Pulse Height Analysis System Research Articles

Theoretical interpretation of W soft X-ray spectra collected by the pulse height analysis system on Wendelstein 7-X stellarator

In many fusion devices, such as tokamaks or stellarators like Wendelstein 7-X (W7-X), soft x-ray pulse height analysis (PHA) system diagnostics are routinely used during the experiments. The PHA system is dedicated to providing information about the impurity content, and average along line-of-sight electron temperature in the plasma conditions. Moreover, it is also able to estimate impurity density and an average effective charge from the comparison of experimental spectra with the modeled ones. However, the experimental x-ray spectra can be interpreted in terms of interesting plasma parameters only when the theoretical radiation models first identify and then take into account all the relevant factors that affect the spectrum. Therefore, for this purpose, a theoretical model has been applied. Flexible Atomic Code, which allows for calculation of various atomic properties such as energy levels, cross sections for excitation and ionization by electron impact, transition probabilities for radiative transitions and autoionization, and any others as needed in the collisional–radiative approximation. The chosen spectra collected during the W7-X campaign (OP1.2b) were examined, trying to obtain an agreement between the observed and simulated spectra. The analysis carried out allowed for a reliable interpretation of experimental x-ray spectra, estimation of the electron temperature, and obtaining information on the content of tungsten impurities.

Microcalorimeter measurement of x-ray spectra from a high-temperature magnetically confined plasma.

A NASA-built x-ray microcalorimeter spectrometer has been installed on the MST facility at the Wisconsin Plasma Physics Laboratory and has recorded x-ray photons emitted by impurity ions of aluminum in a majority deuterium plasma. Much of the x-ray microcalorimeter development has been driven by the needs of astrophysics missions, where imaging arrays with few-eV spectral resolution are required. The goal of our project is to adapt these single-photon-counting microcalorimeters for magnetic fusion energy research and demonstrate the value of such measurements for fusion science. Microcalorimeter spectrometers combine the best characteristics of the x-ray instrumentation currently available on fusion devices: high spectral resolution similar to an x-ray crystal spectrometer and the broadband coverage of an x-ray pulse height analysis system. Fusion experiments are increasingly employing high-Z plasma-facing components and require measurement of the concentration of all impurity ion species in the plasma. This diagnostic has the capability to satisfy this need for multi-species impurity ion data and will also contribute to measurements of impurity ion temperature and flow velocity, Zeff, and electron density. Here, we introduce x-ray microcalorimeter detectors and discuss the diagnostic capability for magnetic fusion energy experiments. We describe our experimental setup and spectrometer operation approach at MST, and we present the results from an initial measurement campaign.

Observation of the TESPEL-injected impurities behaviour by the PHA system at Wendelstein 7-X

The Pulse Height Analysis (PHA) system at Wendelstein 7-X (W7-X) is a broad energy range spectrometer dedicated to the observation of impurity behaviour during the plasma discharges. The system measures spectra in the range between 0.5 and 20 keV, from integrated signals along three lines of sight that pass close to the plasma center. During the recent operational phase of W7-X, the TESPEL (Tracer-Encapsulated Solid PELlet) injector has been commissioned. By this injector, polystyrene pellets with a single tracer impurity as well as multiple tracer impurities have been injected into the W7-X plasmas. The multiple tracer impurities injection allows studying the behavior of various impurities in the same plasma condition. The time resolution of the PHA system in the order of 60–100 ms, is smaller than typical confinement times and sufficient to observe differences in temporal behaviour of injected impurities. The collected PHA spectra consist of Kα lines of vanadium, manganese and nickel in case of the triple tracers, and of iron or copper in case of the single tracer. The temporal evolution of these Kα lines has been obtained in various plasma conditions, which will be presented and discussed in this paper.

Electron temperature estimation using the Pulse Height Analysis system at Wendelstein 7-X stellarator

This paper presents measurements of the electron temperature in Wendelstein 7-X (W7-X) stellarator plasmas heated by electron-cyclotron-resonance (ECRH) during the first operational phase (OP1.1). The analysis of the slope of the observed X-ray continuum emission (in a semi-logarithmic plot) measured by the use of the Pulse Height Analysis (PHA) system, provides the information about the electron temperature (Te) of the hydrogen plasma. The determination of this fundamental plasma parameter is based on the exponential dependence of the continuum radiation (Bremsstrahlung) on photon energy assuming Maxwellian distribution. In this paper, some experimental results of the estimated electron temperature are presented and compared to the results obtained from the simulations of X-ray spectrum and other diagnostic like the Thomson Scattering (TS) system.

