| 1. |
- De Temmerman, G., et al.
(författare)
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Interactions of diamond surfaces with fusion relevant plasmas
- 2009
-
Ingår i: Physica scripta. T. - : Institute of Physics Publishing (IOPP). - 0281-1847 .- 0031-8949 .- 1402-4896. ; T138, s. 014013-
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Tidskriftsartikel (refereegranskat)abstract
- The outstanding thermal properties of diamond and its low reactivity towards hydrogen may make it an attractive plasma-facing material for fusion and calls for a proper evaluation of its behaviour under exposure to fusion-relevant plasma conditions. Micro and nanocrystalline diamond layers, deposited on Mo and Si substrates by hot filament chemical vapour deposition (CVD), have been exposed both in tokamaks and in linear plasma devices to measure the erosion rate of diamond and study the modification of the surface properties induced by particle bombardment. Experiments in Pilot-PSI and PISCES-B have shown that the sputtering yield of diamond (both physical and chemical) was a factor of 2 lower than that of graphite. Exposure to detached plasma conditions in the DIII-D tokamak have evidenced a strong resistance of diamond against erosion under those conditions.
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| 2. |
- Kreter, A., et al.
(författare)
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Fuel retention in carbon materials under ITER-relevant mixed species plasma conditions
- 2009
-
Ingår i: Physica scripta. T. - : Institute of Physics Publishing (IOPP). - 0281-1847 .- 0031-8949 .- 1402-4896. ; T138, s. 014012-
-
Tidskriftsartikel (refereegranskat)abstract
- Samples of CFC NB41 and fine-grain graphite ATJ have been exposed to PISCES plasmas containing (i) pure deuterium, (ii) deuterium and beryllium, (iii) deuterium, beryllium and helium, and (iv) deuterium, beryllium and argon. Thermal desorption spectrometry (TDS) and nuclear reaction analysis (NRA) have been used to measure the amount and distribution of retained deuterium in the samples. For the case of pure deuterium plasma, parametric studies of deuterium retention in NB41 have been done with variations of the incident deuterium fluence (Phi = 1 x 10(25)-5 x 10(26) m(-2)), ion energy (E-i = 20-120 eV) and sample surface temperature (T-s = 370-820 K). It has been found, that for T-s = 470K the retention scales as Phi(0.35). For T-s = 820K the retention saturates at a level of similar to 10(21) Dm(-2). The retention increases with E-i and drops with higher T-s. At T-s = 720 K, the beryllium seeding results in a building of a protective beryllium carbide layer, which appears to prevent the in-bulk diffusion of deuterium, thus reducing the retention. Admixture of Ar and, in the case of low E-i, He leads to a significant reduction of the retention.
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| 3. |
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| 4. |
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| 5. |
- Brage, Tomas, et al.
(författare)
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Core polarization effects on oscillator strengths in neutral zinc
- 1992
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Ingår i: Physica Scripta. Topical Issues. - : IOP Publishing. - 0281-1847. ; 45:1, s. 43-48
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Tidskriftsartikel (refereegranskat)abstract
- The effect of core polarization on the oscillator strength for the resonance transition in neutral zinc is investigated using the multiconfiguration Hartree Fock approach. The use of model potentials and corrections to the dipole operator is compared to a method, where the core polarization is represented by including configuration state functions, with one hole in the 3d core subshell in the CI-expansion. The latter, which is labeled explicit CI, gives results in good agreement with experiment. The reason for deviations in earlier calculations is discussed, together with the validity of the comparison of length and velocity forms of oscillator strengths, as a test of accuracy. The dependence of the model potential results on the choice of cut-off radius is investigated.
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| 6. |
- Brage, Tomas, et al.
(författare)
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Experimental and theoretical study of core-excited states of Mg II
- 1991
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Ingår i: Physica Scripta. Topical Issues. - : IOP Publishing. - 0281-1847. ; 44:4, s. 336-342
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Tidskriftsartikel (refereegranskat)abstract
- The 2p(5)3s3p, 3p2, 3s4s, 3s3d, and 3s4f core-excited configurations of Mg II have been studied experimentally by beam-foil spectroscopy and theoretically by multiconfiguration Hartree-Fock calculations with Breit-Pauli relativistic corrections. The previously established energy levels belonging to the former four configurations have been reexamined leading to significant corrections of the 3p2 4D and 3s4s 4P levels. Many previously unidentified spectral lines have now been assigned allowing a confident set of energy levels of the nearly degenerate 3p2, 3s4s, and 3s3d configurations to be established. in addition, the higher lying 3s4f states have been studied allowing the assignment of the prominent, but unidentified line at 3480 angstrom to the 3s4f 4G11/2 --> 3s3d 4F9/2 transition, and the establishment of some 3s3d states which primarily decay by autoionization.
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| 7. |
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| 8. |
- Carlsson, J, et al.
