| 1. |
- Abel, I, et al.
(author)
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Overview of the JET results with the ITER-like wall
- 2013
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In: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 53:10, s. 104002-
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Journal article (peer-reviewed)abstract
- Following the completion in May 2011 of the shutdown for the installation of the beryllium wall and the tungsten divertor, the first set of JET campaigns have addressed the investigation of the retention properties and the development of operational scenarios with the new plasma-facing materials. The large reduction in the carbon content (more than a factor ten) led to a much lower Z(eff) (1.2-1.4) during L- and H-mode plasmas, and radiation during the burn-through phase of the plasma initiation with the consequence that breakdown failures are almost absent. Gas balance experiments have shown that the fuel retention rate with the new wall is substantially reduced with respect to the C wall. The re-establishment of the baseline H-mode and hybrid scenarios compatible with the new wall has required an optimization of the control of metallic impurity sources and heat loads. Stable type-I ELMy H-mode regimes with H-98,H-y2 close to 1 and beta(N) similar to 1.6 have been achieved using gas injection. ELM frequency is a key factor for the control of the metallic impurity accumulation. Pedestal temperatures tend to be lower with the new wall, leading to reduced confinement, but nitrogen seeding restores high pedestal temperatures and confinement. Compared with the carbon wall, major disruptions with the new wall show a lower radiated power and a slower current quench. The higher heat loads on Be wall plasma-facing components due to lower radiation made the routine use of massive gas injection for disruption mitigation essential.
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| 2. |
- Álvarez Ruiz, Jesús, et al.
(author)
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Neutral dissociation of superexcited states in carbon monoxide
- 2002
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In: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 35:13, s. 2975-2983
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Journal article (peer-reviewed)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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| 3. |
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| 4. |
- García, Emilio Melero, et al.
(author)
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Neutral dissociation of superexcited states in nitric oxide
- 2003
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In: Chemical Physics. - 0301-0104 .- 1873-4421. ; 293:1, s. 65-73
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Journal article (peer-reviewed)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. |
- Jakubowska, Katarzyna, et al.
(author)
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Lyman and Balmer emission following core excitations in methane and ammonia molecules
- 2007
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In: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 40:8, s. 1489-1500
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Journal article (peer-reviewed)abstract
- The intensities of hydrogen Lyman-alpha and Balmer series emission lines as a result of photoexcitation of free CH4 and NH3 molecules at the C 1s and N 1s edges have been measured. For methane, the total fluorescence yield in the visible region ( 300 - 650 nm) was also recorded. Excitation functions of the Balmer lines show relative intensity enhancement of Balmer-beta emission in comparison with Balmer-alpha at higher core- to- Rydberg excitations. The Lyman-alpha emission intensity, in general, follows the relations observed in the corresponding total ion yield measurements. Additionally, the Balmer-gamma and -delta yields were measured for ammonia molecules and they show intensity maxima at photon energies shifted closer to the N 1s threshold than Balmer-alpha and -beta. A quantum defect analysis is performed to find out which core excitations are responsible for this enhanced intensity. Dissociation pathways leading to the emission in H atoms are discussed.
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| 6. |
- Kivimäki, Antti, et al.
(author)
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An energy resolved electron-ion coincidence study near the S 2p thresholds of the SF6 molecule
- 2003
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In: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 36:4, s. 781-791
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Journal article (peer-reviewed)abstract
- The fragmentation dynamics of the SF6 molecule following the excitations of S 2p electrons into unoccupied molecular orbitals has been studied using the energy-resolved electron-ion coincidence technique. Fragmentation patterns were found to depend on the particular excitation and on the electronic state of the molecular ion. The spectator resonant Auger decay at the 2p --> 6a(1g) resonance induces changes in the ion distributions as compared to direct photoionization. Furthermore, coincidence spectra related to the same Auger structure display different ion abundances at the 2t(2g) and 4e(g) shape resonances. Differences were also found in the Auger decay spectra. These findings give further support for the previously suggested many-electron character of the 4e(g) shape resonance.
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| 7. |
- Rius Riu, Jaime, et al.
