| 1. |
- Álvarez Ruiz, Jesús, et al.
(författare)
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Neutral dissociation of superexcited states in carbon monoxide
- 2002
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Ingår i: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 35:13, s. 2975-2983
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Tidskriftsartikel (refereegranskat)abstract
- Neutral photodissociation of CO has been investigated using synchrotron light in the range 19-26 eV by observing dispersed fluorescence from excited neutral C atoms. Follow-up ab initio calculations support the observed neutral carbon excitation functions, which to a large extent are associated with the CO Rydberg - series converging to the CO+ C and D states.
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| 2. |
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| 3. |
- Erman, P., et al.
(författare)
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Non Franck-Condon effects in photoionization of molecular oxygen
- 2000
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Ingår i: Physica scripta. T. - 0281-1847. ; 62:4, s. 294-300
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Tidskriftsartikel (refereegranskat)abstract
- We present a theoretical and experimental analysis of non Franck-Condon effects in photoionization to the b (4)Sigma(g)(-), state of O-2(+). Experimentally, by dispersing the synchrotron radiation induced O-2(+) b (4)Sigma(g)(-) a (IIu)-I-4 fluorescence we derive the b (4)Sigma(g)(-), State vibrational branching ratios in the excitation energy range 21-34 eV. The vibrational branching ratios reveal features in the region 21-28 eV indicating strong non Franck-Condon effects. The experimental results have been analysed by computing ab initio the vibrational population branching ratios using a many-body perturbation method. Additionally the autoionizing neutral states existing in this energy region have been studied. We have computed the energies of the valence states up to an energy of 30 eV their transition moments for excitations from the ground state, and autoionization rates. Our calculations show, that strong non Franck-Condon effects recorded in the branching ratio spectrum (below 25 eV) are actually caused by the narrow 3 sigma(g) --> sigma(u) shape resonance, and its coupling to the 1 pi(u) --> pi(g) channel.
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| 4. |
- García, Emilio Melero, et al.
(författare)
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Neutral dissociation of superexcited states in nitric oxide
- 2003
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Ingår i: Chemical Physics. - 0301-0104 .- 1873-4421. ; 293:1, s. 65-73
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Tidskriftsartikel (refereegranskat)abstract
- Near-infrared dispersed fluorescence measurements of 13 different atomic multiplets of neutral atomic fragments from photon induced neutral dissociation processes in NO are reported. For excitation of the molecules narrow band synchrotron photons of energy 17.2-25.8 eV were used. Neither Rydberg series nor other molecular states in NO known so far can account for the collected data. From ab initio calculations we try to obtain more information regarding the NO precursor states, and the mechanism behind the observed neutral dissociation.
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| 5. |
- Hedqvist, Anders, et al.
(författare)
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Contributions of thermal charge exchange excitation to the Rydberg series of Cl16
- 2000
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Ingår i: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 33:3, s. 375-382
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Tidskriftsartikel (refereegranskat)abstract
- Spectra from the Rydberg series 1s-np for the principal quantum numbers n greater than or equal to 8 of Cl16+ are observed on the JET tokamak. Individual lines up to n = 15 are resolved. The line intensity of n = 10 is enhanced, relative to the underlying 1/n(3) scaling, due to charge exchange collisions with neutral deuterium in the ground state. The observations are compared with predictions based on available partial charge exchange cross section data. There is generally good agreement, however, some details of the predicted n-shell distribution are different from those observed in the experiment.
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| 6. |
- Horvath, Akos, et al.
