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Encyclopedia > Cyclotron
A modern Cyclotron for radiation therapy

A cyclotron is a type of particle accelerator. Cyclotrons accelerate charged particles using a high-frequency, alternating voltage (potential difference). A perpendicular magnetic field causes the particles to spiral almost in a circle so that they re-encounter the accelerating voltage many times. Cyclotron may refer to: Cyclotron, the particle accelerator Cyclotron (band), the metal rock band Cyclotron (comics), a minor character in the DC Universe  See also Cyclotron (album) Cyclotron radiation Cyclotron resonance Category: ... Atom Smasher redirects here. ... In physics, a charged particle is a particle with an electric charge. ... For other uses, see Frequency (disambiguation). ... International safety symbol Caution, risk of electric shock (ISO 3864), colloquially known as high voltage symbol. ... For the indie-pop band, see The Magnetic Fields. ...

Ernest Lawrence, of the University of California, Berkeley, is credited with the invention of the cyclotron in 1929. It is less known outside Hungary that Hungarian Sándor Gaál may have described the workings of a cyclotron at about the same time during the spring of 1929 as Lawrence;[citation needed] although almost all reputable international sources give credit to Lawrence for the invention and construction of the first cyclotron. He used it in experiments that required particles with energy of up to 1 MeV. Ernest O. Lawrence Ernest Orlando Lawrence (August 8, 1901 â€“ August 27, 1958) was an American physicist and Nobel Laureate best known for his invention, utilization, and improvement of the cyclotron beginning in 1929, and his later work in uranium-isotope separation in the Manhattan Project. ... Sather Tower (the Campanile) looking out over the San Francisco Bay and Mount Tamalpais. ... SÃ¡ndor GaÃ¡l (GogÃ¡nvÃ¡ralja (former Hungary, today Romania), October 8, 1885 - CsernÃ¡t (Romania), July 28, 1972) Hungarian physicist, the inventor of the cyclotron. ... An electronvolt (symbol: eV) is the amount of energy gained by a single unbound electron when it falls through an electrostatic potential difference of one volt. ...

## How the cyclotron works GA_googleFillSlot("encyclopedia_square");

Diagram of cyclotron operation from Lawrence's 1934 patent.

The electrodes shown at the right would be in the vacuum chamber, which is flat, in a narrow gap between the two poles of a large magnet. Image File history File links Download high resolution version (1598x862, 45 KB) Summary Image of the principles of a cyclotron. ... Image File history File links Download high resolution version (1598x862, 45 KB) Summary Image of the principles of a cyclotron. ... For other uses, see Electrode (disambiguation). ... A large vacuum chamber. ...

In the cyclotron, a high-frequency alternating voltage applied across the "D" electrodes (also called "dees") alternately attracts and repels charged particles. The particles, injected near the center of the magnetic field, accelerate only when passing through the gap between the electrodes. The perpendicular magnetic field (passing vertically through the "D" electrodes), combined with the increasing energy of the particles forces the particles to travel in a spiral path. City lights viewed in a motion blurred exposure. ... In physics, a charged particle is a particle with an electric charge. ... Acceleration is the time rate of change of velocity, and at any point on a v_t graph, it is given by the gradient of the tangent to that point In physics, acceleration (symbol: a) is defined as the rate of change (or time derivative) of velocity. ... For the indie-pop band, see The Magnetic Fields. ...

With no change in energy the charged particles in a magnetic field will follow a circular path. In the Cyclotron, energy is applied to the particles as they cross the gap between the dees and so they are accelerated (at the typical sub-relativistic speeds used) and will increase in mass as they approach the speed of light. Either of these effects (increased velocity or increased mass) will increase the radius of the circle and so the path will be a spiral.

(The particles move in a spiral, because a current of electrons or ions, flowing perpendicular to a magnetic field, experiences a perpendicular force. The charged particles move freely in a vacuum, so the particles follow a spiral path.) In electricity, current refers to electric current, which is the flow of electric charge. ... The left-handed orientation is shown on the left, and the right-handed on the right. ... In physics, a net force acting on a body causes that body to accelerate; that is, to change its velocity. ...

The radius will increase until the particles hit a target at the perimeter of the vacuum chamber. Various materials may be used for the target, and the collisions will create secondary particles which may be guided outside of the cyclotron and into instruments for analysis. The results will enable the calculation of various properties, such as the mean spacing between atoms and the creation of various collision products. Subsequent chemical and particle analysis of the target material may give insight into nuclear transmutation of the elements used in the target.

## Uses of the cyclotron

For several decades, cyclotrons were the best source of high-energy beams for nuclear physics experiments; several cyclotrons are still in use for this type of research. This box:      Nuclear physics is the branch of physics concerned with the nucleus of the atom. ...

