Active vibration control for free electron lasers
Stetler, Aaron M.
Denardo, Bruce C.
Hofler, Thomas J.
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This thesis is concerned with active control methods for stabilizing the mirror vibrations of free-electron laser weapons on ships so that the laser continues to deliver full power. Alignment of the mirrors is critical for proper operation because the electron beam and optical mode must substantially overlap. The alignment is expected to be difficult to maintain in a shipboard environment. A theory for controlling the vibrations of a single-degree-of-freedom system is developed and checked by numerical simulations. An apparatus consisting of a flexing aluminum strip was constructed in order to probe the fundamental behavior of actual systems which eventually become unstable as the control gains are increased. A computer data acquisition system (LabVIEW) was implemented so that experiments could be more efficiently and accurately performed. Proportional and derivative controls were used to stabilize the motion of the strip. Experiments reveal that the derivative control behaves according to the theory. In particular, the instability is understood as the result of positive feedback due to a phase shift of the unstable mode. However, the instability due to the proportional control does not behave according to the theory. Improvements that would allow for greater control gains and thus greater stabilization are suggested.
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