The Solar Upper Transition Region Imager (SUTRI) is an extreme ultraviolet solar imaging telescope that focuses on dynamically observing the solar transition region within a narrow band at 46.5nm. This paper describes the optical parameters, optomechanical structural design, finite element simulation, and on-ground environmental testing. To satisfy the narrow band requirement, the telescope employs multilayers coated on Ritchey-Chrétien optics and filters mounted at the front aperture and ahead of the focal plane. The primary and secondary mirrors are glued to invar frames that provide peripheral support. The telescope contains three mechanisms, which are a focus mechanism, a filter wheel, and a front door. In addition, this paper carried out finite element simulation of modal analysis, optical performance and structural strength. These simulations verified that the opto-mechanical system design is feasible. Finally, the telescope successfully underwent a series of on-ground environmental testing and was subsequently launched carried by SATech-01 satellite in July 2022.
The Solar Upper Transition Region Imager (SUTRI) onboard the Space Advanced Technology demonstration satellite (SATech-01), which was launched to a sun-synchronous orbit at a height of 500 km in July 2022, aims to test the on-orbit performance of our newly developed Sc-Si multi-layer reflecting mirror and the 2kx2k EUV CMOS imaging camera and to take full-disk solar images at the Ne VII 46.5 nm spectral line with a filter width of 3 nm. SUTRI employs a Ritchey-Chretien optical system with an aperture of 18 cm. The on-orbit observations show that SUTRI images have a field of view of 41.6'x41.6' and a moderate spatial resolution of 8" without an image stabilization system. The normal cadence of SUTRI images is 30 s and the solar observation time is about 16 hours each day because the earth eclipse time accounts for about 1/3 of SATech-01's orbit period. Approximately 15 GB data is acquired each day and made available online after processing. SUTRI images are valuable as the Ne VII 46.5 nm line is formed at a temperature regime of 0.5 MK in the solar atmosphere, which has rarely been sampled by existing solar imagers. SUTRI observations will establish connections between structures in the lower solar atmosphere and corona, and advance our understanding of various types of solar activity such as flares, filament eruptions, coronal jets and coronal mass ejections.
A table-top soft x-ray polarimetry setup has been developed at the Institute of Precision Optical Engineering for characterizing the polarization properties of mirrors designed for the lightweight asymmetry and magnetism probe project. Based on a Co/C multilayer polarizer mirror, linearly polarized soft x-rays were generated at a wavelength of 4.48 nm, which could be rotated around the beam-propagation direction by using a differentially pumped rotary feedthrough. The setup design and the alignment method are described in detail. The capabilities of this spectrometer were demonstrated through a polarization test on a twin Co/C multilayer polarizer sample, and the results agree well with the expected sine wave.
We present an analytical study to provide guide lines to design a block structure hard X-ray supermirror. The block structure supermirror is a kind of layered structure consisting of several "blocks" of multilayer of different d-spacing to obtain broad energy bandwidth response. This structure has been widely applied in X-ray telescopes because it is easy to fabricate. To examine the propagation of X-rays in a supermirror structure, further simplified approximation of Kozhevnikov's theory has been developed. The supermirror structure is described by a structure function. The spectral function of the structure, which is the Laplace transformation of the structure function, turns out to be proportional to the reflectivity profile against X-ray energy. By analyzing the expression of the spectral function, we found the reflectivity of the supermirror could be smooth due to the box-car shaped spectral function if the d-spacing and layer number of each block is arranged with appropriate constraints.