(author)
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Core-excitation-induced dissociation in CD4 after participator Auger decay
- 2003
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In: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 68:2
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Journal article (peer-reviewed)abstract
- The fragmentation of the CD4 molecule after selective ionization of the 1t(2) and 2a(1) electrons with photons from 70 to 290 eV has been studied with the energy-resolved electron-ion coincidence technique. The mass spectra acquired in coincidence with 1t(2) electrons reveal CD4+, CD3+, and CD2+ fragments, depending on the excitation energy used. The production of CD3+ is strongly enhanced after C 1s excitation to different core excited states, with respect to the production observed after direct ionization of the 1t(2) orbital. This enhancement is correlated with the changes of the molecular geometry when it relaxes from the core-excited state.
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| 8. |
- Ruiz, Jesus Alvarez, et al.
(author)
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VUV photon induced fluorescence study of SF5CF3
- 2006
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In: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 8:44, s. 5199-5206
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Journal article (peer-reviewed)abstract
- The interaction of SF5CF3 with vacuum-UV radiation has been investigated by photon induced fluorescence spectroscopy. Total fluorescence yield and dispersed fluorescence spectra of SF5CF3 were recorded in the 200-1000 nm fluorescence window. In all cases, the fluorescence spectra resemble those of CF3X (X H, F, Cl, and Br) molecules. At photon energies below 20 eV, the emission is attributed to the excited CF3 and CF2 fragments. The threshold for the CF3 emission is 10.2 +/- 0.2 eV, giving an upper limit estimate for the SF5-CF3 bond dissociation energy of 3.9 +/- 0.3 eV. The excitation functions of the CF3 and CF2 emissions were measured in the photon energy range 13.6-27.0 eV. The resonant structures observed in SF5CF3 are attributed to electronic transitions from valence to Rydberg orbitals, following similar assignments in CF3X molecules. The photoabsorption spectrum of SF5CF3 shows features at the same energies, indicating a strong contribution from Rydberg excitations.
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| 9. |
- Stankiewicz, Marek, et al.
(author)
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Experimental station for gas phase fluorescence spectroscopy
- 2004
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In: Review of Scientific Instruments. - : AIP Publishing. - 0034-6748 .- 1089-7623. ; 75:7, s. 2402-2408
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Journal article (peer-reviewed)abstract
- The details of an experimental setup for gas phase atomic and molecular fluorescence measurements using synchrotron radiation are described in this article. The most significant part of the apparatus is an optical arrangement, which allows for simultaneous measurements of dispersed as well as total fluorescence intensity using an effusive gas jet and an inbuilt gas cell assembled in a convenient plug and measure configuration. The first measurements concerning fluorescence of the N-2 molecule around the N 1s edge obtained with this setup are presented.
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| 10. |
- Vall-llosera, Gemma, et al.
(author)
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Photofragmentation of 2-deoxy-D-ribose molecules in the gas phase
- 2008
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In: ChemPhysChem. - : Wiley. - 1439-4235 .- 1439-7641. ; 9:7, s. 1020-1029
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Journal article (peer-reviewed)abstract
- We have measured the synchrotron-induced photofragmentation of isolated 2-deoxy-D-ribose molecules (C5H10O4) at four photon energies, namely, 23.0, 15.7, 14.6, and 13.8 eV At all photon energies above the molecule's ionization threshold, we observe the formation of a large variety of molecular cation fragments, including CH3+, OH+, H3O+, C2H3+, C2H4+, CHxO+ (x=1,2,3), C2HxO+ (x=1-5), C3HxO+ (x=3-5), C2H4O2+, C3HxO2+ (x=1,2,4-6), C4H5O2+, C4HxO3+ (x=6,7), C5H7O3+, and C5H8O3+. The formation of these fragments shows a strong propensity of the DNA sugar to dissociate upon absorption of vacuum ultraviolet photons. The yields of particular fragments at various excitation photon energies in the range between 10 and 28 eV are also measured and their appearance thresholds determined. At all photon energies, the most intense relative yield is recorded for the m/q = 57 fragment (C3H5O+), whereas a general intensity decrease is observed for all other fragments- relative to the m/q=57 fragment-with decreasing excitation energy. Thus, bond cleavage depends on the photon energy deposited in the molecule. All fragments up to m/q=75 are observed at all photon energies above their respective threshold values. Most notably, several fragmentation products, for example, CH3+, H3O+, C2H4+, CH3O+, and C2H5O+, involve significant bond rearrangements and nuclear motion during the dissociation time. Multibond fragmentation of the sugar moiety in the sugar-phosphate backbone of DNA results in complex strand lesions and, most likely, in subsequent reactions of the neutral or charged fragments with the surrounding DNA molecules.
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