A spark chamber is a stack of conducting plates separated by a gas gap. When an energetic ionising particle passes through the device, a control circuit applies a high voltage between each pair of neighbouring plates. The voltage generates a spark between each of the plates. The spark prefers to form at the spot where the particle passed through, due to the ionisation trail left by the particle. The path of the traversing particle is thus revealed by the array or line of sparks, which may be seen or photographed through the side of the device. They hey-day of the spark chamber as a research tool for detecting high energy cosmic rays came to an end in the 1960s when it was replaced by better techniques. Nevertheless, spark chambers are still designed for museums and used in education as they are an exciting, visually direct and simple way of demonstrating cosmic rays to an audience.
In this review, it is suggested that the student review the wealth of historical literature relating to the design of spark chambers, with a view to (1) summarising the key physics of their function, and (2) making recommendations for the optimal design parameters of a lightweight transportable spark chamber suitable for use in schools.
The student may wish to consider points like the following: the physics of the gas breakdown; factors determining the optimal choice of gas mixture used, and how this relates to other design parameters; how the optimal voltages vary with plate separation; how much power the chamber might be expected to dissipate in running; what the peak and long-term average currents depend on chamber size, gas, voltages etc; safety aspects to consider (interference, X-rays).