QUANTA TO QUARKSDOT POINT 4.4

Identity ways by which physicists continue to

develop their understanding of matter, using

accelerators as a probe to investigate the

structure of matter.

Andrew, Ray, Jasmine

PARTICLE ACCELERATORS

Particle accelerators are instruments used to

accelerate charged particles to high speeds in

an electric field.

A simple accelerator is the electron gun in a

TV.

In time, particle accelerators have become

more complex.

HOW DOES ACCELERATORS HELP INVESTIGATE

MATTER?

The stability of a nucleus is determined by the

binding energy per nucleon. To investigate the

structure, the nucleus needs to be disrupted by

inputting energy. That’s where particle accelerators

come in.

Mass particle can be created at high energies. These

particles can only be observed at high energies.

CONT.

High energy means high speed of the particle

increase, meaning that they have shorter

wavelength (according to de Broglie

relationship λ = h/mv). This gives the particle

finer detail.

As the energy accelerator was increased,

more and more particles was discovered.

THE TYPE OF PARTICLE ACCELERATORS

The Van de Graaff generators

Linear accelerators

Cyclotrons

Synchrotrons

Other Particle Accelerators

THE VAN DE GRAAFF GENERATORS

In the early 1930s, the British Physicist John

D. Cockroft and Irish physicist Ernest T.S.

Walton created the first particle accelerator.

Van de Graaff devised a continuous supply of

high voltage to accelerate protons and ions to

0.5 MeV.

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THE VAN’S GENERATOR CONT.

Charge is ‘sprayed’ on to an endless belt and is carried to the top of the generator. The charge is transferred to the dome and moves to the outside of the sphere. Charge is continually added to the dome to build up a high potential difference which can be used to accelerate particles to high energies.

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LINEAR ACCELERATORS

Linear accelerators are used individually and in conjunction with

other accelerators. The most famous one is the Stanford Linear

Accelerator Centre (SLAC).

A linear accelerator consists of a series of drift tubes. They are

made progressively longer so that the particle will always arrive

between the tubes at a constant time interval due to a higher

velocity. This must be in synchrony with the timing of polarity

change.

Each second tube is collected to a terminal of a high frequency

AC power supply so that the tubes polarities alternate.

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LINAC. CONT.

Protons were attract to the first tube which is momentarily negative.

The particle accelerates in the electric field that exists in the gap between the tubes and gains energy. (there is a zero electric field inside the drift tube, therefore no acceleration inside the tube. )

When entering the second tube polarities are changed (AC) so that the first tube now repels the proton and proton is attract to the next tube which, provides additional energy.

As this repeats the particle increases in velocity and travels through all the tubes. When leaving the last tube it strikes the target.

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CYCLOTRONS The American Physicist

Ernest Lawrence (1901-1958)

is credited with the invention

of the cyclotron in 1929.

Cyclotrons consists of two D

shaped hollow metal cases

called ‘Dees’ which are

mounted between the poles

of two electromagnets.

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A ion source is placed between

the two Dees which is connected to

a high frequency AC source. The

Dees are placed between the poles

of a powerful electromagnet; the

magnetic field bends the particles

When an electric field is produced

due to the alternating current the

particle will be accelerated and

enter a Dees.

As the particle travels inside the

Deeit experiences no electric force (electric field inside a hollow conductor is 0) and is acted upon by the uniform magnetic field.

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Ions from the source enter the electric field and are accelerated across it to Dee 1, where it moves in a circular path due to the magnetic field.

If when the ion leaves Dee 1, the polarity has switched (AC), ions will be accelerated toward Dee 2 and increase in speed.

By repeated polarity change, the ion particle can be continually accelerated. Once it has reached the desired velocity, it exits the particle accelerator and collides with a target.

DEE 1 DEE 1

DEE 2DEE 2

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SYNCHROTRONThe main accelerators today are Synchrotron. Particle are

introduced into the synchrotron and accelerated to much

higher speeds than in cyclotrons.

Synchrotron uses a variable magnetic field so that the

increase in velocity is coupled with an increase in the

magnetic field so that the radius is kept constant. This keeps

the size of the device small.

The disadvantage of a synchrotron is that it can accelerate

only one packet of charged particles at a time. These must be

removed before another package can be started.

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OTHER PARTICLE ACCELERATOR

Betatron: The betatron is an electron accelerator.

It differs from a cyclotron in that the electrons are

accelerated by a rapidly changing magnetic field and

the circular orbit has a constant radius.

Synchro-cyclotron: Synchro-cyclotron operates

similarly to a cyclotron except it takes into

consideration mass dilation as the particle speeds

up. By taking this into consideration it allows the

particle to be accelerated to a higher velocity.

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Thank

U!