Time projection chamber
Encyclopedia
In physics
, a time projection chamber (or TPC) is a particle detector
invented by David R. Nygren
, an American physicist, at Lawrence Berkeley Laboratory in the late 1970s. Its first major application was in the PEP-4 detector, which studied 29 GeV electron-positron collisions at the PEP storage ring at SLAC
.
A time projection chamber consists of a gas
-filled cylindrical chamber with multi-wire proportional chamber
s (MWPC) as endplates. Along its length, the chamber is divided into halves by means of a central high-voltage electrode
disc, which establishes an electric field
between the center and the end plates. Furthermore, a magnetic field
is often applied along the length of the cylinder, parallel to the electric field, in order to minimize the diffusion of the electron
s coming from the ionization
of the gas. On passing through the detector gas, a particle will produce primary ionization along its track. The z-coordinate (along the cylinder axis) is determined by measuring the drift time from the ionization event to the MWPC at the end. This is done using the usual technique of a drift chamber. The MWPC at the end is arranged with the anode
wires in the azimuthal direction, θ, which provides information on the radial coordinate, r. To obtain the azimuthal direction, each cathode
plane is divided into strips along the radial direction.
Earlier researchers usually made use of a more simplified box shaped geometry arranged directly above or below the beam line, such as in the CERN
NA49
and NA35 experiments.
Physics
Physics is a natural science that involves the study of matter and its motion through spacetime, along with related concepts such as energy and force. More broadly, it is the general analysis of nature, conducted in order to understand how the universe behaves.Physics is one of the oldest academic...
, a time projection chamber (or TPC) is a particle detector
Particle detector
In experimental and applied particle physics, nuclear physics, and nuclear engineering, a particle detector, also known as a radiation detector, is a device used to detect, track, and/or identify high-energy particles, such as those produced by nuclear decay, cosmic radiation, or reactions in a...
invented by David R. Nygren
David R. Nygren
David Robert Nygren is a particle physicist known for his invention of the Time projection chamber. He currently works at Lawrence Berkeley National Laboratory, where he has worked since 1973...
, an American physicist, at Lawrence Berkeley Laboratory in the late 1970s. Its first major application was in the PEP-4 detector, which studied 29 GeV electron-positron collisions at the PEP storage ring at SLAC
SLAC National Accelerator Laboratory
The SLAC National Accelerator Laboratory, originally named Stanford Linear Accelerator Center, is a United States Department of Energy National Laboratory operated by Stanford University under the programmatic direction of the U.S...
.
A time projection chamber consists of a gas
Gas
Gas is one of the three classical states of matter . Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into a liquid at its melting point , boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which the electrons...
-filled cylindrical chamber with multi-wire proportional chamber
Wire chamber
A multi-wire chamber is a detector for particles of ionizing radiation which is an advancement of the concept of the Geiger counter and the proportional counter....
s (MWPC) as endplates. Along its length, the chamber is divided into halves by means of a central high-voltage electrode
Electrode
An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit...
disc, which establishes an electric field
Electric field
In physics, an electric field surrounds electrically charged particles and time-varying magnetic fields. The electric field depicts the force exerted on other electrically charged objects by the electrically charged particle the field is surrounding...
between the center and the end plates. Furthermore, a magnetic field
Magnetic field
A magnetic field is a mathematical description of the magnetic influence of electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude ; as such it is a vector field.Technically, a magnetic field is a pseudo vector;...
is often applied along the length of the cylinder, parallel to the electric field, in order to minimize the diffusion of the electron
Electron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...
s coming from the ionization
Ionization
Ionization is the process of converting an atom or molecule into an ion by adding or removing charged particles such as electrons or other ions. This is often confused with dissociation. A substance may dissociate without necessarily producing ions. As an example, the molecules of table sugar...
of the gas. On passing through the detector gas, a particle will produce primary ionization along its track. The z-coordinate (along the cylinder axis) is determined by measuring the drift time from the ionization event to the MWPC at the end. This is done using the usual technique of a drift chamber. The MWPC at the end is arranged with the anode
Anode
An anode is an electrode through which electric current flows into a polarized electrical device. Mnemonic: ACID ....
wires in the azimuthal direction, θ, which provides information on the radial coordinate, r. To obtain the azimuthal direction, each cathode
Cathode
A cathode is an electrode through which electric current flows out of a polarized electrical device. Mnemonic: CCD .Cathode polarity is not always negative...
plane is divided into strips along the radial direction.
Earlier researchers usually made use of a more simplified box shaped geometry arranged directly above or below the beam line, such as in the CERN
CERN
The European Organization for Nuclear Research , known as CERN , is an international organization whose purpose is to operate the world's largest particle physics laboratory, which is situated in the northwest suburbs of Geneva on the Franco–Swiss border...
NA49
NA49 experiment
The NA49 experiment was a particle physics experiment that took place in the North Area of the Super Proton Synchrotron at CERN. It used a large-acceptance hadron detector to investigate reactions induced by the collision of various heavy ions on targets made of a variety of elements...
and NA35 experiments.