(författare)
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Nuclear power in the 21st century : Challenges and possibilities
- 2016
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Ingår i: Ambio. - : Springer. - 0044-7447 .- 1654-7209. ; 45:Suppl. 1, s. 38-49
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Forskningsöversikt (refereegranskat)abstract
- The current situation and possible future developments for nuclear power—including fission and fusion processes—is presented. The fission nuclear power continues to be an essential part of the low-carbon electricity generation in the world for decades to come.There are breakthrough possibilities in the development of new generation nuclear reactors where the life-time of the nuclear waste can be reduced to some hundreds of years instead of the present time-scales of hundred thousand of years. Research on the fourth generation reactors is needed for the realisation of this development. For the fast nuclear reactors, a substantial research and development effort is required in many fields—from material sciences to safety demonstration—to attain the envisaged goals. Fusion provides a long-term vision for an efficient energy production. The fusion option for a nuclear reactor for efficient production of electricity has been set out in a focussed European programme including the international project of ITER after which a fusion electricity DEMO reactor is envisaged.
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| 7. |
- Jakubowska, Katarzyna
(författare)
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Development of visible spectroscopic techniques for applications in plasma diagnostics
- 2006
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis visible spectroscopy is developed and used for two applications. Studies of motional Stark effect spectra for diagnosing the current distribution in the fusion plasmas with two different spectroscopic diagnostic systems: ratiometry and interferometry. Both systems provide non-invasive method for diagnosis of the internal plasma properties, e.g. magnetic field. Pitch angle of magnetic field lines are obtained from polarisation of Stark split Hα spectral lines emitted by energetic hydrogen atoms injected into the plasma volume by neutral beam. Several methods of calibration of the systems on TEXTOR and JET are discussed. The main result of this work is the first measurement of the safety factor radial profile with new ratiometric MSE system on TEXTOR. Studies of molecular fragmentation of free molecules CH4 and NH3 excited with synchrotron radiation by detection of the fluorescence from the fragments. The results give the decay path ways for the molecules when excited below the N and C ionisation edges.
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| 8. |
- Karawajczyk, A., et al.
(författare)
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Neutral fragmentation of superexcited oxygen molecules
- 2000
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 61:3, s. art. no.-32718
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Tidskriftsartikel (refereegranskat)abstract
- The mechanisms of neutral dissociation of oxygen molecules in the excitation energy range 15-25 eV have been studied in a dispersed fluorescence experiment. By detecting the fluorescence from excited oxygen atoms, we find that neutral superexcited O-2 states below 20 eV dissociate into O(g.s.) + O(3s,3p). At higher excitation energies (h nu = 20-25 eV) the curve-crossing interactions following excitations to members of the Rydberg c (4)Sigma(u)(-) series also yield atoms in Rydberg states (nl,n greater than or equal to 4). The experimental data are analyzed on the ground of many-body perturbation theory, calculations which indicate the structure of the predissociating states converging to the experimentally observed ones.
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| 9. |
- Kuldkepp, Mattias, 1976-
(författare)
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Diagnostics for advanced fusion plasma scenarios
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Over the past decade, fusion research has showed the potential of being a main candidate for energy production for future generations. Further advances in improved fusion performance are therefore vital. This thesis focuses on advanced fusion plasma scenarios and their diagnostic requirements. In particular the design of a motional Stark effect (MSE) diagnostic at the MAST spherical tokamak and the analysis of magneto-hydrodynamic mode feedback control and pulsed poloidal current drive (PPCD) at the reversed field pinch (RFP) experiment EXTRAP T2R are discussed. The MSE diagnostic is important for the determination of the plasma current profile, information that is necessary for studies in advanced confinement scenarios like reversed shear profiles or current holes. The MAST MSE system has two channels and selects the spectral components using 1Å FWHM interference filters. The diagnostic has been commissioned during the fall of 2006 and the results show the feasibility of the technique with rms-noise ~0.5° using a time resolution of 1 ms. Investigations of mirror labyrinths for the future ITER MSE diagnostic highlight the need for careful calibration considerations. Feedback control and PPCD are techniques for improved confinement. Feedback control dramatically decreases impurity influx at the end of discharges while transport in the bulk plasma is largely unaffected. During PPCD the transport is seen to decrease and it is demonstrated that PPCD and feedback control can be employed simultaneously. New and innovative techniques for fusion spectroscopy are furthermore described. This includes the use of correlations in line integrated signals to determine ion emission profiles in poloidally symmetric environments. Good agreement with other diagnostic methods is obtained. The assessment of electron temperature profiles using measured differences between Thomson scattering and vacuum ultra-violet spectroscopy is also shown.
