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Absolute cross-section measurements for resonant double photoexcitation of Li+ions followed by autoionization have been performed at high resolution in the photon energy range from 148 eV, just below the (2s2p, 2(0,1)+2) resonance to 198 eV (the region of the double ionization threshold). The measurements have been made using the photon-ion merged-beam endstation at the Advanced Light Source, Lawrence Berkeley National Laboratory, USA. The absolute cross-section measurements show excellent agreement with theoretical results from the R-matrix plus pseudo-state (RMPS) method.

Absolute cross-section measurements for resonant double photoexcitation of Li + ions followed by autoionization have been performed at high resolution in the photon energy range from 148 eV, just below the 2s2p, 2(0, 1) + resonance, to 198 eV (the region of the double ionization threshold). The measurements have been made using the photon–ion merged-beam endstation at the Advanced Light Source, Lawrence Berkeley National Laboratory, USA. The absolute cross-section measurements show excellent agreement with theoretical results from the R-matrix plus pseudo-state (RMPS) method. Comparisons between theory and experiment for the Auger resonance energies, autoionization linewidth (� ) and the Fano line profile index q for several members of the principal 2snp, 2(0, 1) + and 3snp, 3(1, 1) + Rydberg series found in the photoionization spectra for the 1 P o symmetry show satisfactory accord. (Some figures in this article are in colour only in the electronic version)

Absolute cross-section measurements for K-shell photoionization of Be-like C2+ ions have been performed in the photon energy range 292 325 eV. These measurements have been made using the photon ion merged-beam endstation at the Advanced Light Source, Lawrence Berkeley National Laboratory. Absolute measurements compared with theoretical results from the R-matrix method indicate that the primary C2+ ion beam consisted of 62 percent ground-state (1s22s2 1S) and 38 percent metastable state (1s22s2p 3Po) ions. Reasonable agreement is seen between theory and experiment for absolute photoionization cross sections, resonance energies and autoionization line widths of K-shell-vacancy Auger states.

Anion-yield spectroscopy using x rays is shown to be a selective probe of molecular core-level processes, providing unique experimental verification of shape resonances. For CO, partial anion and cation yields are presented for photon energies near the C K edge. The O- yield exhibits features above threshold related only to doubly excited states, in contrast to cation yields which also exhibit pronounced structure due to the well-known sigma* shape resonance. Because the shape resonance is completely suppressed for O-, anion spectroscopy thus constitutes a highly selective probe, yielding information unobtainable with absorption or electron spectroscopy.

The threshold behavior of two-electron escape and the complementary characterization of doubly-excited resonances have been the subject of investigation for forty years. The conventional view of the physics of these systems has generally been predicated upon a “ridge-state” picture that was first introduced classically by Wannier in 1953 and susequently expanded quantum mechanically by many others. Within the last five years, new experimental results and new theoretical analyses have cast great doubt on the detailed validity of this picture. A close examination of the basis for the old ridge-state view and the impetus for the development of a new description are provided in this paper. Additional speculations are made about the possibly unique role played by the threshold itself.

An adjustable 0.5 to 3.0 MeV monoenergetic positron beam has been developed at Brookhaven National Laboratory. Positrons leaving a 22Na β+ source with a ∼ 6000 A thick W(100) transmission moderator are accelerated to higher energies in a 3.0 MeV Dynamitron. At a target position, located 12 m away from the exit of the accelerator, the beam has a maximum intensity of 5 × 105 e+/s inside a 1.1 mm full width at half maximum (FWHM) spot and is characterized by an energy spread of

The authors extend the formalism introduced by Klar and Schlecht (1976) and more completely developed by Rau and Greene (1982, 1983) to explore the implications of the Wannier threshold theory for the spin dependence of electron impact ionization of atomic hydrogen. By analysing the properties of the contributions to the singlet and triplet cross sections from the multiplicity of (L, S pi ) final states and by combining the results of the investigations of spin-asymmetry measurements of Guo et al. (1990, 1993) and the earlier investigations of spin-averaged cross section measurements of McGowan and Clarke (1968), the authors are able to provide insight into the role played by higher order terms and the possible influence of collisional dynamics. The authors further show that the critical energy above threshold at which the contributions from higher order terms become visible is substantially lower for the singlet and triplet partial cross sections than it is for the spin-averaged cross section.

