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Wulf, F.

Paper Title Page
PT31 Optical Fibre Dosimeter for SASE FEL Undulators 248
 
  • M. Körfer
    DESY, Deutsches Elektronen-Synchrotron, Hamburg, Germany
  • H. Henschel, J. Kuhnhenn
    Fraunhofer-INT, Fraunhofer-INT, Euskirchen, Germany
  • F. Wulf
    HMI, Hahn-Meitner Institut, Berlin, Germany
 
  Single pass Free Electron Lasers (FELs) based on self-amplified spontaneous emission (SASE) are developed for high brightness and short wavelength applications. They use permanent magnet undulators which are radiation sensitive devices. During accelerator commissioning beam losses can appear anywhere along the undulator line. To avoid damage of the permanent magnets due to radiation, an optical fibre dosimeter system can be used. The increase of absorption caused by ionizing radiation is measured in radiation sensitive optical fibers. The dose system enables relatively fast particle loss tuning during accelerator operation and allows the monitoring of the accumulated dose. Dose measurements in narrow gaps which are inaccessible for any other (online) dosimeter type become possible. The electromagnetic insensitivity of optical fibre sensor is an advantage of applications in strong magnetic undulator fields. At each location the light absorption is measured by using an optical power-meter. The dynamic range is about 50 dB and covers the linear range of the dose calibration of the fibre. The resolution of the system is 140 mGy. The time between successive measurements is about 5 minutes. The system was installed and successfully tested at the TESLA Test Facility TTF1. The fibre sensors will be a standard diagnostic tool in the soft X-ray user facility TTF2.