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A System for Measurement of Negative-Ion Charge-Exchange Cross Sections

Description: A radio-frequency positive-ion source and a fifty-kilovolt linear accelerator were designed and constructed in order to produce sizable quantities of hydrogen, helium, nitrogen, neon, and argon. Plans were then made to equip this ion source with charge-exchange apparatus suitable for charge-exchange cross-sectional measurements. It is the purpose of this paper to present the design of the equipment and to present operational knowledge of the equipment and of ion beams which are producible.
Date: January 1960
Creator: Wingo, Dale T.
Partner: UNT Libraries

Comparison of Poloidal Velocity Meassurements to Neoclassical Theory on the National Spherical Torus Experiment

Description: Knowledge of poloidal velocity is necessary for the determination of the radial electric field, Er, which along with its gradient is linked to turbulence suppression and transport barrier formation. Recent measurements of poloidal flow on conventional tokamaks have been reported to be an order of magnitude larger than expected from neoclassical theory. In contrast, recent poloidal velocity measurements on the NSTX spherical torus [S. M. Kaye et al., Phys. Plasmas 8, 1977 (2001)] are near or below neoclassical estimates. A novel charge exchange recombination spectroscopy diagnostic is used, which features active and passive sets of up/down symmetric views to produce line-integrated poloidal velocity measurements that do not need atomic physics corrections. Local profiles are obtained with an inversion. Poloidal velocity measurements are compared with neoclassical values computed with the codes NCLASS [W. A. Houlberg et al., Phys. Plasmas 4, 3230 (1997)] and GTC-Neo [W. X. Wang, et al., Phys. Plasmas 13, 082501 (2006)], which has been updated to handle impurities. __________________________________________________
Date: April 7, 2010
Creator: Bell, R. E.; Kaye, S. M.; Kolesnikov, R. A.; LeBlance, B. P.; Rewolldt, G. & Wang, W. X.
Partner: UNT Libraries Government Documents Department

Initial Assessment of Electron and X-Ray Production and Charge Exchange in the NDCX-II Accelerator

Description: The purpose of this note is to provide initial assessments of some atomic physics effects for the accelerator section of NDCX-II. There are several effects we address: the production of electrons associated with loss of beam ions to the walls, the production of electrons associated with ionization of background gas, the possibly resultant production of X-rays when these electrons hit bounding surfaces, and charge exchange of beam ions on background gas. The results presented here are based on a number of caveats that will be stated below, which we will attempt to remove in the near future.
Date: February 18, 2010
Creator: COHEN, R.H.
Partner: UNT Libraries Government Documents Department

Synthesis and characterization of molecules for electron transfer research.

Description: Dimethoxynaphthalene (donor) and quinone (acceptor) have been chosen as a suitable redox pair and are bonded to either permethylated silane chains or corresponding permethylated alkyl chains to form Acceptor-(Bridge)-Donor molecules. The idea that the s-delocalization phenomenon of silane chains may greatly facilitate ET reactions will be tested. The starting material for the donor precursor, 4-(1,4-dimethoxynaphthyl)bromocyclohexane, was 1,4-naphthoquinone. After methylation and bromination, the Grignard reagent of the resulting bromide was reacted with cyclohexanedione, mono ethylene ketal. The resulting alcohol was changed to the donor precursor through the following functional group transformation steps: dehydration, hydrogenation, deketalization and bromination. 1,4-Dibenzyloxybromobenzene, the precursor for the acceptor, was synthesized from 1,4-hydroquinone through bromination and benzylation. The connection of the two precursors and either permethylated silane chains or permethylated alkyl chains will give the final target molecules for ET research. Progress on this is included.
Date: December 2000
Creator: Xiao, Wu
Partner: UNT Libraries

Excitation Function of the Reaction C12(p,pn)C11 at High Energies

Description: Chupp and McMillan have recently measured the excitation curve for the reaction C{sup 12}(pnpn)C{sup 11} at high energies. Using the model of the nucleus described by Serber, the excitation curve of the above reaction has been calculated for energies up to 100 Mev. The excitation of the nucleus is determined on the basis that the incident proton makes individual collisions with the nucleons, the transferred energy exciting the nucleus. n-p collisions are taken to be three times more probable than n-n or p-p collisions. Charge exchange is assumed. The calculations were made for both 50% and 100% charge exchange. The decay of the excited nucleus is treated by the usual evaporation mode.
Date: November 1, 1947
Creator: Heckrotte, W. & Wolff, Peter
Partner: UNT Libraries Government Documents Department

