Negative Current-Voltage Characteristics in Hydrogen at High Pressure Using Plane Parallel Electrodes

In conjunction with measurements of current-voltage characteristics in hydrogen, a few characteristics have been obtained which include a region with negative slope. The latter characteristics were obtained with plane parallel electrodes at an electrode separation of 2 cm at a pressure of 400 mm Hg and with three values of externally initiated cathode current. The initial currents ranged from about 10^-11 to 10^-9 amp, and the amplified currents reached values as high as 10^-4 amp. The characteristics corresponding to the larger initial currents become negative at large currents ({~}10^-5 amp). The voltage at which a characteristic becomes negative, i.e., the maximum attainable voltage across the electrodes, decreases slightly with increasing initial current. The circuit included a series resistor of 20 megohms.These characteristics can be explained quantitatively on the basis of the first and second Townsend coefficients (previously measured with the same apparatus) acting in conjunction with space charge, if a not unreasonable discharge area is assumed. These calculations were carried out on an IBM 704 computer.