(författare)
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Multiconfiguration Hartree-fock Calculations and Time-resolved Laser Spectroscopy Studies of Hyperfine-structure Constants In Sodium
- 1992
-
Ingår i: Physica Scripta. Topical Issues. - : IOP Publishing. - 0281-1847. ; 46:5, s. 394-398
-
Tidskriftsartikel (refereegranskat)abstract
- Hyperfine structure constants for the ground and first excited states of sodium are calculated using a newly written hyperfine structure program, which is part of the MCHF Atomic Structure Package. The calculated hyperfine structure constants are compared with the most reliable values obtained in other theoretical studies and in experiments. Also, a new accurate experimental determination of the 3p P-2(1/2) state hyperfine structure is presented.
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| 9. |
- Curtis, LJ, et al.
(författare)
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Relativistic empirical specification of transition probabilities from measured lifetime and energy level data
- 1997
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Ingår i: Physica Scripta. Topical Issues. - : IOP Publishing. - 0281-1847. ; 56:3, s. 240-244
-
Tidskriftsartikel (refereegranskat)abstract
- A relativistic extension is made of methods by which intermediate coupling amplitudes are deduced from measured energy levels and combined with measured lifetimes to obtain transition probabilities within a multiplet between two pure configurations. A procedure for incorporating the relativistic j-dependence of the radial transition integral into the empirical data reduction is presented and applied to the isoelectronic formulation of the 2s(2)-2s2p transitions in the Be sequence and the 6s(2)6p(2)-6s(2)6p7s transitions in the Pb sequence.
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| 10. |
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| 11. |
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| 12. |
- Jönsson, Per
(författare)
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Multi-configuration Hartree and Dirac-fock Calculations of Atomic Hyperfine Structures
- 1993
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Ingår i: Physica Scripta. Topical Issues. - : IOP Publishing. - 0281-1847. ; 48:6, s. 678-687
-
Tidskriftsartikel (refereegranskat)abstract
- Recent multi-configuration Hartree-Fock (MCHF) calculations of atomic hyperfine structures are reviewed. In particular, spin-polarization and relativistic effects are considered. Using a systematic active space MCHF approach, combined with large multi-reference configuration interaction (MR-CI) calculations, it is shown that hyperfine structures in many cases can be calculated very accurately. For few-electron systems, like lithium and beryllium, the remaining discrepancies between theory and experiments largely come from neglected relativistic effects, showing the necessity of fully relativistic calculations even for these systems. The physical effects of relativity on the hyperfine structure are discussed and fully relativistic multi-configuration Dirac-Fock (MCDF) calculations using the systematic active space approach are performed for lithium-like fluorine.
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| 13. |
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| 14. |
- Larsson, Jörgen
(författare)
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Vuv Laser Spectroscopy
- 1994
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Ingår i: Physica Scripta. Topical Issues. - : IOP Publishing. - 0281-1847. ; 49:2, s. 173-179
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Tidskriftsartikel (refereegranskat)abstract
- Recently, new optical non-linear materials and frequency-mixing schemes have been developed. This has moved the frontiers of short-wavelength laser spectroscopy into the VUV spectral region. Spectroscopic methods suitable for short-wavelength laser sources are presented.
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| 15. |
- Lundin, Peter, et al.
(författare)
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Metastable levels in ScII : lifetime measurements and calculations
- 2008
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Ingår i: Physica Scripta. - : IOP Publishing. - 0031-8949 .- 1402-4896 .- 0281-1847. ; 78:1, s. 015301-
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Tidskriftsartikel (refereegranskat)abstract
- The lifetime of the metastable level 3d(21)G(4) in a singly charged scandium has been experimentally investigated at the ion storage ring CRYRING. A laser probing technique has been used for the studies. We also report calculated lifetimes and transition rates for 10 metastable levels in Sc II, including the 3d(21)G(4) state, by calculations using configuration interaction wave functions. The lifetime of the (1)G(4) level is experimentally determined to be tau(exp) = 2.64 +/- 0.18 s and is in good agreement with the theoretical calculation tau(th) = 2.84 s.
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| 16. |
- Persson, W, et al.
(författare)
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Spectrum of Doubly Ionized Xenon (xe-iii)
- 1988
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Ingår i: Physica Scripta. Topical Issues. - : IOP Publishing. - 0281-1847. ; 38:3, s. 347-369
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Tidskriftsartikel (refereegranskat)
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| 17. |
- Persson, Willy, et al.
(författare)
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Spectrum of Rb IV
- 1985
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Ingår i: Physica Scripta. Topical Issues. - : IOP Publishing. - 0281-1847. ; 31:6, s. 487-505
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Tidskriftsartikel (refereegranskat)
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| 18. |
- Persson, Willy, et al.
(författare)
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Spectrum of SrV
- 1984
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Ingår i: Physica Scripta. Topical Issues. - : IOP Publishing. - 0281-1847. ; 30:3, s. 169-185
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Tidskriftsartikel (refereegranskat)
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| 19. |
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| 20. |
- Svanberg, Sune, et al.
