The International X-ray Observatory (IXO) - Selected 4th in the NASA decadel survey and subsequently canceled

Prior to its termination, IXO was hosen 4th in the NASA decadal study.  IXO was to be the next observatory class space satellite for X-ray detection across the 0.1 keV to 40 keV energy range.  IXO's aim was to address the following questions in high energy astrophysics:

  1. Black hole formation and evolution

  2. The equation-of-state for neutron stars

  3. Galaxy velocity structure, mass and metallicity distribution

  4. The nature of the cosmic web of baryons (WHIM)

  5. ow feedback mechanisms in the Universe work

As part of the phase zero study a collaboration was formed between the CEI, the Universities of Iowa and Colorado, Northrup Grumman and e2v technologies to investigate the possibility of providing a high resolution soft X-ray spectrometer, based on off-plane gratings, for the IXO mission.  The instrument would have been able to resolve separate absorption lines generated in the Warm-Hot Intergalactic Medium (WHIM) and help identify the location of the missing baryonic content of the Universe.

As part of the CEI I was part of the team that was investigating the type, number and orientation of detectors that would be best used for this instrument and the goal was to use EM-CCDs in the camera final array.

image courtesy of ESA

image courtesy of ESA

The Advanced Telescope for High ENergy Astrophysics (ATHENA) - re-proposed and scheduled for launch in 2028

After IXO was terminated by NASA, ESA re-scaled the L-class mission to allow a scaled down version of IXO to be proposed - ATHENA - that only had European involvement.

This scaled down observatory concept did not include a grating spectrometer; however, the European parts of the IXO off-plane grating spectrometer team were involved in the planning of this mission.  ATHENA's core science objectives were in the fields of:

  1. Black hole and accretion Physics

  2. Cosmic feedback

  3. Large-scale structure of the Universe

While I was involved in ATHENA, The L-class mission was chosen to be JUCIE leading to the end of the ATHENA concept study. It has since be re-proposed and selected.

image courtesy of ESA

image courtesy of ESA

The Warm-Hot Intergalactic Medium Explorer (WHIMEx) - Not selected

WHIMEx was a scaled down version of the instrument designed as the off-plane X-ray grating spectrometer on IXO.  

The concept was to fly a small area X-ray optic on an explorer class mission.  Off-plane gratings mounted directly behind this optic would disperse incident X-rays over a CCD based camera array at the focus of the optic.  WHIMEx would have the ability to meet many of the science goals of IXO but in a more affordable explorer mission with the CEI working on the detector development as planned for IXO.  WHIMEx planned to address the following scientific questions:

  1. What happens close to a black hole?

  2. When and how did super-massive black holes grow?

  3. How does large-scale structure evolve?

  4. hat is the link between super-massive blac hole formation and the evolution of large-scale structure (i.e. cosmic feedback)?

  5. How does matter behave at very high density?

WHIMEx was not chosen as a NASA explorer class mission

image courtesy of Randall McEntaffer

image courtesy of Randall McEntaffer

ARCUS - Selected for Phase A study in 2017

Arcus is a proposed X-ray grating spectrometer mission to be deployed on the International Space Station. The baseline design uses sub-apertured X-ray silicon pore optics feeding into off-plane gratings to achieve both high spectral resolution with a large effective area. The instrument would achieved a resolution of 2800 and and effective area of ~800 sq. cm over the 8-52Å (0.25-1.5 keV) bandpass.  ARCUS would allow the following science to be observed:

  • How mater cycles in and out of galaxies and clusters of galaxies

  • How black holes grow and affect their surroundings

  • How stellar systems & environments form and evolve

  • How stars and protoplanetary disks form and evolve

Arcus was selected for Phase A study in 2017 and was one of two missions considered for Phase B in 2019. SPHEREx was eventually selected for Phase B study.

I was involved in the testing of the Critical Angle Transmission gratings that were proposed to be used as the dispersive element on Arcus and was helping to design the testing facility that would be used if Arcus had been selected for Phase B.

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Euclid is an ESA mission to map the geometry of the dark Universe. It is due for launch in June 2022.

Euclid is optimized for two cosmological probes:

  1. Weak Gravitational Lensing

  2. Baryonic Acoustic Oscillations

To observe Weak Gravitational Lensing, excellent image quality is required because any distortions in the image caused by the instrument could hide true distortions made by gravity. This requires an excellent detector, with high radiation damage tolerance.

As part of my work at the CEI I helped characterize the affect of radiation damage on prototype detectors that are going to be used on Euclid.

