The authors study the flow of current in the plasma of the UMIST quadrupole between two Langmuir probes which served as electrodes. For low frequencies (<10 kHz) the impedance to current flow transverse to the magnetic field behaves as a resistance and capacitance in parallel. Experimental results are in good agreement with the theory and allow a determination of the ion-neutral collision frequency and of the ion density, both of which agree well with values determined by independent methods. They suggest that this may be applicable as a new diagnostic method in suitable cases. There is a definite resistive component of the impedance for measurements along the field lines and the channel for current flow is considerably larger than the tube of flux joining the two probe sheaths. Theory suggest that the actual value of this resistance will be determined almost entirely by the transverse flow of current associated with the current channel expansion, and experiment confirms this.
On attenuation of electron current of flush-mounted probes and electrodes in magnetised plasmas