Particle accelerators
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Particle Accelerators. Atkinson. A particle accelerator is designed 'to speed up and increase the energy of a beam of particles by generating electric fields that accelerate the particles, and magnetic fields that steer and focus them.'. Linear Accelerators.

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Particle Accelerators

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Particle Accelerators


A particle accelerator is designed 'to speed up and increase the energy of a beam of particles by generating electric fields that accelerate the particles, and magnetic fields that steer and focus them.'

Linear Accelerators

In linear accelerators, particles are accelerated in a straight line, often with a target at one to create a collision

The size of linear accelerators varies greatly

A cathode ray tube is small enough to fit inside of a television and computers

Stanford’s linear accelerator is two miles long

Cathode Ray Tube

From small acorns...


  • Small energy 1MeV

  • ....therefore... Not many particle produced.


  • We had LARGE amounts of energy, that large amount of energy can be converted to mass. Therefore more particles! (particle zoo)

Ernest O. Lawrence

An Early Accelerator

In 1929, Ernest Lawrence developed the first circular accelerator, only 4 inches in diameter, and contained two D-shaped magnets. First circular particle accelerator

  • First circular particle accelerator

  • Magnetic fields confine and control the postition of the particle beams

  • Electric fields are used repeatedly to accelerate the particles



-1000 V

+1000 V

+1000 V

-1000 V

Circular Accelerator

Electron “ramps up”to full energy over manyturns!

Accelerating cavities(many of them !!!)

Circular Accelerator

Linear Accelerator

Circular Accelerator

  • Particles go round & round.With each turn, they gainmore & more energy becauseof the accelerating cavities.

  • Particles are kept in a circle by powerful magnetswhich bend their direction !!!

  • The magnets “bending power”has to increase as the particlesenergy increases (big challenge)..

  • The energy limit is restrictedby our ability to keep them goingin a circle…

Circular Accelerator

Particle Acceleration

  • We are able to accelerate electrons because they have electriccharge, and are attracted to a “plate” which has a high POSITIVEvoltage.

  • Using similar principles, we can also accelerate positively charged particles, like protons.

  • You just need to flip the positive & negative voltages !!!.

  • We can therefore also accelerate positrons (positively chargedelectrons). All the voltages are just reversed !!

  • So, we only know how to accelrate things which have electriccharge !

  • How do we create positrons?


Creating Antiparticles

e - this way





Photonsare unaffectedby a magnet



e+ this way

Using magnets, the negative electrons can be bent one wayand the positrons bent the other way, thus “separating” them fromeach other !

Once separated, the positrons can be “focused” and accelerated !

Circular Accelerator


E ~ 5 [MeV]per beam

Because electrons and positrons have the samemass, but opposite charge,they can both be accelerated in the same circularaccelerator !!


Collision !!!!!

Around the collisionpoint, we build adetector to detect theparticles coming out.Using these detectors, we measure:

1. Momentum2. Type of particle3. Charge+ many other quantities




E ~ 5 [MeV]per beam










p -



There are several concentric layers to this detector. Each layer serves a specific function:

1. Tracking – map out the flight path of the particle2. Calorimeter – measure the energy of photons3. Particle identification: detectors capable of distinguishing pions from protons from kaons, etc (I won’t cover this)…

Cms detector - CERN



As charged particle passes through gas, it ionizes the gas.This creates “free” electrons which are attracted toward the 1500 V wireGenerates a voltage pulse !You know thatthis wire “saw”a charged particle !

~1 mm sep.

Box filled with gas,perhaps Argon.

A charged particle, likea proton, or p+

Wires at+1500 V

Detecting Particles

  • Tracking: Detectors are inside a HUGE magnet.

    Measure charge by the direction the particle curvesMeasure momentum by how much it curves. If it curves alot  low momentumIf it only curves a little  high momentum

  • CalorimetryMeasure energy of photons, electrons also!

  • Particle Identification: I skipped this…Allows you to tell what kind of particle it is…

CERN 1954

Probably the best known particle accelerator in the world…

Image courtesy of CERN

The Large HadronCollider

Birth of the WORLD WIDE WEB

  • Tim Berners-Lee, a British scientist at CERN, invented the World Wide Web (WWW) in 1989. The web was originally conceived and developed to meet the demand for automatic information-sharing between scientists in universities and institutes around the world.

  • The first website at CERN - and in the world - was dedicated to the World Wide Web project itself and was hosted on Berners-Lee's NeXT computer. The website described the basic features of the web; how to access other people's documents and how to set up your own server. The NeXT machine - the original web server - is still at CERN.

The first web site


Linear Vs Circular

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