(författare)
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Lund High-power Laser Facility - Systems and 1st Results
- 1994
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Ingår i: Physica Scripta. Topical Issues. - : IOP Publishing. - 0281-1847. ; 49:2, s. 187-197
-
Tidskriftsartikel (refereegranskat)abstract
- A high-power laser facility has been established at the Lund Institute of Technology, Sweden, available to national groups and their international collaboration partners. The laboratory incorporates three major 10 Hz laser systems, that can be operated individually or synchronized in combined use. Each system represents extreme optical powers in a certain sense. The main system is a terawatt laser based on chirped pulse amplification in titanium doped sapphire. It generates radiation tunable in the 760-840 nm region with a maximum power of 1.5TW in 150 fs long pulses. A further system is set up to generate nanosecond pulses of extremely bright VUV radiation (down to 120 nm) by sum-difference four-wave mixing in krypton gas. Finally, a third system generates widely tunable radiation (200-900 nm) of a pulse duration of 10's of picoseconds. The experimental areas incorporate target chambers, spectrometers and fast electronics. The systems have been used in a number of experiments requiring high optical powers, and a brief account of the initial activities is given. Detailed studies of high-harmonic generation in inert gases are reported as well as the generation and application of hard X-rays from microplasmas. Intense white-light generation by self-phase modulation in water has been used for biological tissue studies and for chemical pump/probe experiments. VUV radiation has been used for studies of radiative properties of excited states of free atoms. Finally, the picosecond laser system has been utilized in studies of the temporal structure of harmonics from an inert gas and for soft X-ray generation for high-resolution microscopy. A discussion section concludes the presentation.
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| 21. |
- Wahlström, Claes-Göran
(författare)
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High-order Harmonic-generation Using High-power Lasers
- 1994
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Ingår i: Physica Scripta. Topical Issues. - : IOP Publishing. - 0281-1847. ; 49:2, s. 201-208
-
Tidskriftsartikel (refereegranskat)abstract
- An introduction to high-power lasers and strong-field laser-atom interactions is given, and the main experimental and theoretical results concerning high-order harmonic generation are reviewed. The single atom response as well as the macroscopic phase-matching effect is discussed. The formation and extent of the characteristic plateau in the harmonic spectra are discussed in terms of a physical picture valid in the tunnel-ionisation regime. Very high-order harmonics have been reported, opening the way to construct bright sources of coherent radiation in the XUV and soft X-ray ranges. Some examples of possible applications of such a source are presented.
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| 22. |
- Wallinder, E, et al.
(författare)
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Vertically sounding ozone lidar system based on a KrF excimer laser
- 1997
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Ingår i: Physica Scripta. Topical Issues. - : IOP Publishing. - 0281-1847. ; 55:6, s. 714-718
-
Tidskriftsartikel (refereegranskat)abstract
- A differential absorption (DIAL) lidar system based on a Raman shifted KrF excimer laser was constructed and employed for vertically sounding measurements of tropospheric ozone, This system is described, including a presentation of measurements of Raman shifting efficiencies in hydrogen and deuterium. The performance of the new system was evaluated in measurement campaigns involving two further optical remote-sensing systems: A Nd:YAG/dye laser based lidar and a long-path differential optical absorption spectroscopy (DOAS) system, utilising a high-pressure xenon lamp.
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| 23. |
- Zerne, R, et al.
(författare)
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Oscillator strengths of sulphur 3s(2) 3p(3) 4s S-3(0)-3s(2) 3p(3) 4p P-3 transitions measured by time resolved two-photon laser spectroscopy
- 1997
-
Ingår i: Physica Scripta. Topical Issues. - : IOP Publishing. - 0281-1847. ; 56:5, s. 459-461
-
Tidskriftsartikel (refereegranskat)abstract
- Oscillator strengths for the three 3s(2)3p(3)4s S-3(1)o-3s(2)3p(3)4p P-3(0,1,2) transitions in neutral sulphur have been determined directly from lifetime measurements. Two-photon UV laser excitation and subsequent fluorescence detection have been used on atoms produced in a thermal sulphur beam or in a laser-driven plasma. A good agreement was found between data obtained in both schemes. The lifetime data obtained, tau(P-3(0)) = 46.1(1.0) ns, tau(P-3(1)) = 46.1(1.0) ns and tau(P-3(2)) = 46.1(1.0) ns are compared with results of theoretical and experimental data from literature. The absorption oscillator strengths derived are f(S-3(1)o-P-3(0)) = 0.120(0.003), f(S-3(1)o-P-3(1)) = 0.360(0.008) and f(S-3(1)o-P-3(2)) = 0.600(0.013), respectively. For the next higher member of the series, 3s(2)3p(3)5p P-3(1,2), a substantially longer Lifetime, 188(13) ns, was obtained.
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| 24. |
- Weckmann, Armin, et al.
(författare)
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Ageing of structural materials in tokamaks: TEXTOR liner study
- 2017
-
Ingår i: Physica scripta. T. - : Institute of Physics (IOP). - 0281-1847 .- 0031-8949 .- 1402-4896. ; T170
-
Tidskriftsartikel (refereegranskat)abstract
- After the final shut-down of the tokamak TEXTOR, all of its machine parts became accessible for comprehensive studies. This unique chance enabled the study of the Inconel 625 liner by a wide range of methods. The aim was to evaluate eventual alteration of surface and bulk characteristics from recessed wall elements that may influence the machine performance. The surface was covered with stratified layers consisting mainly of boron, carbon, oxygen, and in some cases also silicon. Wall conditioning and limiter materials hence predominantly define deposition on the liner. Deposited layers on recessed wall elements reach micrometre thickness within decades, peel off and may contribute to the dust inventory in tokamaks. Fuel retention was about 4 at% of the overall layers, with no evidence for diffusion into the Inconel substrate. Inconel 625 retained its mechanical strength despite 26 years of cyclic heating, stresses and particle bombardment.