Excitation Function of the Reaction C12(n,2n)C11 at High Energies

Description: The excitation curve for the reaction C{sup 12}(n,2n)C{sup 11} has been calculated for energies up to 100 Mev. The calculations were done as described in the preceding letter for the similar reaction of C{sup 12} under proton bombardment. The results of the calculations for 50% charge exchange are shown in Figure 1. The calculated cross section for the reaction at 90 Mev is: .011 barns for 100% charge exchange and .013 barns for 50% charge exchange. The experimental value is 0.025 {+-} .004 barns. The ratio of the cross section of the reaction C{sup 12}(pnpn)C{sup 11} to the cross section of the above reaction at 90 Mev is 5.8 for 100% charge exchange and 3.8 for 50% charge exchange. The experimental ratio is 2.7 at 90 Mev. This difference in cross sections between the two reactions is established by two factors. Firstly, there is the part played by charge exchange in the C{sup 12}(pnpn)C{sup 11} reaction which leads to excited N{sup 12} with the subsequent boiling off of a proton, while a similar exchange process cannot take place for the C{sup 12}(n2n)C{sup 11} reaction. Secondly, there is the difference between the contributions of the knock out process as a result of the difference in the n - p and the n - n cross sections, which favors the p + C{sup 12} knock out reaction. It will be noted that the parts of the reactions which go through excited C{sup 12}, while practically equal, are so small that they do not greatly affect either reaction. Although the results of these calculations do not agree too closely with the experimental results, the results are probably as good as are to be expected because of the crudity of the assumed model. The results do, though, seem to give a good qualitative picture ...
Date: November 1, 1947
Creator: Heckrotte, Wolff & Wolff, Peter
Partner: UNT Libraries Government Documents Department

Extraction of Poloidal Velocity from Charge Exchange Recombination Spectroscopy Measurements

Description: A novel approach has been implemented on DIII-D to allow the correct determination of the plasma poloidal velocity from charge exchange spectroscopy measurements. Unlike usual techniques, the need for detailed atomic physics calculations to properly interpret the results is alleviated. Instead, the needed atomic physics corrections are self-consistently determined directly from the measurements, by making use of specially chosen viewing chords. Modeling results are presented that were used to determine a set of views capable of measuring the correction terms. We present the analysis of a quiescent H-mode discharge, illustrating that significant modifications to the velocity profiles are required in these high ion temperature conditions. We also present preliminary measurements providing the first direct comparison of the standard cross-section correction to the atomic physics calculations.
Date: July 16, 2004
Creator: Solomon, W.M.; Burrell, K.H.; Gohil, P.; Groebner, R.J. & Baylor, L.R.
Partner: UNT Libraries Government Documents Department

Initial Neutral Particle Analyzer Measurements of Ion Temperature in NSTX

Description: The Neutral Particle Analyzer (NPA) diagnostic on the National Spherical Torus Experiment (NSTX) utilizes a PPPL-designed E||B spectrometer which measures the energy spectra of minority H and bulk D species simultaneously with 39 energy channels per mass specie and a time resolution of 1 msec. The calibrated energy range is E = 0.5-150 keV and the energy resolution varies from (delta)E/E = 3-7% over the surface of the microchannel plate detector. The NPA measures thermal Maxwellian ion spectra to obtain line integrated ion temperatures, T{sub i}. For line integral electron densities below neL {approx} 3.5 x 10{sup 19} m{sup -2}, good agreement is observed between the line integrated NPA T{sub i} and the central T{sub i}(0) measured by the spatially localized CHarge Exchange Recombination Spectroscopy (CHERS) diagnostic. However, with increasingly higher n{sub eL} the NPA T{sub i} falls below the central T{sub i}(0) measured by CHERS because the charge exchange neutral emissivity weights the line integrated NPA measurement outboard of the plasma core. An analytic neutral analysis code, DOUBLE, has been applied to the NPA data to correct for this effect and restore agreement with T{sub i}(0) measured by CHERS. A description of the NPA diagnostic on NSTX and initial ion temperature measurements along with an illustration of application of the DOUBLE code are presented.
Date: July 8, 2002
Creator: Medley, S.S.; Bell, R.E.; Petrov, M.P.; Roquemore, A.L. & Suvorkin, and E.V.
Partner: UNT Libraries Government Documents Department

