| 1. |
- Murari, A., et al.
(författare)
-
A control oriented strategy of disruption prediction to avoid the configuration collapse of tokamak reactors
- 2024
-
Ingår i: Nature Communications. - 2041-1723 .- 2041-1723. ; 15:1
-
Tidskriftsartikel (refereegranskat)abstract
- The objective of thermonuclear fusion consists of producing electricity from the coalescence of light nuclei in high temperature plasmas. The most promising route to fusion envisages the confinement of such plasmas with magnetic fields, whose most studied configuration is the tokamak. Disruptions are catastrophic collapses affecting all tokamak devices and one of the main potential showstoppers on the route to a commercial reactor. In this work we report how, deploying innovative analysis methods on thousands of JET experiments covering the isotopic compositions from hydrogen to full tritium and including the major D-T campaign, the nature of the various forms of collapse is investigated in all phases of the discharges. An original approach to proximity detection has been developed, which allows determining both the probability of and the time interval remaining before an incoming disruption, with adaptive, from scratch, real time compatible techniques. The results indicate that physics based prediction and control tools can be developed, to deploy realistic strategies of disruption avoidance and prevention, meeting the requirements of the next generation of devices.
|
|
| 2. |
- Aaltonen, T., et al.
(författare)
-
Combination of Tevatron Searches for the Standard Model Higgs Boson in the W+W- Decay Mode
- 2010
-
Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 104:6, s. 061802-
-
Tidskriftsartikel (refereegranskat)abstract
- We combine searches by the CDF and D0 Collaborations for a Higgs boson decaying to W+W-. The data correspond to an integrated total luminosity of 4.8 (CDF) and 5.4 (D0) fb(-1) of p (p) over bar collisions at root s = 1.96 TeV at the Fermilab Tevatron collider. No excess is observed above background expectation, and resulting limits on Higgs boson production exclude a standard model Higgs boson in the mass range 162-166 GeV at the 95% C.L.
|
|
| 3. |
|
|
| 4. |
|
|
| 5. |
|
|
| 6. |
- Kravtsov, Evgeny, et al.
(författare)
-
Onset of spin-density-wave antiferromagnetism in Cr/V multilayers
- 2007
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 76:2, s. 024421-
-
Tidskriftsartikel (refereegranskat)abstract
- Spin-density-wave (SDW) magnetism in a series of Cr/V heterostructures with different Cr thicknesses was systematically investigated by combined resistivity, neutron, and synchrotron scattering measurements. We show that the onset of the bulklike SDW state comes through several necessary steps from a paramagnetic state through a commensurate SDW to an incommensurate SDW. The Néel temperature for the incommensurate SDW is found to scale with Cr thickness and reaches the bulk value at a Cr thickness of about 2000 Å. The proximity effect from Cr/V interfaces is found to lead to (i) the appearance of a 50-Å magnetically dead Cr layer near Cr/V interfaces and (ii) suppression of the spin-flip transition and stabilization of a single-domain SDW with out-of-plane spins and out-of-plane propagation wave vector. Finally, we show that the SDW period increases with decreasing Cr thickness and becomes temperature independent in sufficiently thin Cr layers.
|
|
| 7. |
|
|
| 8. |
|
|
| 9. |
|
|
| 10. |
|
|
| 11. |
|
|
| 12. |
- Piegsa, F. M., et al.
(författare)
-
Polarized neutron Laue diffraction on a crystal containing dynamically polarized proton spins
- 2013
-
Ingår i: Journal of Applied Crystallography. - 1600-5767 .- 0021-8898. ; 46:1, s. 30-34
-
Tidskriftsartikel (refereegranskat)abstract
- A polarized neutron Laue diffraction experiment on a single crystal of neodymium-doped lanthanum magnesium nitrate hydrate containing polarized proton spins is reported. By using dynamic nuclear polarization to polarize the proton spins, it is demonstrated that the intensities of the Bragg peaks can be enhanced or diminished significantly, whilst the incoherent background, due to proton spin disorder, is reduced. It follows that the method offers unique possibilities to tune continuously the contrast of the Bragg reflections and thereby represents a new tool for increasing substantially the signal-to-noise ratio in neutron diffraction patterns of hydrogenous matter.
|
|
| 13. |
|
|
| 14. |
- Ptasiewicz-Bak, H., et al.
(författare)
-
Charge density in NiCl2.4H2O at 295 and 30 K
- 1999
-
Ingår i: Acta Crystallographica Section B. - : International Union of Crystallography (IUCr). - 0108-7681 .- 1600-5740. ; 55:6, s. 830-840
-
Tidskriftsartikel (refereegranskat)abstract
- The charge distribution has been determined by multipole refinements against single-crystal X-ray diffraction data. In the refinements a comparison was made between the densities based on H-atom parameters from X-ray and neutron data, respectively. X-ray study: (Mo K ) = 0.71073 Å, F(000) = 408; at 30 K: R(F) = 0.015 for 6686 reflections; at 295 K: R(F) = 0.022 for 4630 reflections. The nickel ion is octahedrally surrounded by four water molecules and two chloride ions, forming a locally neutral Ni(H2O)4Cl2 complex. Two of the water molecules are coordinated to nickel approximately in one of the tetrahedral (`lone-pair') directions; the other two are trigonally coordinated. At 30 K one H atom in one of the trigonally coordinated water molecules is disordered, with equal occupation of two different positions. Owing to the polarizing influence of the nickel ion there are two peaks in the lone-pair plane of the water molecules when these are tetrahedrally coordinated; for those trigonally coordinated there is just one peak. The individual (`partial') charge densities, calculated from the deformation functions of only nickel or the separate water molecules, have also been calculated to study the effects of superposition of the individual densities. In the individual density of nickel an excess is observed in the diagonal directions and a deficiency in the ligand directions. However, owing to the influence of the whole crystalline environment, the maxima around nickel are not found in the planes defined by nickel and the six ligands.
|
|
| 15. |
- Ptasiewicz-Bak, H., et al.