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| 10. |
- Melero Garcia, Emilio, 1978-
(författare)
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Synchrotron radiation spectroscopy of molecular dynamics beyond the valence shell
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis presents experimental results on molecular spectroscopy of gas phase molecules using synchrotron radiation. It deals mainly with dynamical processes following resonant excitation of electrons from core and inner-valence shells of the following systems H2O, H2, SF6 and CD4. In order to reach these deep electrons and excite them photons in the energy range from 25 to 550 eV were used, depending on the particular system. Two experimental techniques are used. Photon induced fluorescence spectroscopy is used to study the fluorescence emission of fragments after the decay of resonant coreexcited states for the water molecule, and after doubly excited states and resonant excitations of inner-shell electrons for H2 and SF6 respectively. Only the emission in the visible and near infrared range (300-900nm) and the Lyman-α transitions are measured. Energy resolved electron-ion coincidence is used for the study of the fragmentation of CD4 and SF6 after selective ionisation of one of the outer-valence orbitals. In the case of CD4 the fragmentation is compared for the cases in which the ionisation is done directly, or through participator Auger decay of different resonantly core-excited states.
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| 11. |
- Menmuir, Sheena, 1979-
(författare)
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Visible spectroscopic diagnostics : application and development in fusion plasmas
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Diagnostic measurements play a vital role in experiments. Without them we would be in the dark with no way of knowing what was happening; of understanding the processes and behaviour occurring; or even of judging the success or failure of our experiments. The development of fusion plasma devices is no different. In this thesis we concentrate on visible spectroscopy based diagnostics: examining the techniques for measurement and analysis; the breadth of plasma parameters that can be extracted from the spectroscopic data; and how the application of these diagnostic techniques gives us a broader picture of the plasma and the events taking place within. Techniques are developed and applied to plasmas in three fusion experiments, EXTRAP T2R, ASDEX Upgrade and JET. The diagnostic techniques exploit different features of the measurements of the emitted photons to obtain various useful plasma parameters. Determination of the ion temperature and rotation velocity of oxygen impurity ions in the EXTRAP T2R plasma is achieved through measurement and analysis of, respectively, the Doppler broadening and the Doppler wavelength shift of visible wavelength atomic spectral lines. The evolution of the temperature and rotation is studied as a function of the discharge parameters, in particular looking at the effect of applying active feedback control schemes to the resistive wall modes and/or pulsed poloidal current drive. Measurements of multiple ionisation stages are used to estimate radial profiles of the toroidal rotation and the ion temperature and correlations between the ion rotations and the rotation velocities of tearing modes are also established. Radial profiles of the emissivity and density (or concentration) of the oxygen ions are obtained by means of measurements of the spectral line intensities on a small array of linesof- sight through the plasma. Changes to the profiles for different plasma schemes and the implications for particle transport are investigated. The derived emissivity profiles are used in the analysis for some of the other spectroscopic diagnostics. Spectral line intensity measurements (in this case of neutral ions) are also the basis for calculations of both the electron temperature and the particle fluxes at the plasma edge. The latter is an indicator of the degree and type of interaction between the plasma and the surrounding surfaces. Particle fluxes of the operating gas hydrogen and of chromium and molybdenum impurities are investigated in EXTRAP T2R for different operating scenarios, in particular changes in the metallic influx with the application of active feedback mode control are examined along with the correspondence between spectroscopic and collector probe results. In the ASDEX Upgrade divertor estimates of the particle flux of the deuterium operating gas are also made through analysis of spectral intensities. Molecular D2 band structure is explored in addition to the Balmer Dα spectral line intensity to acquire both atomic and molecular particle fluxes, investigate the contribution of the dissociating D2 to the Dα line and study the effect of changes in the divertor. Analysis of the D2 molecular band structure (the relative intensities of the rotational lines and vibrational bands) also enables calculation of the upper state rotational and ground state vibrational temperatures. The locations of emitting atomic ions in JET are estimated from Zeeman splitting analysis of the structure of their spectral lines. The measurement and analysis of visible wavelength light is demonstrated to be a sensitive diagnostic tool in the quest for increased knowledge about fusion plasmas and their operating scenarios.