Euclid vis ccd

Euclid vis ccd

ASTRO-H (Hitomi) - Launched in 2016

ASTRO-H (due for launch in 2015) is the next major space mission to be launched by the Japanese Space Exploration Agency (JAXA) and the 6th dedicated X-ray satellite they have built.  The mission’s goal is to aid our understanding of the structure and evolution of the Universe through the use of the following observational capabilities:

  1. One of the first imaging and spectroscopic observations with a hard X-ray telescope

  2. The first spectroscopic observations with an extremely high resolution micro-calorimeter

  3. The most sensitive wide-band observation over an energy range of 0.3 keV to 600 keV

To achieve its scientific goals, ASTRO-H has a payload made up of 6 different instruments:


  1. The Hard X-ray Telescope (HXT)

  2. The Soft X-ray Telescope (SXT)

  3. The Hard X-ray Imager (HXI)

  4. The Soft X-ray Spectrometer (SXS)

  5. The Soft Gamma Ray Detector (SGD)

Image courtesy of JAXA

Image courtesy of JAXA

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JSPS Summer fellowship, Osaka, Japan  (11th June 2013 to 21st August 2013)

The JSPS Summer Program is implemented as a component of the JSPS Postdoctoral Fellowship for Research in Japan. It provides opportunities for young pre- and post-doctoral researchers from North America and Europe to receive an orientation on Japanese culture and research systems and to pursue research under the guidance of host researchers at Japanese universities and research institutes over a period of two months during the summer.

JSPS seeks cooperation from its overseas partners in recruiting candidates for the program. In implementing this program, our overseas partners are the National Science Foundation (USA), British Council (UK), Centre National de la Recherche Scientifique (France), Deutscher Akademischer Austauschdienst (Germany), the Canadian Embassy in Japan (Canada), and the Swedish Foundation for International Cooperation in Research and Higher Education (Sweden).

Please click on a bullet point for more information

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The Off-plane Grating Rocket for Extended Source Spectroscopy (OGRESS)

Photos from the OGRESS sub-orbital rocket can be found here

The OGRESS sounding rocket payload is capable of moderate spectral resolution (E/ΔE ~ 10-40) between 0.3 – 1.2 keV, while providing FOV large enough to fully encompass nearby diffuse sources. OGRESS’s optical system is identical to that of CODEX , The Extended Off-plane Spectrometer (EXOS), and the Cygnus X-ray Emission Spectroscopic Survey (CyXESS). The payload consists of two nearly-identical spectrographs. Light for each spectrograph is collected by passive focusers consisting of a stack of wire grids which sculpt a converging beam. Each focuser feeds into an array of off-plane gratings located ~2 meters from the detectors. The spectrum is collected by Gaseous Electron Multiplier (GEM) detectors. The position of the detectors relative to the spectrum provides the only difference between the spectrographs. This instrument is capable of generating high-resolution spectra of large diffuse sources such as the Cygnus Loop and Vela SNRs. OGRESS will observe the Cygnus Loop SNR. Cygnus is a high-surface brightness annular soft X-ray source. It is a middle aged (5-8 kyr) shell-type SNR with most emission coming from a ring-like area fitting comfortably into OGRESS’s FOV. It is ~540 pc distant in the constellation Cygnus, spanning ~3° x 3°. Our observations of Cygnus will determine its dominant emission mechanism in the soft X-ray bandpass and the equilibrium state and elemental abundances of the plasma. 

On the morning of the 2nd May 2015, OGRESS was successfully launched from White Sands Missile Range, New Mexico, USA.

Related Papers

  • Rogers - 2017 - Gaseous electron multiplier gain characteristics using low-pressure Ar/CO2

  • Rogers - 2015 - First results from the OGRESS sounding rocket payload

  • Rogers - 2013 - The OGRESS sounding rocket payload

  • Zeiger - 2011 - The CODEX sounding rocket payload

  • Oakley - 2011 - A Suborbital Payload for Soft X-ray Spectroscopy of Extended Sources

  • McEntaffer - 2008 - Soft X-Ray Spectroscopy of the Cygnus Loop Supernova Remnant

The Water Recovery X-ray Rocket (WRXR)

A NASA press-release about WRXR can be found herephotos related to the mission can be found here, and the YouTube channel for the sub-payload SuGRE-1 can be found here

