E821 Magnetic Field Safety Plan
Kim Woodle and Bill Morse
January 1996
The E821 Storage Ring consists of a 711cm radius magnet with an
18cm gap. The gap is on the inside of the ring. The central field
is 
. It is energized with a 6000A-6V power supply. During
normal running, the current is 5200A and the voltage is 
. A
POISSON calculation of the magnetic field distribution is shown in
Fig. 1. The POISSON calculation is not valid close to the POISSON
boundary. Kim Woodle is the Magnetic Field Safety Coordinator (MFSC).
We have identified the following magnetic field safety issues.
1. Health effects due to magnetic fields. Cardiac pacemakers should not be exposed to fields greater than 5 Gauss (ACGIH recommendation). We have signs at the entrance to the high bay area warning of fringe fields. There is also a danger of credit card erasure. You should leave your credit cards in your car, or in a secure place in the Control Room.
There are no other known health effects from static magnetic fields. However, ACGIH recommends exposure of the whole body should be less than 600 Gauss on a daily basis (8-hour time-weighted average) and extremities should be exposed to less than 6000 Gauss (8-hour time-weighted average). We expect to be well within these recommendations. There are several electrical signs which are on when the ring is energized.
2. Physical danger due to force on magnetic material in the fringe field. It is interesting to calculate the distance from the outer coil where the magnetic force equals the weight:
In actuality, it is less than this because the four coils are powered in opposition. However, our plan is to control magnetic materials inside the ring to obtain a reproducible precision magnetic field. All ferromagnetic material within two meters of the gap must be rigidly attached so the effect is reproducible. There is a line on the floor to indicate this. We have a set of non-magnetic tools permanently left inside the ring. The crane should be left parked over the steps from the control room when precision measurements are being taken so the effect will be reproducible. We monitor all ferro-magnetic material which enters the ring. There is a logbook at the gate to the ring with a small magnet to test if the material is ferromagnetic. If ferromagnetic material is brought inside the ring, this must be logged. Kim Woodle is responsible for this log. If anyone is unsure of material they need to bring into the ring, they must first contact either Kim, or someone he will designate. Non-magnetic writing implements are available in the Control Room. If your job requires you to have safety shoes, non-magnetic safety shoes are available from the Lab. See your supervisor.
If a large item must be brought in, we will schedule a time when the magnet is off. Contact the MFSC beforehand to arrange this time. If you wish to repair your system which is inside the 2m line while the magnet is on, you must first get formal approval from the MFSC. Only those with magnetic field safety training are allowed in the ring when it is powered. Otherwise, they must be escorted by a someone with training. We are concerned that someone without training will enter the storage ring area without an escort. For that reason, we have installed the gate. This gate should be normally closed when the magnet is powered. We have also installed signs not to go under or over the magnet, unless it's an emergency situation. The MFSC is responsible for the training and keeps a formal record of who has had the training. This training allows you to enter the ring when it is powered. To operate the power supply, you also need magnet operator training (see Bill Morse). There is a storage ring crash button. This de-energizes all high energy storage ring systems: the storage ring magnet, quad high voltage pulser, and muon kicker high voltage pulser. This should be used only in cases of personal safety! If the ring is powered, there will be a magnet operator present. Only the magnet operator should push the crash button, except in emergencies when immediate action is necessary. The magnet operator will have training in how to respond to an emergency, such as a fire. I give this procedure below.
0. Stay calm and use common sense!
1. Call Main Control X4662 or Lab Emergency X2222.
2. Go to the Slow Control Computer and select basic shut-down. This will turn off the detector high voltage, the storage ring power supply, and beam-line power supplies. This is relatively easily recovered from.
3. If it is verified that the fire is in the storage ring area, push the Storage Ring Crash button. This will de-energize the high storage energy devices in the ring: the storage ring and inflector magnets, the quad high voltage pulser, and the muon kicker high voltage pulser. This takes at least one shift to recover from due to the magnet quench-back.
4. Wait for the AGS Local Emergency Coordinator and the BNL Fire
Chief. The LEC is appointed by Al Pendzick. The E821 experimenter
will assist the LEC. If the smoke/fire is in the high bay, after (3)
the magnetic field and all high voltage will be off. The remaining
systems still energized are the vacuum pumps for the insulating
vacuum for the coils, and the control system power. These systems
are on emergency power. If a vacuum pump is found to cause the fire,
the circuit for that pump needs to be shut down. The location of the
breakers for each of these pumps will be indicated clearly at the
breaker location to the left of the roll-up door.