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| 12. |
- Menmuir, Sheena
(författare)
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Visible spectroscopy as a sensitive diagnostic tool for fusion plasmas
- 2005
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- To further the understanding and knowledge about fusion plasmas and their behaviour during different conditions, it is important to be able to collect information about the plasma and the processes occurring within it. Visible spectroscopy, or the study of the visible wavelength light emitted by the plasma, is a useful tool in this search for knowledge. This thesis is based on experiments where visible wavelength light has been measured and analysed in order to determine quantities about the emitting source. Doppler shift measurements of spectral lines have been utilised to determine the toroidal rotation velocities of plasma impurity ions and to study the correlation with mode rotation and the effect of active feedback control of the resistive wall modes. Information on the impurities present in the plasma has been determined and the calibrated intensities of spectral lines has yielded impurity concentrations, particle fluxes and electron temperature and densities. Ion temperatures have been determined from Doppler broadening measurements. The measured vibrational and rotational band structure of deuterium molecular spectra has been analysed in order to calculate rotational and vibrational temperatures, relative populations and molecular particle fluxes. The effect of the molecular flux on simple calculations of atomic flux has also been studied. Specific molecular states and transitions of deuterium have also been probed with synchrotron radiation to study the level and transition energies. The measurement and analysis of visible wavelength light has been demonstrated to be a sensitive diagnostic tool in the quest for increased knowledge about fusion plasmas and molecular structure.
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| 13. |
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| 14. |
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| 15. |
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| 16. |
- Rachlew (Källne), Elisabeth, 1944-
(författare)
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An elegant method to estimate helium-like ion densities from visible and VUV plasma spectroscopy
- 1993
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Ingår i: Plasma Physics and Controlled Fusion. - IOP. - 0741-3335 .- 1361-6587. ; 35, s. 1553-1561
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Tidskriftsartikel (refereegranskat)abstract
- A method is presented to estimate the densities of He-like carbon and oxygen ionsfrom the observation of the Li-like 3p + 3s transitions inthe visible and the 3p + 2s transitionsin the vacuum ulbaviolet The method is based on a zerodimensional model for plasmas withshort particle confinement times. General coefficients for this study are derived and evaluatednumerically. The method is applied to Extrap-T1 reversed field pinch data
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| 17. |
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| 18. |
- Rachlew (Källne), Elisabeth, 1944-
(författare)
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Argon 3s autoionization
- 1994
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Ingår i: J de physique IV. ; , s. C9-401-C9-404
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Konferensbidrag (refereegranskat)
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| 19. |
- Rachlew (Källne), Elisabeth, 1944-
(författare)
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Autoionization widths of the NO Rydberg-valence state complex in the 11-12 eV region
- 1995
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Ingår i: Chemical Physics Letters. - Elsevier. - 0009-2614 .- 1873-4448. ; 239, s. 6-10
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Tidskriftsartikel (refereegranskat)abstract
- The photoion excitation spectra of 14NO and 15NO have been studied in the 105-112 nm excitation region usinghigh-order harmonic laser spectroscopy. Utilizing the small bandwidth offered by this technique, the natural widths ofprominent lines in this region have been measured. These lines originate from interactions between high-lying Rydberglevels converging to the NO + electronic ground state and a 'new' NO valence state situated close to the latter state. Thepresent measurements show broad resonances corresponding to a decay time of 20-50 fs. This supports the interpretationthat the decay takes place via rapid electronic autoionization.
