Zheng Lou

Conceptual design studies of the 5 m terahertz antenna for Dome A, Antarctica

As the highest, coldest and driest place in Antarctica, Dome A provides exceptionally good observing conditions for ground-based observations over terahertz wavebands. The 5m Dome A Terahertz Explorer (DATE5) has been proposed to explore new terahertz windows, primarily over wavelengths between 350 and 200 mu m. DATE5 will be an open-air, fully-steerable telescope that can function by unmanned operation with remote control. The telescope will be able to endure the harsh polar environment, including high altitude, very low temperature and very low air pressure. The unique specifications, including high accuracies for surface shape and pointing and fully automatic year-around remote operation, along with a stringent limit on the periods of on-site assembly, testing and maintenance, bring a number of challenges to the design, construction, assembly and operation of this telescope. This paper introduces general concepts related to the design of the DATE5 antenna. Beginning from an overview of the environmental and operational limitations, the design specifications and requirements of the DATE5 antenna are listed. From these, major aspects on the conceptual design studies, including the antenna optics, the backup structure, the panels, the subreflector, the mounting and the antenna base structure, are explained. Some critical issues of performance are justified through analyses that use computational fluid dynamics, thermal analysis and de-icing studies, and the proposed approaches for test operation and on-site assembly. Based on these studies, we conclude that the specifications of the DATE5 antenna can generally be met by using enhanced technological approaches.

Hybrid optimization methodology of variable densities mesh model for the axial supporting design of wide-field survey telescope

Abstract. The optimization of a primary mirror support system is one of the most critical problems in the design of large telescopes. Here, we propose a hybrid optimization methodology of variable densities mesh model (HOMVDMM) for the axial supporting design, which has three key steps: (1) creating a variable densities mesh model, which will partition the mirror into several sparse mesh areas and several dense mesh areas; (2) global optimization based on the zero-order optimization method for the support of primary mirror with a large tolerance; (3) based on the optimization results of the second step, further optimization with first-order optimization method in dense mesh areas by a small tolerance. HOMVDMM exploits the complementary merits of both the zero- and first-order optimizations, with the former in global scale and the latter in small scale. As an application, the axial support of the primary mirror of the 2.5-m wide-field survey telescope (WFST) is optimized by HOMVDMM. These three designs are obtained via a comparative study of different supporting points including 27 supporting points, 39 supporting points, and 54 supporting points. Their residual half-path length errors are 28.78, 9.32, and 5.29 nm. The latter two designs both meet the specification of WFST. In each of the three designs, a global optimization value with high accuracy will be obtained in an hour on an ordinary PC. As the results suggest, the overall performance of HOMVDMM is superior to the first-order optimization method as well as the zero-order optimization method.

Study on the optics of the 5 meter Dome A Terahertz Explorer (DATE5) for Antarctica

The 5 m Dome A Terahertz Explorer (DATE5) is a proposed terahertz telescope to be deployed in Dome A, Antarctica, to exploit one of the best observing conditions at terahertz bands on the earth. This paper presents a study on the optics of the proposed DATE5 antenna. Two configurations, namely the Cassegrain and the Coudé configurations, are proposed and their respective optical performances, such as field of view, beam and aperture efficiency, and chopping performance, are simulated and compared. Some engineering considerations, such as system reliability and environmental adaptability are also discussed.

Mode analysis of the 5 meter Terahertz antenna for Dome A, Antarctica

The terahertz windows of the 5 meter Dome A Terahertz Explorer (DATE5) are primarily over the wavelengths between 350 and 200 μm. For studying the performance of the DATE5, based on a finite element model of the whole telescope assembly, the Eigen frequencies and Eigen modes of the DATE5 structure at different elevation angles are studied. The obtained results show the ranges of first 3 Eigen frequencies are in [5.73Hz, 6.22Hz], [6.84Hz, 7.60Hz], and [10.20 Hz, 13.30Hz] respectively, and show dependence with elevation angles. All of the Eigen frequencies are larger than 5 Hz, which meet the performance requirements for this telescope.

