Tomasz Czarski

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.

Cavity control system essential modeling for TESLA linear accelerator

The pioneering TESLA linear accelerator and free electron laser project is initially introduced. Elementary analysis of cavity resonator with signal and power considerations is presented. Two alternative simulation models of cavity control system are proposed.

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.

Functional analysis of DSP blocks in FPGA chips for application in TESLA LLRF system

The paper contains the analysis of the application possibilities offered by the new generation of the FPGA chips. The new generation of the FPGA chips contain DSP blocks. The new functionalities are well suited for the application in the TESLA LLRF cavity simulation and control system (SIMCON). A debate on the programming methods of the new chips and the algorithm parameterization was presented. The aim of the, FPGA chip based, system analysis is the optimal chip usage to increase the maximum frequency at which the system can work efficiently, and the optimal usage of the accessible chip resources (DSP blocks). The exemplary results for a few practical calculated implementations were presented and analyzed. The implementations included some basic DSP operations performed in the FPGA chips of Altera and Xilinx. There were compared the results for a few different chips. The TESLA superconducting cavity simulator was efficiently implemented. The results were presented for the first time, for the pure FPGA/VHDL solution. The realization costs were debated in the dependence of given system parameters and the applied type of the FPGA chip.

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

FPGA-based cavity simulator and controller for TESLA test facility

The paper describes an integrated, hardware system for the control and simulation of a superconducting cavity of the linear accelerator. The photonic and electronic control system was realized using a programmable FPGA chip Xilinx Virtex II 3000. The chip was placed on a board Xtreme DSP Development Kit by Nallatech. The system was implemented using the VHDL technology. The hardware multiplying blocks from the Virtex II series chip were used. The resultant controller device worked in the real time, in accordance with the requirements of the TESLA Test Facility project, for the LLRF sub-system of the resonant cavities. In particular, the paper describes the functional layer of the system. Individual executing blocks of the controller implemented in the FPGA chip were debated. The functional structure and hardware implementation of the controller communication layer were presented. Some examples of the system in action were chosen. A number of the real time processes were monitored.

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.

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

Cavity Control System - Optimization Methods For Single Cavity Driving and Envelope Detection.

The paper is an introduction to the optimization methods of the linear accelerator cavity control system. Three distinct time periods of cavity operation are considered; filling with the EM field energy, field stabilization, and field decay. These periods represent completely different states and behavior of the cavity. The cavity could be operated by several different methods in each work phase: During the filling -- feedback and feed-forward alone, feedback and feed-forward together, self-tuning; During the flattop -- feed-forward and feedback alone or together, During the decay -- detuning and quality factor may be measured. The optimization is understood as a choice of the most efficient way of the cavity control during each period. The control may be done in terms of minimum power consumption from the klystron during whole work cycle and efficient field stabilization in the cavity, during flattop period. The introductory analysis of the cavity operational modes in three mentioned periods is presented in this paper. Additionally the alternative more precise algorithm of the cavity voltage envelope detection is proposed.

Cavity digital control testing system by Simulink step operation method for TESLA linear accelerator and free electron laser

The cavity control system for the TESLA -- TeV-Energy Superconducting Linear Accelerator project is initially introduced in this paper. The FPGA -- Field Programmable Gate Array technology has been implemented for digital controller stabilizing cavity field gradient. The cavity SIMULINK model has been applied to test the hardware controller. The step operation method has been developed for testing the FPGA device coupled to the SIMULINK model of the analog real plant. The FPGA signal processing has been verified according to the required algorithm of the reference MATLAB controller. Some experimental results have been presented for different cavity operational conditions.