X-ray Microcalorimeter Spectrometer Research Articles

Mechanical Cryocooler Noise Observed in the Ground Testing of the Resolve X-ray Microcalorimeter Onboard XRISM

Low-temperature detectors often use mechanical coolers as part of the cooling chain in order to reach sub-Kelvin operating temperatures. The microphonics noise caused by the mechanical coolers is a general and inherent issue for these detectors. We have observed this effect in the ground test data obtained with the Resolve instrument to be flown on the XRISM satellite. Resolve is a cryogenic X-ray microcalorimeter spectrometer with a required energy resolution of 7 eV at 6 keV. Five mechanical coolers are used to cool from ambient temperature to about 4 K: four two-stage Stirling coolers (STC) driven nominally at 15 Hz and a Joule-Thomson cooler (JTC) driven nominally at 52 Hz. In 2019, we operated the flight-model instrument for two weeks, in which we also obtained accelerometer data inside the cryostat at a low-temperature stage (He tank). X-ray detector and accelerometer data were obtained continuously while changing the JTC drive frequency, which produced a unique data set for investigating how the vibration from the cryocoolers propagates to the detector. In the detector noise spectra, we observed harmonics of both STCs and JTC. More interestingly, we also observed the low (<20 Hz) frequency beat between the 4'th JTC and 14'th STC harmonics and the 7'th JTC and the 23--24'th STC harmonics. We present here a description and interpretation of these measurements.

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.

Foundations and trends of high resolution energy dispersive PIXE (HiRED-PIXE)

High Resolution Particle Induced X-ray Emission, for short HR-PIXE, dates back to 1977 and is, therefore, nearly as old as standard PIXE itself. Until roughly ten years ago, High Resolution PIXE (HR-PIXE) work used only wavelength dispersive spectrometers (WDS). The installation, in 2008, of an X-ray Microcalorimeter Spectrometer, XMS at CTN (ITN at the time) 3MV tandetron, altered this situation and, as can be recognised today, will lead to major changes in PIXE, and open up many possibilities that have been hindered so far. In this work, motives, developments, important breakthrough results obtained until now, and a case study displaying speciation data and complementary information from nuclear magnetic relaxometry, are presented and discussed, showing the full quantitative potential of High Resolution Energy Dispersion PIXE (HiRED-PIXE), in particularly the opening up of the possibility to establish fast and efficient methods for quantitative elemental speciation in unknown samples.

Reaching for copper pigments speciation with High Resolution Energy Dispersive PIXE

The C2TN XMS-PIXE system based on a first generation X-ray Microcalorimeter Spectrometer (XMS) having 1.5% relative energy resolution at Si Kα 1.739 keV and 0.5% relative energy resolution at Fe Kα 6.403 keV, became operational in 2008, presaging various developments to emerge from its use and from connected or related but independent advancements by other laboratories. More than ten years having passed since the C2TN XMS-PIXE system first results, knowledge about XMSs use for PIXE has grown meaningfully and new applications are now envisaged and in progress. In the present work, results on the analysis of different copper compounds are presented, and used as an assessment of the capacity of High Resolution Energy Dispersive PIXE (HiRED-PIXE) to provide answers to the problem of copper pigments speciation in Cultural Heritage studies. Related issues of XMS spectra generation and calibration are discussed, as well as first generation systems limitations and its overcome by the use of second and third generation systems.

H + , O 2+ , O 3+ and high resolution PIXE spectra of Yb 2 O 3

Abstract The number of X-ray spectrometry systems having energy resolution of the order of 10 eV, or less, has increasing recently, included already energy dispersive systems (EDS). Access to previous unseen spectra details and enhanced information including speciation, becomes more common and available. Analysis of high resolution EDS PIXE spectra is, nevertheless a complex task due to the need to carefully account for contributions from minor and satellite transitions. In this work, a pure Yb 2 O 3 sample was irradiated at the HRHE-PIXE setup of C2TN, and simultaneous CdTe and X-ray Microcalorimeter Spectrometer (XMS) spectra were collected. The L-shell spectrum of Yb emitted during irradiations using H + , O 2 + and O 3 + ions in the energy range from 1.0 to 6.5 MeV was studied. Measured L X-ray spectra were analysed taking into account the effects of the multiple ionization in the L and M shells. All spectra were analysed using the DT2 code, which allows to include in the fitting model diagram lines as well as multi-ionization satellites and any other contributions. In this communication we present the results and discuss details and problems related to the transition energies, intensity, line width data, and multiple ionization satellites.

