| 1. |
- Jones, Benedict C, et al.
(författare)
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To which world regions does the valence-dominance model of social perception apply?
- 2021
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Ingår i: Nature Human Behaviour. - : Springer Science and Business Media LLC. - 2397-3374. ; 5:1, s. 159-169
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Tidskriftsartikel (refereegranskat)abstract
- Over the past 10 years, Oosterhof and Todorov's valence-dominance model has emerged as the most prominent account of how people evaluate faces on social dimensions. In this model, two dimensions (valence and dominance) underpin social judgements of faces. Because this model has primarily been developed and tested in Western regions, it is unclear whether these findings apply to other regions. We addressed this question by replicating Oosterhof and Todorov's methodology across 11 world regions, 41 countries and 11,570 participants. When we used Oosterhof and Todorov's original analysis strategy, the valence-dominance model generalized across regions. When we used an alternative methodology to allow for correlated dimensions, we observed much less generalization. Collectively, these results suggest that, while the valence-dominance model generalizes very well across regions when dimensions are forced to be orthogonal, regional differences are revealed when we use different extraction methods and correlate and rotate the dimension reduction solution. PROTOCOL REGISTRATION: The stage 1 protocol for this Registered Report was accepted in principle on 5 November 2018. The protocol, as accepted by the journal, can be found at https://doi.org/10.6084/m9.figshare.7611443.v1 .
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| 2. |
- Martin, P., et al.
(författare)
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Overview of the RFX-mod fusion science programme
- 2013
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 53:10, s. 104018-
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Forskningsöversikt (refereegranskat)abstract
- This paper reports the highlights of the RFX-mod fusion science programme since the last 2010 IAEA Fusion Energy Conference. The RFX-mod fusion science programme focused on two main goals: exploring the fusion potential of the reversed field pinch (RFP) magnetic configuration and contributing to the solution of key science and technology problems in the roadmap to ITER. Active control of several plasma parameters has been a key tool in this endeavour. New upgrades on the system for active control of magnetohydrodynamic (MHD) stability are underway and will be presented in this paper. Unique among the existing fusion devices, RFX-mod has been operated both as an RFP and as a tokamak. The latter operation has allowed the exploration of edge safety factor q edge < 2 with active control of MHD stability and studies concerning basic energy and flow transport mechanisms. Strong interaction has continued with the stellarator community in particular on the physics of helical states and on three-dimensional codes.
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| 3. |
- Belitsky, Victor, 1955, et al.
(författare)
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SEPIA - A new single pixel receiver at the APEX telescope
- 2018
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 612
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Tidskriftsartikel (refereegranskat)abstract
- Context. We describe the new Swedish-ESO PI Instrument for APEX (SEPIA) receiver, which was designed and built by the Group for Advanced Receiver Development (GARD), at Onsala Space Observatory (OSO) in collaboration with ESO. It was installed and commissioned at the APEX telescope during 2015 with an ALMA Band 5 receiver channel and updated with a new frequency channel (ALMA Band 9) in February 2016. Aim. This manuscript aims to provide, for observers who use the SEPIA receiver, a reference in terms of the hardware description, optics and performance as well as the commissioning results. Methods. Out of three available receiver cartridge positions in SEPIA, the two current frequency channels, corresponding to ALMA Band 5, the RF band 158-211 GHz, and Band 9, the RF band 600-722 GHz, provide state-of-the-art dual polarization receivers. The Band 5 frequency channel uses 2SB SIS mixers with an average SSB noise temperature around 45 K with IF (intermediate frequency) band 4-8 GHz for each sideband providing total 4 × 4 GHz IF band. The Band 9 frequency channel uses DSB SIS mixers with a noise temperature of 75-125 K with IF band 4-12 GHz for each polarization. Results. Both current SEPIA receiver channels are available to all APEX observers.
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| 4. |
- Barrio, Isabel C., et al.
