The European Solar Telescope (EST) is a 4-m class-solar telescope that will become part of the next generation of groundbased facilities. Located at the “Observatorio del Roque de los Muchachos” in La Palma (Spain), it will be aimed to study the magnetic connectivity of the solar atmosphere with high spatial and temporal resolution. The EST optical design has been optimized during the preliminary design phase to maximize throughput, balance the instrumental polarization and to reduce the image rotation due to the change in orientation during operation. The optical system consists of a 4.2m active primary mirror located above the elevation axis to ensure natural air flushing and minimize local seeing degradation and a secondary mirror assembled as an Adaptive Secondary Mirror (ASM). Both arranged in an on-axis Gregorian configuration to deliver an aplanatic secondary focal plane. These are followed by four fold mirrors, which will be upgraded to deformable mirrors and are conjugated to different layers of the atmosphere. These, together with the ASM, M7 and two wavefront sensors, will make up the Multi-Conjugate Adaptive Optics system. Finally, a dioptric system, housed in a vacuum vessel, transfers the light to the science focus, which will be delivered to the Scientific Instrumentation by a dedicated distribution system. EST ultimately provides a diffraction-limited telecentric F/50 science focal plane covering a FOV of 90×90 arcsec2 over a wavelength range from 380nm to 2300nm. Along the contribution, details about the preliminary optical design of EST and its subassemblies will be presented. The expected performance is also discussed.
In Solar Adaptive Optics (AO), it is common to work with a wide Field of View (FoV), which necessitates special control techniques to enhance system performance. Ground-Layer Adaptive Optics (GLAO) configurations lack sufficient degrees of freedom to correct altitude layers individually, resulting in an averaged correction across the entire FoV. In this work, we introduce alternative, intelligent control schemes to explore options for overcoming current limitations in GLAO.
The European Solar Telescope (EST) is a 4.2-m telescope which has been redesigned with a fully integrated Multi-Conjugate Adaptive Optics (MCAO) into the optical path right after the EST primary mirror. The current baseline configuration considers four altitude Deformable Mirrors (DM) conjugated to 5, 9, 12 and 20 km above the telescope entrance pupil and an Adaptive Secondary Mirror (ASM) conjugated to the entrance pupil. The wavefront sensing will be performed by a set of correlation-based Shack Hartmann wavefront sensors (WFS) combining an on-axis High-Order WFS (HOWFS) to be used either in Single Conjugate AO (SCAO) to drive the ASM as well as operating simultaneously with a Multi-Directional WFS (MDWFS) to drive the MCAO. Beyond the current baseline configuration, different alternatives are currently being investigated both in the wavefront sensing strategy by evolving from a HOWFS+MDWFS into possibly a single High Order Multi Directional WFS (HOMDWFS) and/or wavefront sensors operating at different observing bands.
The European Solar Telescope (EST) is a 4.2-metre telescope that will be equipped with a multi-conjugate adaptive optics (MCAO) system to provide a high spatial resolution over a circular field of view with 60” diameter. The EST-MCAO testbed is a downscaled demonstrator of solar MCAO with similar requirements to those defined for EST. It has been designed and developed to identify and better understand the capabilities of this system. Before MCAO implementation, different AO configurations must be first evaluated in the testbed. Single conjugate adaptive optics for point-like sources has been identified as the first step towards MCAO for the EST. This configuration is based on the use of a deformable mirror with 820 actuators and a Shack-Hartmann wavefront sensor with 33x33 subapertures. The main objective of this paper is to present the results obtained in the EST-MCAO testbed when testing different phase reconstruction algorithms and closed-loop schemes to deal with SCAO for point-like sources. Center of gravity technique was proposed for local slope computation when using point-like sources. Both zonal and modal approaches, including SVD and their regularized least-squares versions, were evaluated and tested for the reconstruction. A closed-loop strategy based on a proportional-integral controller was initially proposed. The benefits of pseudo open-loop control were also evaluated. The performance of the algorithms was tested considering different seeing conditions. Finally, a comparison based on RMS wavefront error and Strehl Ratio was conducted.
