The Big Quench Rancho Feb 2009

MRI Quench Feb 2009

Category:

Science & Technology

Tags:

• Magnet
• MRI
• Quench

[bernadettelkay]

This magnet was being taken out of service, it was 15 years old and we have replaced the building and the magnet with state of the art new equipment and setting.

[bernadettelkay]

The system is built with a "quench button".The primary use for the button is to render the unit non-magnetic in case of an emergency (object projectile into the magnet, etc), but is also utilized to "quech" when the magnet (MRI) is being taken out of service.

[carl95125]

What did you do to cause the magnet to quench...turn up the current or do something to the vacuum insulation? Could you have drained the magnet of some of the LHe first...before the quench?

Carl

[bernadettelkay]

the "quench" button activates a release valve that allows the liquid helium to escape.

[Aquarello7]

A superconducting magnet stays magnetic even when the power is off. Trying to move an operational magnet that can pick up a bus is just asking for trouble. Removing the liquid helium (shown here) renders the coils non-superconductive, and, with the power shut off, therefore non-magnetic.

[bernadettelkay]

even with the power on, after releasing the helium, it is non-magnetic

[JustinRLynn]

Oh man, so much helium gone and it's only getting more expensive... *sad face*

[ChumpusRex]

@ssyreeni Usually, the quench button activates a small resistive heater coil in the magnet, causing a region of the coil to become resistive.

Most medical MRI magnets don't contain enough energy due to the relatively low field strength (1-3 T) to require active protection circuits on the coils. Very high strength scientific magnets typically install diodes between the coil windings, and heat-spreaders to ensure that the whole coil heats and quenches evenly.

[ssyreeni]

Is it really so that the quench button just vents the coolant, letting the magnet internally dissipate the energy stored in the field/recirculating current? That sounds sort of...risky. I mean, if you start with the current still circulating, instead of dumping it into a heatsink in an orderly fashion, how do you guarantee that there won't be resistive hotspots, shockwaves in the surrounding helium, and so on?

[daufas]

@mickd01 Mick, that is exactly right, the other thing not mentioned is that depending upon the power of the quench the coil can be damaged (magnet coil). It is much more preferred to ramp it down with the power supply. I am wondering what type of magnet this was. WE don't normally use that type of quench cap anymore , we use one that is better equipped to keep water out of the quench pipe.

[daufas]

@bernadettelkay I work for Siemens on MR's The quench button is not the preferred method for decommissioning these things , normally we would prefer to ramp the magnet down to avoid all this helium loss as that stuff is very expensive. Must admit it makes a great show though.

[infernoacid]

@dragonxxx53

Jesus predates MRI scanners. You should ask a doctor or a scientist.

[infernoacid]

@bernadettelkay

I hope that this button is easy to reach for us button-philes?

[mhilla02]

ZOMG!!!!