Plasma diagnostics at Aditya Tokamak by two views visible light tomography

This visible light computerized tomography exercise is a part of a project to establish an auxiliary imaging method to assist other imaging facilities at the Institute of Plasma Research (IPR), India. Space constraints around Aditya Tokamak allow only two orthogonal ports. Each port has one detector array (64 sensors) sensitive to the visual spectrum emitted by H_α emission. The objective here is to report the developments on limited view tomography for hot plasma imaging. Spatially filtered entropy maximization algorithm with non-uniform discretization grids is employed. Estimation of unique kernel smoothening parameters (mask size and exponent factor) depends on entropy function and projection data. It removes requirement of any arbitrary/user-based decision for choosing a regularization factor thus minimizes the chance for biasedness or errors. Synthetic projection data is used to analyse the performance of this modification. The error band in the process of recovery remains under acceptable level (less than 15%) irrespective of the origin of the emissions from the core. Reconstructed hot plasma images/profiles from Aditya Tokamak are shown. These profiles may improve the current understanding about (a) plasma–wall interaction or edge plasma turbulence, (b) control and generation of plasma and (c) correlations between theoretical and engineering advancements in Tokamak reactors.     

Design and performance analysis of ITER ex-vessel magnetic diagnostics

Accurate magnetic diagnostics are essential to perform reliable operation of any tokamak. The ITER magnetic diagnostics include a wide variety of sensors located on the inner and outer surfaces of the vacuum vessel, in the divertor cassettes and in the casing of the toroidal field coils. As the measurement accuracy of the inner set of magnetic sensors might be compromised by various radiation effects and high heat loads, the complementary ex-vessel set is essential to provide backup information. This paper is an overview of the ex-vessel magnetic diagnostic which consists mainly of pick-up coils, steady state sensors, Rogowski coils in the toroidal field coil casing and fibre optic current sensors. The work presented aims at designing these sensors to meet the performance requirements in spite of the constraints due to the tokamak environment. The manufacturing constraints and the positioning requirements for all the ex-vessel magnetic sensors are described. The use and expected accuracy of the entire ex-vessel magnetic diagnostic is assessed in terms of magnetic equilibrium reconstruction and plasma current measurement precision.     

Online plasma diagnostics of a laser-produced plasma

In this study,we report a laser interferometry experiment for the online-diagnosing of a laserproduced plasma.The laser pulses generating the plasma are ultra-fast(30 femtoseconds),ultraintense(tens of Terawatt) and are focused on a helium gas jet to generate relativistic electron beams via the laser wakefield acceleration(LWFA) mechanism.A probe laser beam(λ?=?800 nm) which is split-off the main beam is used to cross the plasma at the time of arrival of the main pulse,allowing online plasma density diagnostics.The interferometer setup is based on the No Marski method in which we used a Fresnel bi-prism where the probe beam interferes with itself after crossing the plasma medium.A high-dynamic range CCD camera is used to record the interference patterns.Based upon the Abel inversion technique,we obtained a 3D density distribution of the plasma density.     

The plume diagnostics of 30 cm ion thruster with an advanced plasma diagnostics system

In order to achieve a better understanding of plume characteristics of LIPS-300 ion thruster, the beam current density, ion energy and electron number density of LIPS-300 ion thruster plume are studied with an Advanced Plasma Diagnostics System(APDS) which allows for simultaneous in situ measurements of various properties characterizing ion thruster, such as plasma density, plasma potential, plasma temperature and ion beam current densities, ion energy distribution and so on. The results show that the beam current density distribution has a double‘wing' shape. The high energy ions were found in small scan angle, while low energy ions were found in greater scan angle. Electron number density has a similar shape with the beam current density distribution.     

New developments at JET in diagnostics, real-time control, data acquisition and information retrieval with potential application to ITER

In magnetic confinement fusion, the operation of next generation devices will be significantly different compared to present day machines. The duration length of the discharges will require abandoning the traditional paradigm of processing and storing the data after the shot. In fact most information will have to be made available in real-time. The significant issues of machine protection will require more sophisticated and at the same time more robust feedback control schemes. Another very important issue emerged in the last years of JET operation, and which is expected to become more severe in ITER, is the large amount of data to be analysed, which cannot be handled in the most efficient way with traditional methods.In order to prepare for the operation of ITER, some tests are being performed at JET. The capacity of the real-time network has increased in the last years, and many more systems, mainly diagnostics have been connected to it in order to test their reliability and to assess the quality of the information they can provide for feedback control. To reduce the amount of data, a prototype of real-time adaptive data acquisition techniques is being implemented, to adjust the acquisition frequency to the time resolution of the phenomena to be analysed in the plasma. Lossless data compression techniques have been refined and various intelligent signal processing methods have already been implemented to allow an easier and more objective first screening of the data. To allow scientists from wide and diffuse communities to participate in the scientific and technical programme, various innovative tools for remote participation and experimentation are also being actively investigated.     

