Studies of plasma potential with emissive probes in the low temperature plasma experiment NJORD

Abstract

In this thesis, the concept of an emissive probe has been used to obtain the plasma potential in the low temperature plasma experiment NJORD. An emissive probe is a probe concept in which a wire is heated strong enough to emit a Richardson current. The probe is then swept through several voltage biases and thus, an I-V trace obtained. With the current from the emission and the collected current, this gives in principle very easy access to the plasma potential. NJORD is a plasma discharge driven by a radio frequency in what is called helicon range. This specifies a small frequency band of oscillations that connect well to the electrons. While having good heating properties, it induces a set of problems for the emissive probe due to the oscillations. Applying modelling and monitoring how the recorded traces deviate from the expected ideal traces, however, gives some insight into the physical processes taking place and made it possible to prove the existence of a second electron population. Observing two electron populations with this concept is a novelty and could help completing the theory behind the so called "helicon double layer thruster" concept.