Energy resolution of gamma-ray spectroscopy of JET plasmas with a LaBr3 scintillator detector and digital data acquisition

A new high efficiency, high resolution, fast γ-ray spectrometer was recently installed at the JET tokamak. The spectrometer is based on a LaBr3(Ce) scintillator coupled to a photomultiplier tube. A digital data acquisition system is used to allow spectrometry with event rates in excess of 1 MHz expected in future JET DT plasmas. However, at the lower rates typical of present day experiments, digitization can degrade the energy resolution of the system, depending on the algorithms used for extracting pulse height information from the digitized pulses. In this paper, the digital and analog spectrometry methods were compared for different experimental conditions. An algorithm based on pulse shape fitting was developed, providing energy resolution equivalent to the traditional analog spectrometry method.     

A diamond-detector-based system for spectrometry of fast atoms on the JET tokamak

To study the evolution of the distribution function of fast ions with an ultimately high time resolution during both injection of neutrals and ion cyclotron plasma heating on the JET tokamak, we have developed a system for spectrometry of fast charge-exchange atoms, which consists of a spectrometric natural-diamond detector and a digital spectrometric channel. The main elements of the spectrometric system—the diamond detector, a noise-immune charge-sensitive preamplifier, and a fast analog-to-digital converter (ADC)—have been manufactured explicitly for use in spectrometry of fast charge-exchange atoms on the JET tokamak at high counting rates. The diamond detector that ensures the spectrometry of hydrogen atoms in the energy range 20–5000 keV is installed in the equatorial plane at an 18-m distance from the plasma axis at the end of the vacuum channel created for X-ray spectroscopy. A fast 14-bit ADC with 100-MHz sampling frequency and a 2-GB memory digitizes the preamplifier output signal. The developed digital spectrometric system can operate at a counting rate of up to ～10⁷ counts/s. Laboratory tests of the developed spectrometric system have shown that its energy resolution is no worse than the resolution of a similar analog system. In the experiments on the JET, the diamond digital spectrometric system ensures recording of the energy distributions of fast charge-exchange atoms with energies >40 keV.     

A compact digital time differential perturbed angular correlation-spectrometer using field programmable gate arrays and various timestamp algorithms

A user-friendly fully digital time differential perturbed angular correlation (TDPAC)-spectrometer with six detectors and fast digitizers using field programmable gate arrays (FPGA) is described and performance data are given. The new spectrometer has an online data analysis feature, a compact size, and a time resolution such as conventional analog spectrometers. Its calculation intensive part was implemented inside the digitizer. This gives the possibility to change parameters (energy windows, constant fraction trigger delay) and see their influence immediately in the γ-γ correlation diagrams. Tests were performed which showed that the time resolution using a (60)Co source with energy window set at 1.17 MeV and 1.33 MeV is 265 ps with LaBr(3)(Ce) scintillators and 254 ps with BaF(2) scintillators. A true constant fraction algorithm turned out to be slightly better than the constant fraction of amplitude method. The spectrometer performance was tested with a TDPAC measurement using a (44)Ti in rutile source and a positron lifetime measurement using (22)Na. The maximum possible data rate of the spectrometer is 1.1 × 10(6) γ quanta per detector and second.     

A new method for charged particles identification with a CsI(Tl) crystal

A spectrometer for detecting and identifying light charged particles with low energies (>∼1 MeV) is described. The spectrometer consists of a thin CsI(Tl) crystal, an ФЭУ-176 photomultiplier, and a waveform digitizer. Digital oscillograms of anode pulses are stored and analyzed in off-line processing. In order to reconstruct the energy and specific energy losses, the two-component character of the scintillation fluorescence decay in a CsI(Tl) crystal and the dependence of the fast component on the specific loss value are used. A digital particle identification method is proposed. The results of experimental studies of the CsI(Tl) crystal scintillation properties and efficiency in identifying electrons, protons, and α-particles in an energy range of ∼1–10 MeV are presented. It is shown that the efficiency of the digital method for proton and α-particle identification is 1.5–2 times higher than that of the known analog methods.     

