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Mansa Musa was the ruler of the Mali Empire in West Africa. Details recorded here should be sourced; unknown information is left blank.
MORE →Reflects the personal views, recollections, and perspective of the author, Mike Davis.
This is a personal recollection on the Move fire on May 13, 1985
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A charged particle beam is a spatially localized group of electrically charged particles that have approximately the same position, kinetic energy (resulting in the same velocity), and direction. The kinetic energies of the particles are much larger than the energies of particles at ambient temperature. The high energy and directionality of charged particle beams make them useful for many applications in particle physics (see Particle beam#Applications and Electron-beam technology).
Such beams can be split into two main classes:
Assuming a normal distribution of particle positions and impulses, a charged particle beam (or a bunch of the beam) is characterized by[3]
These parameters can be expressed in various ways. For example, the current and beam size can be combined into the current density, and the current and energy (or beam voltage V) can be combined into the perveance K = I V−3/2.
The charged particle beams that can be manipulated in particle accelerators can be subdivided into electron beams, ion beams and proton beams.
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A particle beam is a stream of charged or neutral particles other than photons. In particle accelerators, these particles can move with a velocity close to the speed of light. There is a difference between the creation and control of charged particle beams and neutral particle beams, as only the first type can be manipulated to a sufficient extent by devices based on electromagnetism. The manipulation and diagnostics of charged particle beams at high kinetic energies using particle accelerators are main topics of accelerator physics.
Particle beam cooling is the process of improving the quality of particle beams produced by particle accelerators, by reducing the emittance. Techniques for particle beam cooling include: Stochastic cooling Electron cooling Ionization cooling Laser cooling Radiation damping Buffer-gas cooling within RF quadrupoles
A charged particle beam is a spatially localized group of electrically charged particles that have approximately the same position, kinetic energy (resulting in the same velocity), and direction. The kinetic energies of the particles are much larger than the energies of particles at ambient temperature. The high energy and directionality of charged particle beams make them useful for many applications in particle physics (see Particle beam#Applications and Electron-beam technology). Such beams can be split into two main classes: unbunched beams (coasting beams or DC beams), which have no longitudinal substructure in the direction of beam motion. bunched beams, in which the particles are distributed into pulses (bunches) of particles. Bunched beams are most common in modern facilities, since the most modern particle accelerators require bunched beams for acceleration. Assuming a normal distribution of particle positions and impulses, a charged particle beam (or a bunch of the beam) is characterized by the species of particle, e.g. electrons, protons, or atomic nuclei the mean energy of the particles, often expressed in electronvolts (typically keV to GeV) the (average) particle current, often expressed in amperes the particle beam size, often using the so-called β-function the beam emittance, a measure of the area occupied by the beam in one of several phase spaces. These parameters can be expressed in various ways. For example, the current and beam size can be combined into the current density, and the current and energy (or beam voltage V) can be combined into the perveance K = I V−3/2. The charged particle beams that can be manipulated in particle accelerators can be subdivided into electron beams, ion beams and proton beams.
A particle-beam weapon uses a high-energy beam of atomic or subatomic particles to damage the target by disrupting its atomic and/or molecular structure. A particle-beam weapon is a type of directed-energy weapon, which directs focused energy toward a target using atomic scale particles. Some particle-beam weapons have potential practical applications, e.g. as an antiballistic missile defense or detection system. They have been known by several names: particle accelerator guns, ion cannons, proton beams, lightning rays, rayguns, etc. The concept of particle-beam weapons comes from sound scientific principles and experiments. One process is to simply overheat a target until it is no longer operational. However, after decades of research and development, particle-beam weapons remain at the research stage, and it remains to be seen if or when they will be deployed as practical, high-performance military weapons. Particle accelerators are a well-developed technology used in scientific research. They use electromagnetic fields to accelerate and direct charged particles along a predetermined path, and a magnetic lens system to focus these streams on a target. The cathode-ray tube in many twentieth-century televisions and computer monitors is a very simple type of particle accelerator. More powerful versions include synchrotrons and cyclotrons used in nuclear research. A particle-beam weapon is a weaponized version of this technology. It accelerates charged particles (in most cases electrons, positrons, protons, or ionized atoms, but very advanced versions can accelerate other particles such as mercury nuclei) to near-light speed and then directs them towards a target. The particles' kinetic energy is imparted to matter in the target, inducing near-instantaneous and catastrophic superheating at the surface, and when penetrating deeper, ionization effects can upset or destroy electronics. However, many accelerators used for high-energy nuclear physics are quite large (sometimes on the order of kilometers in length, such as the LHC), with highly constrained construction, operation, and maintenance requirements. If an accelerator is to be deployed in space, it has to be lightweight and robust.
Before the 1921 destruction of Tulsa’s Greenwood District, Black residents had created a remarkable center of business and community life. The district included stores, professional offices, entertainment venues and homes owned by Black citizens. Understanding Greenwood means learning what was built—not only what was burned.
MORE →Madam C.J. Walker