A particle accelerator is a device that shoots tiny charged
particles super fast. Scientists use these to study atoms, nuclear forces, and
elements not found naturally, like those made in labs. They're also handy for
making stuff like medical isotopes and even dating ancient objects.
Here's how they work:
1.
Making Particles: They start with
materials like hydrogen for protons or just heat up stuff for electrons. These
charged particles are then shot out into a vacuum.
2.
Speeding Up: Electric fields
push these particles along, making them go faster and faster. Think of it like
a battery pushing an electron through a wire, but way faster.
3.
Guiding and Focusing: Magnets bend the
particles' paths, keeping them in line. Other magnets help focus the particle
beams to keep them narrow and intense.
4.
Colliding Particles: Sometimes, they
smash particles together to see what happens. This helps them understand things
like how matter is made up.
5.
Detecting Results: Special detectors
pick up what happens when particles hit targets or other particles. This data
helps scientists understand what's going on.
Particle accelerators come in different shapes and sizes, but
they all follow these basic principles to help scientists unlock the secrets of
the universe.
History
Particle accelerators have been developed mainly to study atoms and
particles. It all began with Ernest Rutherford's 1919 discovery of alpha
particles reacting with nitrogen nuclei. Until 1932, research used naturally
occurring alpha particles. But Rutherford believed artificially accelerating
them could reveal more. John Douglas Cockcroft and E.T.S. Walton's 1932
experiments showed this potential. Robert J. Van de Graaff's 1931 generator and
Rolf Wideröe's 1928 linear resonance accelerator were also significant.
Ernest O.
Lawrence's cyclotron, introduced in 1932, and Donald W. Kerst's betatron in
1940 furthered research. After World War II, Edwin Mattison McMillan and
Vladimir Iosifovich Veksler made significant progress.
In 1947, William W.
Hansen built the first traveling-wave linear accelerator. Alternating-gradient
focusing, introduced in 1952, revolutionized synchrotron design. Donald W.
Kerst's 1956 colliding-beam storage rings increased reaction energies.
Constant-voltage
accelerators are the simplest, using high voltage between ends of a tube. Voltage
multipliers and Van de Graaff generators were early power sources.
Betatrons are electron-only
accelerators, crucial for producing X-rays. They work by accelerating electrons
in a circular orbit, generating intense X-ray beams for various uses.
Cyclotrons: Cyclotrons are key for nuclear research, accelerating particles in a
circular path using magnetic and electric fields.
Classical
Cyclotrons: Particles are accelerated in a fixed-frequency electric field while
spiraling in a magnetic field. Developed in the 1930s, they're still used for
medical isotope production.
Synchrocyclotrons: These vary the
frequency of the accelerating voltage to keep particles in phase, allowing for
uniform acceleration. They're used for research with pi-mesons.
Sector-focused
Cyclotrons: They maintain a constant frequency and intense, non-pulsed beam by
adjusting the magnetic field. This principle, discovered in 1938, is used in
large-scale research cyclotrons like the TRIUMF lab's machine in Vancouver.
Cyclotrons: Cyclotrons are key for nuclear research, accelerating particles in a
circular path using magnetic and electric fields.
Classical
Cyclotrons: Particles are accelerated in a fixed-frequency electric field while
spiraling in a magnetic field. Developed in the 1930s, they're still used for
medical isotope production.
Synchrocyclotrons: These vary the
frequency of the accelerating voltage to keep particles in phase, allowing for
uniform acceleration. They're used for research with pi-mesons.
Sector-focused
Cyclotrons: They maintain a constant frequency and intense, non-pulsed beam by
adjusting the magnetic field. This principle, discovered in 1938, is used in
large-scale research cyclotrons like the TRIUMF lab's machine in Vancouver.
Linear Resonance Accelerators:
Linear resonance accelerators were developed
post-1940, requiring powerful radio-frequency voltage sources. There are two
types: standing-wave for heavy particles like protons and traveling-wave for
electrons. Protons need prolonged acceleration due to changing speeds, while
electrons reach near-light speed quickly.