The WRX-R mission targets the Vela Supernova Remnant (SNR) and measures soft X-rays emanating from this region. The Vela SNR was created when a star, >10 times the mass of the Sun, collapsed and then exploded as a Supernova, the final stage of stellar evolution. Supernova explosions are one of the most energetic events in the Universe, and play a role in recycling material within galaxies. They are responsible for the creation and distribution of elements such as, oxygen, silicon, neon, iron, nickel, and magnesium among others, into the interstellar medium, thereby providing source material for the next generation of stars, planets, and even organic chemistry. The explosions are rarely seen in action, but evidence is left behind as Supernova Remnants. Ejected material from the explosion travels at high speeds and the shockwave sweeps up interstellar material along the way, continuing to heat it to temperatures as high as 10 million Kelvin. Hotter temperatures lead to the emission of higher energy electromagnetic radiation, such as X-rays, from the SNR. WRX-R measures soft X-rays with an energy range of 0.25- 0.8 kilo electron Volts (keV), focusing on emission lines for ions of Oxygen6+, i.e. Oxygen lacking six of its eight electrons, O7+ (seven of eight electrons missing) and Carbon5+ (five of six electrons missing). The data will show how much of each constituent is present, and allow scientists to derive information about the conditions in the Vela SNR such as the temperature, density, chemical composition, and ionization state. Using these characteristics they will also be able to estimate the shock velocity near the SNR limb, the age and type of the SNR, the energy of the supernova, and the mass of the progenitor.

On the night of the 4th April 2018, WRXR was successfully launched from the Reagan Test Site, Roi Namur, Kwajalein Atol, Marshall Islands.

The NASA WRX-R Principal Investigator Professor Randall McEntaffer takes us through X-ray astronomy, why use a sounding rocket and the science of the Water Recovery X-ray Rocket mission

The Water Recovery X-ray Rocket is a re-flight of the OGRESS payload after a significant upgrade. The hardware on OGRESS worked perfectly, but a large background signal was detected during the flight which swamped the X-rays from Cygnus. The background signal was attributed to the high electric field generated by the GEMs detectors used on OGRESS. This upgraded flight will replace the GEMs detectors with a Hybrid CMOS Detector (HCD).

The GEMs detectors on OGRESS were originally chosen as it was possible to cover a large proportion of the focal plane (100 mm x 100 mm on two different channels) with detector at an affordable price. The HCD detector that will be used on WRXR is smaller than the GEM detectors (35 mm x 35 mm) and only a single channel will be used. This loss in effective area due to losing a channel will be partially recovered through the use of new off-plane gratings. These gratings are larger than the OGRESS gratings (100 mm in the groove direction and 110 mm in width) and will be operated at a shallower graze angle (2.2 degrees vs 4.4 degrees). This makes the gratings more efficient.

The second channel that was used on OGRESS is being replaced with a lobster eye experiment that is being developed by the Czech Technical Institute in Prague and Rigaku. This instrument is made up of two different optical systems. The first is a 1D focusing system where a single lobster eye optic focuses X-rays in 1D onto a TimePix detector. The second optical system contains two lobster eye optics and focuses X-rays in 2D onto a focal plane that is ~1.3 meters away.


Also on the WRXR payload is an instrument being developed by Dynamic Imaging Analytics (DIAL) in the UK. The first part of the instrument is designed to image dust in a micro-G environment (samCAM) and the second is an outreach experiment called SuGRE-1. SuGRE-1 plans to test novel 3D imaging techniques by tracking the trajectory and interaction of objects and particles in a micro-gravity environment (sculptures designed by school and college students).

For WRXR, I am leading the team that is co-aligning the off-plane reflection gratings into a module to replace the OGRESS gratings. A series of mirrors to direct the diffracted X-rays onto the HCD are also being developed and my team will lead that alignment effort. In addition I am the lead mechanical engineer for WRXR and assist the lead system engineer.

Related papers

  • Miles - 2017 - An introduction to the water recover x-ray rocket

  • Stehlikova - 2017 - Hard X-ray Vela supernova observation on rocket experiment WRX-R

  • Daniel - 2017 - X-ray Lobster Eye all-sky monitor for rocket experiment



High Speed EM-CCD camera system

Photos from the test at the B16 beamline at the Diamond Light Source can be found here

Many X-ray imaging detectors, from medical diagnosis to the examination of energy levels in atoms, are based on the same technology as found in digital cameras. Most X-rays pass straight through these Charge Coupled Devices (CCDs) and CMOS detectors and it is therefore necessary to use a thicker detector (e.g. CMOS hybrid) or a scintillator. However, current methods produce detector systems with limited performance: CMOS-hybrid technology requires intricate features limiting the minimum pixel size and spatial resolution, whilst the readout speed of CCD-based systems is limited by higher noise levels.

