A5073452290- Nuclear Physics and Applications
- Geophysical Methods and Applications
- High-pressure geophysics and materials
- Magnetic confinement fusion research
- Fusion materials and technologies
- Atomic and Subatomic Physics Research
- Non-Destructive Testing Techniques
- Nuclear reactor physics and engineering
- Magnetic properties of thin films
- X-ray Diffraction in Crystallography
- Physics of Superconductivity and Magnetism
- Quantum, superfluid, helium dynamics
- Superconducting Materials and Applications
- Theoretical and Computational Physics
- Inorganic Fluorides and Related Compounds
- Microwave Imaging and Scattering Analysis
- Seismic Waves and Analysis
- Nuclear Materials and Properties
- Advanced Condensed Matter Physics
- Ultrasonics and Acoustic Wave Propagation
- Magnetism in coordination complexes
- Fatigue and fracture mechanics
- Microstructure and Mechanical Properties of Steels
- Advanced Chemical Physics Studies
- Magnetic Properties and Applications
Oxfam
1978-2022
Tokamak Energy (United Kingdom)
2015-2022
The Open University
2019
Culham Science Centre
2001-2017
Fulbourn Hospital
2005-2015
Culham Centre for Fusion Energy
1997-2011
University of Florence
2005-2009
Research England
2007
University of Wisconsin–Madison
1969-2005
United Kingdom Atomic Energy Authority
1983-1997
Abstract The present situation in theoretical and experimental studies on one-dimensional magnetic systems is fully discussed. Equal-time as well the dynamic properties are included with an emphasis latter. Four model examined detail: TMMC (Heisenberg antiferromagnet), CsNiF3 (planar ferromagnet), CoCl2. 2NC5H5 (Ising CuCl2. antiferromagnet S = ½). equal-time quite understood theory experiment but dynamical much less so. open questions possible investigations for future
The mathematical functions necessary for Rietveld refinement of time-of-flight neutron powder diffraction patterns from spallation sources are developed and a computer program least-squares analysis is described. results refinements nickel low-carbon steel described discussed. method fully exploits the high resolution (Δd/d ~ 0.3 0.5%) available with diffractometers currently in operation on these examples given precise determination atom coordinates, thermal parameters, lattice parameters...
Abstract A technique is described for the measurement of residual stress tensor averaged over a specified volume within component. The method involves small changes in lattice spacing using high resolution neutron diffraction. inferred from these measurements strain, and theory relationship between two quantities described, including effects crystalline anisotropy. various types diffractometer suitable work are described. Experimental results validating given simple bent bar mild steel known...
Abstract By comparing measured and calculated versions of the generalized magnetic response function nickel over a wide range temperatures it is shown that much-discussed simple model an itinerant-electron ferromagnet based on random-phase-approximation treatment Hubbard Hamiltonian accounts, in its essentials, for magnetism substance. Thermal neutron inelastic scattering techniques were used to explore whole Brillouin zone wave vectors K up energies ▄ω some 2k B T C 2T C; computations...
Tokamak Energy Ltd, UK, is developing spherical tokamaks using high temperature superconductor magnets as a possible route to fusion power relatively small devices. We present an overview of the development programme including details enabling technologies, key modelling methods and results, remaining challenges on path compact fusion.
The spin-wave dispersion relations for the simple cubic antiferromagnet RbMnF3 have been determined at 4.2 °K by inelastic neutron scattering. Spin-wave theory is used to interpret results in terms of exchange interactions 2JijSi-Sj between first, second and third neighbours with J1 = 3 4±0.3 J2 0.0±0 2 J3 0 00±0.04 °K. also confirm that anisotropy field less than 400 gauss. above value compared other experimental results, values calculated from Néel temperature. Good agreement suggests one...
A method is presented for isolating the overlapping hyperbolic arcs found when a radar scan made over several adjacent buried objects. The reflected signal first converted into series of data pairs (yj, tj) giving, antennae position yj along scan, times-of-flight tj maxima or minima in amplitude. generalized Hough transform extended to record an associative store sets contributing each bin accumulator space. cluster high bins, defining peak this space, may then be broken down reveal its...
The spin-wave dispersion curve of antiferromagnetic KMnF3 at 4.2°K has been measured by means neutron inelastic scattering. With incident energies 105° and 165°K, propagation was observed out to the zone boundary in pseudocubic (110) plane. Least-squares fitting an expression involving nearest next-nearest-neighbor exchange interactions J1 J2 anisotropy field HA yielded results J1/k=3.80°±0.04°K, J2/k=0.11°±0.02°K HA=3.1±0.4 kOe.
The paramagnetic resonance from ${\mathrm{Fe}}^{3+}$ and ${\mathrm{Gd}}^{3+}$ ions substituted into weakly europium gallium garnet has been investigated at 77\ifmmode^\circ\else\textdegree\fi{}K 26 Gc/sec. spectra have fitted to conventional spin Hamiltonians for occupying the [$a$] site {$c$} site. No was observed ($d$)-site ${\mathrm{Fe}}^{3+}$, indicating a strong preferential population of in these garnets. By comparing spin-Hamiltonian parameters found with those other diamagnetic...
