W. Zabolotny

Development of GEM gas detectors for X-ray crystal spectrometry

Two Triple Gas Electron Multiplier (Triple-GEM) detectors were developed for high-resolution X-ray spectroscopy measurements for tokamak plasma to serve as plasma evolution monitoring in soft X-ray region (SXR). They provide energy resolved fast dynamic plasma radiation imaging in the SXR with 0.1 kHz frequency. Detectors were designed and constructed for continuous data-flow precise energy and position measurement of plasma radiation emitted by metal impurities, W46+ and Ni26+ ions, at 2.4 keV and 7.8 keV photon energies, respectively. High counting rate capability of the detecting units has been achieved with good position resolution. This article presents results of the laboratory and tokamak experiments together with the system performance under irradiation by photon flux from the plasma core.

Distributed embedded-PC-based control and data acquisition system for TESLA cavity controller and simulator

This paper describes an alternative approach for control and data acquisition system to be used in TESLA controller and simulator (SIMCON) boards. The standard VME controller may be replaced with a cheap embedded PC to provide equivalent or even superior functionality. The new approach offers better cost/performance ratio, better scalability of the system and better testability of the SIMCON boards.

FPGA based charge fast histogramming for GEM detector

This article presents a fast charge histogramming method for the position sensitive X-ray GEM detector. The energy resolved measurements are carried out simultaneously for 256 channels of the GEM detector. The whole process of histogramming is performed in 21 FPGA chips (Spartan-6 series from Xilinx) . The results of the histogramming process are stored in an external DDR3 memory. The structure of an electronic measuring equipment and a firmware functionality implemented in the FPGAs is described. Examples of test measurements are presented.

Serial data acquisition for the X-ray plasma diagnostics with selected GEM detector structures

The measurement system based on GEM—Gas Electron Multiplier detector is developed for X-ray diagnostics of magnetic confinement tokamak plasmas. The paper is focused on the measurement subject and describes the fundamental data processing to obtain reliable characteristics (histograms) useful for physicists. The required data processing have two steps: 1—processing in the time domain, i.e. events selections for bunches of coinciding clusters, 2—processing in the planar space domain, i.e. cluster identification for the given detector structure. So, it is the software part of the project between the electronic hardware and physics applications. The whole project is original and it was developed by the paper authors. The previous version based on 1-D GEM detector was applied for the high-resolution X-ray crystal spectrometer KX1 in the JET tokamak. The current version considers 2-D detector structures for the new data acquisition system. The fast and accurate mode of data acquisition implemented in the hardware in real time can be applied for the dynamic plasma diagnostics. Several detector structures with single-pixel sensors and multi-pixel (directional) sensors are considered for two-dimensional X-ray imaging. Final data processing is presented by histograms for selected range of position, time interval and cluster charge values. Exemplary radiation source properties are measured by the basic cumulative characteristics: the cluster position distribution and cluster charge value distribution corresponding to the energy spectra. A shorter version of this contribution is due to be published in PoS at: 1st EPS conference on Plasma Diagnostics

X-ray crystal spectrometer upgrade for ITER-like wall experiments at JET

The high resolution X-Ray crystal spectrometer at the JET tokamak has been upgraded with the main goal of measuring the tungsten impurity concentration. This is important for understanding impurity accumulation in the plasma after installation of the JET ITER-like wall (main chamber: Be, divertor: W). This contribution provides details of the upgraded spectrometer with a focus on the aspects important for spectral analysis and plasma parameter calculation. In particular, we describe the determination of the spectrometer sensitivity: important for impurity concentration determination.

Dual port memory based Heapsort implementation for FPGA

This document presents a proposal of implementation of the Heapsort algorithm, which utilizes hardware features of modern Field-Programmable Gate Array (FPGA) chips, such as dual port random access memories (DP RAM), to implement efficient sorting of a data stream. The implemented sorter is able to sort one data record every two clock periods. This throughput does not depend on the capacity of the sorter (defined as number of storage cells in the sorter). The mean latency (expressed in sorting cycles - each equal to two clock periods) when sorting the stream of data is equal to the capacity of the sorter. Due to efficient use of FPGA resources (e.g. data are stored mainly in internal block RAMs), the complexity of the sorter is proportional to the logarithm of sorter capacity. Only the required RAM size is linearly proportional to the sorter capacity. The proposed sorter has been tested in simulations and synthesized for real FPGA chips to verify its correctness.

Conceptual design and development of GEM based detecting system for tomographic tungsten focused transport monitoring

Implementing tungsten as a plasma facing material in ITER and future fusion reactors will require effective monitoring of not just its level in the plasma but also its distribution. That can be successfully achieved using detectors based on Gas Electron Multiplier (GEM) technology. This work presents the conceptual design of the detecting unit for poloidal tomography to be tested at the WEST project tokamak. The current stage of the development is discussed covering aspects which include detectors spatial dimensions, gas mixtures, window materials and arrangements inside and outside the tokamak ports, details of detectors structure itself and details of the detecting module electronics. It is expected that the detecting unit under development, when implemented, will add to the safe operation of tokamak bringing the creation of sustainable nuclear fusion reactors a step closer. A shorter version of this contribution is due to be published in PoS at: 1st EPS conference on Plasma Diagnostics

Design and simulation of FPGA implementation of a RF control system for the TESLA test facility

This paper presents a new FPGA based solution of the Low Level RF Control System for TESLA Test Facility. The LLRF Control System is responsible for maintaining the constant amplitude and phase of accelerating field in set of accelerators cryomodulaes driven by single klystron. To obtain shorter processing time and less complicated hardware an FPGA based solution was selected. The proposed simulation has been simulated in software, and appeared to be faster and less complex than DSP based solutions.

Determination of tungsten and molybdenum concentrations from an x-ray range spectrum in JET with the ITER-like wall configuration

The W and W 3p-4d inner shell excitation lines in addition to Mo 2p3s lines have been identified from the spectrum taken by an upgraded high-resolution X-ray spectrometer. It is found from analysis of the absolute intensities of the W and Mo lines that W and Mo concentrations are in the range of ∼ 10−5 and ∼ 10−7, respectively. Comparison of the W concentration from the X-ray spectrometer with those from a vacuum-ultra-violet spectrometer and from soft X-ray cameras indicates that the W concentration from the X-ray spectrometer is lower by a factor of ∼ 2 and > 7, respectively. In contrast, comparison of a plasma effective charge determined from the X-ray spectrometer with that from a visible range continuum intensity shows that the plasma effective charge from the X-ray spectrometer is higher by a factor of ∼ 3. Hence it is probable that the W concentration from the X-ray spectrometer is valid within a factor of ∼ 3, while the W concentrations from the vacuum-ultra-violet spectrometer and from the soft X-ray cameras are further higher. Determination of tungsten and molybdenum concentrations from an X-ray range spectrum in JET2 Submitted to: J. Phys. B: At. Mol. Phys. Determination of tungsten and molybdenum concentrations from an X-ray range spectrum in JET3

Fast ADC based multichannel acquisition system for the GEM detector

A novel approach to the Gas Electron Multiplier1 (GEM) detector readout is presented. Unlike commonly used methods, based on discriminators, and analogue FIFOs,[ the method developed uses simultaneously sampling high speed ADCs and advanced FPGA-based processing logic to estimate the energy of every single photon. Such method is applied to every GEM strip signal. It is especially useful in case of crystal-based spectrometers for soft X-rays, where higher order reflections need to be identified and rejected. For the purpose of the detector readout, a novel conception of the measurement platform was developed.