| 1. |
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Overview of the JET results
- 2015
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 55:10
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Tidskriftsartikel (refereegranskat)
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| 2. |
- Abel, I, et al.
(författare)
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Overview of the JET results with the ITER-like wall
- 2013
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 53:10, s. 104002-
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Tidskriftsartikel (refereegranskat)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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| 3. |
- Romanelli, F, et al.
(författare)
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Overview of the JET results
- 2011
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 51:9
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Tidskriftsartikel (refereegranskat)abstract
- Since the last IAEA Conference JET has been in operation for one year with a programmatic focus on the qualification of ITER operating scenarios, the consolidation of ITER design choices and preparation for plasma operation with the ITER-like wall presently being installed in JET. Good progress has been achieved, including stationary ELMy H-mode operation at 4.5 MA. The high confinement hybrid scenario has been extended to high triangularity, lower ρ*and to pulse lengths comparable to the resistive time. The steady-state scenario has also been extended to lower ρ*and ν*and optimized to simultaneously achieve, under stationary conditions, ITER-like values of all other relevant normalized parameters. A dedicated helium campaign has allowed key aspects of plasma control and H-mode operation for the ITER non-activated phase to be evaluated. Effective sawtooth control by fast ions has been demonstrated with3He minority ICRH, a scenario with negligible minority current drive. Edge localized mode (ELM) control studies using external n = 1 and n = 2 perturbation fields have found a resonance effect in ELM frequency for specific q95values. Complete ELM suppression has, however, not been observed, even with an edge Chirikov parameter larger than 1. Pellet ELM pacing has been demonstrated and the minimum pellet size needed to trigger an ELM has been estimated. For both natural and mitigated ELMs a broadening of the divertor ELM-wetted area with increasing ELM size has been found. In disruption studies with massive gas injection up to 50% of the thermal energy could be radiated before, and 20% during, the thermal quench. Halo currents could be reduced by 60% and, using argon/deuterium and neon/deuterium gas mixtures, runaway electron generation could be avoided. Most objectives of the ITER-like ICRH antenna have been demonstrated; matching with closely packed straps, ELM resilience, scattering matrix arc detection and operation at high power density (6.2 MW m-2) and antenna strap voltages (42 kV). Coupling measurements are in very good agreement with TOPICA modelling. © 2011 IAEA, Vienna.
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| 4. |
- Ongena, J., et al.
(författare)
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Recent progress on JET towards the ITER reference mode of operation at high density
- 2001
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Ingår i: Plasma Physics and Controlled Fusion. - 0741-3335 .- 1361-6587. ; 43, s. A11-A30
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Tidskriftsartikel (refereegranskat)abstract
- Recent progress towards obtaining high density and high confinement in JET as required for the ITER reference scenario at Q = 10 is summarized. Plasmas with simultaneous confinement H-98(y.2) = 1 and densities up to n/n(Gw) similar to 1 are now routinely obtained. This has been possible (i) by using plasmas at high (delta similar to 0.5) and medium (delta similar to 0.3-0.4) triangularity with sufficient heating power to maintain Type I ELMs, (ii) with impurity seeded plasmas at high (delta similar to 0.5) and low (delta less than or equal to 0.2) triangularity, (iii) with an optimized pellet injection sequence, maintaining the energy confinement and raising the density, and (iv) by carefully tuning the gas puff rate leading to plasmas with peaked density profiles and good confinement at long time scales. These high performance discharges exhibit Type I ELMs, with a new and more favourable behaviour observed at high densities, requiring further studies. Techniques for a possible mitigation of these ELMs are discussed, and first promising results are obtained with impurity seeding in discharges at high triangularity. Scaling studies using the new data of this year show a strong dependence of confinement on upper triangularity, density and proximity to the Greenwald limit. Observed MHD instabilities and methods to avoid these in high density and high confinement plasmas are discussed.
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| 5. |
- Cogordan, JA, et al.