Over recent years an STFC funded concept study was completedon a novel photon-counting detector. The Electron-Multiplying (EM) CCD was designed for low light level imaging such as night-time surveillance or night-vision. The EMCCD differs from the standard CCD through the addition of a "gain register". By multiplying the signal by thousands, the effective read noise of the device can be reduced to the sub-electron level, allowing operation at very high speeds. If a scintillator is coupled to an EM-CCD then this low effective noise allows analysis of single photon interactions (photon counting), providing higher resolution imaging and energy discrimination.

The small area (8mm x 8mm) scintillator-coupled EM-CCD operated at 2fps, limiting potential applications. Further developments are required to transfer this technology and expertise to the marketplace. 

We aim to produce a large area, high speed X-ray detector module, making use of the now commercially available highspeed electronics developed from the STFC funded 'Lucky Imaging' at the Institute of Astronomy, Cambridge. By coupling a fibre-optic taper to a larger area EM-CCD, an increase in area of over 44 times is possible. It is envisaged that a series of modules will then be formed into an array, creating a much larger system. We also aim to test the suitability of the scintillating fibre-optic (SFO). Whilst the SFO has largely been ignored for use with a CCD due to lower light output, it has a highly structured form, minimising the signal spread. With the EM-CCD's ability to apply gain to the signal, it is expected that a high-resolution integrating system may be produced. 

In comparison to previous detectors, the expected performance of the new module will give a higher resolution, faster speed (increasing beamline throughput), higher effective dynamic range through higher maximum flux before saturation and higher detection efficiency, higher signal to noise and operation at higher temperatures. The projected specifications of the module will provide these substantial benefits to users, including allowing higher throughput in the beamline facilities and shutter-less performance, providing the high speed of the low resolution 'pixel detectors' and the high resolution of the low speed CCD systems. 

Through the production of a proof of concept prototype module, not only will this technology be opened up to the marketplace, but the range of applications for the EM-CCD will be dramatically expanded, opening new markets for this device. 

This detector is aimed towards applications at synchrotron facilities such as macromolecular crystallographysurface diffraction or small-angle scattering techniqueshigh energy X-ray diffraction and phase-contrast imaging. Applications in medical imaging may also be envisaged for a larger array of modules.  To transfer this technology and expertise to the marketplace, we propose to build a proof of concept module with the support of e2v technologies, a leading designer, developer and manufacturer of high performance imaging sensors.

Quantum Efficiency Testing

Swept charge device e2v CCD236

The e2v technologies plc. CCD236 is a Swept Charge Device (SCD) designed as a large area (20 mm × 20 mm) soft X-ray detector for spectroscopy in the range 0.8 keV to 10 keV. It benefits from improvements in design over the previous generation, the e2v CCD54, such as: a 4 times increased detector area, a reduction in split X-ray events due to the 100 µm × 100 µm ‘pixel’ size, and improvements to radiation hardness. The CCD236 will be used in India’s Chandrayaan-2 Large Soft X-ray Spectrometer (CLASS) instrument and China’s Hard X-ray Modulation Telescope (HXMT). Measurements of the Quantum Efficiency (QE) were obtained relative to a NIST calibrated photodiode over the energy range 0.2 keV to 1.9 keV, using the BESSY II X-ray synchrotron in Berlin. Two Xray event counting methods are described and compared, and QE for soft X-ray interaction is reported. Uniformity of QE across the device is also investigated at energies between 0.52 keV and 1.5 keV in different areas of the detector. This work will enable the actual number of photons incident on the detectors to be calculated, thus ensuring that the CCD236 detectors provide valuable scientific data during use. By comparing the QE methods in this paper with the event processing techniques to be used with CLASS, an estimate of the instrument-specific QE for CLASS was provided.

Results of the Quantum efficiency testing of the ccd236 between 50 eV and 2,000 ev


The Quantum Efficiency of the Hamamatsu was measured over a range of X-ray energies from 150 eV to 1900 eV. The Hamamatsu device was the baseline for the WHIMEx proposal and the experiment was designed to test the soft X-ray performance and QE of the device over the mission baseline energy range.

Quantum efficiency of the Hamamatsu devices (HPK CCD) over the WHIMex target bandpass

Detector characterization

I have been involved in the characterization of a variety of silicon-based detectors. These include:

Grating Alignment, Resolution and Diffraction Efficiency

The major research that is being performed at the University of Iowa involves the development of off-plane X-ray diffraction gratings. These gratings are densely ruled to maximise the dispersion of the X-rays, radially grooved to match the convergence of a focusing optic, blazed to preferentially diffraction the X-rays to one side of the specular reflection position (zero-order) and closely packed to maximise effective area. 

