“linear accelerator”的概念、定义、翻译、参考文献-科学参考

linear accelerator

Physics

A type of particle accelerator in which charged particles are accelerated in a straight line, either by a steady electric field or by means of radio-frequency electric fields. There are three main types:

Van de Graaff accelerator.
This device accelerates charged particles by applying a high electrical potential difference generated by a Van de Graaff generator. The potential difference can be kept steady to within one part in a thousand, enabling a very uniformly energetic beam of accelerated particles to be created. The maximum electrical potential attainable is about 10 MV and depends on the insulating properties of the gas around the Van de Graaff sphere. It is increased by enclosing the whole generator in a pressure vessel containing an inert gas at a pressure of about 20 atmospheres. A source, at the same potential as the sphere, produces charged particles that enter a column of cylindrical electrodes, each of which is at a lower potential than the one above it. The ions are accelerated as they pass through the gaps between the cylinders. The nonuniform electric fields between the gaps have the effect of focusing the beam of charged particles.

Drift-tube accelerator.

In this device charged particles are accelerated along a line of hollow metal cylinders called drift tubes. The cylinders are connected alternately to opposite terminals of an alternating potential difference produced by either a magnetron or a klystron. The arrangement ensures that adjacent cylinders are always at opposite electrical potentials. For example, a proton beam may be injected into the first of the line of drift tubes from a Van de Graaff accelerator. Protons reaching the gap between the first two tubes will be accelerated into the second tube, when the alternating potential makes the first tube positive and the second tube negative. This enables the protons emerging into the gap between two cylinders to be accelerated into the next cylinder. All parts of a particular tube are at the same potential, since the metal acts as an equipotential surface. Therefore within a cylinder the particles travel at a constant speed (hence drift tube). It follows that the energy of the beam is increased every time the protons cross between drift tubes, and therefore a device with a large number of gaps can produce extremely high-energy beams using only moderate supply voltages. The Berkeley proton accelerator has a drift-tube arrangement of 47 cylinders, 19 km long. It accelerates protons up to 31.5 GeV.

Travelling-wave accelerator.

This apparatus uses radio-frequency electromagnetic waves to accelerate charged particles. Charged particles are fed into the travelling-wave accelerator at close to the speed of light and are carried through a wave guide by the electric field component of a radio wave. The very high initial speeds for charged particles are needed to match the phase velocity of radio signals propagating along the wave guide. However, this means that travelling-wave accelerators are suitable only for accelerating lighter particles, such as electrons. The electrons can be accelerated to initial speeds of 98% of the speed of light by a Van de Graaff accelerator. At such high initial speeds, there is little scope for further acceleration and any increase in electron energy provided by the accelerator results from the relativistic increase in mass. The Stanford linear accelerator (SLAC) uses the travelling-wave principle. SLAC is capable of accelerating electrons and positrons to 50 GeV in a tube 3 km long.

Electronics and Electrical Engineering

A particle accelerator in which electrons or protons are accelerated as they travel along a straight evacuated chamber. The acceleration is provided by the electric field vector that is associated with the radiofrequency (r.f.) output from a klystron or magnetron.
In the standing-wave accelerator standing waves from an r.f. supply are established between a series of cylindrical electrodes coaxial with the chamber. The standing waves are established with the electric vector aligned axially. The electrons are only accelerated in the gaps between the electrodes; inside the electrodes they drift towards the next electrode. The electrodes are therefore termed drift tubes. The lengths of the drift tubes and the frequency of the r.f. supply is arranged so that the phase of the electric field vector is always in accelerating mode when the electrons emerge from a drift tube. As the energy of the particles increases, the lengths of successive drift tubes must be correspondingly increased in order to maintain the required phase relationship.
Higher particle energies are achieved using a travelling-wave accelerator, in which the accelerating chamber is a long waveguide. An r.f. travelling wave is established from a high-power source and the waveguide is excited so that a large-amplitude travelling wave is produced, travelling with a phase velocity equal to the local velocity of the electrons to be accelerated. Power is transferred from the r.f. wave to the accelerated electrons and the r.f. power is boosted at regular intervals along the length using klystrons.

