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Resonant dissociation in N/sub 2/ by electron impact: a source of heating in the thermosphere and auroras

Description: An electron impact resonant dissociation process, leading to superthermal atom production in molecular nitrogen is described. The maximum cross section for this process is found to be 2.5 x 10/sup -18/ cm/sup 2/ at 10 eV. Measurements of scattered electrons indicate a value of -65 to -90 MeV for the electron affinity of N. The possible role of resonant dissociation as a source of heating in the thermosphere and in auroras is discussed.
Date: January 1, 1979
Creator: Spence, D. & Burrow, P.D.
Partner: UNT Libraries Government Documents Department

Production of negative hydrogen and deuterium ions in microwave-driven ion sources.

Description: The authors report progress they have made in the production of negative hydrogen and deuterium atomic ions in magnetically-confined microwave-driven (2.45 GHz) ion sources. The influence of source surface material, microwave power, source gas pressure and magnetic field configuration on the resulting ion current is discussed. Results strongly suggest that, at least in the source, vibrationally excited molecular hydrogen, the precursor to atomic negative ion production, is produced via a surface mechanism suggested by Hall et al. rather than via a gas phase reaction as is generally believed to be the case in most ion sources.
Date: September 11, 1998
Creator: Spence, D.
Partner: UNT Libraries Government Documents Department

Generation of high purity cw proton beams from microwave driven sources

Description: We describe a technique we have developed to significantly increase the proton fraction extracted from high pressure (mTorr) electron cyclotron resonance (ECR) sources of the type developed by Chalk River Laboratories (CRL). Specifically, this proton enhancement is achieved by the addition of environmentally benign additives (H{sub 2}O being the most effective) to the plasma, in molecular concentrations of the order of 1%. Typically, operating under non- resonant source conditions, this technique will enhance the proton fraction from about 75% to greater than 95% for a power input of 700W at 2.45 GHz. Similar results are achieved for deuteron beams. We believe this technique is capable of similar results in arc-discharge (bucket) sources, Penning sources and any other gas discharge sources, under suitable conditions.
Date: July 1, 1995
Creator: Spence, D. & Lykke, K.R.
Partner: UNT Libraries Government Documents Department

Excitation and dissociation mechanisms in molecules with application to mercuric halide laser system

Description: Although the mercuric halide laser systems have received intensive study in recent years, being one of only two efficient electronic-transition lasers known, the precise collisional mechanisms leding to HgBr(B), formation and subsequent fluorescence are still imperfectly understood. The initial suggestion that direct collisional excitation of, say, HgBr/sub 2/, by electrons (analogous to photoionization), i.e., HgBr/sub 2/ + e ..-->.. HgBr(b) + Br + e, was the dominant mechanism, was temporarily abandoned when a measurement by Allison and Zare yielded a cross section of only < 1 x 10/sup -20/ cm/sup 2/ for low incident electron energy HgBr(B-x) fluorescence, much too small to explain the observed laser efficiency. Subsequent explanations for HgBr(B) formation included energy transfer from excited N/sub 2/ or rare gases, electronic recombination of HgBr/sub 2//sup +/, or dissociative electron attachment. Though it has recently been demonstrated that electronic energy transfer does play a role in HgBr(B) formation in the presence of N/sub 2/ or X/sub e/ buffers, modeling studies of e-beam sustained discharges have now conclusively shown that direct electron-impact excitation of mercuric halides, is indeed the dominant laser mechanism. The technique of electron-energy-loss spectroscopy was used to obtain pseudo-optical absorption spectra in HgBr/sub 2/ and HgCl/sub 2/. Results are presented and discussed. (WHK)
Date: January 1, 1982
Creator: Spence, D.; Wang, R.G. & Dillon, M.A.
Partner: UNT Libraries Government Documents Department

Plasma modified production of high-current, high-purity cw H{sup +}, D{sup +}, and H{sup -} beams from microwave-driven sources

Description: We have recently reported production of cw proton beams from magnetically confined microwave-driven sources, operating under nonresonant (non-ECR) conditions, with proton fractions > 0.95, the remaining fraction consisting of H{sub 2}{sup +} (0.05) with no H{sub 3}{sup +}. We achieve this by adding H{sub 2}O to the plasma at molecular concentrations of 1% and about 700 W 2.45 GHz RF power to the source. High-current (45 mA) high-power (45 kV) beams of >92% proton purity have been produced using this technique. Additional impurity ions O{sup +} at 4ppt and OH{sup +} and H{sub 2}O{sup +} at << 1ppt are produced. We report further progress using this technique and similar results achieved for cw D{sup +} beams with D{sub 2}O and H{sub 2}O additives. Finally, we report progress made in the direct extraction of cw H{sup -} beams from microwave-driven sources in terms of ion source surface material and confining magnetic field configurations. Mechanisms are discussed.
Date: October 1996
Creator: Spence, D.; Lykke, K. R. & McMichael, G. E.
Partner: UNT Libraries Government Documents Department

Improved method for the production of atomic ion species from plasma ion sources

Description: A technique to enhance the yield of neutral atomic and ionic species (H{sup +}, D{sup +}, O{sup +}, N{sup +}, etc.) from plasmas. The technique involves the addition of catalyzing agents to the ion discharge. Effective catalysts include H{sub 2}O, O{sub 2}, and SF{sub 6}, among others, with the most effective being water (H{sub 2}O). This technique has been developed at Argonne National Laboratory, where microwave produced beams consisting essentially of 100% atomic neutral species (H) have been generated, and ion beams of close to 100% purity have been generated.
Date: December 31, 1996
Creator: Spence, D. & Lykke, K.
Partner: UNT Libraries Government Documents Department

Production of high-brightness CW proton beams with very high proton fractions

Description: This paper demonstrates a new technique to significantly enhance the proton fraction of an ion beam extracted from a plasma ion source. We employ a magnetically confined microwave driven source, though the technique is not source-specific and can probably be applied equally effectively to other plasma sources such as Penning and multicusp types. Specifically, we dope the plasma with about 1% H{sub 2}O, which increases the proton fraction of a 45 keV 45 mA beam from 75 to 90% with 375W 2.45 GHz power to the source and from 84% to 92% for 500W when the source is operated under nonresonant conditions. Much of the remaining fraction of the beam comprises a heavy mass ion we believe to be N{sup +} impurity ions resulting from the conditions under which the experiments were performed. If so, this impurity can be easily removed and much higher proton fractions could be expected. Preliminary measurements show the additive has no adverse effect on the emittance of the extracted beam, and source stability is greatly improved.
Date: December 1, 1995
Creator: Spence, D.; McMichael, G.; Lykke, K.R.; Schneider, J.D.; Sherman, J.; Stevens, R. Jr. et al.
Partner: UNT Libraries Government Documents Department