CdTe and EDS HR-PIXE Ta L and M spectra induced by duoplasmatron generated proton and oxygen ion beams

Abstract Particle induced X-ray emission (PIXE) is a powerful technique for quantitative analysis because it is non-destructive, multi-elemental (from Na to U), highly sensitive and requires no special sample preparation. Heavy Ions PIXE (HI-PIXE), may represent a further step in versatility but it comes with added complexity of the physical processes involved in X-ray production, which require among other things new software capabilities. In this work, the specific capacities of the DT2 code are used to simulate and fit Ta L- and M-shell spectra obtained during the irradiation of a Ta2O5 thin film deposited upon a polished vitreous graphite substrate, produced in the frame of the Heavy Ions PIXE workpakage of the IAEA Coordinated Research Project F11019 on analytical uses of MeV focused ion beams. Proton and oxygen beams from a duoplasmatron ion source were used, and spectra were collected using both the CdTe and the X-ray Microcalorimeter Spectrometer detectors of the High Resolution High X-ray Energy PIXE (HRHE-PIXE) facility of C2TN. Results obtained from the simulation and the fitting of these spectra are presented and discussed.

Fixed and free line ratio DT2 PIXE fitting and simulation package

The DATTPIXE software package, which full extent version become operational in 1992, has been largely used both in academic research and for standard analysis. Developments of a new PIXE setup, having an X-ray Microcalorimeter Spectrometer (XMS) EDS high resolution detection system and a CdTe detector, raised the need for a deep revision of the software used to fit PIXE spectra and interpret data. First steps taken in 2007 essentially comprised a new fitting code based on a proven Bayesian inference routine. Meanwhile, fundamental processes associated to PIXE spectra, which became more evident in X-ray Microcalorimeter spectrometer (XMS) high resolution EDS spectra, made clear the need for a full new code. Using some of the routines developed in DATTPIXE, the new DT2 package is written in Fortran 2003 and includes both the fitting and data handling codes. DT2 is now designed to include in the fitting model and deal with diagram lines as well as with satellite lines (Radiative Auger Emission (RAE), multi-ionization satellites and even chemically shifted lines) or even lines having other origins such as low energy γ-rays. In this communication we present the new DT2 package and discuss its new features, such as the possibility of fixing or leave free the relative intensity of spectra lines, even if they belong to transitions to the same shell.

N to K Uranium PIXE spectra obtained at the high resolution high energy PIXE setup

The CTN (previous ITN) high resolution high energy (HRHE) PIXE set-up facility was set in operation on July 2008 and upgrades were being implemented until late in 2011. The study of a pure UO2 sample and the mapping of geological sample are the first results where the whole range of possibilities has been exploited, namely the possibility of obtaining simultaneous spectra covering a very wide energy range of more than 100keV. In this paper, the N-shell to K-shell spectra of Uranium is presented and discussed, as well as the details on the characteristics and capacities of the setup, including the automated X–Y positioning systems installed in the X–Y–Z sample support unit, which allows for the possibility of making macroscopic mappings of geological samples (Chaves et al. (2013) [1]). As for the N-shell lines in the X-ray Microcalorimeter Spectrometer (XMS) spectrum, due to the lack of data (Zschornack (2007) [2]), transition energies were determined using ab initio calculations assuming a closed shell U4+ electronic structure for Uranium prior to the ionisation by proton impact.

H+ and He2 + induced W L X‐rays intensity ratios: part I, Si(Li) data and EDS high resolution insight

