Surface Wave Discharges as Sources of “Super Hot” Hydrogen Atoms E. Felizardo 1 , E. Tatarova 1 , F. M. Dias 1 , C.M. Ferreira 1 and B. Gordiets 2 1 Instituto de Plasmas e Fusão Nuclear – Laboratório Associado, Instituto Superior Técnico, Lisbon, Portugal 2 Lebedev Physical Institute of RAS, Moscow, Russia “Super-hot” (with kinetic energy ~ 4 - 8 eV) and “hot” (kinetic energy ∼ 0.3 eV) hydrogen atoms were detected throughout the volume of a surface wave generated H 2 plasma column, at pressure p = 0.01 mbar, from the analysis of the H β , H γ , H δ , and H ε emission line profiles. Population inversion between the levels 5→4 and 6→4 was also observed. At pressure p = 0.2 mbar, super-hot atoms were not detected while hot atoms are still present. It was also found that the kinetic temperature of excited H (n = 4 -7) atoms, as determined from the fitting of the spectral lines with a single Gaussian profile, increases with the upper level principal quantum number. The discharge takes place inside a Pyrex tube with internal and external radii of 2.25 cm and 2.5 cm, respectively, using a surfatron-based setup [1,2]. The wave power is progressively dissipated by the plasma electrons along the wave path and the absorbed power per unit length, as well as the electron density, decrease gradually towards the plasma column end. The electron density decreases from about 2 × 10 10 cm -3 at the beginning of the column to (1– 2) × N cr (N cr ≈ 7 × 10 9 cm -3 ) at its end, while calculated effective values of the microwave electric field intensity sustaining the discharge are in the range 1-7 V/cm [3]. The H δ line profile at axial distance Δz = 35 cm and pressure p = 0.01 mbar is shown in Fig. 1. The H β , H γ and H ε line profiles have typically the same shape. This type of spectrum reveals the existence of two groups of atoms, viz., a “hot” group corresponding to the central peak, with a kinetic temperature of ~ 1,700 K (average kinetic energy ~ 0.2 eV), and a “super- hot” group corresponding to the broadened part, with a kinetic temperature of ~ 52,000 K (average kinetic energy ~ 7 eV). 37 th EPS Conference on Plasma Physics P4.308