Time projection chamber

A time projection chamber consists of a gas-filled detection volume in an electric field with a position-sensitive electron collection system.

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.

The z coordinate (along the cylinder axis) is determined by measuring the drift time from the ionization event to the MWPC at the end.

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[2] or an active electron-multiplication element like a gas electron multiplier.

[3] 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 and NA35 experiments.

This critical technology enabled the possibility of a time projection chamber based on Nygren's original design, but using liquid argon as the sensitive medium instead of gas.

[5][7][8] In 1977, Carlo Rubbia independently, and nearly simultaneously, proposed to construct an LArTPC at CERN for rare event particle physics experiments.

[9][10] The fact that argon is a noble element and therefore has a vanishing electronegativity means that electrons produced by ionizing radiation will not be absorbed as they drift toward the detector readout.

These are set at lower (more negative) potentials than the outer plane, allowing drift electrons to pass through them, inducing signals that are used for event reconstruction.

Having multiple planes with different wire orientations permits two-dimensional event reconstruction, while the third dimension is found from electron drift times.

The experiment uses a low-pressure time projection chamber in order to extract the original direction of potential dark matter events.

The collaboration took its first data in an underground laboratory at the Waste Isolation Pilot Plant (WIPP) site near Carlsbad, New Mexico in Fall, 2010.

[citation needed] Dark Matter Time Projection Chamber published first results from a surface run in 2010, setting a spin-dependent cross section limit.