Water cooled beryllium lenses have been successfully used in the white beam of an undulator. Note that the temperature of beryllium lenses must nowhere exceed 120°C .

Fig. 1. Left: Water cooled CRL at ESRF (ID10), 12 Be lenses with R = 200 µm. Right: Temperature-time profile in white beam, ca. 100 W/mm², total 40 W