The authors report on the design of a hybrid transport system for slow positrons based upon the high-intensity magnetically transported positron beam, which existed at the Brookhaven (BNL) high-flux beam reactor (HFBR) in 1986. The resulting modified transport, incorporating an initial electrostatic stage followed by a magnetic stage and completed by brightness enhancement moderation leading to a final electrostatic section, represented the minimum alteration of the existing beam to enable it to be used for crossed-beams differential scattering studies involving a variety of atomic and molecular systems, including atomic hydrogen. A recent proposal for constructing a very high-intensity positron beam at the Paul Scherrer Institute (PSI), based upon magnetic confinement premoderation, has rekindled interest in the conclusions of the study.

We report results of an experiment to search for a resonance enhancement of the ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{\ensuremath{-}}}$ scattering cross section in a metallic Li target utilizing an energy-tunable monoenergetic positron beam. Within statistical uncertainties (0.27%) no evidence has been observed for deviations from Bhabha scattering over the entire invariant-mass region 1560 keV/${\mathit{c}}^{2}$${\mathit{M}}_{\mathit{X}}^{0}$1860 keV/${\mathit{c}}^{2}$ that can be associated with the ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{\ensuremath{-}}}$ sum-peak energies in GSI heavy-ion experiments. Under the assumptions that the ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{\ensuremath{-}}}$ channel dominates, we deduce lower limits on lifetimes \ensuremath{\tau}g3.3\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}13}$ sec (J=0) and \ensuremath{\tau}g8.2\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}13}$ sec (J=1), at 90% C.L.

We report the results of an experiment measuring the the parity-violating electroweak asymmetry in the elastic scattering of polarized electrons from 12 C nuclei. We obtain A exp = 0.60 ± 0.14 ± 0.02 ppm. The first error is statistical and the second is systematic. Using our measured beam polarization of 0.37 ± 0.02, we compute the isoscalar vector hadronic coupling constant γ to be 0.136 ± 0.032 ± 0.009. This agrees with the tree level Standard Model prediction of γ = 0.155 .

We have measured the parity-violating electroweak asymmetry in the elastic scattering of polarized electrons from $^{12}\mathrm{C}$ nuclei. Our result is ${\mathit{A}}_{\mathrm{expt}}$=0.60\ifmmode\pm\else\textpm\fi{}0.14\ifmmode\pm\else\textpm\fi{}0.02 ppm, where the first error is statistical and the second is systematic. With a beam polarization of 0.37, we compute the isoscalar vector hadronic coupling constant \ensuremath{\gamma}\ifmmode \tilde{}\else \~{}\fi{} to be 0.136\ifmmode\pm\else\textpm\fi{}0.032\ifmmode\pm\else\textpm\fi{}0.009. The standard model predicts \ensuremath{\gamma}\ifmmode \tilde{}\else \~{}\fi{}=0.155 at the tree level, in agreement with our data.

Using beams of polarised electrons and polarised hydrogen atoms the authors measured the spin antiparallel-parallel ionisation asymmetry from threshold to 500 eV. Their measurements are generally more precise than those of earlier studies and, more significantly, are characterised by an energy spread that is at least an order of magnitude smaller than that of the earlier work. They compare their results with several theoretical models as well as with the results from similar experiments using polarised alkali atoms.

We report on several important features of GaAs polarized electron source operation. Specifically we point out the beneficial effect on crystal lifetime produced by the constant low‐level application of cesium from a dispenser embedded in an extraction anode. Using our experience in low‐energy polarized electron‐atom scattering as a reference, we also discuss the importance of frequent energy calibrations of GaAs electron beams for high‐resolution investigations.