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| 20. |
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| 21. |
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| 22. |
- Rachlew (Källne), Elisabeth, 1944-
(författare)
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Deduction of central plasma parameters from line‐of‐sight averaged spectroscopic observations
- 1991
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Ingår i: Journal of Applied Physics. - AIP. - 0021-8979 .- 1089-7550. ; 70, s. 6732-
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Tidskriftsartikel (refereegranskat)abstract
- A method is presented to deduce central ion temperature and toroidal rotation velocity fromline-of-sight averaged x-ray spectra from hot plasmas. The analysis is based on atomicdata for the processes that give rise to x-ray spectral lines. Combined with measured electrontemperature and density profiles a synthetic spectrum is calculated. The fit of thissynthetic spectrum to the observed one gives a new level of accuracy to line-of-sight integratedobservations in a considerably extended range of ion temperatures and toroidal rotationvelocities. The choice of model for radial profiles for ion temperature and toroidal rotationvelocity is shown not to be critical. The concentration of the emitting impurity isdeduced from the total line intensity, making use of the absolute calibration of the detectorsensitivity. The effective plasma charge ZeE is derived from the absolute level of thecontinuum radiation. These measurements are based on atomic data for x-ray line andcontinuum radiation and measured electron temperature and density profiles. The results forion temperature and toroidal rotation velocity obtained by this analysis are comparedwith those from visible charge exchange spectroscopy. The observed visible lines are shiftedin wavelength, and their width is reduced, due to the velocity dependence of the crosssection for the charge transfer from the neutral beam particles to the observed impurities. Thetheoretically predicted magnitude of these effects is verified. When the results fromvisible charge exchange spectroscopy are corrected for the cross-section effects, excellentagreement of central ion temperature and rotation velocity with the results of this new analysis is obtained
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| 23. |
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| 24. |
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| 25. |
- Rachlew (Källne), Elisabeth, 1944-
(författare)
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Double-crystal spectroscopy at JET
- 1991
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Ingår i: Rev. Sci. Instrum.. ; 62:4, s. 889-898
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Tidskriftsartikel (refereegranskat)
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| 26. |
- Rachlew (Källne), Elisabeth, 1944-
(författare)
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Double ionisation of noble gases.II Formation by photon impact.
- 1976
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - AIP. - 1050-2947 .- 1094-1622. ; 13, s. 1748-1755
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Tidskriftsartikel (refereegranskat)abstract
- Using synchrotron radiation and a new two-grating monochromator to remove higher-order components, the relative intensities of double-photoionization transitions have been measured in helium, neon, and argon between 70 and 200 eV by ion spectrometry. Extensive tests of a new ion spectrometer were undertaken to eliminate any charge discrimination for the ions. These new results resolve discrepancies existing between previous experimental data and favor, in general, the earliest results ofCarlson for photon energies higher than 100 eV. For helium and neon they are in good qualitative agreementwith theoretical calculations that include electron-electron correlations. In particular they agree very well withthe many-body perturbation-theory approach of Chang and Poe in the case of neon.
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| 27. |
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| 28. |
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| 29. |
- Rachlew (Källne), Elisabeth, 1944-
(författare)
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Energy confinement in JET ohmically heated plasmas
- 1988
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Ingår i: Nuclear Fusion. - IOP. - 0029-5515 .- 1741-4326. ; 28, s. 73-
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Tidskriftsartikel (refereegranskat)abstract
- The energy confinement properties of ohmically heated JET discharges are discussed in detail, from both a local and a global point of view. Also, the plasma resistivity and poloidal field diffusion are discussed in some detail.
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| 30. |
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| 31. |
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| 32. |
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| 33. |
- Rachlew (Källne), Elisabeth, 1944-
(författare)
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From X-Rays To Visible Photons : What Do We Learn From The Plasma Observations?
