Hydrogen atom density in narrow-gap microwave hydrogen plasma determined by calorimetry Available to Purchase

The density of hydrogen (H) atoms in the narrow-gap microwave hydrogen plasma generated under high-pressure conditions is expected to be very high because of the high input power density of the order of 10⁴W/cm³. For measuring the H atom density in such a high-pressure and high-density plasma, power-balance calorimetry is suited since a sufficient signal to noise ratio is expected. In this study, H atom density in the narrow-gap microwave hydrogen plasma has been determined by the power-balance calorimetry. The effective input power to the plasma is balanced with the sum of the powers related to the out-going energy per unit time from the plasma region via heat conduction, outflow of high-energy particles, and radiation. These powers can be estimated by simple temperature measurements using thermocouples and optical emission spectroscopy. From the power-balance data, the dissociation fraction of H₂ molecules is determined, and the obtained maximum H atom density is (1.3 ± 0.2) × 10¹⁸cm⁻³. It is found that the H atom density increases monotonically with increasing the energy invested per one H₂ molecule within a constant plasma volume.