 Spark chamber

A spark chamber reveals a charged particle path as a sequence of electrical sparks between conducting plates. The particle first leaves an ionization trail in the intervening gas. A promptly applied high electric potential difference causes discharges preferentially near that trail, making it visible.

External scintillation counters can detect a crossing and trigger the voltage pulse while the trail remains available. Photographing sparks in several gaps samples the trajectory; it does not make each spark a direct photograph of the particle. Timing, gas condition and electrode geometry affect efficiency. ^[ref]