(författare)
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Background invertebrate herbivory on dwarf birch (Betula glandulosa-nana complex) increases with temperature and precipitation across the tundra biome
- 2017
-
Ingår i: Polar Biology. - : Springer. - 0722-4060 .- 1432-2056. ; 40:11, s. 2265-2278
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Tidskriftsartikel (refereegranskat)abstract
- Chronic, low intensity herbivory by invertebrates, termed background herbivory, has been understudied in tundra, yet its impacts are likely to increase in a warmer Arctic. The magnitude of these changes is however hard to predict as we know little about the drivers of current levels of invertebrate herbivory in tundra. We assessed the intensity of invertebrate herbivory on a common tundra plant, the dwarf birch (Betula glandulosa-nana complex), and investigated its relationship to latitude and climate across the tundra biome. Leaf damage by defoliating, mining and gall-forming invertebrates was measured in samples collected from 192 sites at 56 locations. Our results indicate that invertebrate herbivory is nearly ubiquitous across the tundra biome but occurs at low intensity. On average, invertebrates damaged 11.2% of the leaves and removed 1.4% of total leaf area. The damage was mainly caused by external leaf feeders, and most damaged leaves were only slightly affected (12% leaf area lost). Foliar damage was consistently positively correlated with mid-summer (July) temperature and, to a lesser extent, precipitation in the year of data collection, irrespective of latitude. Our models predict that, on average, foliar losses to invertebrates on dwarf birch are likely to increase by 6-7% over the current levels with a 1 degrees C increase in summer temperatures. Our results show that invertebrate herbivory on dwarf birch is small in magnitude but given its prevalence and dependence on climatic variables, background invertebrate herbivory should be included in predictions of climate change impacts on tundra ecosystems.
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| 5. |
- Barrio, Isabel C., et al.
(författare)
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Publisher Correction to : Background invertebrate herbivory on dwarf birch (Betula glandulosa-nana complex) increases with temperature and precipitation across the tundra biome (vol 40, pg 2265, 2017)
- 2018
-
Ingår i: Polar Biology. - : Springer. - 0722-4060 .- 1432-2056. ; 41:8, s. 1653-1654
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Tidskriftsartikel (refereegranskat)abstract
- The above mentioned article was originally scheduled for publication in the special issue on Ecology of Tundra Arthropods with guest editors Toke T. Hoye . Lauren E. Culler. Erroneously, the article was published in Polar Biology, Volume 40, Issue 11, November, 2017. The publisher sincerely apologizes to the guest editors and the authors for the inconvenience caused.
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| 6. |
- Mogard, Elisabeth, et al.
(författare)
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Chronic Pain and Assessment of Pain Sensitivity in Patients With Axial Spondyloarthritis: Results From the SPARTAKUS Cohort
- 2021
-
Ingår i: Journal of Rheumatology. - : The Journal of Rheumatology. - 0315-162X .- 1499-2752. ; 48:11, s. 1672-1679
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Tidskriftsartikel (refereegranskat)abstract
- Objective. To study differences in pain reports between patients with ankylosing spondylitis (AS) and non-radiographic axial spondyloarthritis (nr-axSpA), and to assess how pain sensitivity measures associate with disease and health outcomes. Methods. Consecutive patients with axial SpA (axSpA) were enrolled in the population-based SPARTAKUS cohort (2015-2017) and classified as AS (n = 120) or nr-axSpA (n = 55). Pain was assessed with question-naires (intensity/duration/distribution) and computerized cuff pressure algometry to measure pain sensi-tivity (pain threshold/pain tolerance/temporal summation of pain). Linear regression models were used to compare pain measures between patients with AS and nr-axSpA, and to assess associations between pain sensitivity measures and disease and health outcomes. Results. Of 175 patients with axSpA, 43% reported chronic widespread pain, with no significant differences in any questionnaire-derived or algometry-assessed pain measures between patients with AS and nr-axSpA. Lower pain tolerance was associated with longer symptom duration, worse Ankylosing Spondylitis Disease Activity Score using C-reactive protein (ASDAS-CRP), Bath Ankylosing Spondylitis Functional Index, and Bath Ankylosing Spondylitis Metrology Index (BASMI), more pain regions, unacceptable pain, worse Maastricht AS Enthesitis Score (MASES), fatigue, anxiety, and health-related quality of life. Further, lower pain threshold was associated with worse ASDAS-CRP and MASES, whereas higher temporal summation was associated with longer symptom duration, unacceptable pain, and worse BASMI. Conclusion. Chronic pain is common in axSpA, with no observed differences in any pain measures between patients with AS and nr-axSpA. Further, higher pain sensitivity is associated with having worse disease and health outcomes. The results indicate that patients with AS and nr-axSpA, in line with most clinical char-acteristics, have a similar pain burden, and they highlight large unmet needs regarding individualized pain management, regardless of axSpA subgroup.
