Linear particle accelerator: Difference between revisions

Revision as of 15:44, 3 February 2022

Revision as of 18:13, 3 February 2022

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In 1924, Gustav Ising published the first description of a linear particle accelerator using a series of accelerating gaps. Particles would proceed down a series of tubes. At a regular frequency, an accelerating voltage would be applied across each gap. As the particles gained speed while the frequency remained constant, the gaps would be spaced farther and farther apart, in order to ensure the particle would see a voltage applied as it reached each gap. Ising never successfully implemented this design.<ref name="heibron">{{cite book |last1=Heilbron |first1=J.L. |last2=Seidel |first2=Robert W. |title=Lawrence and His Laboratory: A History of the Lawrence Berkeley Laboratory, Volume I |date=1989 |publisher=University of California Press |___location=Berkeley, CA |url=http://ark.cdlib.org/ark:/13030/ft5s200764/ |access-date=2 February 2022}}</ref>

[[Rolf Wideroe]] discovered Ising's paper in 1927, and as part of his PhD thesis, built an 88-inch long, two gap version of the device. Where Ising had proposed a spark gap as the voltage source, Wideroe used a 25kV [[vacuum tube]] oscillator. He successfully demonstrated that he had accelerated sodium and potassium ions to 50 keV, twice the energy they would have received if accelerated only once by the tube. By successfully accelerating a particle multiple times using the same voltage source, Wideroe demonstrated the utility of [[radio frequency]] acceleration.<ref>{{cite book |last1=Conte |first1=Mario |last2=MacKay |first2=William |title=An introduction to the physics of particle accelerators |date=2008 |publisher=World Scientific |___location=Hackensack, N.J. |isbn=9789812779601 |edition=2nd}}</ref>

This type of linac was limited by the voltage sources that were available at the time, and it was not until after [[World War II]] that [[Luis Walter Alvarez|Luis Alvarez]] was able to use newly developed high frequency oscillators to design the first resonant cavity drift tube linac. An Alvarez linac differs from the Wideroe type in that the RF power is applied to the entire [[Resonator#Cavity_resonators|resonant chamber]] through which the particle travels, and the central tubes are only used to shield the particles during the decelerating portion of the oscillator's phase. Using this approach to acceleration meant that Alvarez's first linac was able to achieve proton energies of 31.5 MeV in 1947, the highest that had ever been reached at the time.<ref>{{cite web |title=Alvarez proton linear accelerator |url=https://www.si.edu/es/object/alvarez-proton-linear-accelerator%3Anmah_700150 |website=Smithsonian Institution |access-date=3 February 2022 |language=es}}</ref>

The initial Alvarez type linacs had no strong mechanism for keeping the beam focused, and were limited in length and energy as a result. The development of the [[strong focusing]] principle in the early 1950s led to the installation of focusing [[quadrupole magnet|quadrupole magnets]] inside the drift tubes, allowing for longer and thus more powerful linacs. Two of the earliest examples of Alvarez linacs with strong focusing magnets were built at [[CERN]] and [[Brookhaven National Laboratory]].<ref>{{cite report |author=Lapostolle, Pierre |date= July 1989 |title= Proton Linear Accelerators: A Theoretical and Historical Introduction |url= https://www.osti.gov/servlets/purl/6038195 |publisher= Los Alamos National Laboratory |docket=LA-11601-MS |access-date= February 4, 2022}}</ref>

==Construction and operation==