next up previous contents
Next: Cryogenic and Oxygen Deficiency Up: Description of Hall C Previous: Fire Hazards

Subsections

Magnets and Magnet Power Supplies

Hall C utilizes a large number of electro-magnets, both resistive and superconducting. The HMS is a QQQD spectrometer. All HMS magnets use superconducting coils with the capability to bend particles with momenta up to 7.3 GeV/c. The SOS is a normal-conducting QD$ {\bar D}$ spectrometer with a maximum central momentum of 1.7 GeV/c. In addition, Hall C contains a number of magnets along the beam line, notably the Møller polarimeter and the Raster Magnets. In Table 1, we give an overview of possible voltages and currents for the main Hall C magnets.


Table 1: Voltages and Currents for the Hall C Magnets
Magnet Current [A] Voltage [V]
     
SOS Quad 1000 160
SOS D1 1000 250
SOS D2 1000 160
HMS Q1,Q2,Q3 1250 10
HMS Dipole 3000 10
Møller Small Quad 300 30
Møller Large Quad 1500 150
Møller Solenoid 120 10
Raster Magnets $ <$100 300-600 (AC)

The magnets in the experimental areas are typically energized by remote control. During major down times the magnets are powered down for personal safety reasons as well as to reduce electrical power consumption. During short interruptions of beam delivery, with hall personnel entering the hall in the controlled access mode, the magnets are typically left energized. The main reason is that the time constants of large size magnets are long (of the order of hours), and frequent ramping or cycling will lead to inefficient operation. Also, every ramp of a large superconducting magnet involves some risk of permanent damage to the magnet coil.

The principal hazards associated with the magnets are:

Electrical
All the spectrometer magnets, and some of the beam line magnets, are high current devices ( $ I_{max} \approx$ 3000 Amps). The power supplies that provide this current are potentially lethal. The most exposed and hence most dangerous places are inside the supplies themselves and at the magnet power leads.
Magnetic
The spectrometer magnets produce large fields ( $ B_{central} \approx$ 10 kG). The magnets all have return yokes and thus the external fields (near the magnets) are not nearly as large as the central fields but they may still be significant (up to about 1 kG). The raster magnets do not have a return yoke and may have external fields of a few hundred Gauss. Personnel working in the proximity of energized magnets are exposed to the following magnetic hazards:
LCW
The magnet coils in the case of the SOS and the magnet power supplies for both spectrometers as well as the current leads of the HMS are all cooled by the Low Conductivity Water, LCW, system. This is a high pressure system, P $ =$ 240 PSI, and an unconfined stream of water at this pressure could cause injury.
Fire
There also exists a potential fire problem associated with the high current power supplies. A short in one of the coils, or insufficient water cooling may lead to a fire in the power lines or the coils.

Hazard Mitigation

Two different modes of operation need to be distinguished: (1) routine operation involving work in the vicinity of the magnets, but not in close proximity to the electrical connections, and not involving any work that could result in purposely getting into contact with the coils or the leads, and (2) non-routine operation involving work on or near the exposed current conductors or connections (typically requiring removal of the shield) or any work that could result in contact, intentional or otherwise, with the coils or the leads.

Routine Operation

The following measures shall be taken by the cognizant hall engineer (or his designee) to mitigate the hazards during routine operation:

Electrical Work Restrictions

are established according to hazard class and mode of work.

The mode of work is determined by the nature of the work:

  1. de-energized
  2. energized with reduced safety and restricted manipulative operations
  3. energized with manipulative operations

The hazard class is determined by the type work (electrical or electronic) and the combination of voltage and current.

Power-on Maintenance

There will be no mode 3 (``hot work'') on any power supply in Hall C. Mode 3 work is defined as manipulative operations that are conducted with equipment fully energized and with some or all normal protective barriers removed.

Emergency Situations

There are crash buttons in the counting house which are interlocked with a key (one for each spectrometer). When the keys are locked off, in crash mode, the power supplies cannot be energized. The keys to the crash button are controlled by W. Vulcan (SOS), and S. Lassiter, M. Fowler, P. Brindza, and W. Vulcan for the HMS. The crash buttons are certified by Hall C electrical personnel.

Conclusion

The practice of keeping electro-magnets energized in the experimental areas during short accesses provides substantial benefits to the quality and effectiveness of the physics program. The resulting hazards have been mitigated by a combination of protective shields, personnel training, warning lights and signs, and administrative procedures.

LCW Hazard Mitigation

The LCW water system for the SOS dipole and quadrupoles has been plumbed using hoses rated for 600 PSI. These hoses have been tested during the magnet mapping. The power supply cooling water hoses have a similar safety margin.

In case of problems with LCW contact one of the responsible personnel listed in Section 4.

next up previous contents
Next: Cryogenic and Oxygen Deficiency Up: Description of Hall C Previous: Fire Hazards
Hall-C Staff
2008-01-17