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| 25. |
- Chen, Fengxiang, et al.
(författare)
-
Robust control of chaos in the Lorenz system with the variable structure control approach
- 2008
-
Ingår i: Physica scripta. T. - : IOP Publishing. - 0281-1847 .- 0031-8949 .- 1402-4896. ; 77:2
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- This paper is concerned with the robust control for a class of the uncertain Lorenz system subject to sector nonlinear input. Based on rigorous mathematical analysis, the proposed variable structure controller can drive the system state exactly to a class of a specific point or in the predictable neighborhood of an arbitrary desired point in the state space even with mismatch uncertainties. Moreover, the controller ensures that one of the error components can approach zero as time approaches infinity. Finally, numerical simulation results show the effectiveness of our work.
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| 26. |
- Ekström, Curt, et al.
(författare)
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Nuclear Spins of Neutron-deficient Promethium, Samarium, Europium and Gadolinium Isotopes
- 1972
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Ingår i: Physica scripta. T. - : IOP Publishing. - 0281-1847 .- 0031-8949 .- 1402-4896. ; 6:4, s. 181-190
-
Tidskriftsartikel (refereegranskat)abstract
- Spin-measurements have been performed on some neutron-deficient promethium, samarium, europium and gadolinium isotopes using conventional atomic-beam magnetic resonance techniques. The results are: 141Pm (20.9 min) I=5/2, 140Sm (14.8 min) I=0, 141Sm (11.3 min) I=1/2, 141mSm (22.9 min) I=11/2, 142Sm (72.5 min) I=0, 143Sm (8.8 min) I=3/2, 145Eu (5.93 d) I=5/2, 146Eu (4.65 d) I=4, 147Eu (22 d) I=5/2, 148Eu (54 d) I=5, 149Eu (93.1 d) I=5/2, 150Eu (12.6 h) I=0, 145Gd (22.9 min) I=1/2, 147Gd (38.5 h) I=7/2, 149Gd (9.4 d) I=7/2, 151Gd (120 d) I=7/2. The investigated nuclei appear close to the shell closure at neutron number N=82. A systematic review of the low-lying states of odd-even and doubly-odd nuclei in this region is presented.
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| 27. |
- Han, Shunhui, et al.
(författare)
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The upper critical-field of pb doped BI-SR-CA-CU-O compounds
- 1991
-
Ingår i: Physica scripta. T. - : IOP Publishing. - 0281-1847 .- 0031-8949 .- 1402-4896. ; 44:11, s. 69-70
-
Tidskriftsartikel (refereegranskat)abstract
- The upper critical field H(c2) of four Bi-(Pb)-Sr-Ca-Cu-O superconductors with the 110 K phase has been measured as a function of temperature. H(c2) exhibited a (T(c) - T)alpha-temperature dependence with alpha > 1 f two impure samples, but showed a linear temperature dependence for the purest sample, which is not expected according to current theories and other experiments.
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| 28. |
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| 29. |
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| 30. |
- Petersson, L-G, et al.
(författare)
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Surface reactions on Pd studied with a hydrogen sensitive MOS-structure andphotoelectron spectroscopy
- 1982
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Ingår i: Physica scripta. T. - 0281-1847. ; 25:6A, s. 818-825
-
Tidskriftsartikel (refereegranskat)abstract
- During the last couple of years catalytic reactions on Pd surfaces have been studied at our department by means of a hydrogen sensitive Pd-MOS structure and work function measurements. These studies have been performed at atmospheric pressures with Ar and O2 as carrier gases. We have now extended this type of measurements to the ultra-high vacuum (UHV) region and also combined them with both UV and, in certain cases, X-ray photoelectron spectroscopy (UPS, XPS) studies. With this technique we are able to detect about 0.001 of a monolayer of hydrogen, and changes in rate or equilibrium constants corresponding to changes in an energy coordinate of less than 10 meV. Furthermore, results from a Cd contaminated Pd-MOS structure indicates that the ability of Pd to dissociate H2 is related to a microscopic parameter and not to any general metal-like parameter.
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| 31. |
- Plashkevych, O., et al.
(författare)
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Near-edge X-ray absorption spectra of carbon-nitride molecules and solids
- 2001
-
Ingår i: Physica scripta. T. - : IOP Publishing. - 0281-1847 .- 0031-8949 .- 1402-4896. ; 63:1, s. 70-86
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Tidskriftsartikel (refereegranskat)abstract
- Near-edge X-ray absorption fine structure spectra have been calculated for different carbon-nitrogen molecules, clusters and solids. The compounds investigated are used to model the chemical bonding in carbon nitride thin films. The molecular and cluster spectra are calculated employing the static exchange ab initio technique, while the solid state calculations are performed with the density functional full potential augmented plane wave method.
