Spark chamber

A spark chamber is a particle detector. Spark chambers were used in particle physics and in the gamma-ray astronomy.

Spark chambers are, inter alia, suitable for the detection of muons (secondary cosmic rays ).

Design and operation

In an optically transparent chamber a plurality of parallel conductive plates are attached. To the plates a high voltage of about 20 kV is applied alternately. The chamber is filled with an inert gas, which is initially electrically neutral. The plates are thus isolated from each other, no current flows.

A penetrating electrically charged particle splits along its trajectory electrons of the atoms from, it leaves a ionisation. The resulting ions are accelerated by the applied voltage, where they trigger an avalanche more charge carriers ( impact ionization ). Between adjacent plates finally jumping over a spark. The spark discharge takes place exactly along the ionisation or the flight path. The path of the particle can be observed across multiple disks when they are penetrated by the particles. This is for example muons, which are caused by cosmic radiation in the upper atmosphere, the case.

The sensitivity can be controlled via the high voltage. In most cases the high voltage of the spark chamber but will not be created when a particle passes flown. This is achieved by ( scintillator detectors or Geiger- Müller counter tubes ) are placed in front of and behind the chamber particle detectors, their simultaneous response indicating the fly-through of a particle. To this end, they are connected to a coincidence detector which generates the trigger pulse for triggering the high voltage pulses. The high voltage pulse is building the electric field between the plates on so fast that the ionisation is still present and the discharge along the track is channeled. The triggering of the high voltage power supply has the advantage that no spontaneous discharge occurs and the high voltage need not be adjusted. Triggering can be, for example, carried out by a switching spark gap, which connects the charged capacitor to the plates.

The color of the discharge is dependent on the inert gas filling.

Today spark chambers are rarely used in research. They are used mainly for demonstration purposes.