The 21cm radiation of the neutral hydrogen can be used to probe the Universe from the nearby Galaxy, to the large scale structures, the epoch of reionization and cosmic dawn, and even the cosmic dark age. It provides a very promising observational tool for cosmology and astrophysics, yet its observation in the distant Universe is very challenging, and many 21cm experiments and surveys are being carried out or planned. There have been  progress in both theory and observational technique of 21cm cosmology. 

The Tianlai experiment is a Chinese effort to explore the techniques of 21cm intensity mapping observation, and use it to probe the dark energy by using the baryon acoustic oscillation (BAO) features in the large scale structure. Located in Hongliuxia, Balikun county, Xinjiang, the pathfinder Tianlai experiment include a cylinder array and a dish array. The construction of the pathfinder arrays have been completed and currently the arrays are being tested. The first light image of the Tianlai cylinder array was obtained in 2016, and the first sample data have been delivered to collaboration members for analysis. We anticipate that Tianlai would begin its prelimnary survey operation later this year. It is time to discuss various issues of the Tianlai data reduction and analysis, its role in the broader context of 21cm research and radio astronomy, testing new techniques and training people for the SKA, as well as the plan for its future development.

Since 2011, annual 21cm cosmology workshop and collaboration meetings have been organized by the Tianlai Collaboration. This year, we plan to hold the meeting in Urumui, the Capital of Xinjiang, right after the annual meeting of the Chinese Astronomical Society. All Tianlai collaboration members and interested researchers are welcomed to join us. 

A Tianlai pipeline hackthon and a visit to the array site will be arranged during the meeting. The site visit will take two full days (day one: go to Balikun county and stay there, day two: visit site and return to Urumuqi for departure). Only a limited number of slots will be available for the site visit, and would be assigned based on first come first serve basis.