synchrotron radiation

There is expected to be no serious background of synchrotron radiations because the aperture of the final quad is optimized with the collimated beam and the synchrotron radiations from upstream of last bend can be shielded by masks. However, SLD experiment observed a large fluctuation of background in the central drift chamber(CDC). What is expected to be a stability of beam with reasonable luminosity ? NLC considers synchrotron radiations from the $7 \sigma_x \times 35 \sigma_y$ beam. The major source is the inner surface(4.5mm radius) of QA closest to the IP, length 1.8m, between 2.0 and 3.8m from the IP by EGS4 and GEANT.