In-vacuum APPLE II undulator with force compensation

In-air APPLE II undulators are the favorite sources for variably polarized synchrotron radiation in many laboratories. The technology for short period in-vacuum and cryogenic planar devices was not transferred to APPLE II devices yet, because several design challenges must be solved. Among them are a precise gap and phase drive on the micrometer level in the presence of strong tree-dimensional forces. Various methods of vertical force compensation for planar devices have been proposed and realized. We present a new dedicated force compensation scheme, which handles the three-dimensional APPLE II forces and permits a conventional in-air motion control. Within an R&D project at HZB all key components for an in-vacuum APPLE II are developed. Utilizing the results of the R&D study, HZB will start the fabrication of a full scale APPLE II end of 2018.