THz Vector Field Measurement Comparison Between On-the-Fly and Step Scan Method

A fast terahertz vector field measurement system based on the on-the-fly (OTF) scan method is investigated. Compared with the step scan method, which samples at certain step, the OTF scan obtains the data with the scanner moving continuously, thus improving the measurement efficiency to some extent. The phase stability of the system is fully studied. Demonstration at approximately 500 GHz is compared with the result by the step scan method, showing that the OTF method can improve the measurement speed by a factor of 7 while the data accuracy is almost the same. Measurements at different scanning speeds and with different probes are also compared to understand their effects.

Gravity loading effect analysis of the 5 meter Terahertz antenna for Dome A, Antarctica

The terahertz windows of 5 meter Dome A Terahertz Explorer (DATE5) are primarily over the wavelengths between 350 and 200 µm. For studying the performance of the DATE5, based on a finite element model of the whole telescope assembly, the deformations of the telescope under gravity load at different pointing are calculated. The obtained results show the ranges of surface RMS errors is in [2.59 µm, 4.11µm]. All of the surface RMS errors are smaller than 5.00µm, which meet the performance requirements for the telescope. Besides, the results show that surface RMS errors due to gravity loading increase as the elevation angle increase. There is a nonlinear dependence of the reflector surface RMS error over the elevation angles. It can be fitted to a sine function.

Research on high precision antenna for DATE5

Dome A 5m Terahertz Explorer (DATE5) is a proposed telescope to be deployed at Dome A, Antarctica to explore the excellent terahertz observation condition unique to the site. The telescope needs to realize and maintain an overall reflector surface accuracy of 10 microns rms and a blind pointing accuracy of 2 arcseconds under the extreme site conditions and unmanned operating mode. Two candidate antenna designs have been proposed, one of which is based on an all-CFRP reflector and slant-axis mount and the other based on aluminum panels on carbon fiber backup structures and altazimuth mount. Both aluminum and CFRP sandwich prototype panels have been fabricated and tested in a climate chamber. The aluminum panel shows desired surface accuracy under both room temperature and low temperatures down to −60°C. CFRP panels with different sandwich structures are fabricated and tested. All of them achieve a surface accuracy around 5 microns rms at room temperature, but their surface accuracy differs significantly when they are cooled, indicating the importance of panel structural design. The aluminum and CFRP panels are equipped with different type of anti-icing heaters, and their performances have been verified respectively. Finally, demonstration experiments on near-field holography are performed and a repeatibility accuracy of 3 microns rms is achieved.

An 8×8 CPW MKIDs developed for terahertz superconducting imaging array

China is planning to construct a 5-meter THz telescope named DATE5 at Dome A, Antarctica. This paper reports on the development of an 8×8 CPW microwave kinetic detectors (MKIDs) for the terahertz superconducting imaging array (TeSIA), which is an instrument proposed for the DATE5. The 8×8 CPW MKIDs, operating at 0.35THz, make use of TiN superconducting film of Tc approximately equal to 4.3K. The resonance frequencies of the MKIDs span the 4-5.575GHz band with an interval of 25MHz. The design, fabrication and characterization of the 8×8 CPW MKIDs are presented.

Conceptual Design of the Aluminum Reflector Antenna for DATE5

DATE5, a 5 m telescope for terahertz exploration, was proposed for acquiring observations at Dome A, Antarctica. In order to observe the terahertz spectrum, it is necessary to maintain high surface accuracy in the the antenna when it is exposed to Antarctic weather conditions. Structural analysis shows that both machined aluminum and carbon fiber reinforced plastic (CFRP) panels can meet surface accuracy requirements. In this paper, one design concept based on aluminum panels is introduced. This includes panel layout, details on panel support, design of a CFRP backup structure, and detailed finite element analysis. Modal, gravity and thermal analysis are all performed and surface deformations of the main reflector are evaluated for all load cases. At the end of the paper, the manufacture of a prototype panel is also described. Based on these results, we found that using smaller aluminum reflector panels has the potential to meet the surface requirements in the harsh Dome A environment.