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| 7. |
- Brunsell, Per, et al.
(författare)
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Resistive wall mode feedback control experiments in EXTRAP T2R
- 2007
-
Ingår i: 34th EPS Conference on Plasma Physics 2007, EPS 2007 - Europhysics Conference Abstracts. - 9781622763344 ; , s. 544-547
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Konferensbidrag (refereegranskat)abstract
- Experiments in EXTRAP T2R on RWM stabilization using intelligent shell feedback with a P-controller showed that mode suppression improves with increasing gain up to the system stability limit. A PD-controller gives faster response and allows operation with higher gain. The PI-controller is useful for suppression of modes driven by external resonant field error. Best mode suppression was in the present study achieved with a PID-controller.
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| 8. |
- Frassinetti, Lorenzo, et al.
(författare)
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A method for the estimate of the wall diffusion for non-axisymmetric fields using rotating external fields
- 2013
-
Ingår i: Plasma Physics and Controlled Fusion. - : IOP Publishing. - 0741-3335 .- 1361-6587. ; 55:8, s. 084001-
-
Tidskriftsartikel (refereegranskat)abstract
- A new method for the estimate of the wall diffusion time of non-axisymmetric fields is developed. The method based on rotating external fields and on the measurement of the wall frequency response is developed and tested in EXTRAP T2R. The method allows the experimental estimate of the wall diffusion time for each Fourier harmonic and the estimate of the wall diffusion toroidal asymmetries. The method intrinsically considers the effects of three-dimensional structures and of the shell gaps. Far from the gaps, experimental results are in good agreement with the diffusion time estimated with a simple cylindrical model that assumes a homogeneous wall. The method is also applied with non-standard configurations of the coil array, in order to mimic tokamak-relevant settings with a partial wall coverage and active coils of large toroidal extent. The comparison with the full coverage results shows good agreement if the effects of the relevant sidebands are considered.
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| 9. |
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| 10. |
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| 11. |
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| 12. |
- Frassinetti, Lorenzo, et al.
(författare)
-
Tearing mode velocity braking due to resonant magnetic perturbations
- 2012
-
Ingår i: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 52:10, s. 103014-
-
Tidskriftsartikel (refereegranskat)abstract
- The effect of resonant magnetic perturbations (RMPs) on the tearing mode (TM) velocity is studied in EXTRAP T2R. Experimental results show that the RMP produces TM braking until a new steady velocity or wall locking is reached. The braking is initially localized at the TM resonance and then spreads to the other TMs and to the rest of the plasma producing a global velocity reduction via the viscous torque. The process has been used to experimentally estimate the kinematic viscosity profile, in the range 2-40 m 2 s -1, and the electromagnetic torque produced by the RMP, which is strongly localized at the TM resonance. Experimental results are then compared with a theoretical model which gives a reasonable qualitative explanation of the entire process.
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| 13. |
- Horvath, Istvan, et al.
