DANFYSIK Part of Danish Technological Institute

2 m long Apple-II Elliptical Polarizing Undulator for the Australian Synchrotron, Melbourne, Australia

Project start 2006. Project completion 2007.

Danfysik has designed and built an Apple-II undulator for the Australian Synchrotron Project including the control system. The magnetic design of both central part of the device and end sections are made using the computer code RADIA. The minimum undulator gap is 16 mm and the maximum gap is 100 mm. With 25 full periods of 75 mm and two end sections the total length of the device is 2.15 meter.

The carriage is of the c-frame type, i.e. it is open at one side. This design is based on the ESRF type of Apple-II but increased in length and modified to allow movement of all four magnetic arrays. The device is made to allow a gap taper of up to 2 mm. The magnetic forces have been evaluated versus gap and phase. Based on these results the carriage is designed such that it can handle the magnetic forces with minimum impact on the device performance. The end section design is optimized to minimize the field integrals at all gaps and phases. A tune shift correction technique was used to minimize the interactions with the stored electron beam.

Parameters for the Apple-II undulator
                                                                                                                  Specifications                  As-built

Undulator type                                                                                        PPM Apple-II                         PPM Apple-II
Gap range                                                                                              16 - 100 mm                         16 - 100 mm
Length of magnet assemblies                                                            < 2.24 m                               2.15 m
Absolute Rotary encoder resolution on gap and phase:               1 mm                                      ≤ 1 mm
Number of movable sub-girders                                                        4                                              4
Gap taper                                                                                                2 mm                                       < 2 mm
Period length                                                                                          75 mm                                    75 mm
Number of full size periods                                                                 25                                             25
Magnet material properties:
Permanent magnet type                                                                      Sm₂Co₁₇                                Sm₂Co₁₇
Minimum remanence, B_r                                                                                                                       1.05 T
Minimum intrinsic coercivity, H_cJ                                                                                                           1500 kA/m
Magnet flux density at minimum gap:
Peak vertical flux density                                                                        ³ 0.68 T                                 ³ 0.72 T
Peak field at circular polarization (RMS)                                                                                            ³ 0.65 T
Peak horizontal flux density                                                                                                                  ³ 0.58 T
Phase error (RMS) at all phases and gaps
Horizontal polarization mode                                                              5                                                  2.3
Planar 45º inclined mode                                                                    5                                                  3.0
Vertical polarization mode                                                                   5                                                  2.6   

Field integrals on-axis (x=0) at all gaps and phases:
Normal and skew first integrals                                                        £ 100×10^-6 Tm                        £ 38×10^-6 Tm  
Normal and skew second integrals                                                 £ 10×10^-4 Tm²                         £ 0.8×10^-4 Tm²

Limits on integrated multipoles for |x| £ 14 mm at all gaps and phases:
Quadrupole                                                                                           £ 50×10^-4 T                            £ 30×10^-4 T
Sextupole                                                                                               £ 0.5 T/m                                £ 0.32 T/m
Octupole                                                                                                 £ 100 T/m²                            £ 50 T/m²

Link
Australian Synchrotron