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Saad, E. & Brunsell, P. R. (2024). Model based optimal magnetic feedback control of multiple resistive wall modes with discrete coil and sensor arrays. Fusion engineering and design, 198, Article ID 114099.
Open this publication in new window or tab >>Model based optimal magnetic feedback control of multiple resistive wall modes with discrete coil and sensor arrays
2024 (English)In: Fusion engineering and design, ISSN 0920-3796, E-ISSN 1873-7196, Vol. 198, article id 114099Article in journal (Refereed) Published
Abstract [en]

A model-based optimal control method for multiple resistive wall mode (RWM) feedback stabilization has been developed and tested in plasma experiments at the EXTRAP T2R reversed field pinch (RFP) device. The controller is designed to target issues that arise in connection with RWM magnetic feedback stabilization systems based on discrete control coil and sensor arrays in tokamak and reversed field pinch devices. Multi-mode control capabilities in these systems is limited due to coupling of modes induced by the control system. The coupling originates from the generation of side-band control field harmonics and from aliasing of multiple harmonics in the sensor measurements. These couplings naturally leads to a multiple-input, multiple-output (MIMO) control problem. A model based state space controller has been designed based on a relatively simple physics model of the RWM plasma response. The physics model, which is applicable for the high aspect ratio RFP, is the basis for Fourier decoupling of the MIMO control problem into a set of single-input, multiple-output (SIMO) systems using the discrete Fourier transform (DFT). The linear, time-invariant physics model allows for the design of a state space model with states representing physical quantities; in this case the Fourier harmonics of the radial field at the resistive wall. Since the states cannot be directly measured, a Kalman filter is used for estimation of the states from the aliased sensor array measurements. A linear–quadratic (LQ) optimal state controller has been implemented. Design parameters, such as the LQ control cost function state weights and the Kalman filter input error covariances have been used to optimize the control operation in various ways. The controller has enhanced multi-mode control capabilities compared to earlier designs. For example it allows the prioritizing of suppression of one of the multiple magnetic field Fourier harmonics produced by a given control current DFT component. The controller has been tested in plasma experiments at EXTRAP T2R device, utilizing a newly installed extended sensor array, and the enhanced capabilities for multiple RWM feedback stabilization has been demonstrated.

Place, publisher, year, edition, pages
Elsevier BV, 2024
Keywords
Multiple modes, Optimal control, Resistive wall mode
National Category
Control Engineering
Identifiers
urn:nbn:se:kth:diva-341605 (URN)10.1016/j.fusengdes.2023.114099 (DOI)001139933200001 ()2-s2.0-85179124176 (Scopus ID)
Note

QC 20231227

Available from: 2023-12-27 Created: 2023-12-27 Last updated: 2024-02-06Bibliographically approved
Saad, E. & Brunsell, P. R. (2022). Experimental characterization and modelling of the resistive wall mode response in a reversed field pinch. Plasma Physics and Controlled Fusion, 64(5), Article ID 055011.
Open this publication in new window or tab >>Experimental characterization and modelling of the resistive wall mode response in a reversed field pinch
2022 (English)In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 64, no 5, article id 055011Article in journal (Refereed) Published
Abstract [en]

Model-based control algorithms have potential advantages for resistive wall mode (RWM) feedback control. In this study, a physics model of the RWM response to externally applied perturbation fields is validated against experiments in a reversed field pinch (RFP). The experimental characterization of the RWM plasma response is performed in the EXTRAP T2R device by the excitation of nonaxisymmetric perturbation magnetic fields utilizing an external array of saddle coils for RWM control. The modelling and experimental validation is carried out with an extended sensor array, resolving a wider spectrum of RWM compared to earlier studies, covering the relevant poloidal m = 1 and toroidal -32 < n < 32 modes for this high aspect ratio RFP device. In addition to the nonresonant unstable modes, which are the primary target of RWM feedback control, this spectrum also includes a wide range of resonant modes. The validated resistive magnetohydrodynamics (MHD) model includes the passive stabilization effect on these modes from intrinsic plasma rotation. The inclusion of resistivity and plasma rotation in the present model provides a substantially better agreement between modelled and experimental growth rates than that observed in earlier studies using the ideal MHD model. The present model provides a realistic description of the plasma response for both nonresonant and resonant modes, which is both relatively simple and compatible with the computing capabilities and latency limitations encountered in practical implementations of model-based control algorithms.

