Linear particle accelerator: Difference between revisions

Revision as of 14:00, 23 November 2021

Revision as of 21:00, 24 December 2021

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The higher the frequency of the acceleration voltage selected, the more individual acceleration thrusts per path length a particle of a given speed experiences, and the shorter the accelerator can therefore be overall. That is why accelerator technology developed in the pursuit of higher particle energies, especially towards higher frequencies.

The linear accelerator concepts (often called accelerator structures in technical terms) that have been used since around 1950 work with frequencies in the range from around {{frequency|100 megahertz (|MHz)}} to a few gigahertz (GHz) and use the electric field component of electromagnetic waves.

=== Standing waves and traveling waves ===

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The acceleration concepts used today for ''ions'' are always based on electromagnetic [[Standing wave|standing waves]] that are formed in suitable [[Resonator|resonators]]. Depending on the type of particle, energy range and other parameters, very different types of resonators are used; the following sections only cover some of them. ''Electrons'' can also be accelerated with standing waves above a few MeV. An advantageous alternative here, however, is a progressive wave, a traveling wave. The [[phase velocity]] the traveling wave must be roughly equal to the particle speed. Therefore, this technique is only suitable when the particles are almost at the speed of light, so that their speed only increases very little.

The development of high-frequency oscillators and power amplifiers from the 1940s, especially the klystron, was essential for these two acceleration techniques . The first larger linear accelerator with standing waves - for protons - was built in 1945/46 in the [[Lawrence Berkeley National Laboratory]] under the direction of [[Luis Walter Alvarez|Luis W. Alvarez]]. The frequency used was {{frequency|200 |MHz}}.  The first electron accelerator with traveling waves of around {{frequency|2 |GHz (gigahertz)}} was developed a little later at [[Stanford University]] by [[W. W. Hansen|W.W. Hansen]] and colleagues.<ref>{{Cite journal|last1=Ginzton|first1=E. L.|last2=Hansen|first2=W. W.|last3=Kennedy|first3=W. R.|date=1948-02-01|title=A Linear Electron Accelerator|url=https://aip.scitation.org/doi/10.1063/1.1741225|journal=Review of Scientific Instruments|volume=19|issue=2|pages=89–108|doi=10.1063/1.1741225|pmid=18908606|bibcode=1948RScI...19...89G|issn=0034-6748}}</ref>

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|+Principle of the acceleration of particle packets