High-energy Measurements Research Articles

IMF By‐related cusp currents observed from the Ørsted satellite and from ground

Ørsted is the first satellite to conduct high‐precision magnetometer observations from low‐altitude noon‐midnight orbits passing through the polar cusp regions. Field‐aligned currents (FAC) derived from Ørsted magnetic field measurements have been combined with ionospheric current patterns inferred from ground‐based magnetic observations to define the structure and location of cusp currents and their dependencies on interplanetary magnetic field (IMF) conditions. Example cases illustrate the close relation between IMF By‐related FAC and horizontal ionospheric currents in the cusp region. Our statistical analysis defines for the noon region the variations in FAC latitude with IMF Bz. Comparisons with the statistical cusp location indicate that the more equatorward region of IMF By‐related FAC is located on field lines closing at the dayside, while the more poleward FAC are on “open” field lines. High‐energy electron measurements from the satellite confirm this result.

Electronic structure of the strongly hybridized ferromagnetCeFe2

We report on results from high-energy spectroscopic measurements on CeFe2, a system of particular interest due to its anomalous ferromagnetism with an unusually low Curie temperature and small magnetization compared to the other rare earth-iron Laves phase compounds. Our experimental results indicate very strong hybridization of the Ce 4f states with the delocalized band states, mainly the Fe 3d states. In the interpretation and analysis of our measured spectra, we have made use of two different theoretical approaches: The first one is based on the Anderson impurity model, with surface contributions explicitly taken into account. The second method consists of band-structure calculations for bulk CeFe2. The analysis based on the Anderson impurity model gives calculated spectra in good agreement with the whole range of measured spectra, and reveals that the Ce 4f -- Fe 3d hybridization is considerably reduced at the surface, resulting in even stronger hybridization in the bulk than previously thought. The band-structure calculations are ab initio full-potential linear muffin-tin orbital calculations within the local-spin-density approximation of the density functional. The Ce 4f electrons were treated as itinerant band electrons. Interestingly, the Ce 4f partial density of states obtained from the band-structure calculations also agree well with the experimental spectra concerning both the 4f peak position and the 4f bandwidth, if the surface effects are properly taken into account. In addition, results, notably the partial spin magnetic moments, from the band-structure calculations are discussed in some detail and compared to experimental findings and earlier calculations.

Diagnosis of peak laser intensity from high-energy ion measurements during intense laser interactions with underdense plasmas

Experiments were performed using high-power laser pulses (greater than 50 TW) focused into underdense helium, neon, or deuterium plasmas (ne ≤ 5 × 1019 cm−3). Ions having energies greater than 300 keV were measured to be produced primarily at 90° to the axis of laser propagation. Ion energies greater than 6 MeV were recorded from interactions with neon. Spatially resolved pinhole images of the ion emission were also obtained and were used to estimate the intensity of the focused radiation in the interaction region.

An experimental correlation of turbulent burning velocities for premixed turbulent methane-air combustion

This paper is devoted to the general correlation of turbulent burning velocities in terms of straining rates for premixed flames propagating in intense turbulence. This problem was investigated by the Leeds group led by Professor Bradley and many other researchers. We present here a new methodology based upon a downward propagating premixed CH4–air flame through a nearly isotropic turbulent flow field with a pair of specially designed ion probes for quantitative measurements of turbulent burning velocities. The improvements are that the flame propagation is not influenced by the ignition source and the unwanted turbulence from walls, effects of buoyancy and pressure rise due to burning are minimized, and a greater parameter range than hitherto is covered. The results show that both the turbulent burning velocity bending and the vitality of turbulent premixed flames are certain and surprising. Logarithmic plots of turbulent burning velocities S T/ S L – 1 against the turbulent intensities u '/ S L reveal a transition, where S L is the laminar burning velocity. Across the transition, the slope n changes from positive to negative when values of u '/ S L and/or Karlovitz number are greater than some critical values. This transition seems to correspond to the Klimov–Williams criterion that separates corrugated flamelets from distributed reaction zones. Interestingly, no global quenching of premixed turbulent flames is observed, even at u ' S L ≊ 40, a value significantly higher than in most previous measurements. At a fixed u '/ S L, values of the S T/ S L data vary with the equivalence ratio ϕ. This indicates that the common expression of the form S T/ S L = 1 + C ( u '/ S L) n cannot be applicable generally, because values of the constant C are different for different mixture compositions. It is found that all of the present data with different values of ϕ can be approximated by a simple expression, ( S T – S L)/ u ' ≊ 0.06 Da 0.59, where Da is the Damkohler number. Hence a better correlation of turbulent burning velocities in terms of straining rates for premixed turbulent (methane–air) combustion is proposed.

