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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

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

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

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

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

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

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


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

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

Temporal Development of Ion Beam Mean Charge State in PulsedVacuum Arc Ion Sources

Description: Vacuum arc ion sources, commonly also known as "Mevva" ionsources, are used to generate intense pulsed metal ion beams. It is knownthat the mean charge state of the ion beam lies between 1 and 4,depending on cathode material, arc current, arc pulse duration, presenceor absence of magnetic field at the cathode, as well background gaspressure. A characteristic of the vacuum arc ion beam is a significantdecrease in ion charge state throughout the pulse. This decrease can beobserved up to a few milliseconds, until a "noisy" steady-state value isestablished. Since the extraction voltage is constant, a decrease in theion charge state has a proportional impact on the average ion beamenergy. This paper presents results of detailed investigations of theinfluence of arc parameters on the temporal development of the ion beammean charge state for a wide range of cathode materials. It is shown thatfor fixed pulse duration, the charge state decrease can be reduced bylower arc current, higher pulse repetition rate, and reduction of thedistance between cathode and extraction region. The latter effect may beassociated with charge exchange processes in the dischargeplasma.
Date: June 21, 2007
Creator: Oks, Efim M.; Yushkov, Georgy Yu. & Anders, Andre
Partner: UNT Libraries Government Documents Department


Description: The differential cross section for charge-exchange scattering of negative pions by hydrogen has been observed at 230, 260, 290, 317, and 371 Mev. The reaction was observed by detecting one gamma ray from the {pi}{sup 0} decay with a scintillation-counter telescope.
Date: March 18, 1960
Creator: Caris, John C
Partner: UNT Libraries Government Documents Department


Description: The total cross sections for resonant charge exchange have been measured as a function of energy in the range from 10 to 500 eV for the Cs{sup +}-Cs, Rb{sup +}-Rb, and K{sup +}-K systems. The agreement with certain data obtained at higher energies for these systems, and with theoretical cross sections of Smirnov is satisfactory.
Date: April 1, 1968
Creator: Gentry, W.R.; Lee, Yuan-tseh & Mahan, Bruce H.
Partner: UNT Libraries Government Documents Department

P-P Elastic and Charge-Exchange Scattering at about 120 Mev

Description: Observation of antiprotons in a propane or hydrogen bubble chamber offers the possiblity of studying several phenomena for which counter or photographic emulsion techniques are less suitable. Because there is a high ratio of pions, muons, and electrons to antiprotons in the available momentum-analyzed beams, these beams cannot be used in the bubble chamber without an initial purification, which increases the ratio of antiprotons to other particles. Such a purification has been achieved by utilizing the difference in rates of momentum loss in absorbers between antiprotons and other particles. The principle of the method is to pass a momentum-analyzed beam through an absorber. Since particles of unequal mass do not have the same specific ionization they lose different amounts of momentum, and a further magnetic deflection suffices to separate the particles physically according to mass. In this experiment a desirable momentum for antiprotons entering the bubble chamber was 684 Mev/c; however, at this momentum the ratio of undesirable particles to antiprotons at the target where they are produced is about 6 x 10{sup 5}. By starting with 970-Mev/c particles at the target and using the method of differential absorption, they decreased the ratio of undesirable particles (87% {mu}{sup -}, 105 {pi}{sup -}, 3% e{sup -}) to antiprotons entering the bubble chamber at 684 Mev/c to 1.5 x 10{sup 4}. A system of counters indicatd when an antiproton entered the bubble chamber, and although the chamber was expanded on every Bevatron pulse, the lights were flashed and the chamber photographed only when an antiproton entered.
Date: March 28, 1958
Creator: Agnew Jr., Lewis; Elioff, Tom; Fowler, William B.; Gilly, Louis; Lander, Richard L.; Oswald, Larry et al.
Partner: UNT Libraries Government Documents Department