Cross-sections for inner-shell photoionization processes in beryllium-like carbon ions are determined both theoretically and experimentally for photon impact energies in the region of the carbon K edge. Measurements of absolute cross-sections, resonance energies, and lifetime/linewidths measured using the merged-beam technique at the Advanced Light Source are in good agreement with R-matrix calculations.

Superconducting magnets have developed at such a rapid pace that large-bore magnets generating fields up to 100 kG are now readily attainable. The recent trend is, however, away from magnets wound from a single wire or tape to multistrand cable and heavy strips containing many embedded wires. The critical current of the individual superconducting wires has also been increased by optimizing heat treatments and alloy compositions. As a result, the operating current level of this new generation of superconducting magnets, constructed of improved wire energized in parallel, has greatly increased. With the introduction of very large currents from outside the dewar to the magnet, heat dissipation and accompanying large helium losses become a major problem.

Recent experimentalstudies of the spin dependence in electron-impact ionization of atomic hydrogen revealed the presence of deviations from the predictions of the conventional Wannier threshold theory of two-electron escape. We provide some insight into the possible origin of these deviations and reexamine the results of previous work that had claimed consistency with the Wannier theory but, with added statistical analysis, also seem to show deviations

We report a verification of the theory of special relativity at a value of $\ensuremath{\gamma}\ensuremath{\approx}2.5\ifmmode\times\else\texttimes\fi{}{10}^{4}$ based upon a comparison of electron $g\ensuremath{-}2$ measurements at meV and GeV kinetic energies. Specially we obtain a measure of the equivalence between the quantities $\ensuremath{\gamma}\ensuremath{\equiv}{(1\ensuremath{-}{\ensuremath{\beta}}^{2})}^{\ensuremath{-}\frac{1}{2}}$ and $\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\gamma}}\ensuremath{\equiv}(\frac{p}{{m}_{0}})\frac{\mathrm{dp}}{\mathrm{dE}}$.

A new experiment is being developed at Brookhaven National Laboratory to measure the g-2 value of the muon to 0.35 ppm. A brief review is given of our knowledge of the muon anomalous magnetic moment, of the motivations for an improved measurement, and of the status of the experiment.

We use beams of polarized electrons and polarized hydrogen atoms to measure the ionization-rate asymmetry, {Delta}{sub {ital I}}=({ital R}({up arrow}{down arrow}){minus}{ital R}({up arrow}{up arrow}))/({ital R}({up arrow}{down arrow})+{ital R}({up arrow}{up arrow})), in the near-threshold region, where {ital R}({up arrow}{down arrow}) and {ital R}({up arrow}{up arrow}) are the ionization rates when the electron spin is antiparallel and parallel, respectively, to the atomic spins. Within 1.7 eV above threshold, our results reveal the presence of structure, which heretofore has not been predicted by any conventional theoretical calculation.

Very large propagation velocities have been observed in the Superconducting Super Collider (SSC) 17-m dipoles: from 75 m/s to 225 m/s, depending on the current. These velocities are much larger than those predicted by the classical conduction theory of normal zone propagation. A plausible explanation for such rapid propagation is hydrodynamic mechanism called thermal hydraulic quenchback (THQ) that has been proposed by Luongo et al. This report supplies an approximate analytic theory of THQ, which is used to analyze the data taken on the SSC 17-m dipoles. It is concluded that THQ in the helium in the interstices of the cable can explain the large propagation velocities observed. Additional experiments are proposed to test the hydrodynamic explanation. 17 refs., 5 figs.