Measurement of the correlation spectrum of electrostatic potential fluctuations in an ECRH Helimak plasma

Measurements of the length and time scales of turbulent potential fluctuations were carried out on the MIT Versatile Toroidal Facility (VTF). Plasmas were produced by ECRF heating in a novel toroidal configuration which we have termed the Helimak. The configuration consists of a toroidal fieldB of approximately 800 gauss and a vertical fieldB _z of typically 10 gauss, produced by a Helmholtz coil.T _e is approximately 10 eV. The density exhibited a peaked profile havingn _max 2×10¹⁰ cm^–3 and a density gradient scale length of 10 cm. The fluctuation experiments were conducted using a mobile vertical array of eight Langmuir probes. At major radii outside the density peak, the vertical correlation lengths _c of fluctuations were found to be on the order of 5–10 cm for fluctuation frequencies below 3–8 kHz, and on the order of 1–2 cm at higher frequencies. At major radii on the inner slope of the density peak, a new feature appears in the spatial coherence function consisting of a second peak at a probe separation which scales linearly with vertical field. This observation indicates that these fluctuations have a correlation length on the order of 2R ₀600 cm in the direction parallel to the helical magnetic field lines.     

Magnetic diagnostics for magnetohydrodynamic instability research and the detection of locked modes in J-TEXT

Magnetohydrodynamic(MHD) instabilities are widely observed during tokamak plasma operation. Magnetic diagnostics provide important information which supports the understanding and control of MHD instabilities. This paper presents the current status of the magnetic diagnostics dedicated to measuring MHD instabilities at the J-TEXT tokamak; the diagnostics consist of five Mirnov probe arrays for measuring high-frequency magnetic perturbations and two saddle-loop arrays for low-frequency magnetic perturbations, such as the locked mode. In recent years, several changes have been made to these arrays. The structure of the probes in the poloidal Mirnov arrays has been optimized to improve their mechanical strength, and the number of in-vessel saddle loops has also been improved to support better spatial resolution. Due to the installation of high-field-side(HFS) divertor targets in early 2019,some of the probes were removed, but an HFS Mirnov array was designed and installed behind the targets. Owing to its excellent toroidal symmetry, the HFS Mirnov array has, for the first time at J-TEXT, provided valuable new information about the locked mode and the quasi-static mode(QSM) in the HFS. Besides, various groups of magnetic diagnostics at different poloidal locations have been systematically used to measure the QSM, which confirmed the poloidal mode number m and the helical structure of the QSM. By including the HFS information, the 2/1 resonant magnetic perturbation(RMP)-induced locked mode was measured to have a poloidal mode number m of ～2.     

Optimisation of design parameters for collimators and pin-holes of bolometer cameras

The total radiation emission profile of fusion experiments is usually determined using the bolometer diagnostic. In order to evaluate the spatially resolved profile, many line integrated measurements are inverted using tomographic reconstruction techniques. Their success depends on a well known and optimised definition of the viewing cones of every line-of-sight. To this aim a set of equations has been derived and put in hierarchical order to define the design parameters for bolometer cameras in fusion experiments. In particular, previous considerations, which focussed on the beam width overlap and light yield optimisation, are extended to explicitly take geometrical boundary conditions imposed by the experimental device into account, with an emphasis on small gap sizes through which viewing cones have to pass through. The equations are derived for both camera types, collimator and pin-hole versions. The results obtained can be used to design bolometer cameras for any fusion device, but in particular also for ITER. An example of such an application is given and implications for the realisation of the optimal design are discussed.     

Development of atomic beam probe for tokamaks

The concept and development of a new detection method for light alkali ions stemming from diagnostic beams installed on medium size tokamak is described. The method allows us the simultaneous measurement of plasma density fluctuations and fast variations in poloidal magnetic field, therefore one can infer the fast changes in edge plasma current. The concept has been worked out and the whole design process has been done at Wigner RCP. The test detector with appropriate mechanics and electronics is already installed on COMPASS tokamak. General ion trajectory calculation code (ABPIons) has also been developed. Detailed calculations show the possibility of reconstruction of edge plasma current density profile changes with high temporal resolution, and the possibility of density profile reconstruction with better spatial resolution compared to standard Li-BES measurement, this is important for pedestal studies.     