X-ray focusing optics is one of the most important technologies for X-ray astronomy with capabilities of direct imaging, low background and high sensitivity. The enhanced X-ray Timing and Polarimetry (eXTP) and hot universe Baryon surveyor (HUBS), are proposed in China as two major X-ray missions for the next decade. The thermally slumping glass optics (SGO) is one of the approaches to satisfy the requirement of large collecting areas and high angular resolution. In the last years, we made a great progress in the research of SGO X-ray focusing telescope and established the whole fabrication platform. This paper will give a review of recent developments in each step, including lens fabrication, multilayer coating, telescope assembly and optical performance testing. We established an in-situ multi-probe platform based on the contact, trigger and non-contact probes. Thus, the radius deviation and the straightness of graphite strip, the surface shape and the radius of the inner surface of each layer can be measured during the telescope assembly process. We also developed a three-dimensional ray-tracing method to calculate the performance degradation induced by the deformed surface appearing on the forming process and optical assembly. Then the result could be feed back into the fabrication process for improving upon the later mounted mirrors in the real time. We have successfully fabricated two telescope prototypes with the focal length of 2000mm in the last years. The optical performance of the two 3-layer and 21-layer prototypes, which was numbered as No.6 and No.7 prototype respectively, were tested in PANTER test facility of MPE in September 2018. The measured angular resolution t of section A of No.6 prototype is 67±2 arc-second at 8keV, and the measured angular resolution in full aperture of No.7 telescope prototype is 96±3 arc-second at 8keV, which is much better than the previous prototypes.
The Solar Upper Transition Region Imager (SUTRI) was proposed to observe for the first time the Ne VII line at 46.5nm emitted from the upper solar transition region. As the key optical elements of the SUTRI, Sc/Si multilayer reflective mirrors are developed to offer high spectral selectivity and high reflectivity at 46.5nm with a normal-incidence angle. To avoid spectral contamination, the reflective bandwidth of the multilayer is required less than 4nm, which is achieved when the Sc layer thickness ratio is tuned to above 0.65. Meanwhile, the mechanical property, resistivity to thermal cycling, and temporal stability of the Sc/Si multilayer are characterized. The addition of an ultrathin Si layer (thickness of 0.6nm) in each Sc layer decreased the crystallization of Sc and flatted the interface, resulting in the enhancement of the mechanical property of the Sc/Si multilayer with new structure. After three times of thermal cycling, the temperature from 5°C to 40°C, the surface morphology of the new Sc/Si multilayer remained unchanged. The grazing incidence reflectometer test results showed that the periodic structure and thickness of the new multilayer were still similar after 2 years of storage. The optimized Sc/Si multilayer has a d-spacing of 24.55nm and a Sc thickness ratio of 0.72, achieving the extreme ultraviolet reflectivity of 28% at 46.1nm obtained from the laboratory-based reflectometer. The optimized Sc/Si multilayer mirrors have been applied in the SUTRI and received bright solar images at 46.5nm.
The Hot Universe Baryon Surveyor (HUBS) mission will carry an imaging X-ray telescope (IXT) for covering an energy range from 0.5 keV to 10 keV to study the hot baryon evolution. In this paper, we report the optical design for HUBS mission and the latest developments at IPOE, Tongji Univeristy. For HUBS mission, we had designed a three-stage conic-approximation type to simplify the manufacturing process. The basic process of imaging X-ray telescopes based on thermal glass slumping has been introduced. Nearly ten prototypes have been fabricated for the process optimization over the years. In August 2018, an IXT prototype with 21 layers was measured at the PANTER X-ray test facility, indicating an HPD of 111″ and an effective area of 39 cm2 at 1.49 keV. In September 2019, the latest prototype with 3 layers reached to an HPD of 58″ at 1.49 keV.
The cold shaping of thin glass foils is a cost-effective method for x-ray optical units realization. This technique allows the manufacturing of cheap and lightweight optics with good angular resolution. The flat glass foils are shaped on curved integration molds and glued ribs freeze their shapes in the assembly. The simplest strategy for the coating deposition would be with the coating process operated on flats, before the bending and the integration steps. This approach can be considered only if the coating on the glass foils does not degrade with the integration process. Given that super-mirror coating is widely used in hard X-ray telescopes, this part of the process need to be carefully evaluated. INAF-OAB collaborates with Tongji University to verify the feasibility of this approach. In this paper, we present the experimental results achieved on glass samples, integrated with the Cold Slumping technique by means of integration mold with different radius of curvature and material. Two flat samples, coated with W/Si multilayer, are characterized before and after the integration. The measurement campaign includes micro-roughness on different spatial frequency and grazing incidence reflection measurements to return the microstructure of the multilayer.
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