Cockcroft-Walton accelerator

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The Cockcroft-Walton accelerator (sometimes also called the Cockcroft-Walton generator , although it actually only describes the high-voltage generating part of the facility) is a type of particle accelerator that works with DC voltage .

Cockcroft-Walton accelerator for 1 megavolt maximum voltage

history

In 1930, its developers John Cockcroft and Ernest Walton succeeded in providing the first evidence of a nuclear reaction triggered by artificially accelerated particles - at the time proudly referred to as nuclear fragmentation . Lithium was irradiated with protons with a kinetic energy of 300 keV . Helium- 4 atomic nuclei (alpha particles) were observed as reaction products . So it was the reaction

.

construction

The actual acceleration part is very similar to that of a Van de Graaff accelerator : a straight tube in which a high vacuum and a longitudinally oriented, temporally constant electrical field are maintained. The difference is that the accelerating voltage is generated by a high voltage cascade . Unlike the Van de Graaff accelerator, the potential rings of the acceleration tube do not require a chain of resistors as a voltage divider , but can simply be connected to the individual voltage levels of the cascade.

Due to difficulties in isolating very high voltages ( leakage current , corona discharge ), the voltage that can be achieved is limited to a few megavolts , as with Van-de-Graaff systems .

A power supply within the high-voltage electrode ( terminal ) is required to operate the ion source . It can consist of a generator driven by an insulating shaft from a motor at ground potential. For small systems for e.g. B. 200 kilovolts can also be supplied by a highly insulating transformer .

use

The high voltage does not have to be built up using electrostatic technology (mechanical transport of charge on a moving insulator), as is the case with Van de Graaff systems, but is obtained from the power grid via transformers and voltage multipliers. Therefore Cockcroft-Walton systems are also suitable for applications with a relatively high current strength of the particle beam (up to many milliamperes). On the other hand, their high voltage and thus the particle energy is less precisely constant, but always shows a certain blurring due to waviness.

Cockroft-Walton accelerators, as independent acceleration systems, hardly play a role in basic physical research. However, in many large accelerators such as synchrotrons they serve as the first acceleration stage directly at the exit of the ion source .

literature

  • Frank Hinterberger: Physics of Particle Accelerators and Ion Optics . 2nd edition, Springer 2008, ISBN 978-3-540-75281-3
  • Ragnar Hellborg (Ed.): Electrostatic Accelerators . Springer Verlag, Berlin 2005, ISBN 3-540-23983-9

Individual evidence

  1. Eric B. Paul, Nuclear and Particle Physics, North-Holland Publ. Comp., 1969