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| 32. |
- Stenström, Bengt
(författare)
-
The Electrical Resistivity of FeSn Single Crystals
- 1972
-
Ingår i: Physica scripta. T. - : IOP Publishing. - 0281-1847 .- 0031-8949 .- 1402-4896. ; 6:4, s. 214-216
-
Tidskriftsartikel (refereegranskat)abstract
- The electrical resistivity of single crystal FeSn (hex B 35) has been measured for current parallel and perpendicular to the c-axis in the temperature range 4.2-420 K. The critical exponent is determined for I//c at the antiferromagnetic ordering temperature TN = 364 K.
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| 33. |
- Stenström, Bengt, et al.
(författare)
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The Electrical Resistivity of Hexagonal FeGe Single Crystals
- 1972
-
Ingår i: Physica scripta. T. - : IOP Publishing. - 0281-1847 .- 0031-8949 .- 1402-4896. ; 6:4, s. 209-213
-
Tidskriftsartikel (refereegranskat)abstract
- Electrical resistivity measurements have been carried out on hexagonal FeGe (B 35), which is a uniaxial antiferromagnet with TN=411 K. The resistivity parallel to the c-axis exhibits a hump below TN, which arises from the magnetic superzones cutting and distorting different contributions to the Fermi surface. For the current in the basal plane a mere change in slope is observed in the resistivity at the Néel temperature. Critical scattering, as well as imperfections, tend to smooth out the transition behaviour and an attempt is made to determine the critical exponent in d/dT = Cε-λ, where ε = |T-TN|/TN. For current parallel to the c-axis λ ≈ 0.8 for T>TN and λ ≈ -0.4 for T<TN. The case of resistivity perpendicular to the c-axis is less amenable to detailed analysis. The strong ferromagnetic ordering in the basal plane gives rise to long-range spin fluctuations, while the weak antiferromagnetic interactions along the c-axis give mainly short-range fluctuations above TN.
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| 34. |
- Syväjärvi, Mikael, et al.
(författare)
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Fluorescent SiC as a new material for white LEDs
- 2012
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Ingår i: Physica scripta. T. - 0281-1847 .- 0031-8949 .- 1402-4896. ; T148, s. 014002-
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Tidskriftsartikel (refereegranskat)abstract
- Current III–V-based white light-emitting diodes (LEDs) are available. However, their yellow phosphor converter is not efficient at high currents and includes rare-earth metals, which are becoming scarce. In this paper, we present the growth of a fluorescent silicon carbide material that is obtained by nitrogen and boron doping and that acts as a converter using a semiconductor. The luminescence is obtained at room temperature, and shows a broad luminescence band characteristic of donor-to-acceptor pair recombination. Photoluminescence intensities and carrier lifetimes reflect a sensitivity to nitrogen and boron concentrations. For an LED device, the growth needs to apply low-off-axis substrates. We show by ultra-high-resolution analytical transmission electron microscopy using aberration-corrected electrons that the growth mechanism can be stable and that there is a perfect epitaxial relation from the low-off-axis substrate and the doped layer even when there is step-bunching.
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| 35. |
- Beckman, O., et al.
(författare)
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Susceptibility Measurements and Magnetic Ordering of Hexagonal FeGe
- 1972
-
Ingår i: Physica scripta. T. - : IOP Publishing. - 0281-1847 .- 0031-8949 .- 1402-4896. ; 6:2-3, s. 151-157
-
Tidskriftsartikel (refereegranskat)abstract
- The spin structure of the metallic hexagonal B 35 phase of FeGe has been studied by means of susceptibility and magnetization measurements. Below the Neel temperature TN = 411 K hexagonal FeGe is a uniaxial antiferromagnet with the spins parallel to the c-axis. In each c-plane all spins are ferromagnetically coupled with an exchange constant J0 ≈ 22 meV. The antiferromagnetic exchange constant between nearest neighbour and next nearest neighbour c-planes are J1 = -3.5 meV and J2 = -0.9 meV resp. in the molecular field model. Susceptibility and spin flop experiments indicate that the spins tilt away from the c-axis below 30 K. We suggest that the spins then form a double cone structure with a cone halfangle of 20° at 4.2 K. In the double cone the c-plane components have a turn angle in the vicinity of 180° between nearest neighbour planes, which implies absence of long range order. The result is in good agreement with Fermi surface calculations by Sundström (Physica Scripta, following paper), which show the existence of several spin density wave vectors between Q = 0.89 π/c and Q = 1.3 π/c calipering different parts of the Fermi surface in a direction parallel to the c-axis.
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| 36. |
- Stenström, Bengt, et al.
(författare)
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Magnetoresistance of Hexagonal FeGe Single Crystals between 4.2 K and 30 K
- 1972
-
Ingår i: Physica scripta. T. - : IOP Publishing. - 0281-1847 .- 0031-8949 .- 1402-4896. ; 6:2-3, s. 164-168
-
Tidskriftsartikel (refereegranskat)abstract
- The low field transverse magnetoresistance of hexagonal FeGe has been measured for the field in the basal plane with current both parallel and perpendicular to the c-axis. At a temperature dependent critical field (Δ/0) // c shows a sharp peak, then decreases rapidly until it levels off at a second critical field. (Δ/0) ⊥ c exhibits a sharp dip at the first critical field followed by rising magnetoresistance with increasing field until the second critical field, where it levels off. The observed anomalies are related to changes in the spin structure and magnetic superzone effects. The possibilities of itinerant antiferromagnetism are also considered.