Cyclotrons can be used to treat cancer. Ion beams from cyclotrons can be used, as in proton therapy, to penetrate the body and kill tumors by radiation damage, while minimizing damage to healthy tissue along their path. Cancer is a class of diseases or disorders characterized by uncontrolled division of cells and the ability of these to spread, either by direct growth into adjacent tissue through invasion, or by implantation into distant sites by metastasis (where cancer cells are transported through the bloodstream or lymphatic system). ... Proton therapy is a kind of external beam radiotherapy where protons are directed to a tumor site. ... Radiation poisoning, also called radiation sickness or a creeping dose, is a form of damage to organ tissue due to excessive exposure to ionizing radiation. ...

Cyclotron beams can be used to bombard other atoms to produce short-lived positron-emitting isotopes suitable for PET imaging. The first detection of the positron in 1932 by Carl D. Anderson The positron is the antiparticle or the antimatter counterpart of the electron. ... Positron emission tomography (PET) is a nuclear medicine medical imaging technique which produces a three dimensional image or map of functional processes in the body. ...

## Problems solved by the cyclotron

60-inch cyclotron, circa 1939, showing a beam of accelerated ions (likely protons or deuterons) escaping the accelerator and ionizing the surrounding air causing a blue glow. This phenomenon of air ionization is analogous to the one responsible for producing the "blue flash" infamously noted by witnesses of criticality accidents. Though the effect is often mistaken for Cherenkov radiation, this is not the case.

The cyclotron was an improvement over the linear accelerators that were available when it was invented. A linear accelerator (also called a linac) accelerates particles in a straight line through an evacuated tube (or series of such tubes placed end to end). A set of electrodes shaped like flat donuts are arranged inside the length of the tube(s). These are driven by high-power radio waves that continuously switch between positive and negative voltage, causing particles traveling along the center of the tube to accelerate. In the 1920's, it was not possible to get high frequency radio waves at high power, so either the accelerating electrodes had to be far apart to accommodate the low frequency or more stages were required to compensate for the low power at each stage. Either way, higher-energy particles required longer accelerators than scientists could afford. 60-inch cyclotron, circa 1939, showing beam of accelerated ions (perhaps protons or deuterons) escaping the accelerator and ionizing the surrounding air causing a blue glow. ... 60-inch cyclotron, circa 1939, showing beam of accelerated ions (perhaps protons or deuterons) escaping the accelerator and ionizing the surrounding air causing a blue glow. ... A criticality accident (also sometimes referred to as an excursion or power excursion) occurs when a nuclear chain reaction is accidentally allowed to occur in fissile material, such as enriched uranium or plutonium. ... Cherenkov radiation glowing in the core of a TRIGA reactor Cherenkov radiation (also spelled Cerenkov or sometimes ÄŒerenkov) is electromagnetic radiation emitted when a charged particle passes through an insulator at a speed greater than the speed of light in that medium. ... A Linear particle accelerator is an electrical device for the acceleration of subatomic particles. ...

Modern linacs use high power Klystrons and other devices able to impart much more power at higher frequencies. But before these devices existed, cyclotrons were cheaper than linacs. Reflex klystron Type 2K25 or 723 A/B. The threaded adjustment rod on the right side allows the position of the reflector to be adjusted (by compressing the reflex cavity), and thus the natural resonant frequency of the device. ...

Cyclotrons accelerate particles in a spiral path. Therefore, a compact accelerator can contain much more distance than a linear accelerator, with more opportunities to accelerate the particles.

• Cyclotrons have a single electrical driver, which saves both money and power, since more expense may be allocated to increasing efficiency.
• Cyclotrons produce a continuous stream of particles at the target, so the average power is relatively high.
• The compactness of the device reduces other costs, such as its foundations, radiation shielding, and the enclosing building.

## Limitations of the cyclotron

The magnet portion of a large cyclotron. The gray object is the upper pole piece, routing the magnetic field in two loops through a similar part below. The white canisters held conductive coils to generate the magnetic field. The D electrodes are contained in a vacuum chamber that was inserted in the central field gap.

The spiral path of the cyclotron beam can only "synch up" with klystron-type (constant frequency) voltage sources if the accelerated particles are approximately obeying Newton's Laws of Motion. If the particles become fast enough that relativistic effects become important, the beam gets out of phase with the oscillating electric field, and cannot receive any additional acceleration. The cyclotron is therefore only capable of accelerating particles up to a few percent of the speed of light. To accommodate increased mass the magnetic field may be modified by appropriately shaping the pole pieces as in the isochronous cyclotrons, operating in a pulsed mode and changing the frequency applied to the dees as in the synchrocyclotrons, either of which is limited by the diminishing cost effectiveness of making larger machines. Cost limitations have been overcome by employing the more complex synchrotron or linear accelerator, both of which have the advantage of scalability, offering more power within an improved cost structure as the machines are made larger. Image File history File links LawrenceCyclotronMagnet. ... Image File history File links LawrenceCyclotronMagnet. ... This article does not cite any references or sources. ... Newtons First and Second laws, in Latin, from the original 1687 edition of the Principia Mathematica. ... For a less technical and generally accessible introduction to the topic, see Introduction to special relativity. ... A part of a magnet from the Orsay synchrocyclotron, now used by the proton therapy center (to be replaced in 2008 by newer technologies) A synchrocyclotron is a cyclotron in which the frequency of the driving RF electric field is varied to compensate for the mass gain of the accelerated... Synchrotrons are now mostly used for producing monochromatic high intensity X-ray beams; here, the synchrotron is the circular track, off which the beamlines branch. ... A Linear particle accelerator is an electrical device for the acceleration of subatomic particles. ...

