Paper 
Title 
Page 
MOP037 
Modeling and Design of the Variable Period and Pole Number Undulator for the Second Stage of the Novosibirsk FEL 
96 

 I. Davidyuk
NSU, Novosibirsk, Russia
 O.A. Shevchenko, V.G. Tcheskidov, N. Vinokurov
BINP SB RAS, Novosibirsk, Russia
 N. Vinokurov
KAERI, Daejon, Republic of Korea



The concept of the permanent magnet variable period undulator (VPU) has been proposed just several years ago and there are few examples of its implementation yet. The VPUs have several advantages compared to conventional undulators. One of them is wider radiation wavelength tunability range and another one is an option to increase the number of poles for shorter periods. Both these advantages will be realized in VPU which is being developed now at Budker INP. In this paper we present the 2D and 3D magnetic field simulation results and discuss the design features of this VPU.



MOP038 
Characterization of the Undulator Magnetic Field Quality by the Angle Averaged Radiation Spectrum 
100 

 O.A. Shevchenko, N. Vinokurov
BINP SB RAS, Novosibirsk, Russia
 N. Vinokurov
KAERI, Daejon, Republic of Korea



The real undulator magnetic field always contains errors which influence undulator performance. The effect of these errors is usually characterized by broadening of the spontaneous emission spectrum at zero angle and corresponding reduction of the spectral intensity. This approach works very well for the phase errors while it does not take into account transversal trajectory displacements. The integrated over the angles radiation spectrum contains more complete information about the undulator field quality but its calculation requires more effort. Therefore the spectral density of emitted radiation (the total number of emitted photons with given energy) can be considered as a figure of merit for an undulator. In this paper we derive analytical formula for this spectrum suitable for doing efficient numerical calculations and demonstrate its application to the case of some typical undulator field errors.