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| 37. |
- Sundström, Lorna J.
(författare)
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Fermi Surface, Electrical Resistivity and Magnetic Ordering of Antiferromagnetic Hexagonal FeGe
- 1972
-
Ingår i: Physica scripta. T. - : IOP Publishing. - 0281-1847 .- 0031-8949 .- 1402-4896. ; 6:2-3, s. 158-163
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Tidskriftsartikel (refereegranskat)abstract
- Nonrelativistic APW calculations of the electronic energy bands of hexagonal (B 35) iron monogermanide (FeGe) have recently been published [15]. The present work extends these to determine the Fermi surface, which is formed from four energy bands. Large portions of the Fermi surface will be destroyed or distorted by magnetic superzones at the onset of antiferromagnetic ordering (TN = 411 K). This is related to experimental resistivity measurements, which show a distinct anomaly at the Néel temperature. We find that "nesting" of Fermi hole and electron surfaces might give rise to a broad maximum in the generalized susceptibility around q = π/c. Further aspects of the role of the Fermi surface in magnetic ordering are briefly discussed.
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| 38. |
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| 39. |
- Johansson, Sveneric, et al.
(författare)
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The FERRUM Project: New f-value Data for Fe II and Astrophysical Applications
- 2002
-
Ingår i: Physica Scripta. - : Institute of Physics Publishing (IOPP). - 0281-1847 .- 0031-8949 .- 1402-4896. ; T100, s. 71-80
-
Konferensbidrag (refereegranskat)abstract
- We present the FERRUM Project, an international collaboration aiming at a production and evaluation of oscillator strengths (transition probabilities) of selected spectral lines of singly ionized iron group elements, that are of astrophysical relevance. The results obtained include measurements and calculations of permitted and forbidden lines of Fe II. The data have been applied to both emission and absorption lines in astrophysical spectra. We make comparisons between experimental, theoretical and astrophysical f-values. We give a general review of the various measurements, and discuss the UV8 multiplet of Fe II around 1610 Šin detail.
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| 40. |
- Bijnens, Johan, et al.
(författare)
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Eta decays at and beyond p(4) in Chiral Perturbation Theory
- 2002
-
Ingår i: PHYSICA SCRIPTA. - 0031-8949 .- 1402-4896. ; 99, s. 34-44
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Konferensbidrag (refereegranskat)abstract
- An overview is given of Chiral Perturbation Theory and various applications to eta decays. In particular. the main decay eta --> 3pi is discussed at the one-loop level, and estimates of the higher order corrections are given. The importance of p(6) and higher order effects in double Dalitz and eta --> pi(0)gammagamma decays is pointed out. In all these cases the need for new experimental results is stressed.
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| 41. |
- Grumer, Jon, et al.
(författare)
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Unexpected transitions induced by spin-dependent, hyperfine and external magnetic-field interactions
- 2014
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Ingår i: Physica Scripta. - : IOP Publishing. - 0031-8949 .- 1402-4896. ; 89:11
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Tidskriftsartikel (refereegranskat)abstract
- Unexpected transitions are induced by weaker interactions not included in the gross structure model of the ion under investigation. We discuss different examples of such decay channels, starting with relativistic spin-induced transitions. These represented an important field of study a few decades ago, and we illustrate how some challenging cases can be treated very accurately with today's computational techniques, while close degeneracy sometimes still prevents ab initio methods from obtaining accurate results. For hyperfine induced transitions we review some recent results and discuss remaining challenges for experiment and theory. Finally, we discuss the newly opened field of accurate calculations for transitions induced by an external magnetic field and point to some examples of where these are accessible for experimental tests.
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| 42. |
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| 43. |
- Broglia, Ricardo, et al.
(författare)
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Pygmy resonances: what's in a name?
- 2019
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Ingår i: Physica Scripta. - : IOP Publishing. - 0031-8949 .- 1402-4896. ; 94:11
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Tidskriftsartikel (refereegranskat)abstract
- The centroid, width and percentage of energy weighted sum rule of dipole resonances can be strongly affected by dynamical fluctuations and static deformations of the nuclear surface, deformations and fluctuations which, in turn, depend on pairing, and thus on Cooper pairs. Because of angular momentum conservation, such insight is restricted, to lowest order, to fluctuations/deformations of quadrupole and monopole type. The latter being closely connected with the neutron (excess) skin and thus with soft dipole modes. From the values (N − Z)/A ≈ 0.18, 0.21, and 0.45 for the nuclei 122Sn, 208Pb, and 11Li, it is expected that the latter system, which is weakly bound by pairing effects (spatially extended single Cooper pair and odd proton acting as spectator), constitutes an attractive laboratory to study the properties of soft E1-modes and thus of isospin nuclear deformation. From the calculation of the full dipole response function in QRPA, discretizing the continuum in a spherical box of radius of 40 fm, one finds a GDR with centroid E x ≈ 24 MeV, width Γ ≈11 MeV and carrying 90% of the EWSR, and a low-lying collective resonance characterized by E X = 0.75 MeV, Γ = 0.5 MeV and 6.2% EWSR. The wave function of the latter resonance is built out of about fifteen components (both protons and neutrons), typical of a collective mode. The transition densities indicate this soft E1-mode to be generated by surface density oscillation of the neutron (halo) skin (Δr np ≈ 1.71 fm) relative to an approximately isospin-saturated core. Through a detailed study of the full dipole response of 11Li we will draw a comparison between the soft E1-mode of this halo nucleus and the PDR of heavy stable nuclei, pointing to the physical similarities and also to the basic differences.