High-energy neutral particle measurement system in the large helical device

The development of a high-energy neutral particle measurement system for ion temperature measurements and high-energy particle confinement analysis during neutral beam injection and ion cyclotron resonance frequency heating experiments in the large helical device (LHD) is described here. We have been improving the time-of-flight neutral particle analyzer for the LHD which had been developed in ENEA Frascati. The control and data acquisition systems were designed to be suitable for long discharges in the LHD. The horizontal and vertical movable stage is prepared to investigate pitch-angle distribution and loss cone. We have resolved many difficulties at installation, for example, the strong leakage magnetic field from the LHD and the limitations of magnetized materials near the LHD, the quench of the superconducting magnetic field, the narrow viewing port, and the fully remote control system. The preliminary results in plasma experiments are also described here.

Accumulation Effect of Bombarding N2+ Ions in Al for Crystal Growth of AlN Film

Dynamic observations of crystallographic structure by reflection high energy electron diffraction (RHEED) and measurement of sputtering yield with a quartz oscillator were performed simultaneously for an Al surface under 12 keV N2+ ion bombardment, in order to elucidate the optimum conditions for crystal growth of AlN. A simple theoretical model of sputtering was used to evaluate the accumulation of N-atoms, and a surface concentration of implanted N-atoms of ∼44 at.% was estimated, close to the stoichiometric concentration of AlN. Thus, AlN crystal growth under 12 keV N2+ ion bombardment was achieved with considerable success.

Feasibility studies of the self-TOF detector for high-energy neutron measurements in shielding experiments

The feasibility of a new type of neutron detector was studied. The detector consists of a radiator, a start counter and a stop counter. The radiator is composed of 20 thin plastic-scintillation detectors and the stop counter is segmented into nine plastic-scintillation detectors. Neutrons impinging on the radiator emit charged particles. The time of flight of protons emitted at a forward angle is measured using the start and stop counters, therefore, we call the detector the “self-TOF detector”. The proton time-of-flight spectrum is converted to the energy spectrum of neutrons using a measured response function. The basic properties of the detector, such as detection efficiency, signal-to-noise ratio, particle identification capability, and energy resolution, were studied.

Precision Measurement of Fundamental Constants Using GAMS4.

We discuss the connection of high-energy gamma-ray measurements with precision atomic mass determinations. These rather different technologies, properly combined, are shown to lead to new values for the neutron mass and the molar Planck constant. We then proceed to describe the gamma-ray measurement process using the GAMS4 facility at the Institut Laue-Langevin and its application to a recent measurement of the 2.2 MeV deuteron binding energy and the neutron mass. Our paper concludes by describing the first crystal diffraction measurement of the 8.6 MeV 36Cl binding energy.

Measurements of the rising photon-photon total cross section at the CERN LEP

Using vector meson dominance we calculate the {gamma}{gamma} total cross section from data on pp, p{bar p} and {gamma}p total cross sections. Our result agrees with recent high energy measurements performed by the L3 experiment at the CERN LEP collider, not with the conflicting preliminary data obtained by OPAL. {copyright} {ital 1998} {ital The American Physical Society}

Development of new scintillator and waveshifter materials

Experimental applications requiring fast timing and/or high efficiency position and energy measurements typically use scintillation materials. Scintillators utilized for triggering, tracking, and calorimetry in colliding beam detectors are vulnerable to the high radiation fields associated with such experiments. We have begun an investigation of several fluorescent dyes which might lead to fast, efficient, and radiation resistant scintillators. Preliminary results of spectral analysis and efficiency are presented.

Bilayer growth period oscillation of the Sb2 reactivity during molecular beam epitaxy of AlSb (001)

We report oscillations in Sb2 reactivity with the growth surface during layer-by-layer deposition of AlSb (001) by molecular beam epitaxy. Real-time measurements of the Sb desorption rate using line-of-sight mass spectrometry, in parallel with reflection high-energy electron diffraction specular beam intensity measurements, suggest that this behavior results from the periodic variation of the surface step density as these steps act as preferential adsorption sites for antimony. This is further supported by computer simulations that examine the surface step density as a function of bilayer coverage.

Low LET cross-section measurements using high energy carbon beam [DRAMs/SRAMs

This paper reports on results from high energy heavy ion testing of devices. The low LET zones of the cross-section curves are explored. High and low energy measurements are compared.

Metrology of scattering with angular limitation projection electron lithography masks

Mask metrology is a vital part of any lithographic technology, both for control of the mask patterning process and also for ensuring that the contribution of the mask to the system error budget is within acceptable limits. For design rules of 0.13 μm and below, errors arising from metrology must be kept to less than 1 nm. We have examined the potential for achieving this, in the case of scattering with angular limitation projection electron lithography (SCALPEL) masks, by using high-energy (100 keV) electron transmission measurements. We have also performed extensive metrology using conventional scanning electron microscope techniques. These results show that the SCALPEL mask has the potential to meet the specifications necessary for lithography at the 0.13 μm generation and beyond.

