Content deleted Content added
Add basic principles of operation section. |
m task, replaced: Annual Reviews of → Annual Review of |
||
Line 16:
[[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#
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
In 1947, at about the same time that Alvarez was developing his linac concept for protons, [[W. W. Hansen|William Hansen]] constructed the first travelling-wave electron accelerator at Stanford University.<ref>{{cite journal |author-last=Ginzton |author-first=Edward L. |date= April 1983| title=Early Accelerator Work at Stanford |journal= SLAC Beam Line | pages=
}}</ref> Electrons are sufficiently lighter than protons that they achieve speeds close to the [[speed of light]] early in the acceleration process. As a result, "accelerating" electrons increase in energy, but can be treated as having a constant velocity from an accelerator design standpoint. This allowed Hansen to use an accelerating structure consisting of a horizontal [[waveguide]] loaded by a series of discs. The 1947 accelerator had an energy of 6 MeV. Over time, electron acceleration at the [[SLAC National Accelerator Laboratory]] would extend to a size of {{convert|2|mi|km}} and an output energy of 50 GeV.<ref>{{cite book |last1=Neal |first1=R. B. |title=The Stanford Two-Mile Accelerator |chapter=Chap. 5 |publisher=W.A. Benjamin, Inc |year=1968 |___location=New York, New York |page=59 |chapter-url=http://www.slac.stanford.edu/spires/hep/HEPPDF/twomile/Chapters_4_5.pdf |access-date=2010-09-17}}</ref>
As linear accelerators were developed with higher beam currents, using magnetic fields to focus proton and heavy ion beams presented difficulties for the initial stages of the accelerator. Because the [[Lorentz force|magnetic force]] is dependent on the particle velocity, it was desirable to create a type of accelerator which could simultaneously accelerate and focus low-to-mid energy [[hadron
Beginning in the 1960s, scientists at Stanford and elsewhere began to explore the use of [[superconducting radio frequency]] cavities for particle acceleration.<ref>{{cite arXiv | last=Padamsee | first=Hasan | date= April 14, 2020 | title= History of gradient advances in SRF | eprint=2004.06720}}</ref> Superconducting cavities made of [[niobium]] alloys allowed for much more efficient acceleration, as a substantially higher fraction of the input power could be applied to the beam, rather than lost to heat. Some of the earliest superconducting linacs included the Superconducting Linear Accelerator (for electrons) at Stanford<ref>{{cite report | first=Catherine | last=Westfall | title=The Prehistory of Jefferson Lab's SRF Accelerating Cavities, 1962 to 1985 | date=April 1997 | publisher=[[Thomas Jefferson National Accelerator Facility]] | docket=JLAB-PHY-97-35 | url=https://misportal.jlab.org/ul/publications/view_pub.cfm?pub_id=11132}}</ref> and the [[Argonne Tandem Linear Accelerator System]] (for protons and heavy ions) at [[Argonne National Laboratory]].<ref>{{cite journal |last1=Ostroumov |first1=Peter |last2=Gerigk |first2=Frank |title=Superconducting Hadron Linacs |journal=Reviews of Accelerator Science and Technology |date=January 2013 |volume=06 |pages=171–196 |doi=10.1142/S1793626813300089}}</ref>
Line 54:
A linear particle accelerator consists of the following parts:
*A straight hollow pipe [[vacuum chamber]] which contains the other components. It is evacuated with a [[vacuum pump]] so that the accelerated particles will not collide with air molecules. The length will vary with the application. If the device is used for the production of X-rays for inspection or therapy the pipe may be only 0.5 to 1.5 meters long.<ref>{{cite book |last1=Podgorsak |first1=E B |title=Radiation Oncology Physics |date=2005 |publisher=[[International Atomic Energy Agency]] |___location=Vienna |isbn=92-0-107304-6 |page=138 |url=https://www.iaea.org/publications/7086/radiation-oncology-physics |language=en |chapter=Treatment Machines for External Beam Radiotherapy}}</ref> If the device is to be an injector for a [[synchrotron]] it may be about ten meters long.<ref>{{cite conference |url=https://s3.cern.ch/inspire-prod-files-b/bf2698b68b2ac10829c592a2137d3ee2 |title=Linear Accelerator Injectors for Proton Synchrotrons |first=J P |last=Blewett |author= |author-link= |date=11 June 1956 |conference=CERN Symposium on High Energy Accelerators and Pion Physics |conference-url= |editor=Edouard Regenstreif |others= |volume=1 |edition= |book-title= |publisher=CERN |archive-url= |archive-date= |___location=Geneva |pages=
*The particle source ''(S)'' at one end of the chamber which produces the [[charged particle]]s which the machine accelerates. The design of the source depends on the particle that is being accelerated. [[Electron]]s are generated by a [[cold cathode]], a [[hot cathode]], a [[photocathode]], or [[RF antenna ion source|radio frequency (RF) ion sources]]. [[Proton]]s are generated in an [[ion source]], which can have many different designs. If heavier particles are to be accelerated, (e.g., [[uranium]] [[ions]]), a specialized ion source is needed. The source has its own high voltage supply to inject the particles into the beamline.<ref>{{cite arXiv |last=Faircloth |first=D C |author-link= |eprint=2103.13231 |title=Particle Sources |class= |date=24 March 2021 }}</ref>
*Extending along the pipe from the source is a series of open-ended cylindrical electrodes ''(C1, C2, C3, C4)'', whose length increases progressively with the distance from the source. The particles from the source pass through these electrodes. The length of each electrode is determined by the frequency and power of the driving power source and the particle to be accelerated, so that the particle passes through each electrode in exactly one-half cycle of the accelerating voltage. The mass of the particle has a large effect on the length of the cylindrical electrodes; for example an electron is considerably lighter than a proton and so will generally require a much smaller section of cylindrical electrodes as it accelerates very quickly.
