| 1. |
- Bombarda, F., et al.
(författare)
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Runaway electron beam control
- 2019
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Ingår i: Plasma Physics and Controlled Fusion. - : IOP Publishing. - 1361-6587 .- 0741-3335. ; 61:1
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Tidskriftsartikel (refereegranskat)
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| 2. |
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- 2018
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 58:9
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Tidskriftsartikel (refereegranskat)
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| 3. |
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- 2018
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 58:1
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Forskningsöversikt (refereegranskat)
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| 4. |
- Aho-Mantila, L., et al.
(författare)
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Assessment of SOLPS5.0 divertor solutions with drifts and currents against L-mode experiments in ASDEX Upgrade and JET
- 2017
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Ingår i: Plasma Physics and Controlled Fusion. - : IOP PUBLISHING LTD. - 0741-3335 .- 1361-6587. ; 59:3
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Tidskriftsartikel (refereegranskat)abstract
- The divertor solutions obtained with the plasma edge modelling tool SOLPS5.0 are discussed. The code results are benchmarked against carefully analysed L-mode discharges at various density levels with and without impurity seeding in the full-metal tokamaks ASDEX Upgrade and JET. The role of the cross-field drifts and currents in the solutions is analysed in detail, and the improvements achieved by fully activating the drift and current terms in view of matching the experimental signals are addressed. The persisting discrepancies are also discussed.
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| 5. |
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| 6. |
- Andersson, Emmi
(författare)
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Mutations and migration : molecular and epidemiological aspects of HIV-1 in Sweden
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The Swedish HIV-1 epidemic is characterized by a wide variation in subtypes due to migration and travel. The aims of this thesis were to investigate molecular methods for estimating time to diagnosis and epidemiological tools for estimating the proportion of undiagnosed individuals with HIV-1 in Sweden, as well as to update the knowledge on transmitted and pre-treatment drug resistance (TDR and PDR) among persons living with HIV-1 in Sweden. In Paper I we found that viral diversity estimated by the proportion of mixed base calls in pol gene sequences is an indicator of whether a HIV-1 infection is recent (≤1 year) or chronic. A cutoff of 0.47% mixed base calls identified recent infections with a sensitivity of 89% and a specificity of 75%. In Paper II we studied TDR in newly diagnosed individuals (n=1,713, 71% coverage) in 2010-2016 in Sweden. The prevalence of TDR was 7.1% (95% CI 5.8-8.3%) and resistance to non-nucleoside reverse transcriptase inhibitors (NNRTI) increased significantly from 1.5% in 2010 to 6.2% in 2016 and was related to infection/origin in sub-Saharan Africa. A transmission cluster in men having sex with men with the M41L mutation was traced back to the 1990´s. In Paper III we evaluated two mathematical models for estimation of the proportion of undiagnosed individuals with HIV-1 in Sweden, SSOPHIE and the ECDC Modelling tool. The model estimates for 2013 were 26% (n=2,100; 90% plausibility range 900-5,000) and 21% (n=2,013; 95% CI 1,831-2,189), respectively. The wide confidence bounds and problems to account for migration limited the value of the results. We concluded that improvements of models and better data on migration are needed. In Paper IV we investigated PDR in individuals diagnosed in Sweden 2017-2019 (n=224) using an in-house high-throughput sequencing (HTS) assay with a detection limit of 1% for minority viral variants. HTS was successful in 87% of samples and failure was associated with low viral loads. Drug resistance mutations (DRMs) in protease/reverse transcriptase were detected in 49% of patients and in 18% of patients the DRMs were at levels ≥20% of the viral population. DRMs above 20% were mainly towards NNRTIs and correlated with previous ART exposure (p=0.001) and origin in Asia (p=0.007). Integrase strand transfer inhibitor (INSTI) DRM were rare and only found in levels <20% of the total viral population. In conclusion, we have confirmed that viral diversity is a useful biomarker of time to diagnosis in HIV-infection and have identified important complications with estimating the proportion of undiagnosed HIV-1 infections in settings with high levels of migration. We have shown that the global increase in NNRTI-resistance is mirrored among HIV-positive migrants in Sweden and we have contributed to the knowledge about the utility of HTS in drug resistance testing of HIV-1.
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| 7. |
- Andersson Sundén, Erik, et al.
(författare)
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An assessment of nitrogen concentrations from spectroscopic measurements in the JET and ASDEX upgrade divertor
- 2019
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Ingår i: Nuclear Materials and Energy. - : Elsevier. - 2352-1791. ; 18, s. 147-152
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Tidskriftsartikel (refereegranskat)abstract
- The impurity concentration in the tokamak divertor plasma is a necessary input for predictive scaling of divertor detachment, however direct measurements from existing tokamaks in different divertor plasma conditions are limited. To address this, we have applied a recently developed spectroscopic N II line ratio technique for measuring the N concentration in the divertor to a range of H-mode and L-mode plasma from the ASDEX Upgrade and JET tokamaks, respectively. The results from both devices show that as the power crossing the separatrix, P-sep, is increased under otherwise similar core conditions (e.g. density), a higher N concentration is required to achieve the same detachment state. For example, the N concentrations at the start of detachment increase from approximate to 2% to approximate to 9% as P-sep, is increased from approximate to 2.5 MW to approximate to 7 MW. These results tentatively agree with scaling law predictions (e.g. Goldston et al.) motivating a further study examining the parameters which affect the N concentration required to reach detachment. Finally, the N concentrations from spectroscopy and the ratio of D and N gas valve fluxes agree within experimental uncertainty only when the vessel surfaces are fully-loaded with N.
