At the cathode distinctly different modes of current transfer occur if the discharge parameters are varied while at the anode by parameter changes only a smooth variation is induced [1-5]. To understand the different behaviour the cathodic and anodic plasma boundary layers (CPBL and APBL) have to be considered. The theoretical treatment of the CPBL is so far advanced that integral parameters like the voltage-current-characteristic UC(I) can be reproduced in accordance with measurements. But it is not so perfect that the calculated electron temperature rec and the electron density ;7ec within the CPBL can be considered as physical facts. It is shown from measurements that the anode power loss Pa is given in a good approximation by P.i=l(+2.5kTt:Je), in which (p is the work function of the electrode material and rea the electron temperature in the APBL. Measurements of anode falls ?/" gave values between 4V and 10V. But its influence on Pa is quite weak [3, 4]. This is very different to the relation between the cathodic power loss Pc and the cathode fall Uc. Up to now the theoretical treatment of the APBL is not able to explain this findings. A detailed spectroscopic investigation of the CPBL and the APBL may advance the theoretical treatment of the APBL.
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