(författare)
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Mechanisms of Protein Oligomerization : Inhibitor of Functional Amyloids Templates α-Synuclein Fibrillation
- 2012
-
Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 134:7, s. 3439-3444
-
Tidskriftsartikel (refereegranskat)abstract
- Small organic molecules that inhibit functional bacterial amyloid fibers, curli, are promising new antibiotics. Here we investigated the mechanism by which the ring-fused 2-pyridone FN075 inhibits fibrillation of the curli protein CsgA. Using a variety of biophysical techniques, we found that FN075 promotes CsgA to form off-pathway, non-amyloidogenic oligomeric species. In light of the generic properties of amyloids, we tested whether FN075 would also affect the fibrillation reaction of human α-synuclein, an amyloid-forming protein involved in Parkinson's disease. Surprisingly, FN075 stimulates α-synuclein amyloid fiber formation as measured by thioflavin T emission, electron microscopy (EM), and atomic force microscopy (AFM). NMR data on (15)N-labeled α-synuclein show that upon FN075 addition, α-synuclein oligomers with 7 nm radius form in which the C-terminal 40 residues remain disordered and solvent exposed. The polypeptides in these oligomers contain β-like secondary structure, and the oligomers are detectable by AFM, EM, and size-exclusion chromatography (SEC). Taken together, FN075 triggers oligomer formation of both proteins: in the case of CsgA, the oligomers do not proceed to fibers, whereas for α-synuclein, the oligomers are poised to rapidly form fibers. We conclude that there is a fine balance between small-molecule inhibition and templation that depends on protein chemistry.
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| 14. |
- Olofsson, K. Erik J., et al.
(författare)
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A first attempt at few coils and low-coverage resistive wall mode stabilization of EXTRAP T2R
- 2012
-
Ingår i: Plasma Physics and Controlled Fusion. - : IOP Publishing. - 0741-3335 .- 1361-6587. ; 54:9, s. 094005-
-
Tidskriftsartikel (refereegranskat)abstract
- The reversed-field pinch features resistive-shell-type instabilities at any (vanishing and finite) plasma pressure. An attempt to stabilize the full spectrum of these modes using both (i) incomplete coverage and (ii) few coils is presented. Two empirically derived model-based control algorithms are compared with a baseline guaranteed suboptimal intelligent-shell-type (IS) feedback. Experimental stabilization could not be achieved for the coil array subset sizes considered by this first study. But the model-based controllers appear to significantly outperform the decentralized IS method.
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| 15. |
- Olofsson, K. Erik J., et al.
(författare)
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A practical approach to input design for modal analysis using subspace methods
- 2012
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Ingår i: 16th IFAC Symposium on System Identification. - : IFAC. - 9783902823069 ; , s. 362-367
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Konferensbidrag (refereegranskat)abstract
- A basic class of multivariate system identification input design methods is proposed. Only reliable numerical linear algebra is used. The underlying idea is to inject energy into the invariant eigenspace for a subset of preestimated plant eigenvalues. Standard Schur pseudotriangular factorisation is used to pretarget a subsequent singular value decomposition. Explicit state-space formulas are given. Examples indicate that the approach may be useful in some practical applications. The approach may be considered user-friendly.
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| 16. |
- Olofsson, K. Erik J., et al.
(författare)
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Cascade and multibatch subspace system identification for multivariate vacuum-plasma response characterisation
- 2011
-
Ingår i: Proceedings of the 50th IEEE Conference on Decision and Control and European Control Conference (CDC-ECC11). ; , s. 2614-2619
-
Konferensbidrag (refereegranskat)abstract
- A particular cascade structure system identification problem is formulated for the purpose of characterizing the vacuum-plasma response for a magnetic confinement fusion experiment. A predictor-form closed-loop subspace system identification approach is advocated due to (i) plant instability (ii) sizes of input-output vectors and (iii) inherent multivariate eigenmodes of the physical system. Since experiment data come in relatively short batches, specialised means for data merging for subspace identification are developed. A batchwise deletegroup jackknife procedure is utilised to estimate the standard error of the estimate of the dominant unstable empirical plasma response eigenvalue.
