Editing Time projection chamber (section)

==The original design==
{{See also|Particle detector}}
The original TPC was invented by [[David R. Nygren]], an American physicist, at [[Lawrence Berkeley Laboratory]] in the late 1970s.<ref name="EOL">{{cite web
 |url=http://science.energy.gov/lawrence/award-laureates/1980s/nygren/
 |title=The Ernest Orlando Lawrence Award: 1980's Laureates
 |access-date=2007-08-18
 |publisher=[[United States Department of Energy|US Department of Energy]]
 |quote=David R. Nygren, 1985: Physics: For the development of experimental techniques in [[particle physics]] and especially for the invention of the Time Projection Chamber
 |archive-date=2011-08-11
 |archive-url=https://web.archive.org/web/20110811230847/http://science.energy.gov/lawrence/award-laureates/1980s/nygren/
 |url-status=dead
 }}</ref> Its first major application was in the PEP-4 detector, which studied 29 GeV electron–positron collisions at the PEP storage ring at [[SLAC National Accelerator Laboratory|SLAC]].

A time projection chamber consists of a [[gas]]-filled detection volume in an electric field with a position-sensitive electron collection system. The original design (and the one most commonly used) is a cylindrical chamber with [[wire chamber|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 [[azimuth]]al 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.

In recent years other means of position-sensitive electron amplification and detection have become more widely used, especially in conjunction with the increased application of time projection chambers in [[nuclear physics]]. These usually combine a segmented anode plate with either just a [[Frisch grid]]<ref name="MAYA">Demonchy et al. 2007.</ref> or an active electron-multiplication element like a [[gas electron multiplier]].<ref name="GEM_TPC">Fenker et al. 2008, Laird et al. 2007.</ref> These newer TPCs also depart from the traditional geometry of a cylinder with an axial field in favour of a flat geometry<ref name="MAYA"/> or a cylinder with a radial field.<ref name="GEM_TPC"/>

Earlier researchers in particle physics also usually made use of a more simplified box-shaped geometry arranged directly above or below the beam line, such as in the [[CERN]] [[NA49 experiment|NA49]] and [[NA35 experiment|NA35]] experiments.