Highly sensitive plasma absorption probe for measuring low-density high-pressure plasmas

This article reports a new type of sensitive plasma absorption probe (PAP), which is characterized with a thin wire antenna directly exposed to plasma. In the sensitive PAP, the power reflection coefficient resonantly decreases at a certain frequency due to absorption of a surface wave, which is excited along a sheath formed around the antenna. The electron density is derived from the measured absorption frequency in comparison to a wave dispersion relation: the dispersion is calculated under assumptions that the sheath width is twice the Debye length and that wavelength is twice the antenna length. This sensitive PAP also enables measurements of very low electron densities (∼108 cm-3) and very high pressures (∼10 Torr), in comparison to a conventional standard PAP. In addition, both electron temperature and electron density can be measured using a pair of sensitive PAPs of different antenna radii