Observation of negative potential depression on double layer during a phase of current disruption

The negative potential depression with a depth of approximately electron temperature is observed on the low potential tail of the double layer just at the moment when the electron current passing through the layer is disrupted. The depression is confirmed to serve as an electron thermal barrier and form as ion hole from phase-space measurements of electrons and ions, respectively. The depth of the depression becomes maximum when the density around the depression becomes most inhomogeneous.