## Mathematics of the cyclotron

The centripetal force is provided by the transverse magnetic field B, and the force on a particle travelling in a magnetic field (which causes it to be angularly displaced, i.e spiral) is equal to Bqv. So, The centripetal force is the external force required to make a body follow a circular path at constant speed. ...

$frac{mv^2}{r} = Bqv$

(Where m is the mass of the particle, q is its charge, v is its velocity and r is the radius of its path.)

The speed at which the particles enter the cyclotron due to a potential difference, V.

$v = sqrt{frac{2Vq}{m}}$

Therefore,

$frac{v}{r} = frac{Bq}{m}$

v/r is equal to angular velocity, ω, so

$omega = frac{Bq}{m}$

And since the angular frequency is

ω = 2πfc

Therefore,

$f_c = frac{Bq}{2mpi}$
A pair of "dee" electrodes with loops of coolant pipes on their surface at the Lawrence Hall of Science. The particle exit point may be seen at the top of the upper dee, where the target would be positioned

This shows that for a particle of constant mass, the frequency does not depend upon the radius of the particle's orbit. As the beam spirals out, its frequency does not decrease, and it must continue to accelerate, as it is travelling more distance in the same time. As particles approach the speed of light, they acquire additional mass, requiring modifications to the frequency, or the magnetic field during the acceleration. This is accomplished in the synchrocyclotron. Cyclotron Dees at the Lawrence Hall of Science. ... Cyclotron Dees at the Lawrence Hall of Science. ... The Lawrence Hall of Science (LHS) is a public science center, run by the University of California, Berkeley. ... A part of a magnet from the Orsay synchrocyclotron, now used by the proton therapy center (to be replaced in 2008 by newer technologies) A synchrocyclotron is a cyclotron in which the frequency of the driving RF electric field is varied to compensate for the mass gain of the accelerated...

The relativistic cyclotron frequency is

$f=f_csqrt{1-v^2/c^2}$,

where fc is the classical frequency, given above, of a charged particle with velocity v circling in a magnetic field.

The rest mass of an electron is 511 keV, so the frequency correction is 1% for a magnetic vacuum tube with a 5.11 kV direct current accelerating voltage. The proton mass is nearly two thousand times the electron mass, so the 1% correction energy is about 9 MeV, which is sufficient to induce nuclear reactions.

An alternative to the synchrocyclotron is the isochronous cyclotron, which has a magnetic field that increases with radius, rather than with time. The de-focusing effect of this radial field gradient is compensated by ridges on the magnet faces which vary the field azimuthally as well. This allows particles to be accelerated continuously, on every period of the radio frequency, rather than in bursts as in most other accelerator types. This principle that alternating field gradients have a net focusing effect is called strong focusing. It was obscurely known theoretically long before it was put into practice.

## Related technologies

• The spiraling of electrons in a cylindrical vacuum chamber within a transverse magnetic field is also employed in the magnetron, a device for producing high frequency radio waves (microwaves).
• The Synchrotron moves the particles through a path of constant radius, allowing it to be made as a pipe and so of much larger radius than is practical with the cyclotron and synchrocyclotron. The larger radius allows the use of numerous magnets, each of which imparts angular momentum and so allows particles of higher velocity (mass) to be kept within the bounds of the evacuated pipe.

A cavity magnetron is a high-powered vacuum tube that generates coherent microwaves. ... Microwave Slang for small waves, like at a beach, often used by surfers. ... Synchrotrons are now mostly used for producing monochromatic high intensity X-ray beams; here, the synchrotron is the circular track, off which the beamlines branch. ...

Results from FactBites:

 Cyclotron - Wikipedia, the free encyclopedia (1320 words) The cyclotron was invented by Ernest Lawrence of the University of California, in 1929. The cyclotron is an improvement of the linear accelerator. As the beam speed increases, cyclotron radiation is emitted from the side of the beam, because the magnet is turning and slowing, ("braking") the beam.
 Cyclotron radiation - Wikipedia, the free encyclopedia (427 words) Furthermore, the period of the orbit is independent of the energy of the particles, allowing the cyclotron to operate at a set frequency, and not worry about the energy of the particles at a given time. Cyclotron radiation from plasma in interstellar space or around fl holes and other astronomical phenomena are an important source of information about distant magnetic fields. Cyclotron radiation has a spectrum with its main spike at the same fundamental frequency as the particle's orbit, and harmonics at higher integral factors.
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