Particle Accelerators

Contents

What is a Particle Accelerator?

An Early Accelerator

Modern Linear and Circular Accelerators

Particle Detectors

Examples of Accelerators

What is a Particle Accelerator?

Any device that accelerates charged particles to very high speeds using electric and/or magnetic fields

http://en.wikipedia.org/wiki/Image:P3280014.JPG

The picture to the right shows an early particle accelerator from 1937. This accelerator was used in the development of the first atomic bomb.

An Early Accelerator

In 1929, Ernest Lawrence developed the first circular acceleratorThis cyclotron was only 4 inches in diameter, and contained two D-shaped magnets separated by a small gapAn oscillating voltage created an electric field across the small gap, which accelerated the particles as they went around the accelerator

An Early Accelerator, cont.

Here is picture of Lawrence’s cyclotron:

http://www.facstaff.bucknell.edu/mvigeant/univ_270_03/Jaime/History.html

Today’s Accelerators

Modern accelerators fall into two basic categories:

Linear Accelerators Circular Accelerators

Linear Accelerators

In linear accelerators, particles are accelerated in a straight line, often with a target at one to create a collisionThe size of linear accelerators varies greatly

A cathode ray tube is small enough to fit inside of a television Stanford’s linear accelerator is two miles long

http://www.exploratorium.edu/origins/cern/tools/linac.html

Linear Accelerator – Example 1(Cathode Ray Tube)

The cathode ray tube is a linear accelerator found in many TVs, computer monitors, etc.

http://science.howstuffworks.com/atom-smasher2.htm

The tubes must have a progressive length

The time needed for a particle to cover the length L of a tube = T/2 or ½ the periodic time.Since the velocity increases progressively then the length of tube number n must be longer than tube number n-1

At tube number s the energy Es of the particle is given by Since the particle starts from rest

QSVmvE oos 2

2

1

QSVE os

QSNVE omax

N = the total number of tubes

V0=the potential difference

m = the mass of the particle

The length of the linear accelerator

nnxm

QVTL

nxm

QVTL

xm

QVTL

xm

QVTL

m

QsVv

mvQSV

ototal

on

o

o

os

so

])()2()1[(2

2

)(2

2

)2(2

2

)1(2

2

2

2

1

2/12/12/1

2/1

2/12

2/11

2

)(2

3

)(2

3

)(2

3

)(2

2

.)(2

2

max

2/3

2/1

2/1

nxm

ETL

nxm

QnVTL

nxm

QVTL

yxm

QVTL

neglectnyxm

QVTL

total

ototal

ototal

n

o

ototal

ototal

The length of the linear accelerator

zeV

EE

m

TL

ototal

max2/1max )(

2

3

Numerical exmple

The maximum energy of accelerated is Hydrogen 20MeV

The applied voltage = 105 Volts

The HF = 10 6 Hz

Of course e=1.6 10-19 C

U = 1.68 10-27 kg

Find the number of tubes and

The average velocity and

The elapsed time to cover the last and first tubes

In practices it is impossible to construct such machine because the wave length

meters 300v

cosc

The accelerator length = 4000 meters

i.e. there is no phase

With such parameters on can achieve protons with only one MeV

Linear Accelerator - Example 2(Stanford Linear Accelerator)

http://en.wikipedia.org/wiki/Image:LINAC.jpg

Electron linear accelerator

Linear electron accelerators are similar to the positive ion accelerators except that the drift tubes are replaced by a wave guide in which a high power electromagnetic wave travels at velocity slightly less than the velocity of light.Electron being ejected from another generator , move along the wave continuously. These electrons travel at very nearly constant velocity. With no radiation losses

Circular Accelerators

Circular accelerators propel particles along a circular path using electromagnets until the particles reach desired speeds/energiesParticles are accelerated in one direction around the accelerator, while anti-particles are accelerated in the opposite direction

www.fnal.gov

Circular Accelerators, cont.

Circular accelerators are able to bring particles up to very high speeds (energies) by allowing each particle to be accelerated for a longer period of time—around the accelerator.The distance around a circular accelerator can be quite large

Fermilab’s Tevatron (Near Chicago, USA) - 4 miles (6.44 km)

CERN’s LHC (Near Geneva, Switzerland) – 16.8 miles (27 km)

Fermilab Accelerators

The protons and anti-protons at Fermilab go through a series of accelerators in order to accelerate them to 1 TeV (just 200 miles per hour slower than the speed of light)At Fermilab, protons are accelerated in one direction around the ring; anti-protons are accelerated in the opposite directionThe series of accelerators at Fermilab is illustrated by an animation located at this website (be sure to press “play”):http://www-bd.fnal.gov/public/index.html

Collisions

The particle and anti-particle beams are focused and directed at particular sites around the ring in order to collide with one anotherThese collisions are designed to occur within detectors, which are able to analyze the many events (particles created, etc.) that result from the collisions of the particles and anti-particles

Particle Detectors

The large detectors are able to trace and characterize the particles that result from the collisionsThe picture to the right shows the 5,000-ton CDF Collider Detector at Fermilab400,000 proton-antiproton collisions occur each second in this detector

http://www.fnal.gov/pub/about/tour/index.html

Particle Detectors, cont.

By analyzing the nature and type of particles resulting from the collisions, scientists are able to learn much about matter at a more fundamental levelhttp://www.fnal.gov/pub/now/live_events/index.html

CERN Accelerators and Detectors

The diagram to the right shows the accelerators and detectors at CERN near Geneva, SwitzerlandThe LHC is the largest circular accelerator at CERN and is to begin operation in 2007CMS and ATLAS are two of the five examples of detectors approved at CERN for the LHC

Fermilab Accelerators and Detectors

The most powerful accelerator (the Tevatron) in the US is at FermilabThe diagram to the right shows the series of accelerators (including the Main Injector and Tevatron) and detectors (including CDF and DZERO) at Fermilab

http://www.fnal.gov/pub/about/whatis/picturebook/descriptions/00_635.html

Accelerators and Detectors as Giant Microscopes

Together, particle accelerators and detectors have helped scientists discover very small building blocks of matterFor instance, scientists now think that protons within atoms are made up of even smaller particles known as quarks Check out www.particleadventure.org for more information

http://www2.slac.stanford.edu/vvc/theory/fundamental.html