Re-commissioning of an electron accelerator: industrial-type in research style

After 25 years of utilization in 1992, the electron linear accelerator was replaced by a modern type, CIRCE III of CGR-MeV (now Thomson-CSF). The goal had been to bring a typical industrial-style machine-source of radiation to the research institute in order to enable it to study any relevant parameter in radiation processing of food under commercial conditions. The machine should be as close in design to industrial practices, but at the same time allow for research into dosimetry and process control. As the FRCN moved to its new site, the decision was to re-install the accelerator there. At this occasion and based on the operating experiences of the recent years, several new features were introduced: the scan mode was changed from during-pulse to shot-by-shot; the bending magnet was modified from 107° to 253° (pretzel-type); the exploitable scanning width was increased from 40 to 80 cm. After this modification, the machine characteristics had to be verified. For the changed scan-mode the adjustment of pulse repetition rate, scan frequency, transport velocity, and beam cross-section in both directions, had to be established for the targeted low-dose treatments (about 100 Gy). Furthermore, the facility has now two separated beam-outlets, one for handling the prepacked materials on a transport system, the other one for bulk material handling (not yet installed) and for bremsstrahlung-mode experiments. First results with the accelerator after its transfer to the new site are reported; the radiation field characteristics after the modifications are given.