From HEP at Tennessee
Limited Streamer Tube (LST)
December 2002 groups from Italy and the US proposed to replace the current BaBar Resistive Plate Chambers (RPC) in the Instrumented Flux Return (IFR) gaps, used to detect muons and neutral hadrons, with plastic Limited Streamer Tubes (LST).
A standard LST cell consists of a silver plated sense wire 100 mm in diameter, located at the center of a cell of 9-mm square section. A plastic (PVC) extruded structure, or profile contains 8 such cells, open on one side (see Fig. right). The profile is coated with a resistive layer of graphite, having a typical surface resistivity between 0.2 and 1 MW/square. The profiles, coated with graphite and strung with wires, are inserted in plastic tubes (sleeves) of matching dimensions for containment of the gas mixture. Other components needed for the complete detector are end pieces with gas inlets, HV and ground connectors; spacers, which keep the wires at the centre of the cell and are installed typically every 40cm; small printed boards and their supports at the two ends of the profile for soldering the wires and providing electrical connections.
The signals for the measurement of one coordinate can be read directly from the wires, but it has become customary instead to read both coordinates with strip planes, thereby avoiding the complications of feed-throughs and blocking capacitors. For such tubes the operating voltage is typically 4.7kV; the plateaus are at least 200V wide; the signals on the wire are of the order of 150/200mV (over 50W), typically 50ns at the base, sometimes with an afterpulse; an average charge per pulse of 300pC can be assumed. The gas mixtures are strongly quenching: the original one (25% Ar, 75% n-pentane) being explosive has been replaced in accelerator use (SLD; ZEUS) by a non-flammable one based on CO2. The LST geometrical efficiency is limited by the plastic sides of the cells (1mm thick) and sleeves (1mm) to a worst-case value of 90%. Fortunately this effect is mitigated by the fact that most tracks area not exactly orthogonal to the profiles, and can be greatly reduced by increasing the cell size.
References
"The Performance of the Limited Streamer Drift Tubes," M. Baubillier et al., NIM A217, 205-207.
"Large-Series of Limited Streamer Tubes," M. Caria et al., NIM A260, 368-372.
"Plastic Streamer Tubes and their Applications in High Energy Physics," E. Iarocci, NIM A217, 30-42.
"Long-Term Tests of Limited Streamer Tubes," Kwong Lau, Drew Parks, Jorg Pyrlik, and Roy Weinstein, NIM A320, 243-248.