First Results from the Soft X-ray Pulse Height Analysis System on Wendelstein 7-X Stellarator

The paper presents experimental results obtained during the first operational phase (called OP1.1) of the Wendelstein 7-X stellarator (W7-X). One of W7-X diagnostics that delivers information about plasma impurities and was commissioned during the OP1.1, is the Pulse Height Analysis (PHA) system which provides soft X-ray spectra of highly ionized impurity species over a very broad energy range with energy resolution not worse than 200 eV and with temporal resolution of 100 ms. The line-of-sight integrated spectra, collected by a Silicon Drift Detector in the energy range between 0.9 and 10 keV, have been analyzed for various experimental conditions and are discussed with respect to results from other diagnostics. In this work, injected impurities (argon and neon) as well as intrinsic impurities (sulphur and chlorine) have been identified. Spectral lines corresponding to heavier impurities have not been observed.

Comparison of silicon drift detectors made by Amptek and PNDetectors in application to the PHA system for W7-X

Abstract The paper presents comparison of two silicon drift detectors (SDD), one made by Amptek, USA, and the second one by PNDetector, Germany, which are considered for a soft X-ray diagnostic system for W7-X. The sensitive area of the first one is 7 mm2 × 450 μm and the second one is 10 mm2 × 450 μm. The first detector is cooled by a double-stage Peltier element, while the second detector is cooled by single-stage Peltier element. Each one is equipped with a field-effect transistor (FET). In the detector from Amptek, the FET is mounted separately, while in the detector from PNDetector, the FET is integrated on the chip. The nominal energy resolution given by the producers of the first and the second one is 136 eV@5.9 keV (at -50°C) and 132 eV@5.9 keV (at -20°C), respectively. Owing to many advantages, the investigated detectors are good candidates for soft X-ray measurements in magnetic confinement devices. They are suitable for soft X-ray diagnostics, like the pulse height analysis (PHA) system for the stellarator Wendelstein 7-X, which has been developed and manufactured at the Institute of Plasma Physics and Laser Microfusion (IPPLM), Warsaw, in collaboration with the Max Planck Institute for Plasma Physics (IPP), Greifswald. The diagnostic is important for the measurements of plasma electron temperature, impurities content, and possible suprathermal tails in the spectra. In order to choose the best type of detector, analysis of technical parameters and laboratory tests were done. Detailed studies show that the most suitable detector for the PHA diagnostics is the PNDetector.

A new electromagnetic calorimeter for the updated VES setup

A complex of the new electromagnetic calorimeter (ECAL-2) for the VES setup is described. It is composed of 1592 “shashlik” type counters consisting of a set of lead−scintillator plates, high-voltage supplies based on cascade voltage multipliers for FEU-84 photomultiplier tubes, an LED-based monitoring system, a slow control system, and a pulse-height analysis system. The procedures of ECAL-2 calibration and online monitoring are described.

Laboratory tests of the Pulse Height Analysis system for Wendelstein 7-X

A pulse height analysis (PHA) system has been designed and manufactured for the Wendelstein 7-X stellarator, in such a way as to be already compatible with later quasi-continuous operation requirements. The diagnostic will provide X-ray spectra with energy resolution better than 180 eV . The system has three energy channels: 0.25–20 keV, 0.95–20 keV and 1.5–20 keV . For each channel a separate Silicon Drift Detector (SDD) equipped with a suitably selected beryllium foil is used. The range of the 3 energy channels can be further adapted to particular experiments by moving via a pneumatic actuator additional beryllium filters in front of the fixed ones. The PHA system is intended for measuring impurity species (e.g. C, Fe, Ni), electron temperature and for investigating possible suprathermal tails in the spectra. The system will be installed on the horizontal port AEK50 on W7-X. The SDD detectors, the replaceable filters and the adjustable piezo driven slits which allow to suitably adapt the X-ray signal intensity are mounted inside a vacuum chamber which is connected to the plasma vessel via a gate valve. The on-air diagnostic components are the preamplifiers, the Digital X-Ray Processor (XIA, U.S.A.), a computer, and an X-ray calibration source. For controlling the operation of the entire diagnostic system, as well as, for the data acquisition of the electrical pulses coming a special code was developed. The paper presents the construction of the PHA system for W7-X and the laboratory tests of its mechanical parts together with the information on the code developed to operate the diagnostic. The diagnostic was also tested and characterised by measuring Fe55 spectrum and fluorescence spectra of Ni, Fe, Cr and Cu induced by an X-ray mini-tube.

