Advanced Technology Solar Telescope: a progress report

The four-meter Advanced Technology Solar Telescope (ATST) will be the most powerful solar telescope and the world's leading resource for studying solar magnetism that controls the solar wind, flares, coronal mass ejections and variability in the Sun's output. Development of a four-meter solar telescope presents many technical challenges, which include: thermal control of optics and telescope structure; contamination control of the primary mirror to achieve low scattered light levels for coronal observations; control of instrumental polarization to allow accurate and precise polarimetric observations of solar magnetic fields; and high-order solar adaptive optics that uses solar granulation as the wavefront sensing target in order to achieve diffraction limited imaging and spectroscopy. We give a status report of the ATST project focusing on the substantial progress that has been made with the design of the ATST. We summarize the design of the major subsystems, including the enclosure, the primary and secondary mirror assemblies, the coude and Nasmyth focal stations, adaptive optics and instrumentation. The site selection has been successfully concluded and we discuss areas where the site selection impacts the design.