The Gas Electron Multiplier (GEM) is a detector used to register ionizing radiation, e.g., soft X-rays. The detector of this type, built and developed at the IPPLM institute, allows registering X-rays in the energy range of 2-20keV and determining its intensity in time, as well as its spatial position and energy. Simulating the work of such a detector, performed in parallel to experimental research, and sometimes preceding it, allows for optimization of construction and operation parameters of this detector with respect to the requirements set in the experiment, and allows for a better understanding of the physical processes occurring in the detector. The paper presents how simulations are performed, i.e. describes applied programs, main stages of simulation such as the construction of a three-dimensional model of the detector for calculations, the efficiency of X-ray detection, its conversion to primary electrons and the process of avalanche formation. Finally, the results obtained in this way are also presented.
KEYWORDS: Systems modeling, Data modeling, Field programmable gate arrays, Control systems, Plasma diagnostics, Plasma systems, Sensors, Human-machine interfaces
The paper describes the communication model implemented for tokamak plasma diagnostics systems. The approach was tested for the SXR measurement system working with the GEM detector. The model describes the interfaces used for integration of various firmware and software implementations, done in the system. The purpose of the applications is to control and manage the system with acquisition of measurement data. The applications are often design by various authors, therefore it is necessary to create a common communication model, for easy integration and upgrades of the components in the system.
KEYWORDS: Field programmable gate arrays, Computing systems, Data acquisition, Signal processing, Sensors, Signal detection, Plasma, Data processing, X-rays, Analog electronics
The presented system is used for monitoring of the plasma impurities in the tokamak. It is done by measuring radiation in Soft X-Ray range with the use of a GEM-based detector. Acquired data is transferred through the whole system with low latency. Presented system can be divided into many parts - detector, analog electronics, FPGA, PCIe transmission line and computer system with high-performance CPU. This work will concentrate on synchronization between FPGA, which write data to the memory on the CPU side and computational part, which is executed in the computer. In long-running measurements, there is a synchronization problems which can arise. There is a difference in variables based on which the execution time of both parts is dependent. Working on measurements of radiation of plasma impurities requires limits in terms of latency. This paper presents reasons, descriptions and solutions for such problems.
The search for new technologies in the field of plasma diagnostics entails the increasing demands on the radiative stability of the used materials due to development and usage of fusion facilities, where the study of processes occurring during the interaction of radiation with matter has become particularly important. Currently, a new X-ray imaging detection technology is required for tokamaks such as ITER. X-ray detectors that are being used in existing equipment may rapidly degrade due to large neutron fluxes characteristic for the tokamak environment. Despite the relatively wide use of semiconductor detectors to record SXR radiation (generally ionizing radiation), gas detectors are promising candidates that are suited much better for use in future fusion reactors given their resistance to neutron radiation. The most promising representative of the new gas detector class is the so called Gas Electron Multiplier (GEM), which is characterized by high amplification factor of the primary charge that is originated from photon absorption. Its main advantages are the compactness of the detector, good temporal and spatial resolutions, the ability to discriminate against photon energy and better neutron resistance compared to existing systems. All this makes such a detection system a potentially better candidate for soft X-ray measurements in the ITER and DEMO reactors. In this work, a new type of detection system based on GEM technology was proposed for soft X-ray measurements in the ITER reactor-oriented research, which is being developed at IPPLM.
The advanced Soft X-ray (SXR) diagnostics setup devoted to studies of the SXR plasma emissivity focusing on the energy range of tungsten emission lines is at the moment a highly relevant and important for ITER/DEMO as W became a plasmafacing material and, therefore, plasma contamination by W and W transport in the plasma must be understood and monitored. The Gas Electron Multiplier (GEM) based SXR radiation detecting system under development by our group with a spatial and energy-resolved photon detecting chamber may become such a diagnostic setup; however, many physical, technical and technological aspects must be taken into consideration. This work presents the results of preliminary tests and simulations of the research into the optimal design of the detector’s internal chamber. The study of the influence of different GEM foils on the properties and distribution of the electron avalanche as well as the effect of the high rate photon flux on GEM foil performance was performed. Effect of electrodes alignment allowed choosing the gap distances which maximize electron transmission was also examined. Finally, the optimal readout structure design was identified suitable to collect a total formed charge effectively.