Once the design phase of the Multi-Conjugated Adaptive Optics (MCAO) testbed for the European Solar Telescope (EST) is completed, the system has been assembled and integrated at the Instituto de Astrofísica de Canarias (IAC). The aim of this highly configurable optical testbed is to study different solar adaptive optics solutions, including Single Conjugated Adaptive Optics (SCAO), Ground Layer Adaptive Optics (GLAO), and MCAO. The testbed will be used to evaluate the performance of different wavefront sensing and correction strategies. It consists of different subsystems that are being integrated with high precision by using optomechanical elements mostly developed at IAC. The testbed emulates a 4-m telescope with a Field of View (FoV) of 70 arcseconds. It currently operates as a SCAO configuration consisting of: an illumination system with point-like and extended source capability coupled with a configurable turbulence simulator based on Phase Screens (PS); a pupil-conjugated Deformable Mirror (DM) with 820 actuators; a high order Shack-Hartmann Wavefront Sensor (SH-WFS) with 33 subapertures across the pupil, which measures on-axis aberrations with a FoV of 10 arcseconds; and the science detector. The next steps include the integration of the elements that will provide GLAO and MCAO capabilities, such as two SH-WFSs with a FoV of 70 arcseconds, and two DMs conjugated to different atmospheric layers. This contribution describes the optomechanical components designed and the alignment procedure carried out to set up each subsystem and configuration to be studied.
One of the main goals of the European Solar Telescope (EST), a 4.2-m telescope, is to clarify the roots of the magnetic processes taking place in the solar atmosphere. This goal has a top-level requirement: perform simultaneous spectropolarimetric measurements in multiple spectral lines. For this purpose, EST will be equipped with a set of instruments working simultaneously in diverse spectral ranges. In this regard, we are designing a Coudé Light Distribution (CLD) responsible for delivering the incoming solar radiation to each instrument. The CLD is formed by a series of optical elements like dichroic and intensity beam splitters, flat mirrors, and optical compensators that will be interchangeable to offer the solar community maximum flexibility for performing observations. In developing the CLD, we are paying great attention to controlling aberration effects generated by the different elements that constitute the light distribution system. Also, we are defining the CLD to reach a balance between throughput, image quality, and a compact distribution of the instruments in the Coudé room. Our aim is to describe in this contribution the current design of the CLD. The present design constitutes the basis of the CLD, with enough flexibility to improve it in the future, if indeed, and adapt it to the evolution of other sub-systems like the instruments, the adaptive optics, or the telescope structure to guarantee that it fulfils the science requirements.
The European Solar Telescope (EST) aims to become the most ambitious ground-based solar telescope in Europe. Its roots lie in the knowledge and expertise gained from building and running previous infrastructures like, among others, the Vacuum Tower Telescope, Swedish Solar Telescope, or the GREGOR telescope. They are installed in the Canary Islands observatories, the selected EST site. Furthermore, the telescope has a novel optical design, including an adaptive secondary mirror (ASM) that allows reducing the number of optical surfaces to 6 mirrors (plus two lenses) before the instruments’ focal plane. The latter, combined with a configuration of mirrors that are located orthogonally oriented to compensate for the instrumental polarisation induced by each surface, makes EST a reference telescope in terms of throughput and polarimetric accuracy. In its main core design, EST also includes a Multi-Conjugated Adaptive Optics (MCAO) system where the ASM compensates for the ground layer turbulence. The rest of the mirrors on the optical train correct for the atmospheric turbulence at different layers of the atmosphere. The MCAO guarantees that the large theoretical spatial resolution of the 4-metre EST primary mirror is achieved over a circular FOV of 60 arcsec. Those main elements, combined with a set of instruments with capabilities for spectropolarimetry, make EST the next frontier in solar ground-based astronomy. In this contribution, we will cover the main properties and status of all the mentioned sub-systems and the following steps that will lead to the construction phase.
The European Solar Telescope (EST) is a 4.2-m solar telescope, based on an aplanatic Gregorian configuration with an alt-azimuthal mount. This contribution presents the status of EST and describes the baseline for the preliminary design of the Telescope Structure (Telescope Mount), Enclosure and Pier. It also introduces the systems engineering, model and tools. In addition, it explains the rationale of the main specifications. The optical design has undergone major changes since the conceptual design. The M2 Assembly has become an Adaptive Secondary Mirror, the f-number has been changed and the number of optical surfaces has been reduced to 6 mirrors and 2 lens barrels. Therefore, part of the system has been updated and new assemblies have appeared: The Transfer Optics and Calibration Assembly (TOCA) and the Pier Optical Path (POP). Some requirements make this telescope unique: the primary mirror is above the elevation axis, the multi-conjugated adaptive optics is integrated in the telescope, the telescope instrumental polarization is minimized and the telescope will observe in open enclosure configuration to improve the natural air flushing. The drawback of the open configuration is that the telescope structure, M1 and M2 will be exposed to the wind load and the thermal load by radiation, forcing the development of a stiffer Telescope Structure, a specific thermal control to achieve the pointing and tracking performances and a low local seeing degradation. The Preliminary Design phase of the Telescope Structure, Enclosure and Pier have been developed by IDOM throughout 2021 and 2022, following technical requirements by the EST Project Office.
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