(författare)
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Relativistic calculation of 2p53s, 3p and 3d energy levels and transition wavelengths in Ti XIII, Fe XVII and some other neon-like ions
- 1985
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Ingår i: Physica Scripta. - 0031-8949. ; 31:6, s. 545-550
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Tidskriftsartikel (refereegranskat)abstract
- Average energies for the configurations 2p5 3s, 3p and 3d in a number of neon-like ions from Al IV to Xe XLV have been calculated by means of the MCDF computer code of Grant et al. The results have been compared with observations and previous non-relativistic calculations. Fine- structure levels and 3s-3p and ip-3d transition wavelengths have also been calculated with the MCDF code for Ti XIII and Fe XVII, both in the single-configuration approximation and in a multiconfiguration treatment including 2s 2p6 nl. The configuration interaction was found to affect 2p5 3p3S1 most seriously. A separate optimization for the 3p1S0 state was needed, due to the particular radial dependence of this state. The calculated wavelengths show excellent agreement with the observations, and the MCDF calculations are well suited for wavelength predictions in neon-like n = 3 systems
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| 6. |
- Ekberg, JO, et al.
(författare)
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Accurate experimental lifetimes of excited levels in sodiumlike sulfur, S VI
- 1983
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Ingår i: Physica Scripta. - : IOP Publishing. - 0031-8949 .- 1402-4896. ; 27:6, s. 425-425
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Tidskriftsartikel (refereegranskat)abstract
- The lifetimes of the terms 3p2P, 3d2D, 4s2S, 4p2P, 4d2D, 4f2F, 5g2G, 6g2G, 6h2H, 7h2H, 7i2I and 8k2K in sodiumlike sulfur, S VI, have been determined using the beam-foil excitation technique. Most of the decay curves were analyzed by means of the ANDC method which corrects for cascading in a very detailed way. Accurate results were thereby obtained which show that an excellent agreement exists between experimental and theoretical values. Some previously noted disagreements between the results of beam-foil experiments and theoretical investigations are explained as being due to less accurate analyses of the experimental data.
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| 7. |
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| 8. |
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| 9. |
- Engström, Lars, et al.
(författare)
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Observation of an intensity anomaly in the 3s23p 2P1/2, 3/2-3s3p22S1/2 and 2P1/2 resonance transitions in the Al I isoelectronic sequence
- 1989
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Ingår i: Physica Scripta. - : IOP Publishing. - 0031-8949 .- 1402-4896. ; 39:1, s. 66-69
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Tidskriftsartikel (refereegranskat)abstract
- The intensity ratio of the two fine structure components in the 3s23p 2PJ–3s3p 2S1/2 and 2P1/2 resonance transitions has been measured in Al-like S IV, Cl V, Ar VI and Ti X, using the beam-foil technique. Unexpectedly large deviations from the LS ratios are found, particularly in the 2P–2S case. Although these deviations can be understood qualitatively from theoretical calculations (also reported), large quantitative discrepancies are observed in the beginning of the sequence.
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| 10. |
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| 11. |
- Giroud, C., et al.
(författare)
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Method for experimental determination of Z dependence of impurity transport on JET
- 2007
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 47:4, s. 313-330
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Tidskriftsartikel (refereegranskat)abstract
- The prediction of impurity peaking in future fusion devices such as ITER necessitates the study of the dependence on Z of the impurity transport in present devices. In this paper we describe a novel technique to determine the transport of impurities with different atomic numbers independently. A technique has been developed that allows simultaneously the measurement of the transport of Ne and Ar in the same discharge while minimizing the systematic errors in the spectroscopic measurements. The reproduction of the charge-exchange measured densities, absolute vaccum ultra-violet line intensities and absolute soft x-ray intensity is achieved in an impurity transport simulation. The method used to estimate the errors on the transport coefficients of neon (Ne) and argon (Ar) is presented. In the plasma region where the diffusion and convection coefficients are determined for hybrid discharges, the transport of Ne and Ar is observed to exceed neoclassical predictions. In the same regions, the diffusion coefficients of both impurities are similar. The convection coefficients are also comparable for Ne and Ar. The peaking of Ne and Ar density profiles are comparable during the period where the intermittent slow reconnecting n = 1 mode is stable in these hybrid discharges.
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| 12. |
- Haar, R. R., et al.
(författare)
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On the 3s-3 and 3p-3d transitions in ne-like ni xix
- 1987
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Ingår i: Physica Scripta. - : IOP Publishing. - 0031-8949 .- 1402-4896. ; 35:3, s. 296-299
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Tidskriftsartikel (refereegranskat)abstract
- An experimental and theoretical study has been made of the 3s-3p and 3p-d transitions in Ni XIX. The method of beam-foil spectroscopy, using 30-64 MeV Ni ions from a tandem accelerator, has been combined with theoretical calculations using the multiconfiguration Dirac-Fock (MCDF) program.