An ultra precise 3 GeV/c storage ring with a 14.5 kG super-ferric magnet is under construction at the Brookhaven AGS for the measurement of the muon anomalous magnetic moment to 0.35 PPM accuracy. This requires a magnetic field which is constant to ≈ 1 PPM and is known sufficiently well that the magnetic field integral averaged over the muon orbits can be calculated to 0.1 PPM. First the magnetic field will be statically shimmed by various techniques. Pole face winding will be used for final small static and dynamic corrections. Very elaborate NMR field monitoring techniques are required. A “movable trolley” located inside the vacuum chamber and the electrostatic focusing quadrupoles will measure the field throughout the muon storage volume. The trolley “siding” is 180˚ from the injection point where no electric quadrupoles are located. Injection can be interrupted so the trolley can circle the ring. Also ≈ 200 NMR probes located outside the vacuum chamber monitor the field during physics running and control the pole face windings. The very large (≈ 15 m diameter) superconducting coils (SC) are designed. Test winding will soon commence. Orders for the magnet steel can now be placed. R and D on various pulsed and SC dc injection methods is ongoing.

At the Oak Ridge National Laboratory (ORNL) there is a broadly based, interactive fusion program, encompassing theory and atomic physics, computing, the technology of heating and fueling plasmas, superconducting magnets, robotics, materials developments, design studies, and experiments and diagnostics.

We describe the design and operating characteristics of a simple polarized atomic hydrogen beam particularly suitable for applications to crossed beams experiments. In addition to experimental measurements, we present the results of detailed computer models, using Monte-Carlo ray tracing techniques, optical analogs, and phase-space methods, that not only provide us with a confirmation of our measurement, but also allow us to characterize the density, polarization, and atomic fraction of the beam at all points along its path. As a subsidiary result, we also present measurements of the relative and absolute efficiencies of the V/G Supavac mass analyzer for masses 1 and 2.

Using a Fano-effect polarized electron source and a state-selected thermally dissociated hydrogen beam, we measured the interference between the direct and exchange scattering amplitudes for electron-impact ionization of atomic hydrogen between 13.8 and 30.0 eV. We report the data from these measurements and the results of corrections applied to previously published data.

We report on the development of several operating procedures that promise to make GaAs photoemission electron sources easier to construct, more reliable to operate, and more amenable to use in dynamic vacuum systems. We describe in particular a method for ‘‘ohmically’’ heating a 〈100〉 crystal of GaAs under vacuum to approximately 600 °C. We also discuss our observations of the role of oxygen in the activation of the crystal surface, the use of continuous cesiation, and of the performance of the crystal under varying vacuum conditions.

With the intention of informing the broad community of fusion researchers, the background, status, and potential future uses of superconducting magnets are covered. After a brief explanation of the principles of superconducting magnets, the technological basis is examined. Major emphasis is on the description of activities in the worldwide development and application of superconducting magnets in fusion programmes through mid-1981. Evaluation of progress and projection of needs for fusion reactors lead to the conclusion that superconducting magnets can be available when required.

Spin-dependent asymmetries have been measured in inclusive deep-inelastic scattering of longitudinally polarized electrons by longitudinally polarized protons. Data were obtained at a scattering angle of 10/sup 0/ and for incident energies of 16.2 and 22.7 GeV, which cover the kinematic range 0.18

With use of a Fano-effect polarized electron source and a state selected thermally dissociated hydrogen beam, the interference was measured between the direct and exchange scattering amplitudes for 90/sup 0/ elastic scattering of electrons from atomic hydrogen for energies between 4 and 30 eV.

We report on a new type of high-energy electron-proton scattering experiment in which longitudinally polarized electrons are scattered from longitudinally polarized protons. The asymmetry in elastic scattering at ${Q}^{2}=0.765$ ${(\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^{2}$ was measured; our result agrees with the theoretical asymmetry and determines the sign of $\frac{{G}_{E}}{{G}_{M}}$ to be positive.

We report a verification of the theory of special relativity at a value of $\ensuremath{\gamma}\ensuremath{\approx}2.5\ifmmode\times\else\texttimes\fi{}{10}^{4}$ based upon a comparison of electron $g\ensuremath{-}2$ measurements at meV and GeV kinetic energies. Specially we obtain a measure of the equivalence between the quantities $\ensuremath{\gamma}\ensuremath{\equiv}{(1\ensuremath{-}{\ensuremath{\beta}}^{2})}^{\ensuremath{-}\frac{1}{2}}$ and $\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\gamma}}\ensuremath{\equiv}(\frac{p}{{m}_{0}})\frac{\mathrm{dp}}{\mathrm{dE}}$.

