N. Balal, V.L. Bratman, and E. Magori,
   "Efficient Electron Sources of Coherent Spontaneous Radiation with Combined Helical and Uniform Magnetic Fields",
   in Proc. 37th International Free Electron Laser Conference, Daejeon, Republic of Korea, August 2015, paper MOP009, pp. 43-45,
    ISBN: 978-3-95450-134-2,
    doi:10.18429/JACoW-FEL2015-MOP009,
    http://accelconf.web.cern.ch/AccelConf/FEL2015/papers/mop009.pdf, 2015.