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| 13. |
- Jupén, C., et al.
(författare)
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Analysis of core-excited n = 3 configurations in S VI, Cl VII, Ar VIII and Ti XII
- 1990
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Ingår i: Physica Scripta. - : IOP Publishing. - 0031-8949 .- 1402-4896. ; 42:1, s. 44-50
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Tidskriftsartikel (refereegranskat)abstract
- By means of the beam-foil method, 74 new lines have been identified as combinations between the core-excited 2p5 3s3p, 3s3d and 3p2 configurations in Na-like sulphur, chlorine, argon and titanium. Relative energies have been determined for most of the quartet levels in S, Cl and Ar with an internal uncertainty of less than 25 cm−1. We also report the first observation in the isoelectronic sequence of Δn = 0, n = 3 transitions from the quasi-metastable 2p5 3p2(3P) 2D5/2 level. The identifications are supported by isoelectronic studies and comparisons with theoretical results obtained in superposition-of-configuration calculations including continuum channels.
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| 14. |
- Jupén, C, et al.
(författare)
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Lifetimes of the 3p 2P1/2, 2P3/2 and 3d 2D3/2, 2D5/2 Levels in Cl VII
- 1984
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Ingår i: Physica Scripta. - 0031-8949. ; 29:3, s. 226-226
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Tidskriftsartikel (refereegranskat)abstract
- The beam-foil excitation technique has been applied to determine lifetimes of the 3p2P1/2, 2P3/2 and 3d2D3/2, 2D5/2 levels in Na-like Cl VII. Using the ANDC method accurate values have been obtained which confirm recent theoretical values and explain some previously noted differences between theoretical and experimental oscillator strengths for transitions in multiply ionized Na-like ions.
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| 15. |
- Jupén, C., et al.
(författare)
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The 2p4 3s, 3p and 3d configurations of thirteen times ionized titanium, ti xiv
- 1985
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Ingår i: Physica Scripta. - : IOP Publishing. - 0031-8949 .- 1402-4896. ; 32:5, s. 527-533
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Tidskriftsartikel (refereegranskat)abstract
- The spectrum of Ti XFV has been observed in the wavelength region 80-550 Å using the fast ion beam spectroscopy method. 47 lines have been identified as transitions between the 2p4 3s, 3p, and 3d configurations in the 360-540 Å interval. The level identifications are supported by comparisons between observations and Hartree-Fock calculations along the F I isoelectronic sequence.
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| 16. |
- Jupén, C, et al.
(författare)
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The 3d-4f Transition in S VII Observed in a Laser-Produced Plasma
- 1984
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Ingår i: Physica Scripta. - 0031-8949. ; 29:4, s. 317-317
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Tidskriftsartikel (refereegranskat)abstract
- The energy levels of the 2p54f configuration in neon-like sulphur, S VII, have been derived from spectral lines in the region 330-375 Å. The lines, which were identified as belonging to the 3d-4f transition, were emitted from a laser-produced plasma. The structure in the 4f configuration has been studied through a parametric fit of Slater integrals.
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| 17. |
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| 18. |
- Pagan, C. J. B., et al.
(författare)
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Wavelengths, Energy Levels, Lifetimes, and Weighted Oscillator Strengths for the S VIII Spectrum
- 2011
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Ingår i: The Astrophysical Journal Supplement Series. - : American Astronomical Society. - 0067-0049 .- 1538-4365. ; 196:2
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Tidskriftsartikel (refereegranskat)abstract
- The weighted oscillator strengths (gf) and lifetimes for S VIII presented in this work were obtained by a multiconfigurational Hartree-Fock relativistic approach. In this calculation, the electrostatic energy parameters were optimized by a least-squares procedure in order to improve the adjustment to experimental energy levels. The values for gf and lifetimes were then calculated on the basis of these adjusted parameters. New classifications are proposed for energy levels belonging to the 4s and 4d configurations and lines related to them.
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| 19. |
- Reistad, N., et al.
