Abstract:
Supercritical gaseous helium at temperatures of $7$ and $11$ K was excited by a corona discharge at negative high voltages. The discharge was maintained by electrons created at the cathode and moving toward the anode through a dense gas. The corona discharge current was measured at a fixed gas temperature with a change in its pressure. At low gas density, the discharge current was large. In this mode, electrons are free and highly mobile. As the pressure increased, the corona discharge current decreased sharply. At high gas density, a weak current of $100$ nA was measured due to the low electron mobility due to their localization. Such a sharp decrease in the discharge current was observed at temperatures of $7$ and $10$ K and pressures of $0.2$–$0.4$ MPa. The current–voltage characteristics of the discharge were measured and analyzed. It is shown that under these conditions, the electron mobility decreases by three orders of magnitude. The transition from a discharge with free electrons to a state with localized electrons occurs in a supercritical gas in a narrow pressure range and is explained by the quantum-mechanical nature of electrons.
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