The major interlock systems at CLASSE are for CESR, ERL, and CHESS; each halts beam transport into certain areas if a perimeter is breached or certain required conditions are not met. Smaller systems can also have interlocks or "interlock chains" to guarantee proper procedures are followed prior to startup.
CESR interlock system
The CESR interlock system is an arrangement of gates and light beams that detect anyone walking into a radiation area at the wrong time. Electronic message boards near each entrance display the access and machine conditions. Signs and sounds provide information about the local environment. Before beam is injected from the linac, the CESR operator searches and resets all the interlocked area to guarantee only people with keys are inside. The keys prevent the accelerator from turning on. If you find yourself inside a radiation area when the warning sounds and the radiation area announcement comes over the PA system, do whichever of these three things is quickest (pull the crash cord, push a crash button, or break a light-beam interlock by stepping through it) to prevent beam coming on. When the machine is running, the board reads "synchrotron on" or "CESR on," and you may not enter. If you enter, you will interrupt the light beams, which sounds a loud siren and automatically shuts off CESR. If you break an interlock, go to the nearest beam phone to explain who you are and where you are to the CESR operator. The board will read "interlocks set" when the machine is ready to run. You may enter the area only if the sign also says "TAKE A KEY," and only with a key (because the key must be used to access controlled areas. Every person in a group must take a key and carry it until exiting interlocked areas, at which point it must be returned to its original location. (CESR cannot be turned on until all keys are returned. If you accidentally take a key from the building, call the CESR operator immediately and return the key to Wilson as soon as possible.
) Never share keys. White keys allow access to all areas. Their storage box is located in the control room. While you have a white key in your possession, it is impossible for the linac, synchrotron, or CESR to generate or transport beams.
When taking a key, you should sign it out. If taking more than one key for a group, inform the CESR operator how many keys are being taken and write the names of the individuals receiving the keys on the sign-out sheet. If returning more than one white key, indicate the individuals for whom the keys are being returned on the sign-out sheet and inform the operator.
Colored keys available for access to specific areas are located near those areas. For example, CHESS West keys, which are yellow, allow access to CHESS West and are located in the CHESS area. To find out more about colored keys and the areas to which they allow access, speak with your supervisor or a CESR operator, or ask to see the short video (?) on the interlock system. If the sign reads "AREA SAFE," then the machine is completely off and the entire experimental area has been surveyed for residual radioactivity
. Once the area has been declared safe, no keys are necessary and all experimental areas are open, but you must still wear a radiation badge (discussed later in this chapter) and pay close attention to posted warnings.
Radiation monitors outside the CESR exclusion area are interlocked to the linac and/or storage ring. If beam conditions deteriorate enough that significant radiation is leaking through (or over) the shielding walls, these monitors trip off the accelerator if the instantaneous dose rate exceeds 2 mrem/hr.
ERL Phase 1 interlock system
The ERL Phase 1 accelerator is located along the south wall of L0 (protruding slightly into L0E) behind large blue shielding blocks, and the ERL control room is in #147, adjacent to an associated laser room in #141/143. Radiation-producing equipment is located inside the shielded area, and access inside the area is prohibited while radiation can be produced. An interlock system with light beams and keys similar to that of CESR enforces the perimeter. There are three floor level entrances to ERL, each through a labyrinth of shielding blocks and protected by light beam interlocks. Similarly, access to the ERL mezzanine from the stairway or the ladder (for emergency escape only) is also protected by light beam interlocks. If the interlocks are broken, the high voltage to the gun (at the east end of the area) and power to the superconducting RF cavity are disabled, and the laser shutter is closed. Electronic message boards outside each floor-level entrance, similar in design to those at CESR entrances, indicate whether the ERL is on, if a key is needed for access, or if the area is safe for access without a key; each status indicator only applies to the ERL area. Before the ERL is turned on, the ERL area is searched by the ERL operator to ensure the absence of personnel, which then allows the setting of interlocks; only then is the gun HV enabled. Always check with the ERL operator in Room 147 and carefully read the message boards before entering the ERL area.
Radiation monitors outside the ERL exclusion area are interlocked to the ERL gun. If beam conditions deteriorate enough that significant radiation is leaking through (or over) the shielding walls, these monitors trip off the ERL gun if the instantaneous dose rate exceeds 2 mrem/hr.
Room 128 interlock system
Rooms 120/128 on the Wilson first floor at the west end house an ERL accelerator development laboratory. The control "room" is on the north side of room 128, and the accelerator runs west to east along the south wall. A laser room is located at the west end of the room. The shielded beam dump is located in Room 120. The gun high voltage cannot be enabled unless all the doors to rooms 128 and 120 are secure and interlocks are unbroken. Unauthorized access through any door while the accelerator is running will disable the gun HV and close the laser shutter immediately. Moreover, the south half of the room, including the accelerator and laser room, are protected by a light beam interlock which, if tripped, will also turn off the gun HV and close the laser shutter.
CHESS interlock system
The CHESS interlock system is described here