The development of the THESEUS SXI optics
Charlotte H. Feldman, Paul O'Brien, Richard Willingale, Emile Schyns, Romain Roudot, Ray Fairbend, Julien Seguy, Hannah Natasha Lerman, Ian Hutchinson, Melissa McHugh, Alexander Lodge, Roisin Speight
TThe development of the THESEUS SXI optics
Charlotte Feldman a , Paul O’Brien a , Richard Willingale a , Emile Schyns b , Romain Roudot b ,Ray Fairbend b , Julien S´eguy b , Hannah Lerman a , Ian Hutchinson a , Melissa McHugh a ,Alexander Lodge a , and Roisin Speight aa University of Leicester, University Road, Leicester, LE1 7RH, UK b Photonis France S.A.S., Avenue Roger Roncier, 19100 Brive, B.P. 520, 19106 Brive Cedex,France
ABSTRACT
The Transient High Energy Sources and Early Universe Surveyor is an ESA M5 candidate mission currently inPhase A, with Launch in ∼ L/d ratio (length of pore L and pore width d ) isupwards of 50 and is constant across the whole optic aperture for the SXI. The performance goal for the SXImodules is an angular resolution of 4.5 arcmin, localisation accuracy of ∼ L/d of 60.During the Phase A study, we are investigating methods to improve the current performance and consistencyof the MPOs, in cooperation with the manufacturer Photonis France SAS. We present the optics design of theTHESEUS SXI modules and the programme of work designed to improve the MPOs performance and the resultsfrom the study.
Keywords:
X-ray astronomy, X-ray telescope, X-ray optics, Lobster eye optic, Micro Pore Optics
1. INTRODUCTION
THESEUS, is a multi-instrument mission to detect and characterize Gamma-Ray Bursts (GRBs). It is an M5candidate mission of the Cosmic Vision programme, consisting of three instruments, X/Gamma-ray ImagingSpectrometer (XGIS), Soft X-ray Imager (SXI) and the InfraRed Telescope (IRT). There are two main scientific goals of the THESEUS mission. The first is to explore the Early Universein particular the cosmic dawn and reionisation era, by unveiling a complete census of the Gamma-Ray Burst(GRB) population in the first billion years. The second is to perform an unprecedented deep monitoring of theX-ray transient Universe. THESEUS will specifically perform a study of global star formation up to z ∼
10. Inaddition it will detect and study the primordial (pop III) star population and investigate the re-ionisation epoch,the interstellar medium (ISM) and the intergalactic medium (IGM), up to z ∼ Further author information: Charly Feldman:E-mail: [email protected], Telephone: +44 (0)116 252 5084 a r X i v : . [ a s t r o - ph . I M ] F e b igure 1. The MPO manufacturing process. (Credit: Photonis France SAS)
2. PHOTONIS FRANCE SAS
Photonis is a high-technology organization with over 75 years of experience in innovating, developing, manu-facturing, and selling sensor technologies for detecting and amplifying very low light levels, charged particlesor harsh radiation. Photonis products are used in a very wide range of applications from night vision imagingdevices to medical and analytical instruments or in nuclear reactors. Since decades Photonis is at the forefrontof Micro Channel Plate (MCP) detector technology and more recently, developing Micro Pore Optics for X-rayinstruments on board of multiple space satellite missions. They produced all of the MPOs for the MIXS instru-ment on the ESA BepiColombo mission, the MXT instrument on the Chinese-French mission SVOM, the SXIinstrument on the ESA-CAS mission SMILE and for the LEXI instrument on NASA’s moon lander payload.The manufacturing of MPOs and MCPs is in many aspects very similar. However, MPOs for X-ray collimationor focussing differ from MCP technology in several ways. MCPs have round pores and are active charge amplifierswith ∼ µ m, 20 µ m, 40 µ m, 83 µ m or 720 µ m andcan be square packed and slumped like a lobster eye, e.g. SVOM’s MXT and SMILE’s SXI, or radially packed,e.g. BepiColombo’s MIXS.MPOs are created in a multi stage production, usually about 40 main stages (Figure 1), but is summarisedhere. First a square core glass is surrounded by an inert cladding glass which will form the micro pore walls.This is then drawn in a tower to form a ∼ ∼
3. SXI DESIGN
The lobster eye geometry for X-ray imaging was first introduced by Angel (1979) and the use of tesselatedslumped Micro Channel Plates (MCPs) in a lobster eye X-ray telescope has been pursued by several authors. This geometry can provide a very large Field of View (FoV) and in addition, due to the low density of the glassused in the optics, has very low mass. A wide-field lobster eye optic configuration maintains the same unvignettedeffective area across the entire FOV. This technology and geometry is currently being explored for multiple X-raytelescope missions including SVOM and SMILE and future proposed missions such as TAP and THESEUS. For further details about lobster eye geometry and the distinctive point spread function produced by singleMPOs and arrays of these devices, see paper 11444-159 in these proceedings.The science goals of THESEUS make a wide-field lobster eye X-ray telescope a perfect candidate for the SXIinstrument. The optics aperture for the SXI modules is formed by an array of 8 by 8 square, MPOs mountedon an aluminium spherical frame with a radius of curvature of 600 mm. Each module provides a FoV of 31 o by31 o and combined a FoV of ∼ L/d ratio (length of pore L and pore width igure 2. A CAD rendering of a THESEUS SXI module on the left and just the optic on the right. d ) of ∼
