Physics design of undulator in high average power free electronic laser terahertz source

The physics design of the undulator in high average power free electronic laser terahertz source is discussed. Hybrid Halbach structure is selected, after the period length, period quantity and peak magnetic field strength, etc. are fixed. The dimension of permanent magnet block is 8 cm1.3 cm6 cm, and the dimension of pole is 5 cm0.6 cm4.8 cm. The gap of the undulator is variable. While the gap range is 1.81-3.05 cm, the range of peak magnetic field strength is 0.529-0.184 T, and the length of good field area is 3.02-2.13 cm. Meanwhile, as the error of undulator magnetic field has effect on free electronic laser, the tolerances of undulator parameters are brought in, and the end design of the undulator is discussed at last.