The Permanent Magnet Hybrid Undulator U27

To produce coherent radiation in the mid-infrared region we installed the undulator U27. It consists of two sections with a length of 0.98 m each and a short drift region in between. Each section consists of Nu = 34 magnetic periods with a length of λu = 27.3 mm. The magnetic structures for both units were test modules for the TTF-Facility at DESY, Hamburg [1,2]. The girders have been constructed and delivered by DANFYSIK.

Fig. 1 shows the completely mounted undulator U27. To match the phases of the two sections the distance between them can be varied over a wide range by means of a stepping motor. The girders are designed such that the undulator gap of both sections can independently be varied. For special applications they can also individually be tapered, what should result in an increase of the extraction efficiency [3,4].


The main parameters of the undulator U27

Period length

2.73 cm

Number of periods


Maximum undulator parameter



The variable undulator gap

Magnetic field amplitude BU on axis and undulator parameter Krms as a function of the undulator gap g.

Details of the magnetic undulator field can be found here.


[1] B. Faatz, J. Pflüger and Y.M. Nikitina, Nucl. Instr. Meth. A 375 (1996) 618

[2] Y.M. Nikitina and J. Pflüger, DESY Report TESLA-FEL 96-03

[3] E.L. Saldin, E.A. Schneidmiller, M.V. Yurkov, Phys. Lett. A 185 (1994) 469

[4] D. Jaroszynski et al., Phys. Rev. Lett. 72 (1994)2387

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