Cryomagnet_BACH

SAFETY AND PRECAUTIONS


SAFETEY AND PRECAUTIONS: LHe DEWARS

 
 

It is of great importance that the user be familiar with the various valves on the dewar, and which valves should be left open/closed at what time, as incorrect handling potentially can cause a severe hazard. The following section therefore describes schematically the dewars and the necessary procedures. As an ABSOLUTE rule - ALWAYS WEAR THICK GLOVES AND SAFETY GLASSES AND CLOSED SHOES WHEN WORKING WITH THE LHE DEWAR. FOR ALL VALVES, THE VALVE IS OPEN WHEN THE HANDLE IS PARALLEL TO THE RELATED TUBES, AND CLOSED WHEN PERPENDICULAR TO THE RELATED TUBES. The dewar has a total of five ports:

  • Pressure gauge, which is preceded by a small pressure relief valve.

  • Coarse pressure relief valve. This valve will open if the pressure becomes very high, and after the fine pressure relief has already opened.

  • Fine pressure relief valve with a manual valve on it. This valve can be briefly closed during cooldown to facilitate He transfer, but at all other times should be open as it is the initial safety valve in that it has the lowest pressure requirement to open. The Oxford system does not require a pressurized dewar to operate.

  • Fill valve for the dewar- SHOULD ALWAYS BE CLOSED. If this valve is left open, air will pull into the dewar and cause an ice plug which could be very dangerous. However, if during installation of the cryostat there is significant overpressure, as judged by the release of He through the fine and/or coarse pressure relief valves the fill valve can temporarily be opened to release overpressure.

  • Top port through which the transfer line vessel leg is inserted. It should ALWAYS BE CLOSED when the dewar is not in use as otherwise an ice plug can be formed.

Before the installation of the cryostat is started, the valve for the top port should be opened to release any overpressure of the dewar. As cold gas will be expelled through this port immediately upon opening the valve, make sure that hands and face are protected.
(information taken from: 
http://www-ssrl.slac.stanford.edu/smbxas/instrumentation/cryoman.html#frost)

SAFETEY AND PRECAUTIONS: MAGNETIC FIELD

• These notes must be read and understood by everyone who comes into contact with a superconducting Magnet System. Special care has to be observed when operating with the superconduction coil since high magnetic field are generated in the area around the cryomagnet.

The area where the magnetic field can be potentially dangerous is delimited and closed by gates and it is a RESTRICTED ACCESS ZONE.

In particular it is forbidden to enter in this area when a magnetic field is set inside the coil. 

The magnetic field can be dangerous. The field measured ouside the cryomagnet is 145 milliTesla when the SC coil is operating at 6 T, which is a quite high value. 
Before operating with the magnet please read the following SAFETY AND PRECAUTIONS rules:
BEFORE RAMPING UP THE SC COIL: REMOVE all metallic objects which could be attracted by the magnetic field (screwdrivers, screws, bolts, nuts, ....), credit cards, self phones, watches, from the magnetic field area (restricted zone delimited by the gates)!!
Exposure should be always avoided for pregnant women, people with  cardiac pacemaker, neurostimulators, cochlear implant, derivation valves, lenses, intra-corporeal metallic foreign objects. 

Due to the presence of a strong magnetic field, certain materials may present a functional or even a vital risk:

Projectile effect (attraction by a static magnetic field and acceleration, with speeds of up to several meters per second): ferromagnetic material (if in doubt about the ferromagnetic nature of a metal object, a test can be carried out using a small magnet). REMOVE all metallic objects which could be attracted by the magnetic field (screwdrivers, screws, bolts, nuts, ....) from the magnetic field area!! Always be aware that even a small object can become a projectile and cause fatal injuries.

Displacement of intra-corporeal metallic foreign objects: Intraocular metallic foreign body (metal worker, history of ballistic orbit trauma, old intra-cranial aneurysm clips)

Perturbed functioning of certain devices: cardiac pacemaker, neurostimulators, cochlear implant, derivation valves, lenses

Credit cards, mobile self phones, watches, tape recorders and cameras, magnetic cards can be permanently damaged and information contained could be corrupted and should stay outside the magnetic field area)

• Electrical transformers may become magnetically saturated in fields above 50 gauss. The safety characteristics of equipment may also be affected.
 

In regard to prostheses, non ferromagnetic materials with no electrical activity (titanium and its alloys, nitinol, tantalum, etc.) carry no particular risks in relation to magnetic field. For low magnetic prostheses (orthopedic material), a delay of 6 to 8 weeks after implantation is advised to avoid displacing the material.
In all cases, it is advisable to check the magnetic field compatibility of the material (see http://www.mrisafety.com/), particularly when operating in high fields.
In this table we report the magnetic field measured along the field at 314 mm from the center of the coil (maximum field in the restricted area external to the cryomagnet):

 
COIL (T) COIL (A) EXTERNAL FIELD (G) EXTERNAL FIELD (T)
0 0 3.4 0.00034
-0.1 -1.43917 22.4 0.00224
-0.2 -2.87833 43.3 0.00433
-0.5 -7.19583 106 0.0106
-0.75 -10.7938 161 0.0161
-1 -14.3917 215 0.0215
-2 -28.7833 435 0.0435
-3 -43.175 665 0.0665
-4 -57.5667 904 0.0904
-5 -71.9583 1147 0.1147
-6 -86.35 1389 0.1389
Last Updated on Friday, 04 July 2014 13:05