Intermittent variation of electron temperature in converging field following a magnetic beach ECR plasma source*

In converging field configuration of cylindrical plasma following electron cyclotron resonance plasma source, intermittent variation of electron temperature is observed. The phenomenon is characterized by higher electron temperature, negative spike in floating potential, exponential distribution of occurrence probability as a function of waiting time, and radially finite and axially elongate correlation. These are similar to a phenomenon observed in diverging field but the first time observation in converging filed configuration.

Experiments were performed using a linear plasma device NUMBER. A 2.45 GHz microwave injected from an end of chamber produces helium plasma by the electron cyclotron resonance in the magnetic beach configuration, B < 0.1 T. The plasma expands along the magnetic field into a higher field test region up to 0.3 T. Electron temperature is obtained from current - voltage characteristics of Langmuir probe using conditional sampling triggered by negative spike in floating potential monitored by another probe.

Electron temperature rising of 2 - 10 eV is observed during negative spikes in floating potential. Cross correlation coefficients between two floating potentials measured at different position indicate correlation along the field line.