Development of a plasma driven permeation experiment for TPE

Experiments on retention of hydrogen isotopes (including tritium) at temperatures less than 800 °C have been carried out in the Tritium Plasma Experiment (TPE) at Idaho National Laboratory [1], [2]. To provide a direct measurement of plasma driven permeation in plasma facing materials at temperatures reaching 1000 °C, a new TPE membrane holder has been built to hold test specimens (≤1 mm in thickness) at high temperature while measuring tritium permeating through the membrane from the plasma facing side. This measurement is accomplished by employing a carrier gas that transports the permeating tritium from the backside of the membrane to ion chambers giving a direct measurement of the plasma driven tritium permeation rate. Isolation of the membrane cooling and sweep gases from TPE's vacuum chamber has been demonstrated by sealing tests performed up to 1000 °C of a membrane holder design that provides easy change out of membrane specimens between tests. Simulations of the helium carrier gas which transports tritium to the ion chamber indicate a very small pressure drop (∼700 Pa) with good flow uniformity (at 1000 sccm). Thermal transport simulations indicate that temperatures up to 1000 °C are expected at the highest TPE fluxes.     

Optimization of the optical system for electron cyclotron emission imaging diagnostics on the HL-2A tokamak

The optical system of the electron cyclotron emission imaging diagnostics on the HL-2A tokamak has been optimized in both the narrow zoom pattern and the wide zoom pattern. The two main features of the improved optical system are(1) larger coverage of the measurement region in the plasma and(2) a flatter imaging surface. The new optics has good focal characteristics over the whole plasma cross section. The curvature of the field of the image surface(ΔR between the core channel and the edge channel) is within 5.3 cm in the narrow zoom pattern and 6.7 cm in the wide zoom pattern after optimization, whereas the values with the present optics were 23 cm in the narrow zoom pattern and 15 cm in the wide zoom pattern. The optics will be fabricated, tested and installed on the HL-2A tokamak before the next experimental campaign.     

An efficient modeling of fine air-gaps in tokamak in-vessel components for electromagnetic analyses

A simple and efficient modeling technique is presented for a proper analysis of complicated eddy current flows in conducting structures with fine air gaps. It is based on the idea of replacing a slit with the decoupled boundary of finite elements. The viability and efficacy of the technique is demonstrated in a simple problem. Application of the method to electromagnetic load analyses during plasma disruptions in ITER has been successfully carried out without sacrificing computational resources and speed. This shows the proposed method is applicable to a practical system with complicated geometrical structures.     

酰基膦氧化物光引发剂在UV光聚合法合成高吸水树脂中的应用

介绍了Irgacure819、Irgacure1800和Irgacure1700三种新型的酰基膦氧化物光引发剂,用紫外．可见分光光度等方法探讨了其结构及光分解的机理。这三种高效的光引发剂可用于紫外光(UV)光聚合法合成聚丙烯酸-丙烯酸铵高吸水树脂。对曝光时间和光引发剂含量对树脂的吸水性能的影响进行了综合比较。以Irgacure1700为光引发剂,UV光聚合法合成的高吸水性树脂,其吸水率最高可达835mL／g,交联率达到94．5％。     

Development and application of core diagnostics and monitoring for the Ringhals PWRS

Noise analysis and reactor diagnostics have been applied at the Ringhals PWRs for a long time. Through a collaboration with the Department of Reactor Physics, Chalmers University of Technology, methods for treating new problems were elaborated, and known methods were developed further to make them more effective or to suit specific applications. All these methods were tested in real measurements, and many of them have been used routinely afterwards. In this paper two particular new methods are described in detail: 1) the determination of the axial position of control rods from the axial shape of the neutron flux with neural network methods, and 2) the use of gamma thermometers for the determination of the MTC and for core flow estimation.     

