H-L transition caused by irregular probe insertion in the JFT-2M tokamak

A pair of probe pins whose lengths differ by 5 mm are inserted into the separatrix of H-mode plasmas. When the long pin is biased positively against the short one, the H-L transition takes place and the current through the resistor making a connection between these pins increases for 10 μs and the potential of the pin increases for 100 μs. The energy dissipated by the resistor during the H-L transition is comparable to the energy of the radial electric field in H-mode plasma. When the long pin is biased negatively, the H-L transition also occurs; however, it takes 1 ms to change the potential of the pin and the plasma returns to H-mode after the extraction of the probe.