单词	linear accelerator
释义	linear accelerator Physics A type of particle accelerator in which charged particles are accelerated in a straight line, either by a steady electric field or by means of radio-frequency electric fields. There are three main types: Van de Graaff accelerator. This device accelerates charged particles by applying a high electrical potential difference generated by a Van de Graaff generator. The potential difference can be kept steady to within one part in a thousand, enabling a very uniformly energetic beam of accelerated particles to be created. The maximum electrical potential attainable is about 10 MV and depends on the insulating properties of the gas around the Van de Graaff sphere. It is increased by enclosing the whole generator in a pressure vessel containing an inert gas at a pressure of about 20 atmospheres. A source, at the same potential as the sphere, produces charged particles that enter a column of cylindrical electrodes, each of which is at a lower potential than the one above it. The ions are accelerated as they pass through the gaps between the cylinders. The nonuniform electric fields between the gaps have the effect of focusing the beam of charged particles. Drift-tube accelerator. In this device charged particles are accelerated along a line of hollow metal cylinders called drift tubes. The cylinders are connected alternately to opposite terminals of an alternating potential difference produced by either a magnetron or a klystron. The arrangement ensures that adjacent cylinders are always at opposite electrical potentials. For example, a proton beam may be injected into the first of the line of drift tubes from a Van de Graaff accelerator. Protons reaching the gap between the first two tubes will be accelerated into the second tube, when the alternating potential makes the first tube positive and the second tube negative. This enables the protons emerging into the gap between two cylinders to be accelerated into the next cylinder. All parts of a particular tube are at the same potential, since the metal acts as an equipotential surface. Therefore within a cylinder the particles travel at a constant speed (hence drift tube). It follows that the energy of the beam is increased every time the protons cross between drift tubes, and therefore a device with a large number of gaps can produce extremely high-energy beams using only moderate supply voltages. The Berkeley proton accelerator has a drift-tube arrangement of 47 cylinders, 19 km long. It accelerates protons up to 31.5 GeV. Travelling-wave accelerator. This apparatus uses radio-frequency electromagnetic waves to accelerate charged particles. Charged particles are fed into the travelling-wave accelerator at close to the speed of light and are carried through a wave guide by the electric field component of a radio wave. The very high initial speeds for charged particles are needed to match the phase velocity of radio signals propagating along the wave guide. However, this means that travelling-wave accelerators are suitable only for accelerating lighter particles, such as electrons. The electrons can be accelerated to initial speeds of 98% of the speed of light by a Van de Graaff accelerator. At such high initial speeds, there is little scope for further acceleration and any increase in electron energy provided by the accelerator results from the relativistic increase in mass. The Stanford linear accelerator (SLAC) uses the travelling-wave principle. SLAC is capable of accelerating electrons and positrons to 50 GeV in a tube 3 km long. Electronics and Electrical Engineering A particle accelerator in which electrons or protons are accelerated as they travel along a straight evacuated chamber. The acceleration is provided by the electric field vector that is associated with the radiofrequency (r.f.) output from a klystron or magnetron. In the standing-wave accelerator standing waves from an r.f. supply are established between a series of cylindrical electrodes coaxial with the chamber. The standing waves are established with the electric vector aligned axially. The electrons are only accelerated in the gaps between the electrodes; inside the electrodes they drift towards the next electrode. The electrodes are therefore termed drift tubes. The lengths of the drift tubes and the frequency of the r.f. supply is arranged so that the phase of the electric field vector is always in accelerating mode when the electrons emerge from a drift tube. As the energy of the particles increases, the lengths of successive drift tubes must be correspondingly increased in order to maintain the required phase relationship. Higher particle energies are achieved using a travelling-wave accelerator, in which the accelerating chamber is a long waveguide. An r.f. travelling wave is established from a high-power source and the waveguide is excited so that a large-amplitude travelling wave is produced, travelling with a phase velocity equal to the local velocity of the electrons to be accelerated. Power is transferred from the r.f. wave to the accelerated electrons and the r.f. power is boosted at regular intervals along the length using klystrons.
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