兰州重离子储存环外靶实验终端时间投影室的动量分辨率模拟

时间投影室(Time Projection Chamber,TPC)是在多丝正比室(Multi Wire Proportional Chamber,MWPC)和多丝漂移室(Multi Wire Drift Chamber,MWDC)的基础上发展起来的一种高空间分辨粒子径迹探测器。因其具有很高的位置分辨能力,从而可以获得很好的动量分辨率。在开展兰州重离子储存环外靶实验终端CEE(Cooler-Storage-Ring External-target Experiment)-TPC的建造之前,估算CEE-TPC的动量分辨能力是一项很有必要的工作。基于Geant4和Kalman Filter等模拟程序,对时间投影室探测器测量带电粒子的整个过程进行了蒙特卡罗模拟,给出了CEE-TPC探测不同种类的带电粒子的动量分辨率,并且对影响探测器动量分辨率的因素进行了分析。通过模拟计算,得到了CEE-TPC对?介子、质子和氘核的典型动量分辨率在5%左右,能够较好地鉴别这三种粒子,为未来CEE-TPC的建造提供了可供参考的技术参数。     

等离子体粒子模拟带电粒子推进算法校正

结合带电粒子回旋运动、漂移运动和螺旋一漂移运动三种典型的运动方式,对现有等离子体粒子模拟的粒子推进算法进行了数值试验和误差分析,通过校正差分格式中的回旋系数和半加速系数,得到了一套完整的校正算法。该校正算法不仅提高了计算精度,而且在确保数值稳定性的前提下降低了对粒子模拟时间步长的要求,从而显著提高计算效率,特别适用于强磁场大尺寸等离子体器件的模拟。     

Indexing of plasma waveforms for accelerating search and retrieval of their subsequences

This paper proposes an indexing method of plasma waveforms for accelerating search and retrieval of their subsequences. The proposed method divides a waveform into fine-grained segments. The similar segments are grouped into a segment group. A multi-dimensional index is used for quick retrieval. Grouping segments could save the amount of the index. In the retrieval, a sequence of segments, which is called a section, is used as a unit in matching subsequences. Overlapping sections could overcome the shift errors of subsequences, and results in good retrieval correctness.     

Development of a compact high resolution gamma-ray detector for E-CT applications

A compact gamma-ray detector with good spatial resolution for emission computed tomography (E-CT) applications has been developed. The detector is composed of NaI(Tl) scintillation pixels array and Hamamastu R2486-05 PSPMT. Having a pixel size of 2 mm × 2 mm and an overall dimension of 48.2 mm × 48.2mm × 5 mm, it has 484 pixels in a 22×22 matrix. An average spatial resolution of 2.5mm (FWHM) was achieved. The slope of position linearity is constant within 10% in a range of 40mm. After corrections, the average value of differential non-linearity and absolute non-linearity were 0.16mm and 0.535mm respectively, and a 17% at FWHM of total energy resolution for 241Am was obtained.     

Electromagnetic and structural analyses of the vacuum vessel and plasma facing components for EAST

During plasma disruptions, time-varying eddy currents are induced in the vacuum vessel (VV) and Plasma Facing Components (PFCs) of EAST. Additionally, halo currents flow partly through these structures during the vertical displacement events (VDEs). Under the high magnetic field circumstances, the resulting electromagnetic forces (EMFs) and torques are large. In this paper, eddy currents and EMFs on EAST VV, PFCs and their supports are calculated by analytical and numerical methods. ANSYS software is employed to evaluate eddy currents on VV, PFCs and their structural responses. To learn the electromagnetic and structural response of the whole structure more accurately, a detailed finite element model is established. The two most dangerous scenarios, major disruptions and downward VDEs, are examined. It is found that distribution patterns of eddy currents for various PFCs differ greatly, therefore resulting in different EMFs and torques. It can be seen that for certain PFCs the transient reaction force are severe. Results obtained here may set up a preliminary foundation for the future dynamic response research of EAST VV and PFCs which will provide a theoretical basis for the future engineering design of tokamak devices.     

An accurate automated technique for quasi-optics measurement of the microwave diagnostics for fusion plasma

A new integrated technique for fast and accurate measurement of the quasi-optics,especially for the microwave/millimeter wave diagnostic systems of fusion plasma,has been developed.Using the LabVIEW-based comprehensive scanning system,we can realize not only automatic but also fast and accurate measurement,which will help to eliminate the effects of temperature drift and standing wave/multi-reflection.With the Matlab-based asymmetric two-dimensional Gaussian fitting method,all the desired parameters of the microwave beam can be obtained.This technique can be used in the design and testing of microwave diagnostic systems such as reflectometers and the electron cyclotron emission imaging diagnostic systems of the Experimental Advanced Superconducting Tokamak.