Startup impurity diagnostics in Wendelstein 7-X stellarator in the first operational phase

An essential element for stationary stellarator operation is the understanding of the impurity transport behavior. Neoclassical theory predicts an impurity transport towards the plasma core for the standard ion root regime in stellarators [1,2]. The performance of a quasi-stationary device like Wendelstein 7-X stellarator (W7-X, presently in the commissioning phase in Greifswald, Germany) could be limited in case of strong impurity accumulation. Therefore, a set of plasma diagnostics is foreseen to obtain key experimental quantities for the neoclassical transport modeling as ion temperature profile, density gradients and impurity concentration [1]. The core impurity content is monitored by the High Efficiency eXtreme ultraviolet Overview Spectrometer system (HEXOS) [2], covering the wavelength range 2.5–160 nm (intermediate ionization states of all relevant heavy intrinsic impurity species) with high spectral resolution and a time resolution of 1 ms, adequate for transport analysis. Impurity radiation at shorter wave lengths (4 nm–0.06 nm) will be monitored with the SX pulse height analysis system (PHA) [3]. The ion temperature profile can be deduced from inversion of data from the High Resolution X-ray Imaging Spectrometer (HR-XIS), which measures the concentration and temperature of argon tracer gas in helium-like ionization stages [6,7,8]. A second X-ray Imaging Crystal Spectrometer (XICS), which will additionally provide the poloidal ion rotation velocity, is under preparation [8,9]. The total radiation will be measured by two bolometer cameras [10,11]. The status of the impurity diagnostics for the first operational phase in W7-X is summarized in this paper and an outlook for the next experimental campaign is given.

A bismuth activation counter for high sensitivity pulsed 14 MeV neutrons

We have built a fast neutron bismuth activation counter that measures activation counts from pulsed 14-MeV neutron generators for incident neutron fluences between 30 and 300neutrons/cm2 at 15.2cm (6in.). The activation counter consists of a large bismuth germanate (BGO) detector surrounded by a bismuth metal shield in front of and concentric with the cylindrical detector housing. The 14MeV neutrons activate the 2.6-millisecond (ms) isomer in the shield and the detector by the reaction 209Bi (n,2nγ) 208mBi. The use of millisecond isomers and activation counting times minimizes the background from other activated materials and the environment. In addition to activation, the bismuth metal shields against other outside radiation sources. We have tested the bismuth activation counter, simultaneously, with two data acquisition systems (DASs) and both give similar results. The two-dimensional (2D) DAS and three dimensional (3D) DAS both consist of pulse height analysis (PHA) systems that can be used to discriminate against gamma radiations below 300keV photon energy, so that the detector can be used strictly as a counter. If the counting time is restricted to less than 25ms after the neutron pulse, there are less than 10 counts of background for single pulse operation in all our operational environments tested so far. High-fluence neutron generator operations are restricted by large dead times and pulse height saturation. When we operate our 3D DAS PHA system in list mode acquisition (LIST), real-time corrections to dead time or live time can be made on the scale of 1ms time windows or dwell times. The live time correction is consistent with nonparalyzable models for dead time of 1.0±0.2μs for our 3D DAS and 1.5±0.3μs for our 2D DAS dominated by our fixed time width analog to digital converters (ADCs). With the same solid angle, we have shown that the bismuth activation counter has a factor of 4 increase in sensitivity over our lead activation counter, because of higher counts and negligible backgrounds.