(författare)
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Lifetime of the 3s3p1p term in s v
- 1985
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Ingår i: Physica Scripta. - : IOP Publishing. - 0031-8949 .- 1402-4896. ; 32:3, s. 164-168
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Tidskriftsartikel (refereegranskat)abstract
- The lifetime of the 3s3p1P term in Mg-like S V has been determined by beam-foil spectroscopy in combination with detailed analyses of cascading processes by means of the ANDC technique. One of the most important cascade transitions was found to be seriously blended by a strong S VII transition. An earlier proposed method for appling the ANDC formalism to correct for blending has been tested for the first time and found to work very well. The resulting 3s3p1P lifetime of 0.19 ± 0.01 ns, corresponding to an absorption oscillator strength of 1.46 ± 0.08, is in good agreement with recent theoretical values. Some previously noted discrepancies between beam-foil measurements and theoretical calculations for Mg-like ions can now be explained as being due to insufficient cascade corrections in previous experimental work.
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| 20. |
- von Hellermann, M G, et al.
(författare)
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Complex spectra in fusion plasmas
- 2005
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Ingår i: Physica Scripta. - 0031-8949. ; T120, s. 19-29
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Tidskriftsartikel (refereegranskat)abstract
- The need for quantitative evaluation of complex line emission spectra as observed in hot fusion plasmas initiated a challenging development of sophisticated interpretation tools based on integrating advanced atomic modelling with detailed treatment of the plasma environment. The successful merging of the two worlds has led to routine diagnostic procedures which have contributed enormously to the understanding of underlying plasma processes and also to a wide acceptance of spectroscopy as a reliable diagnostic method. In this paper three characteristic types of spectra of current and continuing interest are presented. The first is that of medium/ heavy species with many ionisation stages revealed in survey VUV and XUV spectra. Such species occur as control gases, as wall materials, as ablated heavy species and possible as layered wall dopants for monitoring erosion. The spectra are complex with line- like and quasi-continuum regions and are amenable to advanced 'pattern recognition' methods. The second type is of few electron, highly ionised systems observed as line-of-sight integrated passive emission spectra in the soft X-ray region. They are analysed successfully in terms of plasma parameters through matching of observation with predicted synthetic spectra. Examples used here include highly resolved helium-like emission spectra of argon, iron and titanium observed on the tokamaks TEXTOR and Tore Supra. The third type, and the emphasis of this work, comprises spectra linked to active beam spectroscopy, that is, charge exchange recombination spectroscopy (CXRS) and beam emission spectroscopy ( BES). In this case, a complex spectrum is again composed of a ( usually) dominating active spectrum and an underlying passive emission spectrum. Its analysis requires modelling of both active and passive features. Examples used here are from the CXRS diagnostic at JET and TEXTOR. They display characteristic features of the main light impurity ions (C+6, He+2, N+7, Ne+10 and Ar+18), as well as that of the bulk plasma ions, H+, D+ and T+. A main conclusion is that spectral complexity is not necessarily negative, but that 'complex structures' can provide a rich source of information on the plasma and its parameters - provided it is matched with integrated analysis - and that the methods can have universal applicability. In the present preparatory phase of the next generation fusion experiment ITER ( International Thermonuclear Experimental Reactor) the concepts and expectations of complex spectra and integrated data analysis play an important role in the design and optimisation procedure of the ITER diagnostic assembly.
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| 21. |
- Westerlind, M., et al.
(författare)
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Lifetimes of 2p53p and 3d levels in Ne-like chlorine, Cl VIII
- 1988
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Ingår i: Nuclear Inst. and Methods in Physics Research, B. - 0168-583X. ; 31:1-2, s. 300-304
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Tidskriftsartikel (refereegranskat)abstract
- Experimental lifetimes of seven 2p53p and six 2p53d levels in Ne-like chlorine, Cl VIII, have been measured using the beam-foil technique. For the first time in the Ne-sequence, the ANDC method of cascade correction has been applied in the lifetime determination of the 3p levels. This procedure lowered the values by 10 to 30% compared to the results from multiexponential curve-fitting. For all levels studied, except 3p3D2 and 3D1, the experimental lifetimes are in good agreement with recent theoretical values. A comparison between experimental and theoretical lifetimes for some 3p and 3d levels along the isoelectronic sequence is presented.
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