An adaptive γ-ray spectrometer with a high event processing rate

A fast γ-ray spectrometer adaptable to the scintillator type is described. This spectrometer is capable of processing a γ-ray energy spectrum (with a resolution of <4% in the energy range from 20 keV to 10 MeV) in a sequence of time intervals in the real-time mode at a counting rate of up to 10⁶ cps. Digitization of the detector signals by a 14-bit ADC with a sampling rate of 64 MHz and real-time data stream processing are used to separate overlapping events and correctly generate energy spectra.     

Development of neutron spectrometer toward deuterium plasma diagnostics in LHD

Neutron spectrometer based on coincident counting of associated particles has been developed for deuterium plasma diagnostics on Large Helical Device (LHD) at the National Institute for Fusion Science. Efficient detection of 2.5 MeV neutron with high energy resolution would be achievable by coincident detection of a scattered neutron and a recoiled proton associated with an elastic scattering of incident neutron in a plastic scintillator as a radiator. The calculated neutron spectra from deuterium plasma heated by neutral beam injection indicate that the energy resolution of better than 7% is required for the spectrometer to evaluate energetic deuterium confinement. By using a prototype of the proposed spectrometer, the energy resolution of 6.3% and the detection efficiency of 3.3×10(-7)?count/neutron were experimentally demonstrated for 2.5 MeV monoenergetic neutron, respectively.     

Development of a technique for high-speed γ-ray spectrometry

A technique for high-speed γ-ray spectrometry was developed for γ-ray diagnostic experiments on the ITER tokamak and tested at the Ioffe Physico-Technical Institute on the cyclotron and the GLOBUS-M and TUMAN-3M tokamaks. This technique was used to upgrade the γ-ray diagnostic system of the JET tokamak. It was shown by the tests that the new technique compares favorably to the traditional one in that it allows the limiting counting rate of the spectrometer to be increased by at least an order of magnitude without noticeable deterioration of its energy resolution.     

High-energy x-ray backlighter spectrum measurements using calibrated image plates

The x-ray spectrum between 18 and 88 keV generated by a petawatt laser driven x-ray backlighter target was measured using a 12-channel differential filter pair spectrometer. The spectrometer consists of a series of filter pairs on a Ta mask coupled with an x-ray sensitive image plate. A calibration of Fuji? MS and SR image plates was conducted using a tungsten anode x-ray source and the resulting calibration applied to the design of the Ross pair spectrometer. Additionally, the fade rate and resolution of the image plate system were measured for quantitative radiographic applications. The conversion efficiency of laser energy into silver Kα x rays from a petawatt laser target was measured using the differential filter pair spectrometer and compared to measurements using a single photon counting charge coupled device.     

基于ZYNQ的ICP-MS数据采集处理系统设计与实现

数据采集系统是电感耦合等离子体质谱仪(ICP-MS)的重要组成部分。本研究针对ICP-MS需要同步采集脉冲和模拟信号,且信号信噪比低的问题,提出了一种基于ZYNQ芯片的数据采集处理解决方案。利用ZYNQ集处理器和可编程逻辑于一体的特性,在ARM端搭载了用于流程控制及以太网通讯的FreeRTOS实时操作系统,在FPGA端基于FIR compiler和MCDMA IP核实现了数据的采集、缓存、动态滤波及传输。脱机测试结果表明,脉冲计数误差率小于0.000 5%,模拟计数线性度高达0.999 98,数字滤波幅频特性曲线与理论基本一致。在本团队自行研制的ICP-MS仪器中,利用本系统测试标准调谐液TUNE D,数据采集满足仪器需求,配置64阶低通滤波后,模拟计数中¹¹⁵In谱峰信噪比提高了49.59%。该系统FPGA端各资源占用率均小于50%,片上总功耗仅为2.28 W,有利于推动质谱仪小型化、智能化发展。     

