Triumf Cyclotron

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What is a cyclotron?

"atom smashers"

take particles and make them go at extremely high speeds

at very high energy, you can make mesons, particles beyond our traditional proton, neutron, electron view of the atom

makes isotopes and does research for medicinal purposes

How does it work?

It gets protons (ion source, injection)

it makes them go very fast (acceleration)

puts them where we want them (steering)

use them (filters them)

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Lesson 1: The hydrogen minus ion

we create the negative hydrogen ion in order to make removal of the electrons easier later, in order to get bare protons

this lesson is all about ionization energy

triumf knocks off the electrons of hydrogen atoms and then lets them recombine

some atoms will get two electrons and be negatively charged

to calculate the ionization energy of an electron in an atom, we calculate it's kinetic and Coulomb forces. These should add up to a negative answer, which is the exact magnitude of the ionization energy

this is the same process for calculating a planet's escape energy

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Lesson 2: Initial acceleration

The initial acceleration is down a straight path with an electric potential difference, and the hydrogen minus ions fall similarly to how a ball could fall down a gravitational potential difference

Ep=qV

Ek=1/2(mv^2)

In theory, gravity could be used here, but that is not feasible on earth

there are forces affecting this beam on the way to the cyclotron

since the cyclotron is on earth, there is a downward acceleration due to gravity

this turns out to not be an issue since it doesn't have the time to fall

the beam on negatively charged ions also repel each other

this calculation is mathematically complicated and is dodged in this completely

because it is spreading out, possibly by meters before reaching the cyclotron, we have to focus the beam

this is done with quadrupoles, in sets of two

the first one compresses the beam one way and stretches it in the other

the second compresses and stretches the beam oppositely to the first beam

since the force is not even across, these will not cancel each other out and produce a net focusing of the beam

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Lesson 3: Electrostatic beam steering

before getting to the cyclotron the beam has to be bent 90 degrees

we need to create an inward acceleration

to do this we use parallel plates, creating a uniform magnetic field

The bending caused by the curved plates is just like the inward force from a banked curve

imagine the potential difference being the height and the field like the slope

the actual bending is done in two 45 degree pieces to focus in between

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Lesson 4: Circular motion in a magnetic field

In order to do the work of the cyclorton, we need to add a lot of energy, but can't do it all in one shot, that would take a potential difference of over 500 million volts - unthinkable.

Instead, the cyclotron uses thousands of little boosts from a circular path

To keep the hydrogen minus ions going in a circular path, they use a very powerful uniform magnetic field.

since the force created by a magnetic field is always at right angles to the particle's velocity. (right hand rule!)

The cyclotron uses a potential difference between two d-shaped plates to make ions go faster and faster

when the ions go faster, their path's radius increases, so the required frequency of changing potential difference can remain constant

Every time the ion goes around the circle, it gets two energy boosts

How do they extract them from the cyclotron?

put the ions through a thin foil, which removes the electrons leaving a bare proton, which because of the difference in charge will start moving the opposite direction and right out of the cyclotron (clever!)

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Lesson 5: Electromagnetic beam steering

once the protons are out of the cyclotron, they must be steered around, to stay in the pipe

this is done with a magnetic field since the electric potential difference would be unthinkably high

we use the magnetic field inside of a solenoid in order to create the necessary magnetic field to steer the protons