The measurement system based on GEM - Gas Electron Multiplier detector - is developed for soft X-ray diagnostics of tokamak plasmas. The multi-channel setup is designed for estimation of the energy and the position distribution of an Xray source. The focal measuring issue is the charge cluster identification by its value and position estimation. The fast and accurate mode of the serial data acquisition is applied for the dynamic plasma diagnostics. The charge clusters are counted in the space determined by 2D position, charge value and time intervals. Radiation source characteristics are presented by histograms for a selected range of position, time intervals and cluster charge values corresponding to the energy spectra.
We present the concept of data distribution and dispatching software which is prepared for low latency and high throughput SXR measurement system developed by our group. Its scope includes handling data acquisition from multiple FPGA chips, execution of numerical algorithms with the use of multiple threads and post calculation storage and transfer. Data transfer to CPU side is done with usage of DMA via PCIe interface with specially developed Linux driver. This paper describes the need and details of discussed part of the system.
KEYWORDS: Field programmable gate arrays, Diagnostics, Sensors, Plasma diagnostics, Plasma, Data processing, Signal processing, Digital signal processing, Computer architecture, Physics
This paper discusses the model and the development methodology that was proposed in the implementation process of the heterogeneous system for the WEST thermal fusion reactor. The objective was to provide a systematic approach to provide a heterogeneous device to handle high-throughput workloads with low-latency for the WEST Soft X-Ray impurities diagnostic. The presented mechanism is dedicated to augment the system applicability to a wider area of instrumentation for high-scale physics experiments.
This document was prepared to discuss the high voltage generator module which can be used to supply X-ray Gas Electron Multiplier (GEM) detector. Emphasis was placed on the description of the module’s hardware structure. Furthermore, the detector protecting mechanisms the against the damage have been presented and described.
The requirements given for GEM (Gaseous Electron Multiplier) detector based acquisition system for plasma impurities
diagnostics triggered a need for the development of a specialized software and hardware architecture. The amount of
computations with latency and throughput restrictions cause that an advanced solution is sought for. In order to provide a
mechanism fitting the designated tokamaks, an insight into existing solutions was necessary. In the article there is
discussed architecture of systems used for plasma diagnostics and in related scientific fields. The developed solution is
compared and contrasted with other diagnostic and control systems. Particular attention is payed to specific requirements
for plasma impurities diagnostics in tokamak thermal fusion reactor. Subsequently, the details are presented that justified
the choice of the system architecture and the discussion on various approaches is given.
KEYWORDS: Field programmable gate arrays, Feedback loops, Telecommunications, Computing systems, Data communications, Particle accelerators, Data processing, Algorithm development, Operating systems, Control systems
The paper presents the evaluation study of the performance of the data transmission subsystem which can be used in High Energy Physics (HEP) and other High-Performance Computing (HPC) systems. The test environment consisted of Xilinx Artix-7 FPGA and server-grade PC connected via the PCIe 4xGen2 bus. The DMA engine was based on the Xilinx DMA for PCI Express Subsystem1 controlled by the modified Xilinx XDMA kernel driver.2 The research is focused on the influence of the system configuration on achievable throughput and latency of data transfer.
Soft X-ray plasma measurement systems are mostly multi-channel, high performance systems. In case of the modular construction it is necessary to perform sophisticated system discovery in parallel with automatic system configuration. In the paper the structure of the modular system designed for tokamak plasma soft X-ray measurements is described. The concept of the system discovery and further automatic configuration is also presented. FCS application (FMC/ FPGA Configuration Software) is used for running sophisticated system setup with automatic verification of proper configuration. In order to provide flexibility of further system configurations (e.g. user setup), common communication interface is also described. The approach presented here is related to the automatic system firmware building presented in previous papers. Modular construction and multichannel measurements are key requirement in term of SXR diagnostics with use of GEM detectors.
KEYWORDS: Algorithm development, Sensors, Plasma, Field programmable gate arrays, Data acquisition, Signal detection, Calibration, Plasma diagnostics, Diagnostics, Iron
The measurement system based on GEM - Gas Electron Multiplier detector - is developed for soft X-ray diagnostics of tokamak plasmas. The multi-channel setup is designed for estimation of the energy and the position distribution of an Xray source. The focal measuring issue is the charge cluster identification by its value and position estimation. The fast and accurate mode of the serial data acquisition is applied for the dynamic plasma diagnostics. The charge clusters are counted in the space determined by 2D position, charge value and time intervals. Radiation source characteristics are presented by histograms for a selected range of position, time intervals and cluster charge values corresponding to the energy spectra.
