Magnetic Field Integral Requirements and Measurement of 20-mm Period Hybrid Undulator

In this paper, we study the magnetic field measurement of U20 undulator. The U20 is a prototype hybrid structure of NdFeB magnets and cobalt steel poles. The hybrid device is made up of 25 periods with a period length of 20-mm each and is designed to deliver magnetic flux density (in rms) from 2400G to 500G in the 10-20-mm gap range. The validity of the theoretical and analytical formulas is analyzed through the measured field and phase integrals.