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| 44. |
- Ragnarsson, I.
(författare)
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How deformed are the TSD bands in odd Lu isotopes?
- 2017
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Ingår i: Physica Scripta. - : IOP Publishing. - 0031-8949 .- 1402-4896. ; 92:12
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Tidskriftsartikel (refereegranskat)abstract
- The experimental fingerprints for large deformation in the triaxial strongly deformed (TSD) bands of 163,165,167Lu are discussed. It is argued that these fingerprints are not very convincing. On the contrary, especially the fact that there exist strong interactions between the TSD bands and normal-deformed (ND) bands indicates that the deformation of the TSD bands cannot be very different from that of the ND bands. The need for detailed new experimental data is underlined.
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| 45. |
- Thomasson, Anna, et al.
(författare)
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Science facilitets and stakeholder management : How a pan-European research facility ended up in a small Swedish University town
- 2017
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Ingår i: Physica Scripta. - : IOP Publishing. - 0031-8949 .- 1402-4896. ; 92:6
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Tidskriftsartikel (refereegranskat)abstract
- This is the story of how a large research facility of broad European and global interest, the European Spallation Source (ESS), ended up in the small university town of Lund in Sweden. This happened in spite of the fact that a number of influential European countries were at one time or another competitors to host the facility. It is also a story about politics which attempts to illustrate how closely intertwined politics and science are, and how the interplay between those interests affects scientific progress. ESS became an arena for individual ambitions and political manoeuvring. The different stakeholders, in their striving to ensure that their own interests were realised, in various ways and with different degrees of success over the years, have influenced the key decisions that, during the already 30 year history of ESS, have driven the course that this project has taken. What emerges is that the interests of the stakeholders and the interests of the project itself are frequently not in harmony. This imposes challenges on the management of large research facilities as they have to not only navigate in the scientific landscape, which they often are more familiar with, but also in the political landscape. This story is therefore an attempt to shed light on the role of managers of large research facilities and the often delicate balancing act they have to perform when trying to comply with the different and often conflicting stakeholder interests. What is especially worthwhile examining, as we do in this paper, is the role that individuals, and the interaction between individuals, have played in the process. This shows that the focus of stakeholder theory on organisations, rather than the people in the organisations, needs to be redirected on to the individuals representing those organisations and their inter-relationships. At the same time it is clear that the developing field of stakeholder management theory has not emerged into the consciousness of science facility managers or their governing bodies and is far down the list of priorities of researchers who use the facilities.
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| 46. |
- Korn, Andreas, 1972-
(författare)
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NLTE line formation
- 2008
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Ingår i: Physica Scripta. - Bristol : IOP. - 0031-8949 .- 1402-4896. ; T133, s. 014009-
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Tidskriftsartikel (refereegranskat)abstract
- I review some of the present achievements and future challenges of non-local thermodynamicequilibrium (NLTE) line-formation calculations for solar-type stars. It is concluded that thefull potential of NLTE still remains to be tapped, in particular in view of the current transitionfrom one-dimensional (1D) hydrostatic to 3D hydrodynamic model atmospheres.
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| 47. |
- Borodkina, I., et al.
(författare)
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Intra-ELM tungsten sputtering in JET ITER-like wall : analytical studies of Be impurity and ELM type influence
- 2017
-
Ingår i: Physica Scripta. - : IOP PUBLISHING LTD. - 0031-8949 .- 1402-4896. ; T170
-
Tidskriftsartikel (refereegranskat)abstract
- The W source strength in JET H-mode discharges depends on the W sputtering in the inter and the intra-ELM phase due to impinging hydrogenic ions (D or H) and impurities (mainly Be). The analytical approach for interpretation of the Langmuir probe measurements is applied to model the ELM ion parallel transport and the W sputtering flux in intra-ELM and inter-ELM conditions in JET-ITER-like wall (ILW) hydrogen and deuterium plasmas. The impact of the Be ion charge and the Be concentration in the impinging ion flux on the W sputtering was estimated. Be2+ concentrations of 0.5% and 1% in the impinging ion flux increases the W sputtering fluence per ELM by 20%-30% and 35%-55% correspondingly with respect to pure deuterium plasma; the charge state of Be ions has no substantial effect on W sputtering in the intra-ELM phase. The analysis of JET ELMy H-mode discharges in hydrogen with different types of ELMs is presented. The W sputtering source under inter-and intra-ELM conditions is estimated using the analytical approach and validated by optical emission spectroscopy in these discharges. The intra-ELM W sputtering flux increases 2-4 times in comparison to the inter-ELM flux.