Photoionization - excitation of helium using an R-matrix with pseudostates method

We have developed an alternative R-matrix with pseudostates (RMPS) method for incorporating a two-electron continuum description into the wavefunction of electron - ion collision calculations. This method is similar in spirit to various recent treatments of the pseudostate expansion, most notably the R-matrix approaches of Meyer and Greene, and Bartschat et al. Our approach differs in that we: (1) utilize a direct sum of several bases: the physical target orbitals, additional MCHF pseudo-orbitals for the He ground state, R-matrix continuum orbitals, and, on occasion, Laguerre orbitals, and (2) rely on a different approach for the creation of an orthonormal basis. Since we use the Belfast codes that are based on a Wigner - Eisenbud R-matrix treatment, we also need to introduce a modified Buttle correction. The method is first tested on the s-wave (Temkin - Poet) model for electron-impact excitation and ionization of . Then it is applied to the calculation of cross sections and angular distributions for the photoionization - excitation process (n = 2,3). We find that these results are greatly improved by the inclusion of the two-electron continuum description, which is more important for the ground state, but plays a role in the final photoionized states as well. A highly correlated multiconfiguration Hartree - Fock expansion is used to represent the ground state, and from the configuration interaction coefficients, asymptotic ratios are determined and compared with other theoretical results. Results are also compared with recent high-energy measurements for the n = 2,3 cross section ratios and angular distribution parameters. This pseudostate expansion allows us to predict photo - double-ionization cross sections, . Of particular significance, we find good agreement between our length and velocity gauge results, indicating that our ground-state correlation is sufficiently converged for the present system.

Incident ion monitoring during plasma immersion ion implantation by direct measurements of high-energy secondary electrons

The present paper investigates time-resolved monitoring of incident ions during plasma immersion ion implantation (PIII) processes on the basis of high-energy secondary electron measurements with the scintillation technique. Taking into consideration the sheath geometry and the secondary electron emission coefficient of the target material, the experimental data were in a good agreement with theoretical predictions for dependences on target voltage, pressure and plasma density.

Development of a new technique for high-energy secondary-electron measurements in plasma immersion ion implantation

A scintillation technique was applied to directly monitor high-energy secondary electrons during the process of plasma immersion ion implantation (PIII). The spectral peak of the scintillation appeared at the wavelength of nm, and the temporal behaviour of the secondary electrons was measured with a response time as short as several microseconds. A maximum absolute secondary-electron flux for a target peak voltage of 25 kV reached at a measuring point, which showed good agreement with a calculated value. The kinetic energy of the secondary electrons was also measured by penetration depth into an aluminium layer coated on the scintillator surface, revealing acceleration of the secondary electrons up to an energy corresponding to the sheath voltage.

Solar cosmic rays

This report is a brief overview of the energetic-particle phenomena related to solar activity discussed at the XXIV International Cosmic-Ray Conference. In the rapporteur's opinion, the most significant results to be highlighted are: 1) the new higher-energy measurements of the solar energetic ion charge state which seem to be consistent with the older measurements at ∼1 MeV/nucleon, and 2) the many reports of extended gamma-ray production during solar flares with multiple episodes of emission implying multiple episodes of particle acceleration.

THE CASE OF αs: Z VERSUS LOW ENERGIES OR, HOW NATURE SHOWS US NEW PHYSICS

The values of αs determined from low and high energy measurements are in irreconcilable contradiction with each other. The current status of the problem is critically reviewed. Consequences of the αs contradiction, in conjunction with other anomalies detected at the Z peak, are discussed. This article has been updated in accordance with experimental numbers reported at summer conferences.

Harmonic behavior of metallic glasses up to the metastable melt.

In two amorphous alloys ZrTiCuNiBe and ZrAlNiCu coherent neutron scattering has been measured over five decades in energy, including measurements in the metastable melt of a metallic alloy more than 80 K above Tg. In the vibrational spectra a pronounced boson peak is found: Even in crystallized samples the density of states exceeds the Debye ω2 model, and in the amorphous state low-frequency vibrations are further enhanced. The peak position shows no dispersion in q, while intensities are strongly correlated with the static structure factor. Over the full energy range the temperature dependence is strictly harmonic. From high-energy resolution measurements we establish lower bounds for the temperatures at which structural α and fast β relaxation become observable.

Structure and oscillatory magnetoresistance of [formula omitted] sandwiches

We present structural and magnetoresistance studies performed on a series of Co(hcp) Cu sandwiches. We report reflection high-energy electron diffraction analysis and nuclear magnetic resonance measurements showing clearly the hcp structure of the Co layers and we find an oscillatory behaviour of the magnetoresistance with a period of about 13 Å.