50. For the optimum performance of the SXI at 1 keV, the
L/d needs to be 60, and thus for MPOs witha pore width of 40 µ m the required thickness is 2.4 mm. Each MPO is 40 mm by 40 mm square with a 2 mmgap in between for bonding and a 1 mm overlap with the frame. This means that each MPO aperture is 38 mmby 38 mm. The frame is 420 mm square, which includes the MPOs and the surrounding supportive structure.The MPOs are mounted directly onto the frame using a silicon based adhesive. A CAD rendering of a singleTHESEUS module and a single optic are shown in Figure 2. Behind the optics are a set of magnets forming anelectron diverter, along with the heaters to maintain the optics at a constant temperature of 20 o C ± o C duringflight. The full optics assembly of each module will weigh ∼ o wide overlap, co-alignedwith the IRT FoV to provide redundancy. Each SXI module focal plane comprises of 8 CMOS detectors in a2 by 4 arrangement which are slightly tilted in order to simulate the required curved focal plane required for alobster eye optic and to avoid vignetting, and to optimise the FoV imaging area. Further details of the SXI focalplane can be found in paper 11444-284 within these proceedings.
4. FACILITIES AT THE UNIVERSITY OF LEICESTER
There are two X-ray optics testing facilities within UoL, the TTF and the VTF.The Tunnel Test Facility (TTF) is a 28 m long X-ray beam test facility with both soft and hard X-ray sourcesand two imaging detectors, an MCP and a CCD. At the detector end of the facility an ∼ ∼
70 keV. Eithera Scandium or Tungsten anode can be used and can be configured to stimulate X-ray florescence of externaltargets providing a wide range of possible X-ray energies. Figure 3 shows the source and the detector ends ofthe facility.The Vertical Test facility (VTF) is a 1.5 m tall X-ray beam facility with an electron gun to generate theX-rays of characteristic wavelengths at the bottom, a sample stage in the central chamber and an imaging MCPdetector in the upper chamber. The facility has a vertical orientation so that the MPO optic is retained inplace by gravity only eliminating mounting distortion and stress. In addition, MPOs with Al film on the convexsurface can be tested without causing damage to the film. The MPO is tested in out-of-focus mode with the rearsurface towards the source. A parallel beam from the X-ray source is created when the MPO is at (or close to)the expected focal point for a point source at infinity. By using a mask directly above the MPO with a specificsequence of holes, it is possible to select only the single reflection, double reflection and straight through rayswhich constitute the point-spread function of a lobster optic. From a single image of this type, it is possible to igure 3. The TTF beam line at the University of Leicester. The source end is on the left and the detector chamber wherethe optics are mounted on the right.Figure 4. The VTF testing facility at the University of Leicester. calculate the efficiency, radius of curvature, pointing direction of the pores and PSF of the MPO. The facilityallows up to two MPOs to be tested a day giving a very fast turn around time and short feedback loops. Thisfacility will be complete before the end of 2020 and an image of it in its current state is shown in Figure 4.
5. DEVELOPMENT PLAN
A Technology Development Activity (TDA) grant from ESA has been provided to improve the consistency of theMPOs produced by Photonis and to guarantee the science performance. The goal is to achieve a PSF FWHMfor each module of 4.5 arcmin, though the science can still be achieved as long as the FWHM is below 7 arcmin.In order to achieve a module PSF FWHM of < < ∼ Unfortunately, due to the Covid-19 pandemic, this work has been severely delayed. However, the new block hasbeen drawn and fused at Photonis and is waiting to be sliced in to the individual 2.4 mm MPOs. It is hoped thatthe first flat MPOs will be received for testing at UoL by the end of March 2021 and the first slumped MPOswill be received in the summer of 2021. It is planned that this project will be completed by the end of 2021. . SUMMARY AND CONCLUSION
The Transient High Energy Sources and Early Universe Surveyor (THESEUS) is an ESA M5 candidate missionaimed at studying GRBs and transient sources and completing an unprecedented survey of high z sources.Currently in Phase A, with Launch in ∼
7. ACKNOWLEDGEMENTS
We acknowledge contributions from the SXI consortium and the wider THESEUS team to the development ofthe SXI. We also acknowledge funding from ESA (4000129734/20/NL/IB/ig) and several ESA member states,including from the UK Space Agency.