Results are reported on cemented tungsten carbide (cWC) and boride-containing composite materials for the task of shielding centre column a superconducting tokamak power plant. The shield is based five concentric annular shells consisting cWC water layers which innermost can be replaced with boride composites. Sample have been fabricated changing parameters porosity P, binder alloy fraction fbinder boron weight fboron. For materials, other hypothetical samples chosen parameters, Monte Carlo...
The favourable properties of tungsten borides for shielding the central High Temperature Superconductor (HTS) core a spherical tokamak fusion power plant are modelled using MCNP code. objectives to minimize deposition into cooled HTS core, and keep radiation damage acceptable levels by limiting neutron gamma fluxes. shield materials compared W2B, WB, W2B5 WB4 along with reactively sintered boride B0.329C0.074Cr0.024Fe0.274W0.299, monolithic W WC. Of all these gave most results factor ~10 or...
We report neutron-scattering measurements on highly supercooled liquid gallium droplets showing a vanishing quasi-elastic frequency width as the temperature is reduced. The tends towards zero at within 1 standard deviation of value ${T}_{L}=150\ifmmode\pm\else\textpm\fi{}1$ K which always observed to become crystalline. This suggests interpretation ${T}_{L}$ metastability limit, below state becomes unstable with respect infinitesimal fluctuations.
An on-line predictor of the time to disruption has been installed on ASDEX Upgrade tokamak. It is suitable either for avoidance disruptions or mitigation those that are unavoidable. The prediction uses a neural network trained eight plasma parameters and their derivatives extracted from 99 disruptive discharges. was tested off-line over 500 discharges found work reliably be able predict majority disruptions. on-line, 128 used inject killer pellets mitigate loads.
First results are reported on the prediction of disruptions in one tokamak, based neural networks trained another tokamak. The studies use data from JET and ASDEX Upgrade devices, with a network just seven normalized plasma parameters. In this way, simple single layer perceptron solely correctly anticipated 67% advance 0.01 s before disruption. converse test led to 69% success rate 0.04 disruption JET. Only overall time scaling parameter is allowed between which can be introduced theoretical...
Neutron and X-ray small-angle scattering provide, along with electron microscopy diffraction, the principal techniques for microscopic characterization of materials. Neutron, beams each have quite different properties. In fact, has unique advantages. The penetration neutrons through most materials is responsible many applications. ever-increasing intensity available opening new fields. advantage their ability to work in both real reciprocal space. problems transforming results an experiment...
Ultrawideband radar is commonly used in the frequency range of 50-500 MHz to detect buried pipes at a depth about 1-2 m depending on soil characteristics. The typical feature locate hyperbolic pattern time flight generated by linear scan antenna above surface. When are close together, hyperbolas overlap, and straightforward least squares fit not possible. Hough transform provides one possible solution. This paper extends introducing weighting factor differentials unknown parameters with...
A detailed theory is developed for the effects of covalency on magnetic properties a Co 2+ ion surrounded by regular octahedron ligands. In contrast to previous studies cobalt ion, strong-field representation has been used, in which octahedral field diagonalized before electrostatic interactions. Expressions are derived orbital contribution g value, and ligand hyperfine interactions, terms wave function admixture coefficients. The applied electron spin resonance measurements : KMgF 3...
A method based on the band wavefunctions is used to classify contributions Lindhard expression for generalized susceptibility chi 0non(q) arising from various bands near Fermi surface. The applied chromium at its Neel temperature where it shown that position of maximum in ordering wave vector determined by resting electron surface gamma into hole H as proposed Lomer model. However this contribution small compared involving more than 0.5 eV energy, which give rise a broad commensurate...
A computer model of a Heisenberg paramagnet is constructed from thousand classical spin vectors situated on simple cubic lattice and interacting through nearest-neighbour exchange forces. The motion an initial random set spins calculated explicitly used to evaluate the correlations <S0(0).SR(t)> as function time for various neighbours. neutron scattering polycrystalline predicted compared with experimental data RbMnF3.
Numerical studies have been made to improve the performance of central column a superconducting spherical tokamak fusion pilot plant. The assumed neutron shield includes concentric layers tungsten carbide and water. relative thickness water was varied minimum power deposition found at about 17% It advantageous an approximately 1.7 times thicker layer next core similarly thinner plasma. use boride instead shown make improvement especially if placed close core, inner alone reducing by 29%....
The generalized Hough transform method is applied to the measurement of diameters buried cylindrical pipes by Ground Penetration Radar (GPR).600 MHz radar scans across long pipes, in one metre or so soil, show complex reflection patterns consisting a series inverted hyperbolic arcs.The time flight t(y) as probe scanned along an axis, y, perpendicular pipe, shows arc whose shape and position depends on 4 unknown variables: y 0 , center pipe scan, z depth center, R its radius V velocity...