Line 64:
The particles are injected at the right time so that the oscillating voltage differential between electrodes is maximum as the particles cross each gap. If the peak voltage applied between the electrodes is <math>V_p</math> [[volt]]s, and the charge on each particle is <math>q</math> [[elementary charge]]s, the particle gains an equal increment of energy of <math>qV_p</math> [[electron volt]]s when passing through each gap. Thus the output energy of the particles is
:<math>E = qNV_p</math>
electron volts, where <math>N</math> is the number of accelerating electrodes in the machine.
At speeds near the speed of light, the incremental velocity increase will be small, with the energy appearing as an increase in the mass of the particles. In portions of the accelerator where this occurs, the tubular electrode lengths will be almost constant. Additional magnetic or electrostatic lens elements may be included to ensure that the beam remains in the center of the pipe and its electrodes. Very long accelerators may maintain a precise alignment of their components through the use of servo systems guided by a laser beam.
Line 75:
=== Energy Recovery LINAC ===
In previous electron linear accelerators, the accelerated particles are used only once and then fed into an absorber ''(beam dump)'', in which their residual energy is converted into heat. In an ''Energy Recovery Linac'' (ERL; literally: "Energy recovery linear accelerator"), instead, the accelerated in resonators and, for example, in [[
The [[Brookhaven National Laboratory]] and the [[Helmholtz-Zentrum Berlin]] with the project "bERLinPro" reported on corresponding development work . The Berlin experimental accelerator uses superconducting niobium cavity resonators of the type mentioned above. In 2014, three [[
=== Compact Linear Collider ===
Line 86:
===Compact Medical Accelerators ===
The LIGHT program (Linac for Image-Guided Hadron Therapy) hopes to create a design capable of accelerating protons to 200MeV or so for medical use over a distance of a few tens of metres, by optimising and nesting existing accelerator techniques <ref>{{Cite web| url=http://cdsweb.cern.ch/record/2314160/files/frb1io02.pdf| title =LIGHT: A LINEAR ACCELERATOR FOR PROTON THERAPY}}</ref> The current design (2020) uses the highest practical bunch frequency (currently ~
The project aim is to make proton therapy a more accessible mainstream medicine as an alternative to existing radio therapy.
Line 97:
When it comes to energies of more than a few MeV, accelerators for ions are different from those for electrons. The reason for this is the large mass difference between the particles. Electrons are already close to the [[speed of light]], the absolute speed limit, at a few MeV; with further acceleration, as described by [[relativistic mechanics]], almost only their energy and [[momentum]] increase. On the other hand, with ions of this energy range, the speed also increases significantly due to further acceleration.
The acceleration concepts used today for ''ions'' are always based on electromagnetic [[
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}} 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>
Line 118:
===Medical linacs===
[[Image:External beam radiotherapy retinoblastoma nci-vol-1924-300.jpg|thumb|left|Historical image showing Gordon Isaacs, the first patient treated for [[retinoblastoma]] with linear accelerator radiation therapy (in this case an electron beam), in 1957, in the U.S. Other patients had been treated by linac for other diseases since 1953 in the UK. Gordon's right eye was removed on January 11, 1957 because cancer had spread there. His left eye, however, had only a localized tumor that prompted [[Henry Kaplan (physician)|Henry Kaplan]] to treat it with the electron beam.]]
Linac-based [[radiation therapy]] for cancer treatment began with the first patient treated in 1953 in London, UK, at the [[Hammersmith Hospital]], with an 8 MV machine built by [[Metropolitan-Vickers]] and installed in 1952, as the first dedicated medical linac.<ref>Thwaites, DI and Tuohy J, Back to the future: the history and development of the clinical linear accelerator, Phys. Med. Biol. 51 (2006) R343–R36, doi:10.1088/0031-9155/51/13/R20</ref><ref>[http://www.ampi-nc.org/essayresult/LINAC-3.pdf LINAC-3, Advances in Medical Linear Accelerator Technology]. ampi-nc.org. Unavailable 25 Feb 2021.</ref> A short while later in 1954, a 6 MV linac was installed in Stanford, USA, which began treatments in 1956.
[[Medical linear accelerators]] accelerate electrons using a tuned-cavity waveguide, in which the RF power creates a [[standing wave]]. Some linacs have short, vertically mounted waveguides, while higher energy machines tend to have a horizontal, longer waveguide and a bending magnet to turn the beam vertically towards the patient. Medical linacs use monoenergetic electron beams between 4 and 25 MeV, giving an X-ray output with a spectrum of energies up to and including the electron energy when the electrons are directed at a high-density (such as [[tungsten]]) target. The electrons or X-rays can be used to treat both benign and malignant disease. The LINAC produces a reliable, flexible and accurate radiation beam. The versatility of LINAC is a potential advantage over [[cobalt therapy]] as a treatment tool. In addition, the device can simply be powered off when not in use; there is no source requiring heavy shielding – although the treatment room itself requires considerable shielding of the walls, doors, ceiling etc. to prevent escape of scattered radiation. Prolonged use of high powered (>18 MeV) machines can induce a significant amount of radiation within the metal parts of the head of the machine after power to the machine has been removed (i.e. they become an active source and the necessary precautions must be observed).
==Application for medical isotope development==
The expected shortages{{Which
==Disadvantages==
Line 149:
==External links==
{{
*[https://web.archive.org/web/20110726014831/http://www.ionactive.co.uk/multi-media_video.html?m=8 Linear Particle Accelerator (LINAC) Animation by Ionactive ]
*[http://www.rcp.ijs.si/mic/general/accelerator.php 2MV Tandetron linear particle accelerator in Ljubljana, Slovenia]
| |||