M. Hamberg,
   "The Highly Adjustable Magnet Undulator",
   in Proc. 37th International Free Electron Laser Conference, Daejeon, Republic of Korea, August 2015, paper TUP057, pp. 499-500,
    ISBN: 978-3-95450-134-2,
    doi:10.18429/JACoW-FEL2015-TUP057,
    http://accelconf.web.cern.ch/AccelConf/FEL2015/papers/tup057.pdf, 2015.