Introduction to Particle Accelerators
Professor Andrei A. Seryi
John Adams Institute for Accelerator Science
University of Oxford, Royal Holloway University of London and Imperial College London
An electric field (E) is defined as a region of space where a charged particle experiences a force. An example of a charged particle that experiences this force is an electron (e-) moving from negative to positive. A magnetic field (B) is a region of space where a magnetic material experiences a force. A magnetic field also has an effect on charged particles by causing them to change direction.
In order to see smaller and smaller things you need to use higher and higher energies and smaller and smaller wavelengths. De Broglie proposed that all matter has wave properties (this followed on from Einstein’s photoelectric effect where light can be thought of as particles called photons rather than waves). The De Broglie wavelength is the wavelength associated with the particle, p is the momentum of the particle (its mass x its velocity) and h is the Planck constant. This means that particles can replace electromagnetic waves to probe the structure of matter.
Lightning is a massive electrostatic discharge between electrically charged regions within clouds, or between a cloud and the Earth’s surface. The charged regions within the atmosphere temporarily equalize themselves through a lightning flash, commonly referred to as a strike if it hits an object on the ground.
Cosmic rays are very high-energy particles, mainly originating outside the Solar System. They may produce showers of secondary particles that penetrate and impact the Earth’s atmosphere and sometimes even reach the surface. Comprised primarily of high-energy protons and atomic nuclei, their origin has been a mystery.
The Van de Graaff generator is a piece of equipment familiar to most secondary school children mainly for making their hair stand on end. It is an electrostatic generator which uses a moving belt to accumulate very high amounts of electrical charge on a hollow metal globe on the top of the stand. It was invented by American physicist Robert J. Van de Graaff in 1929.
Thermionic emission involves heating a metal (cathode) to a high enough temperature to release the electrons. The electric field causes the electrons to be accelerated away from the cathode. Photoelectric emission occurs if the photons of electromagnetic radiation have enough energy to cause the release of electrons from the surface of a metal. This energy needs to be higher than the work function of the metal (the minimum energy required to remove a delocalised electron from the surface of the metal).
Ions are charged particles and only charged particles can be accelerated by an electric field. Therefore accelerators need charged particles.
An effect of the space charge effect is the repulsion of electrons emitted from the cathode of a thermionic vacuum tube by electrons accumulated in the space charge near the cathode. Coulomb force (also called electrostatic force or Coulomb interaction) is the attraction or repulsion of particles or objects because of their electric charge. One of the basic physical forces, the electric force is named after the French physicist, Charles-Augustin de Coulomb, who in 1785 published the results of an experimental investigation into the correct quantitative description of this force.
A cyclotron is a type of particle accelerator in which charged particles accelerate outwards from the centre along a spiral path. The particles are held to a spiral trajectory by a static magnetic field and accelerated by a rapidly varying (radio frequency) electric field between the “Dees”.
A synchrotron is a particular type of cyclic particle accelerator originating from the cyclotron in which the guiding magnetic field (bending the particles into a closed path) is time-dependent, being synchronized to a particle beam of increasing kinetic energy. The synchrotron is one of the first accelerator concepts that enable the construction of large-scale facilities, since bending, beam focusing and acceleration can be separated into different components. The electromagnetic radiation emitted when charged particles are accelerated radially is called synchrotron radiation.
Focusing is referring to the process of keeping the charged particles moving in the correct direction.
Colliders will allow scientists to investigate the origins of our universe. The most successful outcome occurs when the particles are moving towards each other before collision. g is the Lorentz factor and is an expression which appears in several equations in special relativity. It arises from deriving the Lorentz transformations. Relativistic mass is the mass of an object m in motion and is dependent on g and the rest mass m0:
The International Linear Collider (ILC) is a proposed linear particle accelerator. It is planned to have a collision energy of 500 GeV initially, with the possibility for a later upgrade to 1000 GeV (GeV is an energy unit).
Even Nobel prizes in the other sciences rely on physics.