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| 17. |
- Olofsson, K. Erik J., et al.
(författare)
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Closed-loop MIMO ARX estimation of concurrent external plasma response eigenmodes in magnetic confinement fusion
- 2010
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Ingår i: Proceedings of the 49th Conference on Decision and Control (CDC’10). ; , s. 2954-2959
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Konferensbidrag (refereegranskat)abstract
- Detailed experimental MIMO models of plasma stability behaviour are becoming increasingly important in magnetic confinement fusion (MCF) energy research as an assortment of magnetohydrodynamic (MHD) instabilities develop when fusion performance is pushed. Some of these problems could perhaps be handled by magnetic feedback. We here show a practical method for experimental closed-loop multi-input multi-output (MIMO) characterisation of the macroscopic stability of toroidal MCF devices. It is demonstrated, by application to the MCF experiment EXTRAP T2R, that MHD eigenmodes can be detected using the workhorse MIMO autoregressive exogeneous (ARX) model structure. Plausibly, the presented methodology could significantly improve highly-desired magnetic feedback accuracy in MCF.
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| 18. |
- Olofsson, K. Erik J., et al.
(författare)
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Experimental modal analysis of resistive wall toroidal pinch plasma dynamics
- 2013
-
Ingår i: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 53:7, s. 072003-
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Tidskriftsartikel (refereegranskat)abstract
- The linearized magnetofluid dynamics of a magnetically confined reversed-field pinch plasma is extracted from a set of perturbative randomized nondestructive experiments. The spectrum of the generically estimated linear time-invariant system is compared to solutions of the corresponding eigenvalue problems formed by the ideal magnetohydrodynamic model. Stable and unstable nonresonant resistive wall modes are accurately identified.
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| 19. |
- Olofsson, K. Erik J.
(författare)
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Extended benchmark results for impulse response estimation
- 2013
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Ingår i: 2013 IEEE 52nd Annual Conference on Decision and Control (CDC). - : IEEE conference proceedings. - 9781467357173 ; , s. 7168-7173
-
Konferensbidrag (refereegranskat)abstract
- Recent attention has been given to the use of regularised least-squares methods for improving the quality of classical impulse response estimates from short/noisy datasets. This paper significantly augments and contextualises previously reported benchmark results by inclusion of a larger set of standard and non-standard methods in the comparison. The numerical experiments are summarised using several metrics. There is no obvious winner method.
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| 20. |
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| 21. |
- Olofsson, K. Erik J., 1982-, et al.
(författare)
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Measurements of the vacuum-plasma response in EXTRAP T2R using generic closed-loop subspace system identification
- 2012
-
Ingår i: Fusion engineering and design. - : Elsevier BV. - 0920-3796 .- 1873-7196. ; 87:12, s. 1926-1929
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Tidskriftsartikel (refereegranskat)abstract
- A multibatch formulation of a multi-input multi-output closed-loop subspace system identification method is employed for the purpose of obtaining control-relevant models of the vacuum-plasma response in the magnetic confinement fusion experiment EXTRAP T2R. The accuracy of the estimate of the plant dynamics is estimated by computing bootstrap replication statistics of the dataset. It is seen that the thus identified models exhibit both predictive capabilities and physical spectral properties.
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| 22. |
- Olofsson, K Erik J, 1982-
(författare)
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Nonaxisymmetric experimental modal analysis and control of resistive wall MHD in RFPs : System identification and feedback control for the reversed-field pinch
- 2012
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The reversed-field pinch (RFP) is a device for magnetic confinement of fusion plasmas. The main objective of fusion plasma research is to realise cost-effective thermonuclear fusion power plants. The RFP is highly unstable as can be explained by the theory of magnetohydrodynamics (MHD). Feed-back control technology appears to enable a robustly stable RFP operation. Experimental control and identification of nonaxisymmetric multimode MHD is pursued in this thesis. It is shown that nonparametric multivariate identification methods can be utilised to estimate MHD spectral characteristics from plant-friendly closed-loop operational input-output data. It is also shown that accurate tracking of the radial magnetic field boundary condition is experimentally possible in the RFP. These results appear generically useful as tools in both control and physics research in magnetic confinement fusion.