Preliminary observation of medium-Z impurities by means of the soft x-ray pulse height analysis diagnostic on EAST

A soft x-ray pulse height analysis (PHA) system, based on a silicon drift detector (SDD), has been successfully implemented on EAST to measure spectra of soft x-ray emission. Utilizing the soft x-ray PHA diagnostic, the behavior of intrinsic and injected medium-Z impurities is first investigated on EAST and the preliminary observations are presented. There are hardly any Kα emission peaks of metallic impurities including Ti (Z = 22), Cr (Z = 24), Fe (Z = 26), Ni (Z = 28) and Cu (Z = 29) in the soft x-ray spectra for an ohmic heating plasma due to lower electron temperatures, while remarkable peaks can be seen in a lower hybrid wave (LHW) heated plasma. The profiles of Kα intensities of these metallic elements have been obtained with about 7 cm spatial resolution. It is observed that the Kα emissions come mainly from the core plasma column of ρ ⩽ 0.3 and found that their intensities are roughly proportional to the power of the LHW launched into the plasma. The Ar Kα peaks can also be monitored when argon gas is puffed into the plasma. It is qualitatively confirmed that the Kα lines of argon emitted from the lower ionic states are predominantly located in the outer plasma region, whereas the Kα lines with higher energies are mainly from high ionization stages in the central region.

First results obtained from the soft x-ray pulse height analyzer on experimental advanced superconducting tokamak

An assembly of soft x-ray pulse height analyzer system, based on silicon drift detector (SDD), has been successfully established on the experimental advanced superconducting tokamak (EAST) to measure the spectrum of soft x-ray emission (E=1-20 keV). The system, including one 15-channel SDD linear array, is installed on EAST horizontal port C. The time-resolved radial profiles of electron temperature and K(alpha) intensities of metallic impurities have been obtained with a spatial resolution of around 7 cm during a single discharge. It was found that the electron temperatures derived from the system are in good agreement with the values from Thomson scattering measurements. The system can also be applied to the measurement of the long pulse discharge for EAST. The diagnostic system is introduced and some typical experimental results obtained from the system are also presented.

Soft x-ray PHA measurement of the long pulse discharge in HT-7 tokamak

By analyzing the soft x-ray energy spectrum measured by the soft x-ray pulse height analysis (PHA) system, the electron temperature ( T e ) and the effective charge number ( Z eff ) of the ultra-long pulse discharge driven by lower hybrid wave (LHW) were obtained in the HT-7 tokamak. Moreover, the information of medium- Z impurities such as Ti, Cr, Fe, and Ni intrinsic to HT-7 tokamak can also be inspected. The accuracy of the electron temperature derived from the soft x-ray energy spectrum measurements is verified by comparing with the temperature measured by the Thomson scattering system for various plasmas and electron cyclotron emission diagnostic system for ohmic plasmas. The bulk electron temperature of about 1 keV and Z eff ≈ 2 were achieved for long pulse plasma. The appreciable K α lines of Ti, Cr, Fe and Ni metallic impurities released from the antennas of radio frequency wave and/or the first wall and Ar injected into plasma can be observed, and they kept stable during the long duration discharges. As a result, the longest pulse discharge with relatively high temperature of T e ( 0 ) ∼ 1 keV , and n e ( 0 ) ∼ 0.5 × 10 19 m − 3 has been achieved with a duration of 400 s in the HT-7 experimental campaign in 2008.

Soft X-ray PHA Diagnostic for the Electron Temperature Measurements on EAST

Two soft X-ray pulse height analysis (PHA) systems, based on silicon drift detector (SDD), were established on the experimental advanced superconducting tokamak (EAST) to measure spectrum of soft X-ray emission. In this paper, the soft X-ray PHA systems on EAST are introduced and some experimental results of electron temperature in EAST obtained from the soft X-ray PHA diagnostic are presented.

The Low-Energy Telescope (LET) and SEP Central Electronics for the STEREO Mission

The Low-Energy Telescope (LET) is one of four sensors that make up the Solar Energetic Particle (SEP) instrument of the IMPACT investigation for NASA’s STEREO mission. The LET is designed to measure the elemental composition, energy spectra, angular distributions, and arrival times of H to Ni ions over the energy range from ∼3 to ∼30 MeV/nucleon. It will also identify the rare isotope 3He and trans-iron nuclei with 30≤Z≤83. The SEP measurements from the two STEREO spacecraft will be combined with data from ACE and other 1-AU spacecraft to provide multipoint investigations of the energetic particles that result from interplanetary shocks driven by coronal mass ejections (CMEs) and from solar flare events. The multipoint in situ observations of SEPs and solar-wind plasma will complement STEREO images of CMEs in order to investigate their role in space weather. Each LET instrument includes a sensor system made up of an array of 14 solid-state detectors composed of 54 segments that are individually analyzed by custom Pulse Height Analysis System Integrated Circuits (PHASICs). The signals from four PHASIC chips in each LET are used by a Minimal Instruction Set Computer (MISC) to provide onboard particle identification of a dozen species in ∼12 energy intervals at event rates of ∼1,000 events/sec. An additional control unit, called SEP Central, gathers data from the four SEP sensors, controls the SEP bias supply, and manages the interfaces to the sensors and the SEP interface to the Instrument Data Processing Unit (IDPU). This article outlines the scientific objectives that LET will address, describes the design and operation of LET and the SEP Central electronics, and discusses the data products that will result.

