Delivery of a Cryo-cooled Undulator to the Diamond Light Source

Undulator before shipment from Danfysik factory

The cryo-cooled undulator for Diamond Light Source has been successfully tested at Danfysik. The undulator was tested both at room temperature and at temperatures between 130 K and 157 K. At room temperature, we measured a phase error of 2.3 degrees.  This increased to around 6 degrees at cryogenic temperatures.  By shimming the center columns, we were able to reduce the phase error to 3.5 degrees at 157 K.   The Hall scans at 5 mm gap are shown in Figure 1, at room temperature and at 157 K.  As a result of the cooling, an angular kick is seen at both ends, which is easily removed by use of the installed short vertical correction coils.  

We observed an increase in the effective field of around 7.1 % at 5 mm gap.

Figure 1: Hall scans at room temperature and cryogenic temperature. The room temperature result has been offset 3 microns for clarity. At cryogenic temperatures, effects of end coils have been simulated.

Main parameters for the undulator:

Gap:                                                                        4 - 30mm
Length:                                                                   2080mm
Period length:                                                       17.7mm
Effective K value @ 5mm gap:                           1.7
Maximum phase error:                                        3.5 degrees