History and Development of Cyclotrons
– Max Steenbeck formulated the concept of the cyclotron in 1927.
– Leo Szilárd filed patent applications for the cyclotron in 1928-1929.
– Ernest Lawrence independently conceived the cyclotron concept in 1929.
– Lawrence published the first description of the cyclotron concept in 1930.
– The first working cyclotron became operational in January 1931.
– Lawrence used electromagnets recycled from obsolete arc converters to construct the first cyclotron.
– Lawrence and his collaborators constructed a series of cyclotrons, including a 27-inch machine (1932), a 37-inch machine (1937), and a 60-inch machine (1939).
– The first European cyclotron was constructed in the Soviet Union in 1937.
– Two cyclotrons were built in Nazi Germany, one in Berlin and one in Heidelberg.
– Synchrocyclotrons and isochronous cyclotrons were developed to overcome limitations of traditional cyclotrons.
– Synchrocyclotrons were quickly overtaken by isochronous cyclotrons due to their higher beam intensities.
– The first isochronous cyclotron was built in the Netherlands in 1956.
– Spiral-sector cyclotrons allowed the acceleration and control of more powerful beams.
– Superconducting magnets and discrete sector magnets improved cyclotron design.
– Manufacturing and design techniques gradually improved the energy capabilities of cyclotrons.
Principle of Operation
– Charged particles are accelerated by applying an electric field across a gap.
– The Lorentz force law describes the force on a particle in a magnetic field.
– A static magnetic field alone cannot accelerate particles.
– The cyclotron uses a flat vacuum chamber between two poles of a large magnet.
– The RF accelerating potential is applied to the dees in the chamber.
Applications of Cyclotrons
– Cyclotrons were the most powerful particle accelerators until the 1950s.
– Cyclotrons are still widely used for nuclear medicine and basic research.
– Over 1,500 cyclotrons were in use worldwide for the production of radionuclides for nuclear medicine in 2020.
– Cyclotrons can be used for particle therapy in direct application to patients.
– Cyclotrons are used for measuring basic properties of isotopes and decay schemes.
– Cyclotron beams can be used to produce short-lived isotopes for medical imaging and radiotherapy.
– Cyclotron produced radioisotopes are widely used for diagnostic purposes.
– Therapeutic uses of cyclotron produced radioisotopes are still largely in development.
Particle Energy and Trajectory in Cyclotrons
– Particle energy gain in a cyclotron is calculated by multiplying the increase per crossing by the number of crossings.
– Energy can also be estimated using the equation for frequency in circular motion and the cyclotron frequency equation.
– The kinetic energy for particles with speed v is given by the equation E = (1/2)mv^2.
– The beam energy produced by a cyclotron depends on the maximum radius reached by the magnetic field and the accelerating structures.
– The beam energy also depends on the maximum strength of the magnetic field that can be achieved.
– The trajectory followed by a particle in a cyclotron is a series of arcs of constant radius.
– The particle speed and orbital radius only increase at the accelerating gaps.
– A simple spiral is a useful approximation for the particle trajectory.
– Stability and focusing of particles in a cyclotron depend on various factors such as initial spread of positions and velocities, mutual repulsion of the beam particles, and synchronization between the particle and the RF field.
Cyclotron Types, Beam Types, and Target Types
– Classical cyclotron: Simplest type with uniform magnetic fields and constant accelerating frequency.
– Synchrocyclotron: Extends energy into the relativistic regime by decreasing the frequency of the accelerating field as particles increase orbit.
– Isochronous cyclotron (isocyclotron): Extends output energy into the relativistic regime by altering the magnetic field to compensate for change in cyclotron frequency.
– Separated sector cyclotron: Magnet is in separate sections, separated by gaps without field.
– Superconducting cyclotron: Uses superconducting magnets to bend particle orbits into a spiral, allowing for more compact and powerful machines.
– Proton beams: Created by ionizing hydrogen gas.
– Heavy ion beams: Beams of particles heavier than hydrogen, ranging from deuterium nuclei to uranium nuclei.
– Internal targets: Inserted directly into the path of the cyclotron beam.
– External targets: Beam is extracted from the cyclotron to impinge on an external target.
– Cyclotrons are more space efficient and cost efficient than linear accelerators.
– Relativistic effects limit the speed of particles that can be accelerated in a classical cyclotron.
– Notable examples of cyclotrons include Lawrence 4.5-inch Cyclotron, Lawrence 184-inch Cyclotron, TU Delft Isochronous Cyclotron, RIKEN Superconducting Ring Cyclotron. Source: https://en.wikipedia.org/wiki/Cyclotron
A cyclotron is a type of particle accelerator invented by Ernest Lawrence in 1929–1930 at the University of California, Berkeley, and patented in 1932. A cyclotron accelerates charged particles outwards from the center of a flat cylindrical vacuum chamber along a spiral path. The particles are held to a spiral trajectory by a static magnetic field and accelerated by a rapidly varying electric field. Lawrence was awarded the 1939 Nobel Prize in Physics for this invention.
The cyclotron was the first "cyclical" accelerator. The primary accelerators before the development of the cyclotron were electrostatic accelerators, such as the Cockcroft–Walton generator and the Van de Graaff generator. In these accelerators, particles would cross an accelerating electric field only once. Thus, the energy gained by the particles was limited by the maximum electrical potential that could be achieved across the accelerating region. This potential was in turn limited by electrostatic breakdown to a few million volts. In a cyclotron, by contrast, the particles encounter the accelerating region many times by following a spiral path, so the output energy can be many times the energy gained in a single accelerating step.
Cyclotrons were the most powerful particle accelerator technology until the 1950s, when they were surpassed by the synchrotron. Nonetheless they are still widely used to produce particle beams for nuclear medicine and basic research. As of 2020, close to 1,500 cyclotrons were in use worldwide for the production of radionuclides for nuclear medicine. In addition, cyclotrons can be used for particle therapy, where particle beams are directly applied to patients.