One of the requests from the ongoing ITER-Like Wall Project is to have diagnostics for Soft X-Ray (SXR) monitoring in tokamak. Such diagnostics should be focused on tungsten emission measurements, as an increased attention is currently paid to tungsten due to a fact that it became a main candidate for the plasma facing material in ITER and future fusion reactor. In addition, such diagnostics should be able to withstand harsh radiation environment at tokamak during its operation. The presented work is related to the development of such diagnostics based on Gas Electron Multiplier (GEM) technology. More specifically, an influence of neutron radiation on performance of the GEM detectors is studied both experimentally and through computer simulations. The neutron induced radioactivity (after neutron source exposure) was found to be not pronounced comparing to an impact of other secondary neutron reaction products (during the exposure).
The paper presents feasibility and design studies of Cherenkov-type probes, a development of the measuring head construction designed for different tokamak devices, and in particular the acquisition of optical signals to a data storage system. In order to lower the energy threshold of the electron detection the authors applied radiators with the highest values of the refractive index. Different radiator materials, such as aluminium nitride and CVD diamond were applied. Several versions of measuring heads and different manipulators, e.g., a movable vacuum-tight shaft or a fast-moving reciprocating probe, were manufactured and used. The practical application of the Cherenkov probes required also a consideration of spectral characteristics of optical fibres and photomultipliers. The Cherenkov radiation, as generated inside the radiators, is lead out through separate fibres (optical cables) to the atmospheric pressure side. The emitted radiation in the blue (near ultraviolet) spectrum range should be collected and delivered through appropriate optical cables to a control room, amplified within photomultipliers and recorded in a digital form. In order to investigate an electron energy distribution the multi-channel probes have also been designed and applied.
An increased attention to tungsten material is related to a fact that it became a main candidate for the plasma facing material in ITER and future fusion reactor. The proposed work refers to the studies of W influence on the plasma performances by developing new detectors based on Gas Electron Multiplier GEM) technology for tomographic studies of tungsten transport in ITER-oriented tokamaks, e.g. WEST project. It presents current stage of design and developing of cylindrically bent SXR GEM detector construction for horizontal port implementation. Concept to overcome an influence of constraints on vertical port has been also presented. It is expected that the detecting unit under development, when implemented, will add to the safe operation of tokamak bringing creation of sustainable nuclear fusion reactors a step closer.
KEYWORDS: Sensors, Signal detection, X-rays, Field programmable gate arrays, X-ray detectors, Fusion energy, Data acquisition, Diagnostics, Amplifiers, Signal processing
The Triple Gas Electron Multiplier (T-GEM) is presented as soft X-ray (SXR) energy and position sensitive detector for high-resolution X-ray diagnostics of magnetic confinement fusion plasmas. Multi-channel measurement system and serial data acquisition for X-ray energy and position recognition is described. Fundamental characteristics are presented for two dimensional detector structure. Typical signals of ADC – Analog to Digital Converter are considered for charge value and position estimation. Coinciding signals for high flux radiation cause the problem for cluster charge identification. The amplifier with shaper determines time characteristics and limits the pulses frequency. Separation of coincided signals was introduced and verified for simulation experiments. On line separation of overlapped signals was implemented applying the FPGA technology with relatively simple firmware procedure. Representative results for reconstruction of coinciding signals are demonstrated.
This invited talk describes spectroscopic studies of high-current plasma discharges within PF- and RPI-type facilities, used for basic and application-oriented research. Particular attention is paid to measurements of temporal changes of spectral lines from working gases and impurities. Time-resolved spectral measurements were carried out by means of a Mechelle(R)900 spectrometer, operating in the wavelength range from about 200 nm to 1100 nm, with exposition times varied from 100 ns up to 50 ms. That spectrometer was equipped with a cooled CCD camera coupled with a PC and GRAMS-32(R) software. Spectroscopic studies of the deuterium Balmer-lines and some impurity lines, as observed within the PF-360 experiment, are presented and discussed. Estimates of temporal changes in the electron concentration and temperature are given. Measurements of temporal changes in the emission of the deuterium- and impurity-lines emitted from a mega-joule PF-1000 facility are also described. Capabilities of optical techniques to study the interaction of PF discharges with different targets are discussed. Time-resolved spectroscopic studies of plasma discharges within the RPI-IBIS facility, used for material engineering, are also presented. Optical spectra, as recorded for different operational modes, are compared. The use of spectroscopic techniques to study the interaction of pulsed plasma-ion streams with different materials is considered. The presented results of research on dynamics of pulsed plasma streams (produced in different experimental facilities) as well as the described optical diagnostic techniques are important not only for basic physical studies but also for application-oriented research.
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