A free-electron laser (FEL), is a type of laser that shares the same optical properties as conventional lasers such as emitting a beam consisting of coherent electromagnetic radiation that can reach high power, but that uses some very different operating principles to form the beam. Unlike gas-, liquid-, or solid-state lasers such as diode lasers, in which electrons are excited in bound atomic or molecular states, free-electron lasers use a relativistic (travelling close to the speed of light) electron beam that moves freely through a magnetic structure, hence the term free electron as the lasing medium. The free-electron laser has the widest frequency range of any laser type, and can be widely tunable, currently ranging in wavelength from microwaves, through terahertz radiation and infrared, to the visible spectrum, ultraviolet, and X-ray.
Diffraction is the sprading of a wave due to the presence of a gap or an obstacle. Maximum diffraction occurs when the wavelength is about the same size as the obstacle/gap. Diffraction can cause interference. When interfering, two waves can add together to create a wave of greater amplitude than either one (constructive interference) or subtract from each other to create a wave of lesser amplitude than either one (destructive interference), depending on their relative phase. Two waves are said to be coherent if they have a constant relative phase (for instance a peak matching a peak). The degree of coherence is measured by the interference visibility, a measure of how perfectly the waves can cancel due to destructive interference.
Coherent diffractive imaging (CDI) also coherent diffraction imaging is a “lensless” technique for 2D or 3D reconstruction of the image of nanoscale structures such as nanotubes, nanocrystals, defects, potentially proteins, and more. In CDI, a highly coherent beam of x-rays, electrons or other wavelike particle or photon is incident on an object. The beam scattered by the object produces a diffraction pattern downstream which is then collected by a detector. This recorded pattern is then used to reconstruct an image via an iterative feedback algorithm. Effectively, the objective lens in a typical microscope is replaced with software to convert from the reciprocal space diffraction pattern into a real space image. The advantage in using no lenses is that the final image is aberration–free and so resolution is only diffraction and dose limited (dependent on wavelength, aperture size and exposure). A simple Fourier transform retrieves only the intensity information and so is insufficient for creating an image from the diffraction pattern due to the phase problem.
ISIS is a world-leading centre for research in the physical and life sciences at the Rutherford Appleton Laboratory near Oxford in the United Kingdom. The suite of neutron and muon instruments allows the properties of materials to be understood at the scale of atoms. A neutron is the neutral particle found inside the nucleus of an atom and a muon is an elementary particle similar to the electron, with unitary negative electric charge (−1) and a spin of 1⁄2. Together with the electron, the tau, and the three neutrinos, it is classified as a lepton. As is the case with other leptons, the muon is not believed to have any sub-structure at all (i.e., is not thought to be composed of any simpler particles).
Plasma acceleration is a technique for accelerating charged particles, such as electrons, positrons and ions, using an electric field associated with electron plasma wave or other high-gradient plasma structures (like shock and sheath fields). The plasma acceleration structures are created either using ultra-short laser pulses or energetic particle beams that are matched to the plasma parameters. These techniques offer a way to build high performance particle accelerators of much smaller size than conventional devices
Photons produced by the betatron oscillation of electrons in a beam-driven plasma wake provide a high-energy source of hard X-rays and gamma rays. This betatron radiation is interesting not only for its high intensity and spectral characteristics, but also because it can be used as a diagnostic for beam matching into the plasma, which is critical for maximizing the energy extraction efficiency of a plasma accelerator stage.
The transuranium elements (also known as transuranic elements) are the chemical elements with atomic numbers greater than 92 (the atomic number of uranium). All of these elements are unstable and decay radioactively into other elements.
For protons and heavier ions the dose increases while the particle penetrates the tissue and loses energy continuously. Hence the dose increases with increasing thickness up to the Bragg peak that occurs near the end of the particle’s range. Beyond the Bragg peak, the dose drops to zero (for protons) or almost zero (for heavier ions). The advantage of this energy deposition profile is that less energy is deposited into the healthy tissue surrounding the target tissue.
The Bragg peak is a pronounced peak on the Bragg curve which plots the energy loss of ionizing radiation during its travel through matter. For protons, αlpha-rays, and other ion rays, the peak occurs immediately before the particles come to rest. This is called Bragg peak, for William Henry Bragg who discovered it in 1903.