- 2012
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Ingår i: AIP Conference Proceedings. - : American Institute of Physics (AIP). - 0094-243X .- 1551-7616. ; 1438:67, s. 67-72
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Tidskriftsartikel (refereegranskat)abstract
- Photon spectroscopy from plasmas has proven to give new insights into the dynamics of the hot plasmas through multifaceted observations using absolute intensity and wavelength measurements.The spectroscopy observations have given a multitude of comparisons of theoretical modeling with experimental observations. Doppler, Zeeman and Stark effects have proven to be important ingredients in the observed spectra from the visible to the x-ray region.PACS: 32.60.+i, 32.30.Jc, 32.30.Rj, 33.70.Jg, 34.50.Fa, 34.70.+e, 95.30.Dr, 07.60.Rd, 07.85.-m
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| 34. |
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| 35. |
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| 36. |
- Rachlew (Källne), Elisabeth, 1944-
(författare)
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High power heating results on JT-60
- 1988
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Ingår i: Plasma phys Control Fusion. ; 30:11, s. 1405-1416
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Tidskriftsartikel (refereegranskat)
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| 37. |
- Rachlew (Källne), Elisabeth, 1944-
(författare)
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IMPURITY AND RADIATION STUDIES DURING THE JET OHMIC HEATING PHASE
- 1986
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Ingår i: Nuclear Fusion. - 0029-5515 .- 1741-4326. ; 26, s. 751-768
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Tidskriftsartikel (refereegranskat)abstract
- During the Ohmic Heating Phase of JET operation (June 1983 - September 1984), impurities in the plasma have been studied by visible and VUV spectroscopy, and from bolometer and soft X-ray signals.The measurements provide information on impurity influxes and impurity densities in the plasma. Plasmadimensions and parameters were a =1.1 m, b= 1.3-1.5 m, R = 3m, lp<3.7MA, ne < 3.3 X 1019m"3. -Oxygen, carbon, wall material (Ni, Cr, Fe), molybdenum and chlorine have been identified as the main impuritiesin the plasma. The metal impurities came mainly from the carbon limiter surfaces, where they had been depositedduring operation and cleaning procedures. The metal densities increased with plasma current and decreased withelectron density, while light impurities depended more on the state of the vacuum vessel and size and elongationof the plasma. There is a consistent anti-correlation of light impurities and metals. - There were two maincampaigns to clean the plasma: a period of 12 000 PDC pulses and repetitive carbonization of the vessel walls. Inthe first case, some reduction of oxygen and chlorine was noted, and the molybdenum fraction in the plasmadecreased. However, at densities of 2 X 1019 m~3, the radiated power was still about 80% of the Ohmic inputpower, and Zeff was about 4.5. Carbonization reduced the metal content by about a factor of five, and oxygenand chlorine decreased gradually. Thus the radiated power was as low as 40% P n . High electron densities(~ 3 X 1019m"3) led to higher radiated power (80% P n , hollow radiation profiles), but reduced Zeff to values belowthree. The impurity levels of high density pulses after carbonization were as low as 2.5% C, 1% O, 0.05% Cl and 0.01 5% metals, resulting in Ze f f« 2.6 and a fraction of deuterons of about 75%.
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| 38. |
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| 39. |
- Rachlew (Källne), Elisabeth, 1944-
(författare)
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Impurity fluxes and concentrations in the ISX-B beryllium limiter experiment
- 1985
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Ingår i: Nuclear Fusion. - : Institute of Physics (IOP). - 0029-5515 .- 1741-4326. ; 25, s. 1635-1655
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Tidskriftsartikel (refereegranskat)abstract
- An experiment to test beryllium as a limiter material has been performed in the ISX-B tokamak. One facet of the studies centred on characterizing impurity influxes and concentrations. The radiation from both low-Z (Be, C, N, O) and intermediate-Z (Ti, Cr) contaminants was measured at the limiter surface and at a wall location 90° away from the limiter to assess the relative contributions of metallic impurities from the two different sources. The effect of limiter melting, with concomitant reduction of both low-Z and intermediate-Z elements, was also documented. The analysis, including atomic rate coefficients, for interpreting spectral radiation in terms of production rates is discussed in detail.
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| 40. |
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| 41. |
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| 42. |
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| 43. |
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