Linear Electron Accelerators:
Using microwaves, electrons are accelerated in a
waveguide chamber. Electrons gain energy as they travel through the chamber,
reaching speeds close to that of light. These accelerators are used in radiography,
cancer treatment, and for electron synchrotron injections.
Linear Proton Accelerators:
Proton linear accelerators, developed by Luis
Alvarez in 1946, use standing electromagnetic waves in cylindrical tanks.
Protons cross gaps between drift tubes to maintain synchronization with
accelerating fields. These accelerators require large amounts of
radio-frequency power and operate in pulsed mode. The Los Alamos National
Laboratory hosts the highest-energy proton linear accelerator.
Synchrotrons
Synchrotrons
accelerate particles while keeping their orbit radius nearly constant by
increasing the magnetic field strength. This method requires smaller magnets
compared to cyclotrons for the same energy levels. The particles are
accelerated using radio-frequency voltages, with their synchronization
maintained by phase stability. These synchrotrons allow for stable acceleration
across a range of energies and phases, producing intense particle beams.
The magnetic field
shape is crucial for focusing the particle beam. Early synchrotrons used weak
focusing, while modern ones use alternating-gradient focusing, allowing for
higher energies. This technique involves magnets with pole-tips shaping the
field to focus the beam, resulting in smaller, more intense beams.
Electron
Synchrotrons
Synchrotrons
resolved the energy limit issue posed by electron radiation. These machines can
operate at higher energies without significant energy loss due to radiation.
They typically use linear accelerators as injectors. The practical energy limit
for electron synchrotrons is determined by the cost of the radio-frequency
system needed to compensate for radiation losses.
Proton Synchrotrons
Proton synchrotrons
operate similarly to electron synchrotrons but with some differences. Protons
require modulated accelerating voltages due to their slower speed. The energy
limit for proton synchrotrons is determined by the cost of the magnet ring,
which increases with energy but at a slower rate than for electrons. The
highest-energy accelerators, such as the Tevatron at Fermilab, operate using
superconducting magnets to guide and focus the proton beams effectively.
Colliding-beam storage rings:
Storage rings allow particles moving in opposite directions to collide
with maximum kinetic energy, unlike stationary targets. Donald W. Kerst's idea
of colliding beams in storage rings revolutionized high-energy experiments. By
using circulating beams, interactions can occur in the rings. These rings may
contain identical particles or oppositely charged ones, such as electrons and
positrons. The collision energies achieved in these rings are unmatched, making
them crucial for cutting-edge research.
Electron storage
rings:
Electron-positron storage rings, found in
various research centers globally, are pivotal for subatomic particle studies.
These machines accelerate electrons and positrons in opposite directions,
colliding them at specific points for analysis. Notable examples include
Cornell University, Stanford University, and CERN's Large Electron-Positron
Collider (LEP), which reached energies surpassing 100 GeV.
Proton storage
rings:
Proton storage rings, like CERN's Intersecting
Storage Rings (ISR) and the Tevatron at Fermilab, accelerate protons and
antiprotons in counter-rotating beams for collision. Techniques like stochastic
cooling ensure intense and focused beams. The highest-energy collider, the
Large Hadron Collider (LHC), operates at CERN, reaching 7 TeV and facilitating
groundbreaking discoveries in particle physics.
Electron-proton
storage rings:
The Hadron-Electron Ring Accelerator (HERA) at
DESY laboratory accommodates both electrons and protons in separate rings. This
unique setup allows for experiments involving particles of different masses,
contributing to diverse research endeavors.
Impulse
accelerators:
High-intensity electron accelerators, like
those used in thermonuclear fusion research, generate short but powerful
electron beams for various applications, including flash radiography and
microwave production. These accelerators employ pulse transformers and
capacitors to produce brief but intense pulses of electrons, facilitating a
range of scientific investigations.
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