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Manual number:Physikpraktikum für Vorgerückte (VP)vp.phys.ethz.chDrift ChamberInstructionsD. Hits, G. Guyer, M. Setzrev. D. Hits, October 5, 20181
1 IntroductionThis manual is contains only brief introduction to the processes occurring in adrift chamber.In order to gain more complete understanding of the physics ofthe drift chamber a references at the end of this manual should be consulted[1, 2, 3].Drift chambers belong to the most important measurement devices ofnuclear and particle physics. They are a central aspect of nearly every largeexperiment in high energy physics. In this experiment a small drift chamberis operated and characterized. After that the trajectories of particles fromthe cosmic radiation should be reconstructed.If a charged particle travels through a gas volume, it leaves a trail ofionized gas atoms and free electrons behind. By applying an electric fieldthe ions and electrons can be separated and generate an electric signal. Thissignal, however, is very small. A high-energy particle with an elementarycharge produces only about 100 electron/ion-pairs by going through one cen-timeter of air. Single particles are therefore only detectable after amplifyingthis signal.In a detector filled with gas there is a simple way to amplify the signalinside the detector, even before it is measured on the outside. If the electricfield is sufficiently strong, the free electrons can be accelerated to the energieslarge enough to ionize gas atoms and create and avalanche which will resultin an electric signal many times higher than the original one. The requiredelectric field strengths are easily generated around very thin wires. By usingvery thin signal wires, one can therefore easily create a detectable signal.Hence already a simple structure allows the detection of particle radiation.Many detectors are based on this principle, from a simple Geiger counter upto time projection chambers in high energy experiments with several thou-sand wires.A drift chamber additionally makes use of the fact, that the amplificationof the signal only occurs, when the free electrons reach the region of strongfields in the immediate proximity to a wire. Before reaching this point theelectrons simply drift along the electric field lines, without increasing theirnumbers. With a known drift velocity and a measured time difference be-tween the arrival of the particle and the detection of the electric signal thedistance between the signal wire and the trajectory of the particle can there-fore be calculated. The location can be reconstructed in such a chamberwith a resolution to a fraction of a millimeter. By combining the position2

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