BigBite Drift Chambers

The drift chambers of the BigBite spectrometer consist of three separate horizontal drift chambers spaced approximately 35cm apart. The drift chambers are the first set of detectors after the magnet and are the highest spacial resolution detectors in the full set. The approximate configuration of the three chambers are found in the table:

Chamber	Plane Pattern	Number of Wires	Wire Spacing (cm)	Height (m)	Width (m)	z detector (m)
1	UUXXVV	142	1.0	1.40	0.35	0.00
2	UXV	200	1.0	2.00	0.50	0.36
3	UUXXVV	200	1.0	2.00	0.50	0.71

To achieve the ability to resolve points in three dimensions, three different types of planes are used, which we call U, X, and V. All three plane types reside in a plane of constant zdetector. X wires run parallel to the Y axis and U and V wires are 30 to that axis (see figure). In each plane, the sense wires are spaced 1cm apart, with a field shaping wire in between each pair. Planes of the same type, when next to each other, are staggered 0.5cm relative to one another. The chambers are filled with a 50% argon-50% ethane gas mixture kept at slightly above atmospheric pressure.

The sense wires are triggered as a charged particle ionizes the gas when it passes through the chamber. If the wires are then put at some potential difference, the free floating charges drift towards the wires and generate an electrical signal which is then read out by a time-todigital converter. The amount of time it takes to drift from the track to the wire can then be converted into a distance.

The purpose of the tracking code is to take these times, convert them to a distance, and then use these distances to fit a straight line across several planes.

Drift chamber wire orientation

See also: BigBite Databases