Abstract:
In an oscillator FEL, higher-order harmonic radiation
from wigglers can cause serious damage to the
downstream FEL resonator mirror or limit the maximum
electron beam current for FEL operation due to thermal
overload. With a helical wiggler, higher-order harmonic
radiation is peaked off-axis. By blocking the off-axis
wiggler harmonic power, the radiation damage to the FEL
resonator mirror can be reduced. In this paper, we report a
recently developed scheme to control the off-axis
harmonic radiation from helical FEL wigglers using a set
of motorized, water-cooled, in-vacuum apertures. These
apertures can reduce the harmonic power load on the
downstream FEL resonator mirror by one order of
magnitude. With these apertures, high power FEL
operation with a high electron beam current will become
feasible in the UV-VUV wavelength range with Duke
storage ring FELs.