We have measured the interference between the direct and exchange scattering amplitudes in electron impact ionization of atomic hydrogen over the energy range 15 to 197 eV in a crossed-beams experiment utilizing spin-polarized electrons and spin-polarized hydrogen atoms. The experimental values for the asymmetry $A=\frac{({\ensuremath{\sigma}}^{\ensuremath{\uparrow}\ensuremath{\downarrow}}\ensuremath{-}{\ensuremath{\sigma}}^{\ensuremath{\uparrow}\ensuremath{\uparrow}})}{({\ensuremath{\sigma}}^{\ensuremath{\downarrow}\ensuremath{\uparrow}}+{\ensuremath{\sigma}}^{\ensuremath{\uparrow}\ensuremath{\uparrow}})}$ in the total ionization cross section for antiparallel and parallel incident- and atomic-electron spins are inconsistent with all theoretical calculations below 50 eV.

A 100‐kG, 8.26‐cm‐bore, 40‐kJ Nb3Sn magnet and a 75‐kG, 10.2‐cm‐bore, 95‐kJ twisted filament NbTi magnet have been constructed and tested. A number of other magnets of smaller size using both the Nb3Sn and twisted filament NbTi conductors will also be described. Material evaluation tests leading to these magnet designs will be reported. They include short sample tests with controlled surface cooling conditions and cusp coil tests in which an external field is applied perpendicular to the cusp coil axis. Finally, two successful stabilization techniques for Nb3Sn ribbon will be presented with coil performance data before and after the stabilization has been employed.

The ratio of maximum radial field to maximum axial field has been calculated numerically for axisymmetric solenoids of rectangular cross section and constant current density over a wide range of coil configurations. It is also shown that for a certain range of coil shapes the maximum modulus of the magnetic field occurs on the end faces of the windings. These considerations are pertinent in the design of superconducting magnets for two reasons: (i) Many superconductors have lower critical current in a field normal to the wide surface than in a field parallel to the surface, and (ii) large radial fields can cause catastrophic flux jumps.

Polarized cesium atoms were ionized by circularly polarized light. The cesium-ion intensities obtained with positive and negative photon helicities were measured at various wavelengths. The results demonstrate that the wave functions for the continuum states of cesium are perturbed by a spin-orbit interaction in accordance with the theoretical interpretations given by Seaton and Fano.

In a photoionization experiment involving polarized alkali atoms and circularly polarized photons we measured the strength of the spin-orbit perturbation in potassium, rubidium, and cesium. Our results are pertinent to the theory of photoionization and to the production of polarized electrons. Extrapolation of the results to photon energies below the ionization threshold provides access to the anomalous doublet line-strength ratio of discrete $P$ states.

The thermoelectric properties of the alloy 0·9 GeTe+0·1 TlBiTe 2 are shown over a wide temperature range (300–725°K) for both pressed and sintered and Bridgman specimens. It is shown that the counter-doping of p -type germanium telluride by TlBiTe 2 leads to optimally doped material at high temperatures. While the figure of merit of this material is not quite as high as germanium telluride doped with Bi 2 Te 3 , the material may still prove useful because of the lower phase transition temperature and better mechanical stability under thermal cycling.

The critical current vs preset magnetic field has been measured for a number of multilayer bifilar noninductive coils wound with cold‐worked 0.025‐cm‐diam Nb‐25% Zr wire. In an applied field greater than 8 kG and less than 24 kG the superconducting to normal transitions are not single‐valued and show an effect analogous to ``antitraining.'' It is shown that the anomalous critical currents are due to cooling in a constant applied field. The conditions for obtaining, avoiding, and eliminating the different values of critical current have been investigated and the results are compared with short‐sample and magnet data. The experimental results suggest the unorthodox view that high transport currents are obtained when induced magnetization currents are initially present and low transport currents are measured when only the reversible magnetization is present in part of the noninductive coil.