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| 8. |
- Angioni, C., et al.
(författare)
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Dependence of the turbulent particle flux on hydrogen isotopes induced by collisionality
- 2018
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Ingår i: Physics of Plasmas. - : American Institute of Physics (AIP). - 1070-664X .- 1089-7674 .- 1070-6631 .- 1089-7666. ; 25:8
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Tidskriftsartikel (refereegranskat)abstract
- The impact of the change of the mass of hydrogen isotopes on the turbulent particle flux is studied. The trapped electron component of the turbulent particle convection induced by collisionality, which is outward in ion temperature gradient turbulence, increases with decreasing thermal velocity of the isotope. Thereby, the lighter is the isotope, the stronger is the turbulent pinch, and the larger is the predicted density gradient at the null of the particle flux. The passing particle component of the flux increases with decreasing mass of the isotope and can also affect the predicted density gradient. This effect is however subdominant for usual core plasma parameters. The analytical results are confirmed by means of both quasi-linear and nonlinear gyrokinetic simulations, and an estimate of the difference in local density gradient produced by this effect as a function of collisionality has been obtained for typical plasma parameters at mid-radius. Analysis of currently available experimental data from the JET and the ASDEX Upgrade tokamaks does not show any clear and general evidence of inconsistency with this theoretically predicted effect outside the errorbars and also allows the identification of cases providing weak evidence of qualitative consistency.
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| 9. |
- Angioni, C., et al.
(författare)
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The impact of poloidal asymmetries on tungsten transport in the core of JET H-mode plasmas
- 2015
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Ingår i: Physics of Plasmas. - : AMER INST PHYSICS. - 1070-664X .- 1089-7674. ; 22:5
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Tidskriftsartikel (refereegranskat)abstract
- Recent progress in the understanding and prediction of the tungsten behaviour in the core of JET H-mode plasmas with ITER-like wall is presented. Particular emphasis is given to the impact of poloidal asymmetries of the impurity density. In particular, it is shown that the predicted reduction of temperature screening induced by the presence of low field side localization of the tungsten density produced by the centrifugal force is consistent with the observed tungsten behaviour in a JET discharge in H-mode baseline scenario. This provides first evidence of the role of poloidal asymmetries in reducing the strength of temperature screening. The main differences between plasma parameters in JET baseline and hybrid scenario discharges which affect the impact of poloidally asymmetric density on the tungsten radial transport are identified. This allows the conditions by which tungsten accumulation can be avoided to be more precisely defined.
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| 10. |
- Appel, L. C., et al.
(författare)
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Equilibrium reconstruction in an iron core tokamak using a deterministic magnetisation model
- 2018
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Ingår i: Computer Physics Communications. - : ELSEVIER. - 0010-4655 .- 1879-2944. ; 223, s. 1-17
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Tidskriftsartikel (refereegranskat)abstract
- In many tokamaks ferromagnetic material, usually referred to as an iron-core, is present in order to improve the magnetic coupling between the solenoid and the plasma. The presence of the iron core in proximity to the plasma changes the magnetic topology with consequent effects on the magnetic field structure and the plasma boundary. This paper considers the problem of obtaining the free-boundary plasma equilibrium solution in the presence of ferromagnetic material based on measured constraints. The current approach employs, a model described by O'Brien et al. (1992) in which the magnetisation currents at the iron-air boundary are represented by a set of free parameters and appropriate boundary conditions are enforced via a set of quasi-measurements on the material boundary. This can lead to the possibility of overfitting the data and hiding underlying issues with the measured signals. Although the model typically achieves good fits to measured magnetic signals there are significant discrepancies in the inferred magnetic topology compared with other plasma diagnostic measurements that are independent of the magnetic field. An alternative approach for equilibrium reconstruction in iron-core tokamaks, termed the deterministic magnetisation model is developed and implemented in EFIT++. The iron is represented by a boundary current with the gradients in the magnetisation dipole state generating macroscopic internal magnetisation currents. A model for the boundary magnetisation currents at the iron-air interface is developed using B-Splines enabling continuity to arbitrary order; internal magnetisation currents are allocated to triangulated regions within the iron, and a method to enable adaptive refinement is implemented. The deterministic model has been validated by comparing it with a synthetic 2-D electromagnetic model of JET. It is established that the maximum field discrepancy is less than 1.5 mT throughout the vacuum region enclosing the plasma. The discrepancies of simulated magnetic probe signals are accurate to within 1% for signals with absolute magnitude greater than 100 mT; in all other cases agreement is to within 1 mT. The effect of neglecting the internal magnetisation currents increases the maximum discrepancy in the vacuum region to >20 mT, resulting in errors of 5%-10% in the simulated probe signals. The fact that the previous model neglects the internal magnetisation currents (and also has additional free parameters when fitting the measured data) makes it unsuitable for analysing data in the absence of plasma current. The discrepancy of the poloidal magnetic flux within the vacuum vessel is to within 0.1 Wb. Finally the deterministic model is applied to an equilibrium force-balance solution of a JET discharge using experimental data. It is shown that the discrepancies of the outboard separatrix position, and the outer strike-point position inferred from Thomson Scattering and Infrared camera data are much improved beyond the routine equilibrium reconstruction, whereas the discrepancy of the inner strike-point position is similar.
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