Self-Consistent 3D Modeling of Electron Cloud Dynamics and Beam Response

Description: We present recent advances in the modeling of beam electron-cloud dynamics, including surface effects such as secondary electron emission, gas desorption, etc, and volumetric effects such as ionization of residual gas and charge-exchange reactions. Simulations for the HCX facility with the code WARP/POSINST will be described and their validity demonstrated by benchmarks against measurements. The code models a wide range of physical processes and uses a number of novel techniques, including a large-timestep electron mover that smoothly interpolates between direct orbit calculation and guiding-center drift equations, and a new computational technique, based on a Lorentz transformation to a moving frame, that allows the cost of a fully 3D simulation to be reduced to that of a quasi-static approximation.
Date: April 2, 2007
Creator: Furman, Miguel; Furman, M.A.; Celata, C.M.; Kireeff-Covo, M.; Sonnad, K.G.; Vay, J.-L. et al.
Partner: UNT Libraries Government Documents Department


Description: A beam of D{sup -} ions has been produced at 7-13 keV, with currents up to 2.2 {angstrom}, using charge exchange in sodium vapor. The beam profile is bi-Gaussian with angular divergence 0.7{sup o} x 2.8{sup o} and peak current density 15 mA/cm{sup 2}. The characteristics of the beam are in excellent agreement with predictions based on atomic cross sections. The sodium vapor target is formed by a jet directed across the beam. The sodium density drops rapidly in the beamline downstream from the charge exchange region, decreasing three orders of magnitude in 15 cm. Measurement and analysis of the plasma accompanying the beam demonstrate that plasma densities nearly equal to the beam density are obtained 1 m from the charge exchange medium. The plasma produced in the sodium is thus well confined to the charge exchange region and does not propagate along the beam.
Date: February 1, 1981
Creator: Hooper, E.B.; Poulsen, P. & Pincosy, P.A.
Partner: UNT Libraries Government Documents Department

Measurements of the Total Charge-Changing Cross Sections for Collisions of Fast Ions with Target Gas Using High Current Experiment

Description: The sum of ionization and charge-exchange cross sections of several gas targets (H2, N2, He, Ne, Kr, Xe, Ar, and water vapor) impacted by 1MeV K+ beam are measured. In a high current ion beam, the self-electric field of the beam is high enough that ions produced from the gas ionization or charge exchange by the ion beam are quickly swept to the sides of accelerator. The flux of the expelled ions is measured by a retarding field analyzer. This allows accurate measuring of the total charge-changing cross sections (ionization plus charge exchange) of the beam interaction with gas. Cross sections for H2, He, and N2 are simulated using classical trajectory Monte Carlo (CTMC) method and compared with the experimental results, showing good agreement.
Date: April 13, 2009
Creator: Covo, Michel Kireeff; Molvik, Arthur W.; Kaganovich, Igor D.; Shnidman, Ariel & Vujic, Jasmina L.
Partner: UNT Libraries Government Documents Department

Efficiency and lifetime of carbon foils

Description: Charge-exchange injection by means of carbon foils is a widely used method in accelerators. This paper discusses two critical issues concerning the use of carbon foils: efficiency and lifetime. An energy scaling of stripping efficiency was suggested and compared with measurements. Several factors that determine the foil lifetime--energy deposition, heating, stress and buckling--were studied by using the simulation codes MARS and ANSYS.
Date: November 1, 2006
Creator: Chou, W.; /Fermilab; Kostin, M.; /Michigan State U., NSCL; Tang, Z. & /Fermilab
Partner: UNT Libraries Government Documents Department

Contemporary Instrumentation and Application of Charge Exchange Neutral Particle Diagnostics in Magnetic Fusion Experiments

Description: An overview of the developments post-circa 1980's of the instrumentation and application of charge exchange neutral particle diagnostics on Magnetic Fusion Energy experiments is presented.
Date: July 21, 2007
Creator: S.S. Medley, A.J.H. Donné, R. Kaita, A.I. Kislyakov, M.P. Petrov, and A.L. Roquemore
Partner: UNT Libraries Government Documents Department

Some physics issues of carbon stripping foils

Description: Carbon foils are widely used in charge-exchange injection in high intensity hadron accelerators. There are a number of physics issues associated with the use of carbon foils, including stripping efficiency, energy deposition and foil lifetime (temperature rise, mechanical stress and buckling, etc.). This paper will give a brief discussion of these issues.
Date: June 1, 2007
Creator: Chou, W.; Lackey, J.; Tang, Z.; Yoon, P.; /Fermilab; Kostin, M. et al.
Partner: UNT Libraries Government Documents Department