Recently, the authors have presented experimental evidences that for some energy windows, proton‐induced W L shell X‐rays intensity ratios of transitions to L1 subshell depend on the ion beam energy and on the chemical species even after known matrix effects are subtracted. These results, which put in question the assumption of the invariance of the relative intensity of X‐ray transitions to the same atomic subshells, are further exploited in this work, where more data for three different W compounds (W, Li2WO4 and P2O5.24WO3.xH2O) are presented followed by a detailed study using an ultra‐pure (99.995%) W thick foil, used to avoid any possible target contamination interference on the results. Samples were irradiated by H+ beams in various conditions in the energy range between 0.25 and 2.38 MeV and by He2 + beams having energies between 3.5 and 5.0 MeV. Spectra were collected using the Si(Li) detector at CTN 2.5 MV Van de Graaff standard Proton‐Induced X‐ray Emission (PIXE) set‐up as well as using the Energy Dispersive Spectrometry (EDS) high resolution X‐ray microcalorimeter spectrometer (XMS) at CTN 3.0 MV Tandetron accelerator high resolution high energy (HRHE) PIXE end station. Results were normalized to the theoretical intensity ratios and plotted as function of the ratio of collision characteristic times allowing the comparison of H+ and He2 + results. W L X‐rays intensity ratio variations are presented and compared with theoretical expected results. Radiative Auger emission transitions observed in an EDS high resolution XMS spectra are shown to probably play a crucial role in the highly unexpected results obtained for intensity ratios of transitions to the same subshell. Copyright © 2013 John Wiley &amp; Sons, Ltd.

Estimate of the impact of background particles on the X-ray Microcalorimeter Spectrometer on IXO

We present the results of a study on the impact of particles of galactic (GCR) and solar origin for the X-ray Microcalorimeter Spectrometer (XMS) aboard an astronomical satellite flying in an orbit at the second Lagrangian point (L2). The detailed configuration presented in this paper is the one adopted for the International X-ray Observatory (IXO) study, however the derived estimates can be considered a conservative limit for ATHENA, that is the IXO redefined mission proposed to ESA. This work is aimed at the estimate of the residual background level expected on the focal plane detector during the mission lifetime, a crucial information in the development of any instrumental configuration that optimizes the XMS scientific performances. We used the Geant4 toolkit, a Monte Carlo based simulator, to investigate the rejection efficiency of the anticoincidence system and assess the residual background on the detector.

Kapton Polymeric Films to Shield X-Ray Detectors in Orbit

We are investigating possible technical solutions to minimize the instrumental non X-ray background (NXB) of the X-ray Micro-calorimeter Spectrometer (XMS) for the ATHENA space mission. In the proposed design, XMS will be provided with an anti-coincidence system in order to reject most of the X-ray-like events produced by primary solar and cosmic particles that are expected to populate the L-2 space environment. However, the rejection efficiency of events produced by secondary particles cannot be as good as that of events produced directly by primary particles. Among secondary emitted particles, knock-on electrons have in general a major impact in determining the NXB level of X-ray detectors. For this reason, it may be helpful to adopt some techniques of passive shielding together with the use of the active anti-coincidence. We present preliminary results of a study on polyimide sheets, which could be employed to reduce the fluence of knock-on electrons onto XMS and, more in general, to optimize the design and configuration of X-ray detectors in orbit.

Optimization of the TES-Bias Circuit for a Multiplexed Microcalorimeter Array

A transition-edge-sensor (TES) microcalorimeter’s shunt resistor (Rsh) and thermal conductance to the cryogenic bath (G) are often considered to be interchangeable knobs with which to control detector speed. Indeed, for otherwise-identical TES-parameter models, there are many combinations of Rsh and G that give the same decay time-constant (τcrit). However, our previous work showed that with time- or code-division-multiplexed readout, the distribution of signal-to-noise ratio with frequency, which depends strongly on Rsh and G, is just as important as τcrit. Here, we present a set of calculations to select the optimal values of Rsh and G, given a linear TES model and count-rate and energy-resolution requirements. Lower G and lower Rsh make multiplexing easier. Our calculations also determine the allowed combination of SQUID-readout noise (SΦ) and multiplexer row-period (trow) and row-count (Nrows). Recent improvements to SΦ and trow in the NIST time-division-multiplexing architecture have allowed a NIST eight-pixel TES array to be read out with 2.70 eV (full-width at half-maximum) average energy resolution at 6 keV. The improvements make the X-ray Microcalorimeter Spectrometer co-proposed by NASA and NIST for ESA’s Athena X-ray observatory straightforwardly achievable, including engineering margin, with Nrows=16.

