About superconduct MRI quench protection

[yunaijun]

Hi,I study protection of superconducting coils.I adopt heaters to protect coils.The circuit is in attachment.

There are 6 coils,so I use 6 quench heaters.I want to know how I choose the heaters?

It must do the Quench Heater Simulation for protection of superconducting coils before experimenting.

So I need help about quench heater simulation.

who can tell me?Maybe you could tell me which website I should visit or which article i should read.
thanks
my email:

 

[Dale]

Usually magnets are ramped to field and quenched in the factory before shipment and ramped back to field again just to ensure that they can handle quenching. So what is your goal?

 

[yunaijun]

thank you,I design the quench heater which prevent the superconduct coil from exceeding temperature and high voltage.

I don't know how design it.Could you introduce something to me?

 

[Bob S]

The problem with quench protection in superconducting coils is that when a small section goes normal (quenches), the normal zone boundaries propagate away from the center with a velocity that depends on the current in the coil. At high currents the length of the resistive zone and the total resistance of the coil increases rapidly, which increases the voltage drop across the coil and causes the magnet current to be shunted through an external circuit (diode or thyristor). At very low currents, the normal zone will not grow, and there will be no damage to the coil. At intermediate cuurents, The normal zone will increase slowly, and if the total resistance of the coil does not grow sufficiently, the normal zone will heat up and damage the superconducting cable. The purpose of the heater is to cause the whole coil to go normal to limit the localized heat build up at the point of the quench. Usually the superconducting cable has a MIIT (pronounced "mite") limit. This stands for time integral of (mega amp*amp)dt, i.e., the heating at any point in the cable is integral[(I^2 R) dt] where R is the resistance per unit length of the normal (quenched) cable.

 

[f95toli]

You mention experiments, how big is the magnet?
Always keep in mind that quench protection is NOT a "physics experiments"; it is a very important safety feature: get it wrong and things can go REALLY bad.
I don't know if anyone has ever been killed by a quenching magnet; but it could certainly happen; all you need is e.g. a blocked safety valve and you could get a pretty big explosion (remember what recently happened at LHC).
A few years ago I worked in a lab where a small cryostat (maybe 5l of helium) exploded, someone was warming it up when an ice-plug formed in the return-line and the safety valve didn't work for some reason. Fortunately, no one was in the lab at the time so no one was injured but the cryostat was just scrap.

My point is that you shouldn't be designing this unless you know what you doing. Get some help or hire a company to do it for you.
Also remember that all magnets/cryostats MUST be properly quench tested -not just simulated- before they are used routinely.

 

[yunaijun]

the circuit of quench protection is simple.(you could find it in the attachment)

MRI: 1.5T ,liquid helium 4.2K, NbTi/Cu .

the heating at any point in the cable is integral[(I^2 R) dt] ,I konw how calculate the propagation velocity (longitude,transverse),but how I could get I(CURRENT) or J(current density).Therefore,I couldn't get R,I.

could you give me some imply?
thanks

 

[yunaijun]

who could tell me quench programm(fortran or C++ or matlab)?

 

[Vanadium 50]

Always keep in mind that quench protection is NOT a "physics experiments"; it is a very important safety feature: get it wrong and things can go REALLY bad. ...
My point is that you shouldn't be designing this unless you know what you doing. Get some help or hire a company to do it for you.

who could tell me quench programm(fortran or C++ or matlab)?

Please read f95toli's message. Quench protection is not a computer program. It is an important safety feature.

It's evident that you don't know what you are doing. Given that, asking a bunch of people on the internet for advice is not all that much safer. You really need to get professional help with this.