and fluctuation of 8x10(14) cm(-3) can be simultaneously and accurately measured in a 4x4-cm conventional shock tube. Experimental results in reflected shock waves are presented.     

A Complex of Imaging Diagnostic Devices of Vacuum UV Radiation for the GOL-3 Multimirror Trap

A complex of imaging diagnostic devices of vacuum UV radiation based on the GOL-3 multimirror trap is described. The characteristics of the devices included in the complex and examples of their operation are presented. The diagnostic techniques are intended for obtaining information on the basic plasma parameters and monitoring the operating modes of the facility. In combination with spectroscopic systems, these diagnostics allow one to determine the impurity diffusion dynamics in a plasma.     

Feedback-stabilized fractional fringe laser interferometer for plasma density measurements

A feedback stabilization technique is described for a fractional fringe interferometer measuring plasma electron densities. Using this technique, a CO2 laser Michelson interferometer with a pyroelectric detector exhibited a sensitivity of 3.4 x 10(-4) fringe on a 1-ms time scale and, due to acoustic pickup, 1.8 x 10(-2) fringe on a 10-ms time scale. The rise time is 45 micros. Stabilization against slow drifts in mirror distances is achieved by an electromechanically translated mirror driven by a servo system having a 0.2-s response time. A mechanical chopper in one of the two beam paths generates the signal which drives the servo system.     

A new method for determining the plasma electron density using three-color interferometer

A new method for determining the plasma electron density using the fractional fringes on three-color interferometer is proposed. Integrated phase shift on each interferometer is derived without using the temporal history of the fractional fringes. The dependence on the fringe resolution and the electrical noise are simulated on the wavelengths of CO(2) laser. Short-time integrations of the fractional fringes enhance the reliability of this method.     

Dual laser interferometer for plasma density measurements on large tokamaks

A two-wavelength plasma density interferometer utilizing a CO(2) laser and an HeNe laser is described. The interferometer is being designed for use on Doublet III, a large noncircular cross-section tokamak. The use of the two wavelengths allows the distinction between fringe shifts due to plasma density and fringe shifts due to mirror vibrations. Plasma density fringe shifts of 1/10 of a fringe shift can be measured in the presence of mirror vibrations which cause several fringe shifts. A simple digital phase comparing electronic system is used.     

Methods for investigating the spatial distribution of ion emission from micropinch-discharge plasma

A technique for investigating the spatial structure of X-ray and ion-emission sources from micropinch- discharge plasma (MDP) is described and the investigation results are presented. A spectrometric system has been developed that allows measurements of the spectral characteristics of the ion emission for ions of different degrees of ionization from different MDP regions in a device of the low-inductance vacuum-spark type.     

激光测量几何误差补偿算法

激光技术作为重要的测量手段,已经被广泛的应用到精密运动控制系统中。激光测量误差直接影响到运动控制系统的控制精度,其中阿贝与余弦误差等几何误差对激光测量精度影响显著,在精密运动控制中必须予以补偿与校正。以精密运动台多维激光测量模型为基础,介绍了阿贝与余弦误差产生原因。在不考虑激光干涉仪的加工和安装误差的情况下,推导了运动台存在倾斜角度下的阿贝与余弦误差计算模型,在此基础上给出了激光测量数据误差补偿模型,以实现测量数据的实时补偿与修正。算法已经成功应用在实例中,表明该算法的有效性与可靠性。     

A microwave interferometer with increased stability for diagnostics of steady-state plasma

The schematic and results of studying an interferometer for a wavelength of 8 mm with homodyne frequency conversion for measuring the electron density of a steady-state plasma are described. The design of its waveguide system allows the drift of the indicated initial phase to be reduced to a level of ±0.1°/h. The maximum phase shift measured is 360°, the tolerable signal-power decay in plasma is 16 dB, and the maximum phase measurement error is ～5%.