Low Energy Booster Personnel Access Safety System

The Low Energy Booster, like any high-energy accelerator contains serious personnel hazards with the potential for deleterious results if precautions are not implemented. Hazards for most accelerators include: electrical hazards (high voltage and high current), ionizing and non-ionizing radiation, flammable gases, and high magnetic fields. For the LEB, the predominate hazards of concern are electrical shock and ionizing radiation exposure to the primary beam, both of which can be obviated or mitigated by controlling personnel accesses into the tunnel enclosure. Outside the enclosure radiation levels are much less of a danger due to the radiation shielding. However, radiation interlocks are still used to insure the beam is inhibited at its source in the event of excessively high radiation levels outside the enclosure. The LEB Personnel Access Safety System (PASS) is used to protect personnel from these hazards in underground enclosures by controlling electrically hazardous power supplies and beam safety devices. Electrical hazards are controlled by a robust fail-safe interface between power supplies and other similar devices. Specifically, the control point is as close as possible to the power source so as to bypass less reliable shut off mechanisms. In most devices this is the power supply contactor that turns off all power to the device. A contactor acts much like a relay. To further ensure the integrity of the interface, a feedback signal is provided by the contactor to sense that it functioned properly. In the event that devices are inhibited by the system and feedback from the system indicates a malfunction, an alarm is initiated and personnel access into the LEB tunnel is not allowed. The proton beam from the LINAC into the LEB is controlled in a similar manner. The devices used to control beam, typically referred to as radiation critical devices are power supplies that control bending of the beam into the LEB. By controlling and monitoring these devices, beam can be inhibited if necessary. Although the actual design discussed herein was not implemented in the LEB, a very similar system was installed and remained operational for two years in the Accelerator Systems String Test (ASST) facility [1]. The ASST differs from the LEB in being smaller (600’ in length) and does not produce radiation; however, in most other respects it serves as a testing ground for the LEB PASS and a proof-of-concept.