Measurements of the Ion Species of Cathodic Arc Plasma in an Axial Magnetic Field

Description: Metal and gas ion species and their charge state distributions were measured for pulsed copper cathodic arcs in argon background gas in the presence of an axial magnetic field. It was found that changing the cathode position relative to anode and ion extraction system as well as increasing the gas pressure did not much affect the arc burning voltage and the related power dissipation. However, the burning voltage and power dissipation greatly increased as the magnetic field strength was increased. The fraction of metal ions and the mean ion charge state were reduced as the discharge length was increased. The observations can be explained by the combination of charge exchange collisions and electron impact ionization. They confirm that previously published data on characteristic material-dependent charge state distributions (e.g., Anders and Yushkov, J. Appl. Phys., Vol. 91, pp. 4824-4832, 2002) are not universal but valid for high vacuum conditions and the specifics of the applied magnetic fields.
Date: October 19, 2010
Creator: Oks, Efim & Anders, Andre
Partner: UNT Libraries Government Documents Department

Prompt Loss of Energetic Ions during Early Neutral Beam Injection in the National Spherical Torus Experiment

Description: Early neutral-beam injection is used in the National Spherical Torus Experiment (NSTX) to heat the electrons and slow current penetration which keeps q(0) elevated to avoid deleterious MHD activity and at the same time reduces Ohmic flux consumption, all of which aids long-pulse operation. However, the low plasma current (I{sub p} {approx} 0.5 MA) and electron density (n{sub e} {approx} 1 x 10{sup 13} cm{sup -3}) attending early injection lead to elevated orbit and shine through losses. The inherent orbit losses are aggravated by large excursions in the outer gap width during current ramp-up. An investigation of this behavior using various energetic particle diagnostics on NSTX and TRANSP code analysis is presented.
Date: March 25, 2005
Creator: Medley, S.S.; Darrow, D.S.; Liu, D. & Roquemore, A.L.
Partner: UNT Libraries Government Documents Department

MEETING IX - BEVATRON RESEARCH CONFERENCE--BEVATRON PHYSICS

Description: A large number of experiments relating to nuclear structure and materialization of energy will fall within the energy range of primary and secondary particles available from the Bevatron. Some experiments of interest are outlined below with pertinent comments. Proton-proton scattering can be extended to the high energy range using liquid hydrogen targets and hydrogenous materials by bombarding the target with the internal beam or using externally scattered protons. Proton-deuteron scattering measurements using liquid deuterium targets or solid materials can also be extended. Proton scattering from heavier nuclei may be found less difficult to interpret at these level energies as the nucleons will interact more or less independently. The wavelength of the bombarding particles will now be much smaller than nucleon diameters. Nuclear collisions represent by far the most important interaction between high energy nucleons and matter. Proton-neutron charge exchange interaction within the internal target will provide an external flux of neutrons which can be used directly for total nuclear cross section measurements and neutron-proton scattering. Low energy measurements, say below 200 Mev; show that nuclear interaction cross sections do not go down as 1/{lambda} as reactions become predominantly nuclear rather than electromagnetic. Measurements can now be extended into the Bev range to investigate the complex as opposed to the point charge concept of nuclear interactions. The external neutron beam may also provide high energy protons in charge exchange interactions with external targets. Mesons produced in the internal target will provide external meson beams of all types for cross section measurements over a large range of energies. Sufficient energy will be available for production of V particles with reasonable cross sections. The primary event leading to the production of V particles and the characteristic mode of decay can be studied. These events are best adapted to cloud chamber techniques wherein co-planer ...
Date: December 15, 1953
Creator: Karplus, Robert
Partner: UNT Libraries Government Documents Department

Synthesis of Crown Ether/Ammonium Salt for Electron Transfer Study

Description: The theoretical model of Beratan and Onuchic predicts a large attenuation of ET rates through hydrogen bonds; however, the effect of individual hydrogen bond on electron transfer reaction has not been systematically studied. The organic complexes in this study are a series of crown ether/ammonium salt, which incorporate a redox partner on each component of the complex. The dimethoxynaphthalene redox donor was attached to the crown ether and a series of ammonium salts was synthesized which bear substituted quinone and naphthoquinone acceptor. The complexes characterization and preliminary electron transfer rate measurement were completed with UV/Vis and steady-state emission spectroscopy.
Date: May 2002
Creator: Han, Dong
Partner: UNT Libraries

COLLIMATOR DESIGN FOR THE HEBT LINE OF THE SNS PROJECT.