Hard X-Ray PHA System on the HT-7 Tokamak

A new hard X-ray pulse-height analysis (PHA) system has been established on HT-7 tokamak for long pulse steady-state operation. This PHA system consists of hard X-ray diagnostics and multi-channel analysers (MCA). The hard X-ray diagnostics consists of a vertical X-ray detector array (CdTe) and a horizontal X-ray detector array (NaI). The hard X-ray diagnostics can provide the profile of power deposition and the distribution function of fast electron during radio frequency (RF) current drive. The MCA system is the electronic part of the PHA system, which has been modularized and linked to PC through LAN. Each module of MCA can connect with 8 X-ray detectors. The embedded Ethernet adapter in the MCA module makes the data communication between PC and MCA very convenient. A computer can control several modules of MCA through certain software and a hub. The RAM in MCA can store 1024 or more spectra for each detector and therefore the PHA system can be applied in the long pulse discharge of several minutes.

Characterisation of [formula omitted] proportional counters

This paper describes the characterisation of a set of 3 He proportional counters differing in gas composition and pressure. Each step of the signal generation in the detector is analysed. Optimal working conditions are defined in order to choose the high voltage to be applied. Dead time with short shaping time is measured in such optimal conditions. In addition, the overall neutron efficiency and the gamma sensitivity are reported. Such characterisation is required for a correct choice of the associated counting electronics and the applications of the counters. A complete pulse processing modular system, consisting of a pulse height analysis system and a pulse correlation analysis system equipped with a time of arrival recorder, is used for the characterisation.

Design and noise model for CCD-based, time-resolved PHA measurements

A CCD pulse height analysis system is considered for the measurement of electron temperature on the Pegasus Toroidal Experiment. The first-generation CCD/PHA system will have one spatial point and obtain seven time points with a time resolution of 2.4 ms. Time resolution is achieved by shifting the exposed rows of the CCD behind a masked off portion of the chip during the plasma discharge. Criteria for valid photon detection are developed to account for pulse pileup effects and maximize count rate. Error analysis and Monte Carlo calculations indicate that the CCD/PHA system should achieve typical uncertainties to <5% of the deduced temperature.

High-speed nuclear quality pulse height analyzer for synchrotron-based applications

A high-throughput pulse height analyzer system for synchrotron-based applications requiring high resolution, high processing speed, and low dead-time has been developed. The system is composed of a 120 ns 12-bit nuclear quality analog-to-digital converter with a self-adaptive fast peak detector stretcher and a custom-made fast histogramming memory module that records and processes the digitized data. The histogramming module is packaged in a VME/VXI compatible interface. Data is transferred through a fast optical link from the memory interface to a computer. A dedicated data acquisition program matches the hardware characteristics of the histogramming memory module. The data acquisition system allows for different data collection modes. The system can acquire data in synchronization with an external trigger or operate as a standard pulse-height analyzer. Acquisition can be performed on several channels simultaneously. A two-channel prototype has been demonstrated at the Stanford Synchrotron Radiation Laboratory accelerator in conjunction with a fluorescence X-ray Absorption Fine Structure Spectroscopy experiment. A detailed description of the entire system is given and experimental data shown.

Application of avalanche photodiode for soft X-ray pulse-height analyses in the Ht-7 tokamak

An avalanche photodiode (APD) has been used as soft X-ray energy pulse-height analysis system for the measurement of the electron temperature on the HT-7 tokamak. The experimental results obtained with the APD with its inferior energy resolution show a little difference compared to the conventional high energy-resolution Si (Li) detector. Both numerical analysis and experimental results prove that the APD is good enough for application of the electron temperature measurement in tokamaks.