CONSTRUCTION OF SHORT PERIOD APPLE II TYPE UNDULATORS AT SOLEIL

We present here the conception, construction and magnetic measurements of APPLE II type undulators of 44 and 36 mm period at SOLEIL. Such short period undulators are difficult to design and construct because of the reduced dimensions of the magnets, leading to small support structures which are more easily bent by the magnetic forces. The design of the support structures consists in individual aluminium holders grouped in assemblies of three or five magnets called modules and fixed on the girders using dovetails. Special extremity modules are designed to reduce field integrals of the undulator. The magnets are independently measured using Helmoltz coils, sorted and assembled in modules. Then the modules are measured using Hall probes and bodyless coil, and sorted to assemble the undulator. After assembling, a shimming process is performed to correct radiation phase errors and field integrated multipoles, and a final correction of the integrated effects is made by little extremity magnets called "Magic Fingers". For each step of sorting, we use the home-made IDBuilder software, based on genetic algorithms. Short period undulators are of interest for the 4th generation sources ARC-EN-CIEL project, which considers APPLE II with a 30 mm period