Striation excitation in a conical discharge tube

The excitation of ionization-diffusion waves (striations) is considered for the positive column of a direct-current discharge in a conical tube at high current levels. The condition for striation self-excitation is derived. It is found that the upper self-excitation limit for argon in tubes with small semivertex angles is lower than that in a cylindrical tube whose radius lies between the radii for the ends of the cone.