(författare)
-
Charge Density in Orthorhombic NiSO4.7H2O at Room Temperature and 25 K
- 1997
-
Ingår i: Acta Crystallographica Section B. - : International Union of Crystallography (IUCr). - 0108-7681 .- 1600-5740. ; 53:3, s. 325-336
-
Tidskriftsartikel (refereegranskat)abstract
- The charge-density distribution in the title compound nickel sulfate heptahydrate has been determined by multipole refinement against single-crystal X-ray intensity data. For the refinement at 25 K hydrogen positions and displacement parameters were fixed to values determined from neutron data. The charge density based on the deformation functions of all atoms in the structure is compared with the individual densities calculated from the deformation functions of only nickel or the separate water molecules. In this way the effects of simple superposition of the individual densities have been studied. The individual deformation density around nickel is in good qualitative agreement with that expected for an approximately octahedral Ni(H2O)62+ complex in a weak ligand field. However, the maximum densities are not found precisely in the planes defined by nickel and the six water ligands, which illustrates that it is necessary to consider the crystal field due to the whole crystalline environment. The individual densities of the water molecules show clear polarization of the lone-pair densities according to the coordination of the water molecules: tetrahedral coordination leads to two resolved lone-pair peaks, whereas planar trigonal coordination leads to just one single peak. Crystal data: NiSO4.7H2O, Mr = 280.87, P212121, Z = 4. At T = 25 K: a = 6.706 (3), b = 11.796 (6), c = 11.949 (6) Å, V = 945 (1) Å3, Dx = 1.977 Mg m-3. At 295 K: a = 6.751 (4), b = 11.746 (7), c = 12.003 (8) Å, V = 952 (1) Å3, Dx = 1.959 Mg m-3. X-ray study: F(000) = 584, (Mo K ) = 0.71069 Å, = 2.255 mm-1. At 25 K: R(F) = 0.014 for 10 185 reflections. At 295 K: R(F) = 0.015 for 5723 reflections. Neutron study at 25 K: = 1.215 Å, = 0.261 mm-1, R(F) = 0.034 for 1381 reflections.
|
|
| 16. |
- Ptasiewicz-Bak, H., et al.
(författare)
-
Structure, Charge and Spin Density in Na2Ni(CN)4.3H2O at 295 and 30 K
- 1998
-
Ingår i: Acta Crystallographica Section B. - : International Union of Crystallography (IUCr). - 0108-7681 .- 1600-5740. ; 54:5, s. 600-612
-
Tidskriftsartikel (refereegranskat)abstract
- The earlier reported structure of the title compound,disodium tetracyanonickelate(II) trihydrate,Na 2 Ni(CN) 4.3H 2O, has been found to be incorrect andhas now been redetermined. The charge distribution hasbeen determined by multipole reÆnements againstsingle-crystal X-ray diffraction data. In the reÆnementbased on 30 K data a comparison was made between theresults obtained using hydrogen positions and displace-ment parameters from X-ray diffraction with those usingthe values determined by neutron diffraction. The spindensity was investigated by polarized neutron diffrac-tion at 1.6 K. Crystal data: at T = 30 K: a = 7.278 (4), b =8.856 (5), c = 15.131 (8) A, = 89.32 (5), = 87.39 (4),= 83.61 (4); at 295 K: a = 7.392 (4), b = 8.895 (4), c =15.115 (8) A, = 89.12 (2), = 87.46 (2), = 84.54 (2).The structure contains practically square planarNi(CN) 2ˇ4 ions, which are stacked on top of each otherin almost linear chains along the a direction. Theseparation between the Ni(CN) 2ˇ4 planes is rather large,with Ni–Ni distances around 3.7 A. The six crystal-lographically independent water molecules are eachcoordinated to two sodium ions, approximately in thetetrahedral (lone-pair) directions, and the polarizinginØuence of these sodium ions also appears to bereØected in the deformation density in the lone-pairplane. The charge density based on the deformationfunctions of all atoms in the structure is compared withthe individual densities calculated from the deformationfunctions of only nickel or the separate water molecules.In this way the effects of simple superposition of theindividual densities have been studied. In the planarNi(CN) 2ˇ4 ion the individual deformation density ofnickel is in qualitative agreement with that expectedfrom crystal-Æeld theory. As the repulsion from theelectrons is much weaker perpendicular to the Ni(CN) 2ˇ4plane than within this plane, the deformation density isconsiderably larger in the perpendicular direction.However, the largest maxima in the individual deforma-tion density around nickel are not found precisely in theplanes deÆned by nickel and the four cyanide ligands orin the perpendicular direction just mentioned, whichillustrates that it is necessary to consider the crystal Æelddue to the whole crystalline environment.
|
|
| 17. |
|
|
