TIPP 2011 - 2nd International Conference on Technology and Instrumentation in Particle Physics

Trigger induced mechanical resonance of gating wires in the multi-wire proportional chambers of the ALICE-TPC

Not scheduled

1m

Sheraton Hotel (Chicago)

Poster Presentation Gaseous Detectors

Speaker

Mr Magnus Mager (CERN)

Description

The need of applying large electrical potential differences between thin long wires imposes some of the tightest requirements in the design of modern multi-wire proportional chambers (MWPCs) [1] and similar in Geiger-Müller-like tubes. Relatively high stretching forces are needed to ensure a stable equilibrium of the wire positions [2]. Moreover the sensitivity to (random) event-related excitations due to ionisation has to be considered carefully as the latter may lead to oscillations and deterioration of the signal [3, 4]. When used for the read-out of time projection chambers (TPCs), and in particular when they are operated in a high flux environment, a special layer of "gating" wires may be added to MWPCs in order to screen their amplification region whenever the detector is not triggered. This is achieved by applying different potential configurations to these wires: they can either be held at a potential that makes them transparent to drift-electrons ("open" state) or be configured to intercept them ("close" state). This trigger-induced variation of electrical potential leads to a phenomenon recently observed at the ALICE-TPC: albeit the residual forces are rather small (about 1 uN/cm) they may give rise to sizeable (order of 10 um) resonant oscillations of the wires. The oscillations resemble themselves as a systematic pick-up signal, reaching amplitudes comparable to those of minimum ionising particles. We isolate this signal and give a model description for its creation. We conclude our study with an exhaustive series of laboratory measurements carried out at an opened chamber that is exposed to a microscope. References [1] J. Dieperink, K. Kleinknecht, P. Steffen, J. Steinberger, T. Trippe, and F. Vannucci, "Construction problems with large proportional wire chambers." CERN NP Internal Report 69-28, 1969. [2] T. Trippe, "Minimum tension requirement for Charpak chamber wires." CERN NP Internal Report 69-18, 1969. [3] I. R. Boyko, G. A. Chelkov, V. I. Dodonov, M. A. Ignatenko, and M. Y. Nikolenko, "Vibra- tion of signal wires in wire detectors under irradiation," Nucl. Instr. Meth. A, vol. 367, no. 1-3, pp. 321-325, 1995. [4] M. Anderson, J. Godlewski, A. Romaniouk, S. Sutchkov, and V. Tikhomirov, "Studies of wire vibrations in TRT straw tubes." ATL-INDET-2000-018, 2000.