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
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.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.