A highly integrated FPGA-based nuclear magnetic resonance spectrometer

The digital circuits required for a nuclear magnetic resonance (NMR) spectrometer, including a pulse programmer, a direct digital synthesizer, a digital receiver, and a PC interface, have been built inside a single chip of the field-programmable gate-array (FPGA). By combining the FPGA chip with peripheral analog components, a compact, laptop-sized homebuilt spectrometer has been developed, which is capable of a rf output of up to 400 MHz with amplitude-, phase-, frequency-, and pulse-modulation. The number of rf channels is extendable up to three without further increase in size.     

Evaluation of a digital data acquisition system and optimization of n-γ discrimination for a compact neutron spectrometer

A compact NE213 liquid scintillation neutron spectrometer with a new digital data acquisition (DAQ) system is now in operation at the Physikalisch-Technische Bundesanstalt (PTB). With the DAQ system, developed by ENEA Frascati, neutron spectrometry with high count rates in the order of 5×10(5) s(-1) is possible, roughly an order of magnitude higher than with an analog acquisition system. To validate the DAQ system, a new data analysis code was developed and tests were done using measurements with 14-MeV neutrons made at the PTB accelerator. Additional analysis was carried out to optimize the two-gate method used for neutron and gamma (n-γ) discrimination. The best results were obtained with gates of 35 ns and 80 ns. This indicates that the fast and medium decay time components of the NE213 light emission are the ones that are relevant for n-γ discrimination with the digital acquisition system. This differs from what is normally implemented in the analog pulse shape discrimination modules, namely, the fast and long decay emissions of the scintillating light.     

基于PC机的方波信号周期测试方法研究与应用

给出了用 PC机测量方波信号周期的两种测试方法 :一种是将方波信号作为模拟信号送入计算机 ,通过 A/D转换为数字信号后再经过相应计算得出方波信号的周期 ;另一种是将方波信号作为开关量送入计算机 ,通过软件计数的方法直接得出方波信号的周期。同时 ,对这两种方法进行了较为详细的比较研究 ,指出了这两种方法各自的优缺点 ,并给出了一些应用实例     

泓格I-7000系列模块在温度控制系统中的应用

泓格I-7000系列模块是网络数据采集和控制模块的一员,提供模拟/数字、数字/模拟转换,数字输入/输出,定时/计数和其他的一些功能。介绍了基于泓格I-7000系列模块实现的典型温度控制系统的设计与调试方法。     

Time resolved measurements by the pulse height analysis soft x-ray diagnostic on TCV

A single chord, single processing chain, hybrid (analog/digital) pulse height analysis diagnostic has been developed for the TCV tokamak, aiming to provide the evolution of the plasma electron temperature with a software selectable minimum temporal resolution of 100 ms. The high count rate (approximately 65 kHz) together with an energy resolution of 190 eV (at 5.9 keV) were achieved by encoding the data stream with an on-site developed interface amplifier and time generator. The diagnostic was also used to investigate the non-Maxwellian behavior of the electron energy distribution function with strong electron cyclotron resonance heating and to monitor the presence of intrinsic and injected impurities in the 700 eV-20 keV energy range. The conversion of this diagnostic into a real-time control tool is under development.     

High Counting Efficiency Compton Suppression System for Automatic‐INAA

Abstract

An automatic counting system for high counting efficiency and Compton suppression has been constructed. The system consists of a sample exchanger, a well‐type HPGe detector, a high count rate digital spectrometer (Dspec‐plus), a Compton suppression system and a software package. The detector for Compton suppression (BGO; Bi(GeO₄)₃) consists of eight segments, 140 mm in length and 35 mm in depth. The segments are arranged to surround the HPGe well‐detector (120 cc). A software package was also developed to facilitate automatic short‐time activation analysis and optimization of the counting procedure according to the activity of the analyzed samples, with or without compton suppression system (CSS). The counting system enables sensitive, dynamic and accurate analysis of different sample matrices and improves by means of CSS the detection limits two fold up to input count rates of 40 kcps.     