Description: This paper summarizes the design of the HBBT clean-up system consisting of a combination of charge exchange foils and absorbers. Pairs of foils moving in-and-out of the beam in both planes help guide the halo protons into respective absorbers that feature a double wall beam-tube, a water-cooled particle bed responsible and heavy radial shielding. Off-momentum protons are directed to a momentum dump via similar charge exchange foils and in combination with a dipole magnet. The paper addresses the survivability of the double beam tube in the absorber and the special window in the momentum dump that intercept halo protons over a relatively small footprint under normal operating conditions and potentially full beam under accident conditions.
Date: June 3, 2002
Creator: SIMOS,N.; LUDEWIG,H.; RAPARIA,D.; CATALAN - LASHERAS,N.; BRODOWSKI,J.; KOROSTYSHEVSKY,A. et al.
Partner: UNT Libraries Government Documents Department

The theory of hadronic systems. Annual progress report

Description: This report briefly discusses progress on the following topics: isospin breaking in the pion-nucleon system; the np charge-exchange reaction; energy dependence of pion DCX; pion absorption in nuclei; quantum effects in inclusive reactions; and pion scattering from polarized nuclei.
Date: April 8, 1994
Creator: Gibbs, W.R.
Partner: UNT Libraries Government Documents Department

Improvements in the CHERS system for DT experiments on TFTR

Description: Improvements in the charge exchange recombination spectroscopy (CHERS) system have resulted in accurate measurements of T{sub i} and V{sub {phi}} profiles during DT experiments. These include moving the spectrometer detector array and electronics farther away from the tokamak to a low neutron flux location. This relocation has also improved access to all components of the system. Also, a nonplasma-viewing calibration fiber system was added to monitor the change in fiber transmission due to the high flux DT neutrons. Narrowband filtered light transmitted through the calibration fiber is now used as a reference for the VO measurement. At the highest neutron flux of {approximately} 2.5 {times} 10{sup 18} neutrons/see (fusion power {approximately} 6.2 MW) a modest 5% decrease in fiber transmission was observed. Corrections for transmission loss are made and T{sub i} (r,t) and absolute V{sub phi} (r,t) profiles are automatically calculated within four minutes of every shot.
Date: March 1, 1995
Creator: Bush, C.E.; Bell, R. & Synakowski, E.J.
Partner: UNT Libraries Government Documents Department

Operation of the TFTR Pellet Charge Exchange Diagnostic in the Pulse Counting Mode during H+ RF-minority Heating

Description: The Pellet Charge Exchange technique on TFTR has been used primarily to obtain active charge exchange measurements using a high energy (0.5 - 4.0 MeV) neutral particle analyzer (NPA) in conjunction with impurity pellet injection (Li and B) with the scintillator-photomultiplier detector system operated in the current mode. While passive measurements using pulse counting were also obtained using this instrumentation, operation in this mode was very restrictive with pulse counting rates limited to less than {approximately}10 kHz in the absence of any significant neutron and gamma induced background signal. An upgrade to a specialized pulse counting capability which was developed by the Ioffe Institute was implemented which consisted of CsI(Tl) scintillators having features designed to minimize signals induced by background neutron and gamma rays and 16-channel pulse height analysis electronics on each of the eight NPA energy channels. Passive measurements of RF-driven energetic hydrogen minority ions which served to verify operation of the pulse counting mode are reported. It is shown that in the passive mode the main donors for the neutralization of H+ ions in this energy range are C5+ ions. The measured effective H+ tail temperatures range from 0.15 MeV at an RF power of 2 MW to 0.35 MeV at 6 MW.
Date: May 1998
Creator: Medley, S. S.
Partner: UNT Libraries Government Documents Department

