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Cyclotron
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==Classifications== [[File:1937-French-cyclotron.jpg|thumb|A French cyclotron, produced in [[ZΓΌrich]], Switzerland in 1937. The vacuum chamber containing the dees ''(at left)'' has been removed from the magnet ''(red, at right)''.]] ===Cyclotron types=== There are a number of basic types of cyclotron:<ref name="Chao">{{cite book | last1 = Chao | first1 = Alex | title = Handbook of Accelerator Physics and Engineering | publisher = World Scientific | date = 1999 | pages = 13β15 | url = https://books.google.com/books?id=Z3J4SjftF1YC&q=cyclotron&pg=PA13 | doi = | id = | isbn = 9789810235000 }}</ref> {{glossary}} {{term|Classical cyclotron}} {{defn|The earliest and simplest cyclotron. Classical cyclotrons have uniform magnetic fields and a constant accelerating frequency. They are limited to [[nonrelativistic]] particle velocities (the output energy small compared to the particle's [[rest energy]]), and have no active focusing to keep the beam aligned in the plane of acceleration.<ref name="seidel">{{cite report |last=Seidel|first=Mike |date= 2013|title=Cyclotrons for high-intensity beams |url=https://cds.cern.ch/record/1513944/files/CERN-2013-001-p17.pdf |publisher= [[CERN]] |access-date= June 12, 2022}}</ref>}} {{term |Synchrocyclotron}} {{defn |The synchrocyclotron extended the energy of the cyclotron into the relativistic regime by decreasing the frequency of the accelerating field as the orbit of the particles increased to keep it synchronized with the particle revolution frequency. Because this requires pulsed operation, the integrated total beam current was low compared to the classical cyclotron. In terms of beam energy, these were the most powerful accelerators during the 1950s, before the development of the [[synchrotron]].{{r|craddock}}{{r|Bryant}}}} {{term |Isochronous cyclotron (isocyclotron)}} {{defn |These cyclotrons extend output energy into the relativistic regime by altering the magnetic field to compensate for the change in cyclotron frequency as the particles reached relativistic speed. They use specially shaped magnet pole pieces that are wider near the outer diameter of the cyclotron to create a nonuniform magnetic field stronger in peripheral regions. Most modern cyclotrons are of this type. The pole pieces can also be shaped to cause the beam to keep the particles focused in the acceleration plane as they orbit. This is known as "sector focusing" or "azimuthally-varying field focusing", and uses the principle of [[alternating-gradient focusing]].{{r|craddock}}}} {{term | Separated sector cyclotron}} {{defn| Separated sector cyclotrons are machines in which the magnet is in separate sections, separated by gaps without field{{r|craddock}}.}} {{term | Superconducting cyclotron}} {{defn | "Superconducting" in the cyclotron context refers to the type of magnet used to bend the particle orbits into a spiral. Superconducting magnets can produce substantially higher fields in the same area than normal conducting magnets, allowing for more compact, powerful machines. The first superconducting cyclotron was the K500 at the [[Michigan State University]], which came online in 1981.<ref name="austin">{{cite book |last1=Austin |first1=Sam M. |title=Up from nothing : the Michigan State University Cyclotron Laboratory |date=2015 |publisher=Michigan State University |location=[East Lansing, Michigan] |isbn=978-0-99672-521-7}}</ref>}} {{glossary end}} ===Beam types=== The particles for cyclotron beams are produced in [[ion source]]s of various types. {{glossary}} {{term|Proton beams}} {{defn|The simplest type of cyclotron beam, proton beams are typically created by ionizing hydrogen gas.<ref name="clark">{{cite conference |url= https://accelconf.web.cern.ch/c81/papers/di-01.pdf|title= Ion Sources for Cyclotrons|last1=Clark |first1=David |date= September 1981 |pages= 231β240 |location= Caen, France |conference= 9th International Conference on Cyclotrons and their Applications }}</ref>}} {{term|Hβ beams|H<sup>β</sup> beams}} {{defn|Accelerating negative hydrogen ions simplifies extracting the beam from the machine. At the radius corresponding to the desired beam energy, a metal foil is used to strip the electrons from the H<sup>β</sup> ions, transforming them into positively charged H<sup>+</sup> ions. The change in polarity causes the beam to be deflected in the opposite direction by the magnetic field, allowing the beam to be transported out of the machine.<ref>{{cite journal |last1=Muramatsu |first1=M. |last2=Kitagawa |first2=A. |title=A review of ion sources for medical accelerators (invited) |journal=Review of Scientific Instruments |date=February 2012 |volume=83 |issue=2 |pages=02B909 |doi=10.1063/1.3671744 |pmid=22380341 |bibcode=2012RScI...83bB909M |doi-access=free}}</ref>}} {{term|Heavy ion beams}} {{defn|Beams of particles heavier than hydrogen are referred to as heavy ion beams, and can range from deuterium nuclei (one proton and one neutron) up to uranium nuclei. The increase in energy required to accelerate heavier particles is balanced by stripping more electrons from the atom to increase the electric charge of the particles, thus increasing acceleration efficiency.{{r|clark}}}} {{glossary end}} ===Target types=== To make use of the cyclotron beam, it must be directed to a target.<ref>{{cite conference |title= The Operation of Cyclotrons Used for Radiopharmaceutical Production |last1= Grey-Morgan |first1= T. |last2= Hubbard |first2= RE|date= November 1992 |publisher= World Scientific|pages=115β118 |location= Vancouver, Canada|conference= 13th International Conference on Cyclotrons and their Applications}}</ref> {{glossary}} {{term|Internal targets}} {{defn|The simplest way to strike a target with a cyclotron beam is to insert it directly into the path of the beam in the cyclotron. Internal targets have the disadvantage that they must be compact enough to fit within the cyclotron beam chamber, making them impractical for many medical and research uses.<ref name=Gelbart>{{cite conference |url=https://accelconf.web.cern.ch/c98/papers/a-21.pdf |title= Solid Targetry Systems: A Brief History|last1= Gelbart |first1=W.Z.|last2=Stevenson|first2=N. R. |date=June 1998 |pages= 90β93 |location= Caen, France|conference= 15th International Conference on Cyclotrons and their Applications }}</ref>}} {{term|External targets}} {{defn|While extracting a beam from a cyclotron to impinge on an external target is more complicated than using an internal target, it allows for greater control of the placement and focus of the beam, and much more flexibility in the types of targets to which the beam can be directed.{{r|Gelbart}}}} {{glossary end}}
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