Magnet Technology at NSCL

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Figure 1. The prism spreads light according to color. If the light is a single color then it is simply bent.


Figure 2. A quadrupole magnet can be modeled by placing four bar magnets around the beam pipe.

In order to do experiments with the beams of particles produced in the cyclotrons we have to bring them to the areas where they are used. We do this with magnets, which everyone probably has stuck to their refrigerator door. One type of magnet is a dipole, which is nothing more than two refrigerator magnets placed so they attract each other. The beam goes through the space between the two magnet poles and is bent by the magnetic field. A good analogy is the prism shown in Figure 1. The dipole does exactly the same thing to the beam.

A toy telescope makes things look big when you look in one end and smaller when you look in the other. We use quadrupole magnets to do the same thing to the beam. Think of placing four refrigerator magnets as shown in Figure 2. Particles that are closer to the poles experience a stronger magnetic field and are bent back towards the middle. This is how we keep the beam in the pipe.

Instead of refrigerator magnets we use magnets composed of iron and special superconducting wire. The superconducting wire is kept at the temperature of liquid helium, -452.06 °F or 4.23 Kelvin, in order for it to work.

Obviously, we have to get the beam from one place to another; but just as obvious there are many ways to do this that don't use superconducting wire. We could really use refrigerator magnets, but to duplicate the bending power of one of our dipole magnets we would need a string of them almost 700 feet long. This would be a very costly way of transporting the beam. So, superconductivity gives us the means of keeping the lab compact and affordable. Even as it is, the magnets are a major part of the cost of building a lab like NSCL. We have devoted considerable effort into making the magnets as compact, powerful, efficient, and cost effective as possible. This has resulted in worldwide recognition for the lab, both for its scientific discoveries and its technology for making the discoveries.