Kilopixel X-ray Microcalorimeter Arrays for Astrophysics: Device Performance and Uniformity

We are developing kilopixel arrays of TES microcalorimeters to enable high-resolution x-ray imaging spectrometers for future x-ray observatories and laboratory astrophysics experiments. Our current array design was targeted as a prototype for the X-ray Microcalorimeter Spectrometer proposed for the International X-ray Observatory, which calls for a 40×40-pixel core array of 300 μm devices with 2.5 eV energy resolution (at 6 keV). Here we present device characterization of our 32×32 arrays, including x-ray spectral performance of individual pixels within the array. We present our results in light of the understanding that our Mo/Au TESs act as weak superconducting links, causing the TES critical current (I c ) and transition shape to oscillate with applied magnetic field (B). We show I c (B) measurements and discuss the uniformity of these measurements across the array, as well as implications regarding the uniformity of device noise and response. In addition, we are working to reduce pixel-to-pixel electrical and thermal crosstalk; we present recent test results from an array that has microstrip wiring and an angle-evaporated copper backside heatsinking layer, which provides copper coverage on the four sidewalls of the silicon wells beneath each pixel.

The Cryogenic Anticoincidence Detector for ATHENA-XMS

The TES cryogenic detectors, due to their high spectral resolution and imaging capability in the soft X-ray domain, are the reference devices for the next proposed space missions whose aims are to characterize the spectra of faint or diffuse sources. ATHENA is the re-scoped IXO mission, and one of its focal plane instrument is the X-ray Microcalorimeter Spectrometer (XMS) working in the energy range 0.3–10 keV. XMS will be able to achieve the proposed scientific goals if a background lower than 0.02 cts/cm2/s/keV is guaranteed. The studies performed by GEANT4 simulations depict a scenario where it is mandatory to use an active Anti-Coincidence (AC) to reduce the expected background in the L2 orbit down to the required level. This is possible using a cryogenic AC detector able to provide a rejection efficiency of about 99%. We are developing for this purpose a TES-based detector made by Silicon absorbers (total assembled area about 1 cm2 and 300 μm thick) and sensed by a Ir:Au TES. All the work done for IXO is applicable to ATHENA, with more margins due to the smaller area required for the detector. Here we present the results obtained from different samples, as a step towards the final detector design.

X-RAY SIGNATURES OF NON-EQUILIBRIUM IONIZATION EFFECTS IN GALAXY CLUSTER ACCRETION SHOCK REGIONS

The densities in the outer regions of clusters of galaxies are very low, and the collisional timescales are very long. As a result, heavy elements will be under-ionized after they have passed through the accretion shock. We have studied systematically the effects of non-equilibrium ionization for relaxed clusters in the LambdaCDM cosmology using one-dimensional hydrodynamic simulations. We found that non-equilibrium ionization effects do not depend on cluster mass but depend strongly on redshift which can be understood by self-similar scaling arguments. The effects are stronger for clusters at lower redshifts. We present X-ray signatures such as surface brightness profiles and emission lines in detail for a massive cluster at low redshift. In general, soft emission (0.3-1.0 keV) is enhanced significantly by under-ionization, and the enhancement can be nearly an order of magnitude near the shock radius. The most prominent non-equilibrium ionization signature we found is the O VII and O VIII line ratio. The ratios for non-equilibrium ionization and collisional ionization equilibrium models are different by more than an order of magnitude at radii beyond half of the shock radius. These non-equilibrium ionization signatures are equally strong for models with different non-adiabatic shock electron heating efficiencies. We have also calculated the detectability of the O VII and O VIII lines with the future International X-ray Observatory (IXO). Depending on the line ratio measured, we conclude that an exposure of ~130-380 ksec on a moderate-redshift, massive regular cluster with the X-ray Microcalorimeter Spectrometer (XMS) on the IXO will be sufficient to provide a strong test for the non-equilibrium ionization model.

Calibration of a flat field soft x-ray grating spectrometer for laser produced plasmas

We have calibrated the x-ray response of a variable line spaced grating spectrometer, known as the VSG, at the Fusion and Astrophysics Data and Diagnostic Calibration Facility at the Lawrence Livermore National Laboratory (LLNL). The VSG has been developed to diagnose laser produced plasmas, such as those created at the Jupiter Laser Facility and the National Ignition Facility at LLNL and at both the Omega and Omega EP lasers at the University of Rochester's Laboratory for Laser Energetics. The bandwidth of the VSG spans the range of ∼6-60 Å. The calibration results presented here include the VSG's dispersion and quantum efficiency. The dispersion is determined by measuring the x rays emitted from the hydrogenlike and heliumlike ions of carbon, nitrogen, oxygen, neon, and aluminum. The quantum efficiency is calibrated to an accuracy of 30% or better by normalizing the x-ray intensities recorded by the VSG to those simultaneously recorded by an x-ray microcalorimeter spectrometer.

