Chinese Giant Solar Telescope (CGST) is the next generation infrared and optical solar telescope of China, which is proposed and pushed by the solar astronomy community of China and listed into the National Plans of Major Science and Technology Infrastructures. CGST is currently proposed to be an 8 meter Ring Solar Telescope (RST) with width of 1 meter, the hollow and symmetric structure of such an annular aperture facilitates the thermal control and high precision magnetic field measurement for a solar telescope. Adaptive optics (AO) is an indispensable tool of RST to obtain diffraction limited observations. How to realize AO involved wavefront sensing and correcting, and the degree of compensating in a narrow annular aperture is the primary problem of AO implementation of RST. Wavefront reconstruction involved problems of RST are first investigated and discussed in this paper using end to end simulation based on Shack-Hartmann wavefront sensing (SHWFS). The simulation results show that performance of zonal reconstruction with measurement noise no more than 0.05 arc sec can meets the requirement of RST for diffraction-limited imaging at wavelength of 1μm, which satisfies most science cases of RST in near infrared waveband.
The Chinese Giant Solar Telescope (CGST) is the next generation solar telescope of China with diameter of 8 meter. The unique feature of CGST is that its primary is a ring, which facilitates the polarization detection and thermal control. In its present design and development phase, two primary mirror patterns are considered. For one thing, the primary mirror is expected to construct with mosaic mirror with 24 trapezoidal (or petal) segments, for another thing, a monolithic mirror is also a candidate for its primary mirror. Both of them depend on active control technique to maintain the optical quality of the ring mirror. As a solar telescope, the working conditions of the CGST are quite different from those of the stellar telescopes. To avoid the image deterioration due to the mirror seeing and dome seeing, especially in the case of the concentration of flux in a solar telescope, large aperture solar projects prefer to adopt open telescopes and open domes. In this circumstance, higher wind loads act on the primary mirror directly, which will cause position errors and figure errors of the primary with matters worse than those of the current 10-meter stellar telescopes with dome protect. Therefore, it gives new challenges to the active control capability, telescope structure design, and wind shielding design. In this paper, the study progress of active control of CGST for its mosaic and monolithic mirror are presented, and the wind effects on such two primary mirrors are also investigated.
The Chinese Giant Solar Telescope (CGST) is the China’s next generation solar telescope with an aperture of 8 m in
diameter. The unique feature of the CGST is its ring primary, which facilitates the polarization detection and thermal
control. The CGST is now in its design and development phase. A mosaic mirror with 24 trapezoidal segments is a
candidate for its primary mirror, which highly relies on a segment active control system to achieve competitive optical
quality of a monolithic mirror. The CGST is designed to operate in open-air observation mode, its active control system
thus faces new challenges. As the CGST has an aperture larger than that of current solar telescopes, and as the magnitude
of wind load in open air is greater than that of a stellar telescope with a similar aperture yet under the protection of a
dome and/or an enclosure. Furthermore, as a mosaic mirror, high precision real-time tip sensing is required to serve the
feedback of its control system. The accuracy depends on integration time (or working bandwidth) when an optical
metrology is adopted, which should match the bandwidth of the segment control system. In this paper, a dynamic
analysis of the segment control system of the CGST is presented. We demonstrate how the dynamic interaction between
the segment control system and the telescope structure impacts the telescope’s optical performance under wind
disturbances. The dynamic analysis helps to understand the bandwidth limit for the segment control system, and further
to clarify technical requirements for tip sensing implementation, telescope structure design and wind shielding design.
Ring aperture telescope is a new kind of telescope, it has complete U-V coverage and the limiting resolution equivalent to that of a full aperture telescope with the same diameter. There are two ring telescope proposals in China. One is 30m Ring Interferometric Telescope (RIT), its primary mirror is expected to be composed by 90 segments; another is 8m Chinese Giant Solar Telescope (CGST), its primary mirror is expected to be composed by 24 segments if segmented mirror scheme is adopted . In this paper, an overview of ring telescope and modeling for it are introduced. The main difference and characteristic in active control strategy and adaptive optics implementation between ring segmented telescope and full segmented telescope are pointed out. Detailed analysis about these two aspects are presented. The results of simulation and analysis show that the current strategies on active control and adaptive optics could meet the demand of most science cases not only in infrared waveband but also in near infrared even in visible waveband.
As one of the preliminary research projects of Chinese ELT, 30m RIT--Ring Interferometric Telescope are being
simulated and tentatively designed by Yunnan Astronomical Observatory, CAS. The simulations of 30m RIT are mainly
included as follows: PSF transform and the image quality at limited photons mode, active control mode of the primary
ring mirror, the phasing mode of 30m segmented ring mirror, the turbulent atmosphere and adaptive optics etc. This
paper also introduces some tentative design results of 30m RIT, such as the optical design, the conceptual design of the
enclosure. The astronomical experiments at seeing limited case and diffraction limited case are introduced in this paper
too. A ring aperture mask was put on the entrance pupil of a one meter telescope, real astronomical objects were
observed by this "ring telescope" and reconstructed by high resolution imaging techniques such as speckle masking,
iterative shift and add methods. The diffraction imaging ability and the full u-v coverage property of a ring aperture were
proved by these astronomical experiments.