REFERENCES [1] Labanti, C., Campana, R., Fuschino, F., and Amati, L., “The x/gamma-ray imaging spectrometer (xgis)on-board theseus: Design, main characteristics, and concept of operation,”
Proc. of SPIE (2020).[2] O’Brien, P., Hutchinson, I., Lerman, H., Feldman, C., McHugh, M., Beardmore, A., Willingale, R., Drumm,P., Speight, R., and Lodge, A., “The soft x-ray imager on theseus: The transient high energy survey andearly universe surveyor,”
Proc. of SPIE (2020).[3] G¨ o tz, D., Basa, S., Bozzo, E., and Tenzer, C., “The infra-red telescope on board the theseus mission,” Proc.of SPIE (2020).[4] Amati, L., O’Brien, P., G¨ o tz, D., and Bozzo, E., “The transient high-energy sky and early universe surveyor,” Proc. of SPIE (2020).[5] Fraser, G., Carpenter, J., Rothery, D., Pearson, J., Martindale, A., Huovelin, J., Treis, J., Anand, M.,Anttila, M., Ashcroft, M., Benkoff, J., Bland, P., Bowyer, A., Bradley, A., Bridges, J., Brown, C., Bulloch,C., Bunce, E., Christensen, U., Evans, M., Fairbend, R., Feasey, M., Giannini, F., Hermann, S., Hesse, M.,Hilchenbach, M., Jorden, T., Joy, K., Kaipiainen, M., Kitchingman, I., Lechner, P., Lutz, G., Malkki, A.,Muinonen, K., Nrnen, J., Portin, P., Prydderch, M., Juan, J., Sclater, E., Schyns, E., Stevenson, T., Strder,L., Syrjasuo, M., Talboys, D., Thomas, P., Whitford, C., and Whitehead, S., “The mercury imaging x-rayspectrometer (mixs) on bepicolombo,”
Planetary and space science , 79–95 (2010).[6] G¨ o tz, D., Adami, C., S. Basa, S., Beckmann, V., Burwitz, V., Chipaux, R., Cordier, B., Evans, P., Godet,O., Goosmann, R., Meidinger, N., Meuris, A., Motch, C., Nandra, K., O’Brien, P., Osborne, J., Perinati, E.,Rau, A., Willingale, R., Mercier, K., and Gonzalez, F., “Microchannel x-ray telescope on board the svomsatellite,” ArXiv e-prints AGU Fall Meeting 2020
SM029-01 (2020).[9] Angel, J., “Lobster eyes as x-ray telescopes,”
Ap. J. , 364–373 (1979).[10] Chapman, H., Nugent, K., and Wilkins, S., “X-ray focusing using cylindrical-channel capillary arrays, i.theory,”
Appl. Opt. , 6316 (1993).[11] Wilkins, S., Stevenson, A., Nugent, K., Chapman, H., and Steenstrup, S., “On the concentration, focusing,and collimation of x-rays and neutrons using microchannel plates and configurations of holes,” Review ofscientific instruments , 1026–1036 (1989).[12] Fraser, G. W., Lees, J. E., Pearson, J. F., Sims, M. R., and Roxburgh, K., “X-ray focusing using microchan-nel plates,” Proc. of SPIE (1992).[13] Kaaret, P., Geissbuhler, P., Chen, A., and Glavinas, E., “X-ray focusing using microchannel plates,”
Appl.Opt. (1992).14] Camp, J. and Gehrels, N., “Whitepaper on transient astrophysics probe (tap).” https://pcos.gsfc.nasa.gov/physpag/probe/Transient Astrophysics Probe.pdf (2020).[15] Amati, L., Bozzo, E., O’Brien, P., and G¨ o tz, D., “The transient high-energy sky and early universe surveyor(theseus),” Mem. S.A.It. , 282 (2019).[16] Feldman, C., Willingale, R., Pearson, J., Aslanyan, V., Crawford, T., Houghton, P., Sykes, J., Bicknell, C.,Osborne, J., O’Brien, P., Bradshaw, M., Burwitz, V., Hartner, G., Langmeier, A., Liao, Y., Pellilciari, C.,G¨ o tz, D., Mercier, K., Le Duigou, J. M., and Gonzalez, F., “Calibration of a fully populated lobster eyeoptic for svom,” Proc. of SPIE11444-159