Place, publisher, year, edition, pages
IOP Publishing, 2022
Keywords
resistive wall mode, reversed field pinch, experimental characterization, modelling, plasma response, feedback control
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-311531 (URN)10.1088/1361-6587/ac5cf9 (DOI)000780055800001 ()2-s2.0-85128840364 (Scopus ID)
Note

QC 20220429

Available from: 2022-04-29 Created: 2022-04-29 Last updated: 2022-06-25Bibliographically approved
Moon, S., Petersson, P., Brunsell, P. R., Rubel, M., Goriaev, A., Ragona, R., . . . Wauters, T. (2021). Characterization of neutral particle fluxes from ICWC and ECWC plasmas in the TOMAS facility. Physica Scripta, 96(12), Article ID 124025.
Open this publication in new window or tab >>Characterization of neutral particle fluxes from ICWC and ECWC plasmas in the TOMAS facility
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2021 (English)In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 96, no 12, article id 124025Article in journal (Refereed) Published
Abstract [en]

Electron- (ECWC) and ion- (ICWC) cyclotron wall conditioning are essential means for controlled fusion to modify the surface state of plasma-facing components in order to reduce impurity generation and fuel accumulation in the wall. Development of ECWC and ICWC requires characterization of neutral particle fluxes generated in discharges, because neutrals enhance the homogeneity of the conditioning, which may contribute to remote or shadowed areas, especially in the presence of a permanent magnetic field (e.g. W7-X, ITER). A time-of-flight neutral particle analyzer (ToF-NPA) with 4.07 m flight distance is employed to measure time- and energy-resolved low energetic (<1 keV) neutral particle distributions. The ToF-NPA setup tested at the EXTRAP T2R reversed field pinch was installed at the TOMAS toroidal plasma facility to determine low energy neutral particle fluxes while investigating the impact of the gas pressure in the instrument and compatibility with low count rates during EC- and ICWC discharges. TOMAS has a major radius of 0.78 m and provides various plasma operation conditions: toroidal magnetic field up to 0.12 T, EC frequency 2.45 GHz with the power of 0.6-6 kW, IC frequency of 10-50 MHz with the power of up to 6 kW. Early results on the characterization of three phases (EC only, EC + IC, and IC only) of hydrogen discharges demonstrate: (i) the low energy (10-725 eV) neutrals distribution has been determined by the NPA system, (ii) the mixed EC + IC phase produces the highest population of neutral particles, while the EC only provides one order of magnitude lower rate, (iii) the neutrals produced in IC only have higher average energy (28 eV) than EC only (7 eV) and EC + IC (16 eV).

Place, publisher, year, edition, pages
IOP PUBLISHING LTD, 2021
Keywords
neutral particle analyzer, ICWC, ECWC, EXTRAP T2R, TOMAS facility
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-302639 (URN)10.1088/1402-4896/ac2494 (DOI)000696686000001 ()2-s2.0-85116395099 (Scopus ID)
Note

QC 20211004

Available from: 2021-10-04 Created: 2021-10-04 Last updated: 2022-06-25Bibliographically approved
Goriaev, A., Wauters, T., Moeller, S., Brakel, R., Brezinsek, S., Buermans, J., . . . Van Schoor, M. (2021). The upgraded TOMAS device: A toroidal plasma facility for wall conditioning, plasma production, and plasma-surface interaction studies. Review of Scientific Instruments, 92(2), Article ID 023506.
Open this publication in new window or tab >>The upgraded TOMAS device: A toroidal plasma facility for wall conditioning, plasma production, and plasma-surface interaction studies
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2021 (English)In: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 92, no 2, article id 023506Article in journal (Refereed) Published
Abstract [en]

The Toroidal Magnetized System device has been significantly upgraded to enable development of various wall conditioning techniques, including methods based on ion and electron cyclotron (IC/EC) range of frequency plasmas, and to complement plasma-wall interaction research in tokamaks and stellarators. The toroidal magnetic field generated by 16 coils can reach its maximum of 125 mT on the toroidal axis. The EC system is operated at 2.45 GHz with up to 6 kW forward power. The IC system can couple up to 6 kW in the frequency range of 10 MHz-50 MHz. The direct current glow discharge system is based on a graphite anode with a maximum voltage of 1.5 kV and a current of 6 A. A load-lock system with a vertical manipulator allows exposure of material samples. A number of diagnostics have been installed: single- and triple-pin Langmuir probes for radial plasma profiles, a time-of-flight neutral particle analyzer capable of detecting neutrals in the energy range of 10 eV-1000 eV, and a quadrupole mass spectrometer and video systems for plasma imaging. The majority of systems and diagnostics are controlled by the Siemens SIMATIC S7 system, which also provides safety interlocks.