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| 23. |
- Olofsson, K. Erik J., et al.
(författare)
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Predictor-based multivariable closed-loop system identification of the EXTRAP T2R reversed field pinch external plasma response
- 2011
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Ingår i: Plasma Physics and Controlled Fusion. - : IOP Publishing. - 0741-3335 .- 1361-6587. ; 53:8, s. 084003-
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Tidskriftsartikel (refereegranskat)abstract
- The usage of computationally feasible overparametrized and nonregularized system identification signal processing methods is assessed for automated determination of the full reversed-field pinch external plasma response spectrum for the experiment EXTRAP T2R. No assumptions on the geometry of eigenmodes are imposed. The attempted approach consists of high-order autoregressive exogenous estimation followed by Markov block coefficient construction and Hankel matrix singular value decomposition. It is seen that the obtained 'black-box' state-space models indeed can be compared with the commonplace ideal magnetohydrodynamics (MHD) resistive thin-shell model in cylindrical geometry. It is possible to directly map the most unstable autodetected empirical system pole to the corresponding theoretical resistive shell MHD eigenmode.
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| 24. |
- Olofsson, K Erik J, 1982-, et al.
(författare)
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Stability analysis and model-based control in EXTRAP-T2R with time-delay compensation
- 2008
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Ingår i: Proceedings of the 47th IEEE Conference on Decision and Control, Cancun, Mexico, Dec. 9-11, 2008. - : IEEE conference proceedings. - 9781424431236 ; , s. 2044-2049
-
Konferensbidrag (refereegranskat)abstract
- In this paper, we investigate the stability problems and control issues that occur in a reversed-field pinch (RFP) device, EXTRAP-T2R (T2R), used for research in fusion plasma physics and general plasma (ionized gas) dynamics. The plant exhibits, among other things, magnetohydrodynamic instabilities known as resistive-wall modes (RWMs), growing on a time-scale set by a surrounding non-perfectly conducting shell.We propose a novel model that takes into account experimental constraints, such as the actuators dynamics and control latencies, which lead to a multivariable time-delay model of the system. The open-loop field-error characteristics are estimated and a stability analysis of the resulting closed-loop delay differential equation (DDE) emphasizes the importance of the delay effects. We then design a structurally constrained optimal PID controller by direct eigenvalue optimization (DEO) of this DDE. The presented results are substantially based on and compared with experimental data.
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| 25. |
- Olofsson, K. Erik J., et al.
(författare)
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Subspace identification analysis of RFX and T2R reversed-field pinches
- 2013
-
Ingår i: Control Engineering Practice. - : Elsevier BV. - 0967-0661 .- 1873-6939. ; 21:7, s. 917-929
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Tidskriftsartikel (refereegranskat)abstract
- Input-output datasets from two magnetic confinement fusion (MCF) experiments of the reversed-field pinch (RFP) type are examined. The RFP datasets, which are samples of the distributed magnetic field dynamics, are naturally divided into many smaller batches due to the pulsed-plasma operation of the experiments. The two RFP experiments considered are (i) EXTRAP T2R (T2R) with 64 inputs and 64 outputs and (ii) RFX-mod (RFX) with 192 inputs and 192 outputs. Both T2R and RFX are magnetohydrodynamically unstable and operates under magnetic feedback with optional dither injection. Using subspace system identification techniques and randomised cross-validation (CV) methods to minimise the generalisation error, state-space orders of the empirical systems are suggested. These system orders are compared to "stabilisation diagrams" commonly used in experimental modal analysis practice. The relation of the CV system order to the decay of the singular values from the subspace method is observed. Both (i) stable vacuum diffusion and (ii) unstable plasma response datasets are analysed. Apparent simulation and prediction errors are quantified for both cases using a deviation-accounted-for index. These results are purely data-driven. A simple approach towards exploitation of the subspace techniques for finite-element model refinement and data confrontation is presented.
