McEntaffer Group History
The McEntaffer group formed at the University of Iowa in 2008 under Randall McEntaffer. In July 2016 the group then moved to The Pennsylvania State University and continued its research.
The Water Recovery X-ray Rocket
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 WRX-R 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 WRX-R payload are two instruments being developed by Dynamic Imaging Analytics (DIAL) in the UK. The first instrument is designed to image dust in a micro-G environment (samCAM) and the second is an outreach experiment called SuGRE-1.
For WRX-R, 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 WRX-R and assist the lead system engineer.
The Off-plane Grating Rocket Experiment (OGRE)
I work with a group at the University of Iowa, run by professor Randall McEntaffer, that is working on a sub-orbital rocket mission (OGRE). The payload of this mission is designed to test the effectiveness of off-plane gratings in a high resolution soft X-ray spectrometer. The goal of the mission is to show that such an instrument could improve understanding of shock fronts in supernova remnants and find the WHIM. My primary responsibility is to oversee the specification, design, fabrication, testing and launch of the X-ray CCD camera intended for the mission. In addition I assist in the integration and testing of the rocket spectrometer optics.
- Lewis - 2016 - Development of the x-ray camera for the OGRE sub-orbital rocket
- DeRoo - 2013 - Pushing the boundaries of x-ray grating spectroscopy in a suborbital rocket
- McEntaffer - 2013 - First results from a next-generation off-plane X-ray diffraction grating
- Allured - 2013 - Analytical alignment tolerances for off-plane reflection grating spectroscopy
- Bautz - 2012 - Concepts for high-performance soft X-ray grating spectroscopy in a moderate-scale mission
- McEntaffer - 2011 - Development of off-plane gratings for WHIMex and IXO
- Cash - 2011 - X-ray optics for WHIMex: the Warm Hot Intergalactic Medium Explorer
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.
- McEntaffer - 2008 - Soft X-Ray Spectroscopy of the Cygnus Loop Supernova Remnant
- Zeiger - 2011 - The CODEX sounding rocket payload
- Oakley - 2011 - A Suborbital Payload for Soft X-ray Spectroscopy of Extended Sources
- Rogers - 2013 - The OGRESS sounding rocket payload
- Rogers - 2015 - First results from the OGRESS sounding rocket payload
- Rogers - 2017 - Gaseous electron multiplier gain characteristics using low-pressure Ar/CO2
Grating Alignment at Pennsylvania State University
The grating alignment method developed at the University of Iowa was found to have some flaw. The first, and major concern was that the grating position was shown to be highly dependent on the temperature in the room while the epoxy was curing. If the temperature changed, so would the position of the grating.
Better temperature control is imperative if we are to precisely control the alignment of the gratings. To control the temperature, a Praecis temperature control ATCU-5 unit was purchased. This unit is able to control the temperature in the enclosure to 50 times better than the control of the room.
Further upgrades are also planned to the Shack-Hartmann Sensor which will be replaced with an interferometer and to the module motion control which will be completed using a hexpod. These upgrades will not be in place for the WRX-R grating alignment campaign, but will be operational for OGRE.
The tolerance on the alignment of the grating for WRX-R are loose enough that the setup used in Iowa can be used. The tolerances are loose as WRX-R is a diffuse spectrometer and so high resolving power will not be possible.
Grating Alignment, Resolution and Diffraction Efficiency - pre 2017
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).
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.
- McEntaffer - 2013 - First results from a next-generation off-plane X-ray diffraction grating
- Miles - 2015 - Diffraction efficiency of radially-profiled off-plane reflection gratings
- Marlowe - 2015 - Performance testing of a novel off-plane reflection grating and silicon pore optic spectrograph at PANTER
- Peterson - 2015 - Off-plane x-ray reflection grating fabrication
- Allured - 2015 - Optical and x-ray alignment approaches for off-plane reflection gratings
- Tutt - 2016 - Diffraction Efficiency Testing of Sinusoidal and Blazed Off-Plane Reflection Gratings
Lobster Eye Optics
As part of a collaboration between our group at the University of Iowa and a Czech institution, we have been able to adapt our soft X-ray beamline to be able to test a Lobster Eye optic system.
- Dániel - 2017 - X-ray Lobster Eye all-sky monitor for rocket experiment