Cyclotron & Synchrotron Designed by : Mona K h a l e g h y R a d Advisor: Dr. A g h a m i r y
Introduction Accelerators and Detectors • First Cyclotron : How came to the world and when? • What did scientists do with accelerators? • Other accelerators and detectors during these years • First Synchrotron : How came ,why and when? • Other recent accelerators and their goals and results
For producing beams of energetic particles • Protons, antiprotons and light ions • heavy ions • electrons and positrons • (secondary) neutral beams (photons, neutrons, neutrinos)
Accelerator • Type of accelerators: 1) Fixed Target accelerators 2) Colliding beam accelerators : a) Electrostatic b) Cyclic : linear circular Betatron • Cyclotron • Synchrocyclotron • Synchrotron • Colliders
Accelerator types • electrostatic • battery, lightning, van de Graff, Pellatron: to about 30 MeV; for nuclear physics and isotope production • cascade • Cockcroft-Walton: to several MeV; cheap; for X-ray sources and injectors • Linear • RFQ • drift-tube(Wideroe, Alvarez):preaccelerators, LAMPF • Waveguide:electrons only(SLAC, NLC)
Particle accelerators are used to investigate the structure of subatomic particles. • The motivation to strive for higher energy came from quantum mechanics, which describes particles as waves whose length is related to the momentum of particle by de Broglie’s expression : λ=h/p • Higher momentum brings shorter wavelengths and the capability to reveal the structure of matter with more details. • Discovery of smaller particles reveals more massive particles, which require, according to Einstein’s E=mc^2 , more and more energy to produce them. As particles are accelerated to energies many times their rest mass, momentum and energy will be calculated in terms of the special relativity. Although velocity saturates asymptotically – always below the speed of light-, momentum and energy continue to increase as particles are accelerated.
As a basic principle, accelerators use powerful electric fields to push energy into a beam of charged particle. According to Lorentz force: • F=q (E +v *B) • one can see that particles gain energy only due to the electric field. Particles acquire an energy which is just their charge multiplied by the electric potential difference. • But, building up high-voltage electrostatic generators creates many difficulties because of the electrical breakdown, which becomes a serious problem above a few tens of KV.
Characteristics of an accelerator: • Continuous or pulsed mode of operation; • The type of accelerated particles; • The maximum particle energy; • The intensity of the particle beam; • The particle energy resolution.
Electrostatic accelerators: • Particles accelerated by a constant voltage difference Example: Van de Graaff accelerators , which have Van de Graaff generator with tandem van de Graaff accelerator. (Fig) The Cockroft-Walton generator is another kind of generators for electrostatic accelerators. (Fig)
Cyclic accelerators:(Linear or Linac) • In linear accelerators, particles travel in a vacuum down a long, copper tube. The electrons ride waves made by wave generators called klystrons. Electromagnets keep the particles confined in a narrow beam. When the particle beam strikes a target at the end of the tunnel, various detectors record the events -- the subatomic particles and radiation released. These accelerators are huge, and are kept underground. An example of a linear accelerator is the linac at the Stanford Linear Accelerator Laboratory (SLAC) in California, which is about 1.8 miles (3 km) long.
LINAC’s basic scheme • The idea of overcoming the voltage breakdown problem of a single stage of acceleration was to place a series of cylindrical electrodes one after another in a straight line to form linear accelerators, called LINACs, and use an alternative field.
Charged particles enter on the left and are accelerated towards the first drift tube by an electric field. Once inside the drift tube, they are shielded from the field and drift through a constant velocity. When they arrive, at the next gap, the field accelerates them again until they reach the next drift tube. This continues with the particles picking up more and more energy in each gap, until they shoot out of the accelerator on the right. The drift tubes shield the particles for the length of time that the field would be decelerating. • But, to reach high energy, it would require extremely long linear accelerators.
Linac of CERN • CERN’s accelerator complex, one of the world’s complex scientific instruments, includes particle accelerators and colliders and handles beams of electrons, positrons, protons, antiprotons and ions. The achieved energies are about 100GeV in the Large Electron-Positron Collider LEP2, and will increase up to 7TeV in the future Large Hadron Collider LHC.
Circular Accelerators • betatron • electrons only, cheap, portable, to ~500 MeV • cyclotron • Protons to ~500 MeV (TRIUMF, PSI) • Synchrotron • 100 GeV electrons (LEP) • 1 TeV protons and antiprotons (FNAL) • 7 TeV protons (LHC)
The following step was the cyclotron invention (1929), based on making a particle follow a circular path in a magnetic field through the same accelerating gap. • The balance between centripetal acceleration of motion in a circle and Lorentz’s force is: • evB =mv^2/r • The radius of the orbit in cyclotron is proportional to the velocity and the frequency of revolution: f=v/2r=eB/2m • For low energy particles, the revolution frequency of cyclotron is constant as far as the particle mass remains into the classic limit.
Circular accelerators do essentially the same jobs as linacs. However, instead of using a long linear track, they propel the particles around a circular track many times. At each pass, the magnetic field is strengthened so that the particle beam accelerates with each consecutive pass. When the particles are at their highest or desired energy, a target is placed in the path of the beam, in or near the detectors. Circular accelerators were the first type of accelerator invented in 1929. In fact, the first cyclotron (shown below) was only 4 inches (10 cm) in diameter
cyclotron • Particles being accelerated move inside a vacuum chamber comprising two dees that are connected to a radio frequency (rf) generator with a frequency between 10-30 Mhz. (Fig) • Cyclotron works with fixed frequency and it is possible until the mass of the particle approaches its rest mass.
