The DELPHI Time Projection Chamber (TPC)

Technical description

The DELPHI Time Projection Chamber (TPC) is composed of plenty of nice things ... ( I will do a more precise description in the next version of this help)

Geometry

Clic here for a zoom or here for the eps file.

The TPC is a cylinder of 2x1.3 m situated between the radii 0.29 m and 1.22 m .The two drift volumes are separated by a HT (20 kVolts) plate producing an electric field of 150 Volts cm-1. A charged particle crossing the TPC produces by ionisation around 70 electrons per cm of gaz (80% Ar 20% CH4). Under the action of the electric field these primaires electrons drift in the direction of the proportional chambers ( 6 at each TPC extremities).

Sectors

Clic here for a zoom or here for the eps file.	Clic here for a zoom

Each of 2x6 TPC sectors have 16 raws of pads , alowing the reconstruction of 16 space points per track. In each sectors there is 1680 pads. In front of the pads plates there is 3 levels of grid. the one closest to the pad ( the anode at a HV of 1430 volts ) contains 192 "active" wires (sensitive wires) per sector performing the dE/dx measurement.

Grids

Clic here for a zoom or here for the eps file.

The 3 levels of grid are composed ( starting from the one closest to the drift volume) :

• The Gate grid

  (Clic here for a zoom or here for the eps file.

  It's used to collect the positive ions produced in the showers at the level of the sensitive wires. (this is done to avoid a distortion of the drift field ) (by an acumulation of the ions ) To close the electric lines for the ions , a small alternate potential (+/- 30 volts) is applied on 2 consecutive wires of this grid. The primary electrons ( 6 cm/micro.sec ) much faster than the ions ( 0.3 cm/ms ) are not realy afected by this grid.

• The cathod grid : wich "limit" the electric field of the proportionnal chamber.
• The anod grid : which count 192 sensitive wires separated by 4 mm and between them we found the field wires , performing the shielding between the sensitive vires.

Electronic

Clic here for a zoom or here for the eps file.

The 22464 electonic chanels of the TPC ( 2304 for the wires and 20160 for the pads) folow the same idea:

• The signal is pre-amplified at the level of the sector
• runs along 30 meters in pair-wires
• goes to a shaping device ( output -> pulse of 180 ns )
• is sampled on 8 bits at 15 MHz. To cover the needed scale (factor 500) the caracteristic of the digitatisation has a double slope ( the change in the slope is done chanel 191)
• To reduce the amount of data saved, a zero skiping is performed to keep from the initial 6 10**6 bytes the 3 10**3 bytes above the noise expected for 30 tracks.

Quantities measured

For each event, 3 types of information are produced :

• 3d information for the charged tracks reconstruction ( A maximum of 16 space points can be reconstructed for a non_looping track)
• Ionisation measurement ( 192 dE/dx measurements can be performed on these tracks)
• trigger : the TPC contribute to the T1,T2 and T3 triggers.

Accuracy

• The precision over the measure of the r-(phi) coordinate is 250(mu) per point.
• The accuracy of the z measurement is of 900 (mu) per point.

Social Description

A lot of people are contributing to the running of the DELPHI TPC , we can distinguish between the software field and the hardware field of the activities :

Software

• Distorsions : Bernard Bouquet, Enrico Piotto, Ahmimed Ouraou and Yves Sacquin.
• Alignments : Enrico Piotto, Yves Sacquin , Ahmimed Ouraou.
• Calibrations : Vanina Ruhlmann.
• Lasers : Bernard Jeanmarie , Vincent Lepeltier.
• Slow Control : Jeanne Mas.
• Monitoring : Patrick Jarry with the help of Valerie Chorowicz and Iura Belokopytov, Didier Vilanova, Marc Donszelmann, Carlos Lacasta.
• dE/dX : Pierre Antilogus.
• Silicon Detector : Morgan Lethuillier, Maarten Boonekamp, Marc Besancon, Patrick Jarry, Marcos Gaspar, Yannick Arnoud.
• Software tools : John Wickens, Anita Bjorkebo, Tsanko Spassoff.
• Delana / Delpit support : Jean Philippe Laugier, John Wickens, Iura Belokopytov.

Hardware

• Coordination : Daniel Treille, Henrik Foeth, Philippe Gavillet , data taking coordinator and run coordinator.
• DAS : Philippe Charpentier, Clara Gaspar, Pavel Jalocha, Marc Donzelmann.
• Triggers : Lisa Matthis, G. Darbo, V. Canale, G. Valenti, B. Heck.
• System managers : D. Ruffinoni, Diego Carvalho, Yvon Miere.
• TPC opening : Claude Brand, Jean Renaud, Bernard Corajod.
• Water survey : Bernard Corajod, Jean Renaud.
• Gas survey : Gerard Cerruti, Ferdinand Hahn, Andre Augustinus.
• TPC maintenance : Bernard Corajod.
• SLOW CONTROL : Jeanne Mas, Andre Augustinus, SC Coordinator, Gareth Smith.
• LASERS : Bernard Jeanmarie, J.M. Noppe.
• Electronics maintenance : K. Truong (Orsay), Erik Zonka ( Saclay ), Michel Mur (Saclay), Michel Ferrat.
• Cabling : Philippe Mouillot.
• TPC Experts : Yannick Arnoud, Patrick Jarry, Pierre Antilogus, Patrice Siegrist.