Development of Spark Chambers for Use in Measurements of the Charge Spectrum of High Energy Cosmic Rays

Abstract

The High Energy Cosmic Ray Experiment, flown on balloons by a group at Goddard Space Flight Center, is designed to measure the charge, the energy, and the arrival direction of high-energy cosmic rays. A wiregrid spark chamber is employed to determine the trajectory of each incident primary particle which satisfies the experiment trigger criteria. Optimum trajectory-determination efficiency depends on parameters, the values of which vary with the charge of the incident particle. The functional dependence on the voltage applied to the wire grids and on the delay in application of the high voltage trigger for several different values of the DC clearing field was measured for fully ionized nitrogen nuclei and for singly charged particles. The voltage was found to be the most suitable parameter to vary in order to maximize the spark formation efficiencies and to minimize spurious spark formation. Because of the low fluxes of high-Z, high-energy cosmic rays, long experiment exposure times such as those obtained in satellites are desirable. To adapt the spark chambers for use with experiments with a duration of more than one year and total accumulated events in excess of 3 × 108, the useful life times of both the high-voltage triggering circuit and the spark-chamber gas needed to be improved. Krytron high-voltage triggering devices have been developed which will perform satisfactorily for more than 3 × 108 simulated events at a rate of 10 events/ sec, an improvement of approximately a factor of 10.