Ballistic compressors are well-known tools for investigations of non-ideal plasmas [ 11.In such devices a plasma is generated by rapid compression of gases in a closed barrel with the aid of a piston accelerated by a driver gas, without the influence of external electric fields or currents. I n our apparatus, called AIKA, we get a plasma disc (diameter 150 mm, thickness z,ln a few mm, see Fig. l), surrounded by metallic walls (piston front plate, small part of inner barrel surface, barrel closure). These walls give rise to energy losses and the formation of boundary layers which complicate theoretical treatment of the plasmas generated. Due to leakages between piston and barrel (slit width about 5 to 10 pm) and between closure part and barrel, particle losses must be taken into