As part of this work, I have developed a setup in a CAD program (Solidworks) that can be used to align the closely packed gratings in pitch, roll, yaw, x, y and z dimensions.  To do this we utilize the unique ability of a hexapod to access all 6 of the degrees of freedom that we require.  The pitch and roll of the grating is measured using a theodolite and Shack-Hartmann sensor, the yaw is measured using the diffraction of an optical laser from an optical grating on the X-ray grating and x, y and z is constrained through kinematic mounts.

This setup is under construction in the lab and first testing of aligned gratings should occur in early 2016.


UPDATE: The setup was constructed and 4 off-plane reflection gratings were co-aligned into a grating module. The alignment of these gratings to one-another were tested at the Stray-light facility at Marshall Space Flight Center in mid-2016 and they were shown to be co-aligned within the errors of the experiment. The gratings were then put through vibration testing and re-measured to ensure they could survive launch. Again, within the errors of the experiment, the gratings were co-aligned. Finally, the module underwent thermal cycling testing and survived. A paper on this work is in the final stages of being written.


Grating resolution has been tested and shown to be >3000 (E/dE) at the stray-light facility at Marshall Space Flight Center (USA) and at the MPE PANTER facility (Germany). The PANTER test was the first to test two gratings co-aligned to each other in the converging beam of a Silicon Pore Optic (SPO) provided by cosine (Netherlands). Photos of the test performed at PANTER can be found here



Grating diffraction efficiency is tested using the PTB EUV reflectometer at BESSY II in Germany.  Their highly tuneable pencil X-ray beam is used to measured the diffraction efficiency of single gratings between 300 eV and 2000 eV in 50 eV steps across all visible diffracted orders.  Photos taken at this facility can be seen here.

Related Papers

  • Donovan - 2018 - X-ray verification of an optically aligned off-plan grating module

  • Tutt - 2016 - Diffraction Efficiency Testing of Sinusoidal and Blazed Off-Plane Reflection Gratings

  • Allured - 2015 - Optical and x-ray alignment approaches for off-plane reflection gratings

  • Peterson - 2015 - Off-plane x-ray reflection grating fabrication

  • Marlowe - 2015 - Performance testing of a novel off-plane reflection grating and silicon pore optic spectrograph at PANTER

  • Miles - 2015 - Diffraction efficiency of radially-profiled off-plane reflection gratings

  • McEntaffer - 2013 - First results from a next-generation off-plane X-ray diffraction grating

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Development of CCD and EM-CCD technology for high resolution X-ray spectrometry

PhD thesis



This thesis discusses the development of Charge-Couple Device (CCD) and Electron Multiplying CCD (EM-CCD) technology for high resolution X-ray spectroscopy.  Of particular interest is the spectral resolution performance of the devices alongside the optimisation of the quantum efficiency through the use of back-illuminated CCDs, thin filter technology and improved passivation techniques.  The early chapters (1 through 5) focus on the background and theory that is required to understand the purpose of the work in this thesis and how semiconductors can be used as the detector of high resolution X-ray spectrometers.  Chapter 6 focuses on the soft X-ray performance of three different types of conventional CCD using the PTB beamline at BESSY II.  The results show that there is degradation in spectral resolution in all three devices below 500 eV due to incomplete charge collection and X-ray peak asymmetry.  The Hamamatsu device is shown to degrade faster than the CCD30-11 variants and this is attributed to the thickness of the active silicon (>50 μm) in the device and also its thicker dead-layer (~75 nm) which is found by evaluating the device’s soft X-ray QE).  The charge loss at the back-surface generation/recombination centres is also investigated and is found to be higher in the Hamamatsu device, again due to its thicker dead-layer.  Chapter 7 is an investigation of the Modified Fano Factor which aims to describe the spectral resolution degradation that is expected when an EM‑CCD is used to directly detect soft X-rays.  The factor is predicted analytically, modelled and then verified experimentally allowing EM-CCD performance over the soft X-ray range to be predicted with high levels of confidence.  Chapter 8 is a detailed look into work completed for the phase 0 study of the off plane X-ray grating spectrometer on the International X-ray Observatory.  The work includes a detailed contamination study, effective area analysis, the pointing knowledge requirement and the use of filters to minimise optical background.

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