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| 48. |
- Catarino, N., et al.
(författare)
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Time-resolved deposition in the remote region of the JET-ILW divertor : measurements and modelling
- 2017
-
Ingår i: Physica Scripta. - : IOP PUBLISHING LTD. - 0031-8949 .- 1402-4896. ; T170
-
Tidskriftsartikel (refereegranskat)abstract
- One crucial requirement for the development of fusion power is to know where, and how much, impurities collect in the machine, and how much of the fuelling isotope tritium will be trapped therein. The most relevant information on this issue comes from the operation of the Joint European Tokamak (JET), which is the world's largest operating tokamak and has the same interior plasma-facing materials as the next step machine, ITER. Much of the information gained so far has been from post-mortem analysis of samples collected after whole campaigns involving varied types of operation. This paper describes time-resolved measurements of the deposition rate using rotating collectors (RC) placed in remote areas of the JET divertor during the 2013-2014 campaign with the ITER-like Wall (ILW). These techniques allow the effects of different types of operation to be distinguished. Rotating collectors made of silicon discs housed behind an aperture are exposed to the plasma. Each time the magnetic field coils are ramped up for a discharge the disc rotates, providing a linear relationship between the exposed region and the discharge number. Post-mortem ion beam analyses provide information on the deposit composition as a function of the discharge number. The results show that the Be deposition average for the RC in the corners of the inner and outer divertor are 4.9 x 10(16) cm(-2) and 1.8 x 10(17) cm(-2), respectively, accumulated over an average of similar to 25 pulses. Data from the rotating collector below Tile 5 in the central region of divertor indicate a Be deposition rate of 9.3 x 10(15) cm(-2), per similar to 25 pulses.
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| 49. |
- Coenen, J. W., et al.
(författare)
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Transient induced tungsten melting at the Joint European Torus (JET)
- 2017
-
Ingår i: Physica Scripta. - : IOP PUBLISHING LTD. - 0031-8949 .- 1402-4896. ; T170
-
Tidskriftsartikel (refereegranskat)abstract
- Melting is one of the major risks associated with tungsten (W) plasma-facing components (PFCs) in tokamaks like JET or ITER. These components are designed such that leading edges and hence excessive plasma heat loads deposited at near normal incidence are avoided. Due to the high stored energies in ITER discharges, shallow surface melting can occur under insufficiently mitigated plasma disruption and so-called edge localised modes-power load transients. A dedicated program was carried out at the JET to study the physics and consequences of W transient melting. Following initial exposures in 2013 (ILW-1) of a W-lamella with leading edge, new experiments have been performed on a sloped surface (15 degrees slope) during the 2015/2016 (ILW-3) campaign. This new experiment allows significantly improved infrared thermography measurements and thus resolved important issue of power loading in the context of the previous leading edge exposures. The new lamella was monitored by local diagnostics: spectroscopy, thermography and high-resolution photography in between discharges. No impact on the main plasma was observed despite a strong increase of the local W source consistent with evaporation. In contrast to the earlier exposure, no droplet emission was observed from the sloped surface. Topological modifications resulting from the melting are clearly visible between discharges on the photographic images. Melt damage can be clearly linked to the infrared measurements: the emissivity drops in zones where melting occurs. In comparison with the previous leading edge experiment, no runaway melt motion is observed, consistent with the hypothesis that the escape of thermionic electrons emitted from the melt zone is largely suppressed in this geometry, where the magnetic field intersects the surface at lower angles than in the case of perpendicular impact on a leading edge. Utilising both exposures allows us to further test the model of the forces driving melt motion that successfully reproduced the findings from the original leading edge exposure. Since the ILW-1 experiments, the exposed misaligned lamella has now been retrieved from the JET machine and post mortem analysis has been performed. No obvious mass loss is observed. Profilometry of the ILW-1 lamella shows the structure of the melt damage which is in line with the modell predictions thus allowing further model validation. Nuclear reaction analysis shows a tenfold reduction in surface deuterium concentration in the molten surface in comparison to the non-molten part of the lamella.
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| 50. |
- Drenik, A., et al.
(författare)
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Evaluation of the plasma hydrogen isotope content by residual gas analysis at JET and AUG
- 2017
-
Ingår i: Physica Scripta. - : IOP PUBLISHING LTD. - 0031-8949 .- 1402-4896. ; T170
-
Tidskriftsartikel (refereegranskat)abstract
- The isotope content of the plasma reflects on the dynamics of isotope changeover experiments, efficiency of wall conditioning and the performance of a fusion device in the active phase of operation. The assessment of the isotope ratio of hydrogen and methane molecules is used as a novel method of assessing the plasma isotope ratios at JET and ASDEX-Upgrade (AUG). The isotope ratios of both molecules in general shows similar trends as the isotope ratio detected by other diagnostics. At JET, the absolute values of RGA signals are in relatively good agreement with each other and with spectroscopy data, while at AUG the deviation from neutral particle analyser data are larger, and the results show a consistent spatial distribution of the isotope ratio. It is further shown that the isotope ratio of the hydrogen molecule can be used to study the degree of dissociation of the injected gas during changeover experiments.
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