Two APPLE II type twin undulators are installed at BESSY II. They can eithe
r be operated in a chicane mode providing variable polarization at high swi
tching rates or in a combined mode using a modulator for phase adaption. St
udies on magnet block inhomogeneities have started to further improve the f
ield quality and to reduce the effort on shimming. (C) 2001 Elsevier Scienc
e B.V. All rights reserved.