Secondary ion counting for surface-sensitive chemical analysis of organic compounds using time-of-flight secondary ion mass spectroscopy with cluster ion impact ionization

We report suitable secondary ion (SI) counting for surface-sensitive chemical analysis of organic compounds using time-of-flight (TOF) SI mass spectroscopy, based on considerably higher emission yields of SIs induced by cluster ion impact ionization. A SI counting system for a TOF SI mass spectrometer was developed using a fast digital storage oscilloscope, which allows us to perform various types of analysis as all the signal pulses constituting TOF SI mass spectra can be recorded digitally in the system. Effects of the SI counting strategy on SI mass spectra were investigated for C(8) and C(60) cluster ion impacts on an organically contaminated silicon wafer and on polytetrafluoroethylene targets by comparing TOF SI mass spectra obtained from the same recorded signals with different SI counting procedures. Our results show that the use of a counting system, which can cope with high SI yields, is necessary for quantitative analysis of SI mass spectra obtained under high SI yield per impact conditions, including the case of cluster ion impacts on organic compounds.     

Inverse photoemission with energy resolution better than 200 meV

We present a spectrometer for inverse photoemission in the vacuum ultraviolet range with variable energy resolution between 400 and 165 meV full width at half maximum. The energy distribution of the electron beam used for excitation can be adjusted between 300 and 125 meV by the use of a toroidal 90 degrees electrostatic deflector combined with a slit aperture. The emitted photons are detected by Geiger-Muller counters filled with either acetone or iodine as counting gas. The optical bandpasses of the detectors can be tuned between 100 and 330 meV by varying the temperature of their entrance windows. The overall resolution of the spectrometer is determined by measuring the Fermi-level onset in inverse-photoemission data of polycrystalline gold. Furthermore, the resolution enhancement is demonstrated by spectra of image-potential-induced surface states at Cu(001).     

高精度数据采集系统在近红外光谱测量仪中的应用

为了满足近红外测量对近红外光谱仪高精度的要求,采用AD公司的低噪声放大器ADA4841—1以及24位A／D芯片AD7767,设计了包括运算放大电路,A／D转换电路在内的数据采集系统。实现了对微弱信号的放大和A／D转换。用软件对采集的数字信号进行中值滤波后,将数据送到PC机进行算法分析。多次测试的结果表明,在采样速率为1kHz／s时,数据精度可达到13bit,满足了滤光片透射式近红外光谱仪的要求。     

A digital method for pulse-shape discrimination between particles

Results from experimental and theoretical investigations of a digital technique for pulse-shape discrimination are presented. Pulses from a scintillation (stilbene-based) detector are recorded by a digital oscilloscope and transmitted to a computer for carrying out particle identification. For a stilbene scintillation detector irradiated by neutrons and γ rays, the γ-ray suppression factor is ～0.5 × 10³?10⁴ and the neutron identification efficiency is ～0.70-0.90 over an energy range of ～30–500 keV at a counting rate up to ～10⁵ pulse/s. It is shown that this technique can form the basis for developing a detector unit that comprises a fast ADC and a digital signal processor and provides online identification of particles by scintillation pulse shape.     

An electron magnetic spectrometer for experiments on a terawatt femtosecond laser

Photonuclear methods used earlier in experiments at electron accelerators have been adapted for femtosecond pulsed lasers. In particular, the problem of measuring wide electron spectra under conditions of a high counting rate and, hence, a high probability of pulse pileup has been solved. To provide long-term stability of electron beams from plasma, a magnetic spectrometer combined with a magnetic-induction sensor has been developed. This spectrometer is capable of measuring the electron-beam characteristics in each ultrashort laser pulse. The results of the experiments carried out with the femtosecond laser system at the International Laser Center of the Moscow State University are presented.