CORONA DISCHARGE IN FLUID HELIUM: DRASTIC GROWTH OF ELECTRON MOBILITY

Abstract. Liquid Helium (LHe) at 4.2K was excited using a corona discharge for negative high voltages. The experiments were carried out with temperature increasing and different pressures. Current-voltage characteristics were measured and analyzed. The sharp increasing of the corona current was observed at temperatures 7K and 10K under pressure in the range 0.2-0.4 MPa. The analysis showed the electron mobility increasing by 3 orders of magnitude in these conditions. Measurements have been started in normal liquid He (LHe) at the temperature of T=4.2K with following temperature increasing using dc high voltage. Tungsten needle electrode with point radii rp=2.5m was used. The point-plane distance was in the range of 0.65-0.8cm. The starting material was helium gas N60 (99.99990 % pure, Air Liquide) which had an impurity concentration of about 0.1 ppm of oxygen. After the purification, the gas is liquefied in a cell housed in a cryostat. The temperature in the cell is measured by a germanium resistor. Special equipment allows us to increase the temperature and keep it during measurements with different pressures. The cell can withstand pressure up to 11MPa. The stabilized dc voltage (up to 20 kV) was connected to the tungsten point electrode. The Tektronix TDS540 oscilloscope or the Keithley 610C current meter wa