Lawrence's cyclotron used two D-shaped magnets (called Dee) separated by a small gap. The magnets produced a circular magnetic field. An oscillating voltage created an electric field across the gap to accelerate the particles (ions) each time around. As the particles moved faster, the radius of the their circular path became bigger until they hit the target on the outermost circle. Lawrence's cyclotron was effective, but could not reach the energies that modern circular accelerators do.
Modern circular accelerators place klystrons and electromagnets around a circular copper tube to speed up particles. Many circular accelerators also have a short linac to accelerate the particles initially before entering the ring. An example of a modern circular accelerator is the Fermi National Accelerator Laboratory (Fermilab) in Illinois, which stretches almost 10 square miles (25.6 square km).
The first particle accelerator (cyclotron) developed by Ernest O. Lawrence in 1929
Betatron • Another electron accelerator (Fig) • It is now mainly used for : tumour therapy using either the electron beam or the X-rays radiated by the accelerated electrons as they circulated on their orbits, and for metal radiography using the X-radiation
How Atom Smashers Work • Did you know that you have a type of particle accelerator in your house right now? In fact, you are probably reading this article with one! The cathode ray tube (CRT) of any TV or computer monitor is really a particle accelerator. • The CRT takes particles (electrons) from the cathode, speeds them up and changes their direction using electromagnets in a vacuum and then smashes them into phosphor molecules on the screen. The collision results in a lighted spot, or pixel, on your TV or computer monitor. • Particles are accelerated by electromagnetic waves inside the device, in much the same way as a surfer gets pushed along by the wave. The more energetic we can make the particles, the better we can see the structure of matter. It's like breaking the rack in a billiards game. When the cue ball (energized particle) speeds up, it receives more energy and so can better scatter the rack of balls (release more particles).
TRIUMF(kind of cyclotron) • TR13 CyclotronThe TR13 is a small production cyclotron accelerating protons to 30 MeV (MeV = million electron volts). It was designed by TRIUMF staff, built by EBCO Technologies (Richmond, BC), and is owned by the University of British Columbia. Operated by TRIUMF staff, the TR13 is used in the research and production of radioisotopes for medical purposes. To the right (south) of the TR13
Clean RoomThe clean room is kept dust-free by maintaining a positive atmospheric room pressure. This is accomplished by constantly pumping in filtered air such that the total room air volume is replaced every 4 minutes. In this dust-free environment TRIUMF technicians construct specialized equipment such as this module destined for the ATLAS particle detector at CERN, Switzerland. (TRIUMF's contribution to the ATLAS project consists of building 4 detector "wheels" at 32 modules/wheel - 2 "wheels" are placed at each end of the ATLAS tracking chamber.)
Contraband Detection SystemTRIUMF has developed a new detection system that can "see" plastic explosives or illicit drugs in luggage and cargo. Even if the contraband is hidden, by scanning with gamma rays the Contraband Detection System (CDS) will provide 3-dimensional images of even small amounts of plastic explosives or illicit drugs
ScintillatorsScintillators are tested in the meson hall service annex (situated next to the meson hall extension). These plastic materials emit photons of visible light when they are struck by energetic particles or photons. In this display they are made to fluoresce by an ultraviolet lamp. Scintillators are used extensively at TRIUMF to detect particles, in conjunction with a photomultiplier tube which amplifies the light and converts it to an electric pulse. The scintillators are covered in black tape to exclude all outside light. Often complex-shaped light pipes are used to connect the scintillator to the photomultiplier, as the phototubes are too big to fit in the crowded area around the target. (Next: Meson Hall)
Meson HallMost of the protons extracted from the cyclotron are used to create an intense beam of pions (or "pi-mesons") for use in the meson hall. In an average of 26 billionths of a second the pions decay into muons (which last, on average, for 2.2 millionths of a second). Separating the pion beam into different "beam lines" allows several pion/muon experiments to be performed simultaneously. Looking down two stories to the meson hall floor below, we see some of the individual beam lines emerging from the yellow shielding blocks.
Concrete BlocksThis first thing you will notice about the meson hall is the number of huge yellow blocks, piled up like a giant brick wall, along the south side. As you may have guessed, these "bricks" are made of concrete. Concrete is used as a shielding material wherever possible. It is reasonably effective and inexpensive. Also, the modular blocks are easily moved, by one of the twin 50-ton travelling overhead cranes, for maintenance or changing of beam line elements. The whole building contains 45,000 tonnes of concrete shielding to absorb the radiation given off by the cyclotron and beam lines.
Cave InterlocksTo visit one of the experimental areas, we walk down two flights of stairs. The area around the beam line where the experiment is mounted is known as a "cave". A cave is typically surrounded by shielding blocks and secured with an interlock system, which prevents beam delivery to the beam line when the cave door is open. Experimenters set up their equipment, including particle detectors, and must leave before the control room personnel allow the beam to enter the experimental area.