A High Sensitivity Wire Spark Chamber Readout Useful in Strong Magnetic Fields

A developmental wire spark chamber is described which can detect extremely weak discharges The readout circuits are not affected by magnetic fields, thus offering the opportunity to use such chambers in strong magnetic field areas. Each wire in the chamber is in series with a memory capacitor. A discharge in the chamber charges this capacitor. However, the displacement current's charge, associated with pulsing the chamber, averages to zero, thus making it possible to detect very weak discharges. Readout consists of discharging each memory capacitor with a Field Effect Transistor (FET) into a digital scanner. Preliminary tests indicate that a charge gain of 106 to 107 in the chamber is the lower limit of useful operation of the present capacitor - FET readout combination. By using small diameter wires in the chamber, discharges as low as .02μ Coulombs will give efficient operation.