The mutual solubility of GeTe, SnTe, and PbTe was examined by x‐ray diffraction techniques. The rhombohedral to cubic phase transformation of GeTe and GeTe in various solid solutions were determined. The transformation temperature is shown to vary inversely with cation mass.

Experiments concerning termination of the flux‐flow state have been performed on bare NbTi strips. For these strips of low heat capacity, take‐offs occurred at powers less than the maximum heat flux in nucleate boiling. We conclude that take‐off resulted from the simultaneous occurrence of a normal zone (caused by a local heat transfer fluctuation) and a current equal to or greater than the minimum propagating current.

The magnetic diffusivity D=109ρ/4π has been measured for a cylinder of Nb‐25% Zr at T=4.2°K. The cylinder was brought to the shielding portion of the creep curve by a coaxial magnetic field increasing linearly with time. By means of a magnetoresistance probe, we observed the propagation of small coaxial magnetic steps (ΔH=2 to 20 Oe) into the center of a cylinder which remained in a critical state. Fitting the diffusion equation solution for a step function to the measured delay times of the penetrating field, we obtained a value for the resistivity, ρΔ=1.5×10−10 (dH/dt) Ω·cm for dH/dt in the range 2 to 40 Oe/sec. The dependence on both the magnitude of the step and the field was weak. Extrapolation of our data to ΔH=0 yields ρΔ=1×10−10 dH/dt Ω·cm. If on the other hand, the resistivity for the creep state is calculated either by dividing the induced voltage multiplied by geometric factors by the shielding current, or by a steady‐state solution of the diffusion equation for a ramp function, one obtains ρcr...

Flux jumping has been investigated in both cold‐worked and heat‐treated (1 h at 700°C) 0.025‐cm‐diam Nb+25% Zr wire wound into solenoids and noninductive coils of approximate dimensions: i.d.=0.3 cm, o.d.=1.2 cm, length=2.6 cm. The measurements taken at 4.2°K were: (1) The induced voltage pulses vs applied magnetic field with both I=0 and a preset transport current. (2) The induced voltage pulses vs coil current for H=0 and with a preset uniform external field.For the case with no transport current in the coil (I=0) when the external field was increased smoothly from zero, a squence of very sharp voltage pulses (flux jumps) were induced in the coil, and recorded simultaneously on both an X‐Y recorder and an oscilloscope. These flux jumps had the following general characteristics for all the cases discussed in this paper: (1) Starting from well defined initial conditions, the pulse always appeared at about the same place in the field sweeping cycle. (2) The polarity of the pulses is reversed when the direc...

Using crossed beams of polarized electrons and polarized hydrogen atoms we have investigated the effect of spin exchange on 90\ifmmode^\circ\else\textdegree\fi{} elastic scattering from 4.4 to 30.3 eV and impact ionization from 14.1 to 197.0 eV. Our results suggest that the range of validity of various theoretical approximation methods is more restricted than had been assumed previously.

The results and accomplishments of the Superconducting Magnet Development Program for the period June 1, 1976--October 1, 1976 are summarized in this report. The presentations are arranged according to projects. A new format has been adopted for convenience in reporting. Only projects which have reached some milestone or completed tasks are discussed.

A polarized electron source based upon the photoionization of unpolarized Cs atoms by circularly polarized light (Fano effect) has been developed and applied to the study of spin dependence in low-energy electron–atom scattering. Electron intensities of 10 nA with polarizations of 0.63±0.03 have been obtained routinely during continuous runs of up to 75 h. Frequent optical reversal of the direction of the longitudinal electron polarization minimizes systematic effects so that helicity dependent electron-scattering asymmetries smaller than 4×10 to the power of -4 can be measured.

We are constructing a polarized electron source in order to study parity violation in elastic electron‐carbon scattering at the MIT Bates Linac. The source uses a GaAs photocathode illumiated by light from an infrared krypton ion laser. Our design, which uses a multi‐chamber vacuum system, meets the special requirements for operation at Bates.