LARGE RARE-EARTH MAGNETS FOR A FOCUSING WIGGLER

An important requirement for wigglers and undulators is that the magne ts must be monolithic. Also, besides the usual high magnetic propertie s, the maximum dipole inclination angle from the mechanical axis of th e magnets must be less than 2-degrees. We developed three types of lar ge monolithic rare earth magnets. Each magnet weighs over 2 kg. We fou nd that the inclination angle of these magnets is very small, within 1 -degrees. We could cooperate with JAERI in manufacturing focusing wigg lers using pieces of such large magnets for a millimeter FEL experimen t. The pole pieces are permanent magnets with a curved surface. The wi ggler period is 5 cm and the total pitch number is 30. The power and t he spectrum of the FEL superradiation were observed in this experiment . Therefore we could make sure that such a pole piece is effective.