| 摘要 |
A gain-expanded free electron laser in which a relativistic electron beam exchanges energy with an electromagnetic wave in an interaction region defined by a magnet system is configured to suppress betatron excitation. The magnet system, the electromagnetic wave, and electron beam are characterized by a net optical phase slip qL during the interaction between the phase of the electromagnetic wave and the phase of the electron transverse velocity, and a net betatron phase advance LAMBDA L. The optical phase slip and the betatron phase advance are chosen to satisfy the following constraints ¦qL¦=K pi ¦qL- LAMBDA L¦=M 2 pi where K is an integer and M is a positive integer. These constraints suppress the excitation of the betatron motion that is excited during the pass of the electrons through the interaction region. The constraints are typically realized by first choosing the operating wavelength or electron energy to satisfy the constraint on q, and then choosing the dispersion constant or the magnetic field to generate a value of LAMBDA differing from qL by a multiple of 2 pi .
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