Mini environment control for the elliptical polarization undulator

The elliptical polarization undulator (EPU) has been constructed at SRRC for creating a high quality and high photon flux. The EPU consists of two fixed diagonal magnet arrays and the other free diagonal arrays to create the right/left circular polarization. The magnetic field uniformity of the magnet blocks will influence on the storage beam orbit, the beam lifetime, light source quality and brightness and it is very important to shim the magnet blocks for magnetic field control. The environmental temperature variation in the storage ring will deform the EPU structure and change the clearance between the diagonal magnet arrays. The deformation will influence on EPU performance and impinge on the beam stability. The mini environment design concept will be employed to eliminate the EPU surrounding temperature fluctuation. From the mini environment air conditioning design, the temperature variation of the four EPU magnet arrays during 4 days operation can be limited to less than 0.1 deg C. The temperature distribution fluctuation can be reduced to 0.22 deg C.