The Wide Field Imager of the International X-ray Observatory

The International X-ray Observatory (IXO) will be a joint X-ray observatory mission by ESA, NASA and JAXA. It will have a large effective area (3 m 2 at 1.25 keV) grazing incidence mirror system with good angular resolution (5 arcsec at 0.1–10 keV) and will feature a comprehensive suite of scientific instruments: an X-ray Microcalorimeter Spectrometer, a High Time Resolution Spectrometer, an X-ray Polarimeter, an X-ray Grating Spectrometer, a Hard X-ray Imager and a Wide-Field Imager. The Wide Field Imager (WFI) has a field-of-view of 18 ft×18 ft. It will be sensitive between 0.1 and 15 keV, offer the full angular resolution of the mirrors and good energy resolution. The WFI will be implemented as a 6 in. wafer-scale monolithical array of 1024×1024 pixels of 100 × 100 μ m 2 size. The DEpleted P-channel Field-Effect Transistors (DEPFET) forming the individual pixels are devices combining the functionalities of both detector and amplifier. Signal electrons are collected in a potential well below the transistor's gate, modulating the transistor current. Even when the device is powered off, the signal charge is collected and kept in the potential well below the gate until it is explicitly cleared. This makes flexible and fast readout modes possible.

High-energy electron-impact excitation cross sections of hydrogenlike iron and nickel ions

We present a measurement of the cross section for electron-impact excitation of Lyman-α1 in hydrogen-like iron (Z = 26) and nickel (Z = 28) over a broad range of energies using the Lawrence Livermore National Laboratory SuperEBIT electron beam ion trap facility. The measurement was performed with electron beam energies between 35 keV and 85 keV. The hydrogen-like spectrum of iron and nickel was observed, and fully resolved, with the XRS/EBIT x-ray microcalorimeter spectrometer, which allowed for an absolute cross section to be measured by normalizing to the RR x-ray emission. These results are compared to theory.

Energy Splitting of the Ground-State Doublet in the NucleusTh229

The energy splitting of the 229Th ground-state doublet is measured to be 7.6+/-0.5 eV, significantly greater than earlier measurements. Gamma rays produced following the alpha decay of 233U (105 muCi) were counted in the NASA/electron beam ion trap x-ray microcalorimeter spectrometer with an experimental energy resolution of 26 eV (FWHM). A difference technique was applied to the gamma-ray decay of the 71.82 keV level that populates both members of the doublet. A positive correction amounting to 0.6 eV was made for the unobserved interband decay of the 29.19 keV state (29.19-->0 keV).

The Suzaku High Resolution X-Ray Spectrometer

Abstract The X-Ray Spectrometer (XRS) has been designed to provide the Suzaku Observatory with non-dispersive, high-resolution X-ray spectroscopy. As designed, the instrument covers the energy range 0.3 to 12 keV, which encompasses the most diagnostically rich part of the X-ray band. The sensor consists of a 32-channel array of X-ray microcalorimeters, each with an energy resolution of about 6 eV. The very low temperature required for operation of the array (60 mK) is provided by a four-stage cooling system containing a single-stage adiabatic demagnetization refrigerator, a superfluid-helium cryostat, a solid-neon dewar, and a single-stage, Stirling-cycle cooler. The Suzaku/XRS is the first orbiting X-ray microcalorimeter spectrometer and was designed to last more than three years in orbit. The early verification phase of the mission demonstrated that the instrument worked properly and that the cryogen consumption rate was low enough to ensure a mission lifetime exceeding 3 years. However, the liquid-He cryogen was completely vaporized two weeks after opening the dewar guard vacuum vent. The problem has been traced to inadequate venting of the dewar He and Ne gases out of the spacecraft and into space. In this paper we present the design and ground testing of the XRS instrument, and then describe the in-flight performance. An energy resolution of 6 eV was achieved during pre-launch tests and a resolution of 7 eV was obtained in orbit. The slight degradation is due to the effects of cosmic rays.