Research proposal on certain atomic physics measurements associated with the laser isotope separation method

Description: Research proposed in the following areas are briefly described: the measurement of photoionization cross sections near threshold for the excited states of uranium; measurement of the symmetric charge exchange cross section; and measurement of chemiionization cross sections for electronically excited uranium atoms.
Date: March 6, 1973
Creator: Dubrin, J. & Duewer, W.
Partner: UNT Libraries Government Documents Department

Experimental studies of pion-nucleus and nucleon-nucleus interactions at intermediate energies. Progress report, April 1, 1991--March 31, 1994

Description: This report summarizes the work on experimental research in intermediate energy nuclear physics carried out at New Mexico State University in 1991-94 under a grant from the U.S. Department of Energy. Most of these studies involved investigations of various pion-nucleus interactions and nucleon-nucleus charge-exchange reactions. The work was carried out with the LAMPF accelerator at the Los Alamos National Laboratory and the cyclotrons at the Paul Scherrer Institute (PSI) near Zurich, Switzerland, at Indiana University (IUCF), and at TRIUMF in Vancouver, Canada, as collaborative efforts among several laboratories and universities. We have also worked on plans and preparations for new experiments involving studies of the quark structure of nucleons and nuclei, which would be carried out at Fermilab (FNAL), near Chicago, and at the HERA facility at the DESY laboratory in Hamburg, Germany. The NMSU personnel included two faculty members, five postdoctoral research associates, nine graduate students, and one undergraduate student.
Date: September 30, 1993
Partner: UNT Libraries Government Documents Department

Stability of Trapped Electrons in SiO(2)

Description: Thermally stimulated current and capacitance voltage methods are used to investigate the thermal stability of trapped electrons associated with radiation-induced trapped positive charge in metal-oxide-semiconductor capacitors. The density of deeply trapped electrons in radiation-hardened 45 nm oxides exceeds that of shallow electrons by a factor of {approximately}3 after radiation exposure, and by up to a factor of 10 or more during biased annealing. Shallow electron traps anneal faster than deep traps, and seem to be at least qualitatively consistent with the model of Lelis et al. Deeper traps maybe part of a fundamentally distinct dipole complex, and/or have shifted energy levels that inhibit charge exchange with the Si.
Date: January 29, 1999
Creator: Fleetwood, D.M. & Winokur, P.S.
Partner: UNT Libraries Government Documents Department

Fast ion physics from neutral particle analysis on the large helical device

Description: Time-resolved measurements of the energetic ion distribution from different viewing angles allow study of some important aspects of stellarator physics. Examples from the Advanced Toroidal Facility (ATF) of measurements of the ion distribution function and the variation of orbits with pitch {nu}{parallel}/{nu} and electric field are used to illustrate some of these points; ATF`s magnetic configuration was similar to that of the Large Helical Device (LHD). Silicon ion-implanted detectors should allow measurements of the ion distribution function that are not practical with conventional neutral particle analyzers (NPAs) on LHD. Initial implementation of a silicon-detector NPA array on LHD is discussed.
Date: December 1, 1997
Creator: Lyon, J.F. & Spong, D.A.
Partner: UNT Libraries Government Documents Department

Tagging of Isobars Using Energy Loss and Time-of-flight Measurements

Description: The technique for tagging isobars in a mixed beam by measuring energy loss by time-of-flight has been tested. With this method, isobar separation should improve by allowing more energy loss (thicker absorber), but only if one can control absorber homogeneity. Measurements of beam energy toss and energy spread obtained under such conditions were shown to be close to predicted values using both collisional and charge exchange contributions to energy straggling. The calculation of energy straggling allows us to study the efficacy of this method for isobar separation when applied to different mass ranges and beam energies. Separation in a most difficult case, an analyzed beam of A = 132 isobars at energies near 3 MeV/A has been demonstrated. The time-of-flight information can be added on line as an additional tag to the data stream for events of interest. Such event by event tagging enables one to study the effect of differences in isobaric mixture in the beam on the reaction outcome even when isobar separation is not complete.
Date: November 2, 2001
Creator: Shapira, D.
Partner: UNT Libraries Government Documents Department