Relative densities of H atoms and Yiiiv") molecules in vibrational levels up to i/'=5, effusing from a metal box containing heated tungsten filaments, were detected by a resonance-enhanced multiphoton ionization technique. The atom production is compatible with dissociation of molecules at the filament. The formation of Hiiv") is attributed to an Eley-Rideal-type reaction, in which a free atom recombines with an adsorbed atom at the cold wall, followed by desorption. Above 2800 K we observe an abrupt drop in the atom and the Hiiv") densities. It is ascribed to the effects of annealing on the filament surface.PACS numbers: 79.20. Nc, 33.80.Rv, 52.50.Dg, 82.65.Yh It is commonly accepted that in a hydrogen volume source the negative hydrogen ions (H~) are formed by dissociative attachment of slow electrons to vibrationally excited molecules Wiiv") 1 ' 1 where v" is the vibrational quantum number. The vibrational excitation is attributed to electron-impact excitation of molecules (in v" -0) by the fast primary electrons in the discharge. 4 To gain information on these processes one is interested in the measurement of the distribution of vibrationally excited molecules. 5 We have chosen resonance-enhanced multiphoton ionization (RMI) 6 as the method to study the discharge in our volume source. RMI is a powerful method because it allows the efficient detection of (metastable) molecules in specific rotational and vibrational states, 7 as well as atoms.The present Letter is concerned with the discovery that with the filaments heated, but the discharge turned off, we have been able to detect vibrationally excited molecules with v " up to 5. In a similar experiment, Hall et a/. 8 observed the formation of H2(i>") molecules with v" up to 9, using dissociative attachment of slow electrons to H2

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Reported are measurements on the interaction between a relativistic electron beam (REB) with the parameters 800 kV, 6 kA, 50–150 nsec, and a plasma with a density of ne=1.0×1019 m−3–1.0×1020 m−3. The electron temperature during and after the beam pulse is obtained by means of Thomson scattering. Also measured is the angular distribution of the beam electrons as a function of time and position. By varying the angular spread of the beam it is possible to pass from a kinetic to a quasihydrodynamic interaction. In both regimes measurements are compared with the appropriate theoretical model. Energy transfer is largest in the quasihydrodynamic regime and amounts to 2.5×103 J/m3 or 2.2×1016 eV/cm3. The electron temperature reaches values of 150 eV and appears limited by the electron heat conduction along the magnetic field.

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