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| 26. |
- Olofsson, K. Erik J., et al.
(författare)
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Synthesis and operation of an FFT-decoupled fixed-order reversed-field pinch plasma control system based on identification data
- 2010
-
Ingår i: Plasma Physics and Controlled Fusion. - : IOP Publishing. - 0741-3335 .- 1361-6587. ; 52:10, s. 104005-
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Tidskriftsartikel (refereegranskat)abstract
- Recent developments and applications of system identification methods for the reversed-field pinch (RFP) machine EXTRAP T2R have yielded plasma response parameters for decoupled dynamics. These data sets are fundamental for a real-time implementable fast Fourier transform (FFT) decoupled discrete-time fixed-order strongly stabilizing synthesis as described in this work. Robustness is assessed over the data set by bootstrap calculation of the sensitivity transfer function worst-case H(infinity)-gain distribution. Output tracking and magnetohydrodynamic mode m = 1 tracking are considered in the same framework simply as two distinct weighted traces of a performance channel output-covariance matrix as derived from the closed-loop discrete-time Lyapunov equation. The behaviour of the resulting multivariable controller is investigated with dedicated T2R experiments.
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| 27. |
- Olofsson, K. Erik J., et al.
(författare)
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Vector dither experiment design and direct parametric identification of reversed-field pinch normal modes
- 2009
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Ingår i: Proceedings of the IEEE Conference on Decision and Control. - 9781424438716 ; , s. 1348-1353
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Konferensbidrag (refereegranskat)abstract
- Magnetic confinement fusion (MCF) research ambitiously endeavours to develop a major future energy source. MCF power plant designs, typically some variation on the tokamak, unfortunately suffer from magnetohydrodynamic (MHD) instabilities. One unstable mode is known as the resistive-wall mode (RWM) which is a macroscopically global type of perturbation that can degrade or even terminate the plasma in the reactor if not stabilized. In this work the topic of RWMs is studied for the reversed-field pinch (RFP), another toroidal MCF concept, similar to the tokamak. The problem of identifying RWM dynamics during closed-loop operation is tackled by letting physics-based parametric modeling join forces with convex programming experiment design. An established MHD normal modes description is assessed for the RFP by synthesizing a multivariable dither signal where spatial fourier modes are spectrally shaped, with regard to real experiment constraints, to yield minimum variance parameter estimates in the prediction-error framework. The dithering is applied to the real RFP plant EXTRAP-T2R, and experimental MHD spectra are obtained by an automated procedure.
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| 28. |
- Volpe, F. A., et al.
(författare)
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Error field assessment from driven rotation of stable external kinks at EXTRAP-T2R reversed field pinch
- 2013
-
Ingår i: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 53:4, s. 043018-
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Tidskriftsartikel (refereegranskat)abstract
- A new non-disruptive error field (EF) assessment technique not restricted to low density and thus low beta was demonstrated at the EXTRAP-T2R reversed field pinch. Stable and marginally stable external kink modes of toroidal mode number n = 10 and n = 8, respectively, were generated, and their rotation sustained, by means of rotating magnetic perturbations of the same n. Due to finite EFs, and in spite of the applied perturbations rotating uniformly and having constant amplitude, the kink modes were observed to rotate non-uniformly and be modulated in amplitude. This behaviour was used to precisely infer the amplitude and approximately estimate the toroidal phase of the EF. A subsequent scan permitted to optimize the toroidal phase. The technique was tested against deliberately applied as well as intrinsic EFs of n = 8 and 10. Corrections equal and opposite to the estimated error fields were applied. The efficacy of the error compensation was indicated by the increased discharge duration and more uniform mode rotation in response to a uniformly rotating perturbation. The results are in good agreement with theory, and the extension to lower n, to tearing modes and to tokamaks, including ITER, is discussed.
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