QUANTA TO QUARKS DOT 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 The Van de Graaff generators  Linear accelerators Linear accelerators  Cyclotrons Cyclotrons  Synchrotrons Synchrotrons  Other Particle Accelerators 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. < Back

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. < Back

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. < Back

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. < Back

CYCLOTRONS  The American Physicist Ernest Lawrence ( ) is credited with the invention of the cyclotron in  Cyclotrons consists of two D shaped hollow metal cases called ‘Dees’ which are mounted between the poles of two electromagnets. < Back

 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 Dee it experiences no electric force (electric field inside a hollow conductor is 0) and is acted upon by the uniform magnetic field. < Back

 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 2 < Back

SYNCHROTRON  The 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. < Back

OTHER PARTICLE ACCELERATOR  Betatron:  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: 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. < Back

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