• Y. Tsunawaki
  OSU, Daito, Osaka
• M. Asakawa, N. Ohigashi
  Kansai University, Osaka
• K. Imasaki
  ILT, Suita, Osaka

We have been constructed a solenoid-induced helical wiggler for a compact free electron maser operated in a usual small laboratory which does not have electric source capacity available enough. It consists of two staggered-iron arrays inserted perpendicularly to each other in a solenoid electromagnet. In order to lead/extract an electron beam into/from the wiggler, adiabatic transition (AT) field is necessary at both ends of the wiggler. In this work the AT field was produced by setting staggered-nickel plates with different thickness in the five periods. The thickness of each nickel plate was decided by the field analysis using the MAGTZ computational code based on a magnetic moment method. Exact thickness was, however, found by the precise measurement of the field distribution with the greatest circumspection to obtain a homogeneous increment of the AT field. The change of AT field distribution was studied by referring to an equivalent electric circuit of the wiggler.

• D. Li, K. Imasaki
  ILT, Suita, Osaka
• G.S. Park, Y. Yang
  SNU, Seoul

A renewed interest of Smith-Purcell system has been raised since J. Urata et.al observed a possible exponential gain in their experiment using electron microscope beam. Several theories were presented to calculate the exponential gain. We analyzed this problem in the way of particle in cell simulation, which provides many details in understanding the physics of the radiation from a grating.