Place, publisher, year, edition, pages
AMER INST PHYSICS, 2021
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-292455 (URN)10.1063/5.0033229 (DOI)000630917800005 ()33648119 (PubMedID)2-s2.0-85100904017 (Scopus ID)
Note

QC 20210415

Available from: 2021-04-15 Created: 2021-04-15 Last updated: 2022-10-24Bibliographically approved
Saad, E. & Brunsell, P. R. (2019). Experimental validation of resistive wall mode instability models for active magnetic feedback control. In: 46th EPS Conference on Plasma Physics, EPS 2019: . Paper presented at 46th European Physical Society Conference on Plasma Physics, EPS 2019, 8-12 July 2019, Milan, Italy. European Physical Society (EPS)
Open this publication in new window or tab >>Experimental validation of resistive wall mode instability models for active magnetic feedback control
2019 (English)In: 46th EPS Conference on Plasma Physics, EPS 2019, European Physical Society (EPS) , 2019Conference paper, Published paper (Refereed)
Place, publisher, year, edition, pages
European Physical Society (EPS), 2019
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-274843 (URN)2-s2.0-85084022645 (Scopus ID)
Conference
46th European Physical Society Conference on Plasma Physics, EPS 2019, 8-12 July 2019, Milan, Italy
Note

QC 20200618

Available from: 2020-06-18 Created: 2020-06-18 Last updated: 2022-06-26Bibliographically approved
Fridström, R., Chapman, B. E., Almagri, A. F., Frassinetti, L., Brunsell, P. R., Nishizawa, T. & Sarff, J. S. (2018). Dependence of Perpendicular Viscosity on Magnetic Fluctuations in a Stochastic Topology. Physical Review Letters, 120(22), Article ID 225002.
Open this publication in new window or tab >>Dependence of Perpendicular Viscosity on Magnetic Fluctuations in a Stochastic Topology
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2018 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 120, no 22, article id 225002Article in journal (Refereed) Published
Abstract [en]

In a magnetically confined plasma with a stochastic magnetic field, the dependence of the perpendicular viscosity on the magnetic fluctuation amplitude is measured for the first time. With a controlled, similar to tenfold variation in the fluctuation amplitude, the viscosity increases similar to 100-fold, exhibiting the same fluctuation-amplitude-squared dependence as the predicted rate of stochastic field line diffusion. The absolute value of the viscosity is well predicted by a model based on momentum transport in a stochastic field, the first in-depth test of this model.

Place, publisher, year, edition, pages
American Physical Society, 2018
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-230495 (URN)10.1103/PhysRevLett.120.225002 (DOI)000433425500007 ()29906181 (PubMedID)2-s2.0-85047758978 (Scopus ID)
Note

QC 20180614

Available from: 2018-06-14 Created: 2018-06-14 Last updated: 2022-06-26Bibliographically approved
Setiadi, A. C., Brunsell, P. R., Villone, F., Mastrostefano, S. & Frassinetti, L. (2017). Gray-box modeling of resistive wall modes with vacuum-plasma separation and optimal control design for EXTRAP T2R. Fusion engineering and design, 121, 245-255
Open this publication in new window or tab >>Gray-box modeling of resistive wall modes with vacuum-plasma separation and optimal control design for EXTRAP T2R
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2017 (English)In: Fusion engineering and design, ISSN 0920-3796, E-ISSN 1873-7196, Vol. 121, p. 245-255Article in journal (Refereed) Published
Abstract [en]

This paper presents a graybox methodology to model the resistive wall mode instability by combining first principle approach and system identification technique. In particular we propose a separate vacuum and plasma modeling with cascade interconnection. The shell is modeled using CARIDDI code which solves the 3D integral formulation of eddy current problem, whereas the plasma response is obtained empirically by system identification. Furthermore the resulting model is used to design an optimal feedback control. The model and feedback control is validated experimentally in EXTRAP T2R reversed-field pinch, where RWMs stabilization and non-axisymmetric mode sustainment is considered. 

Place, publisher, year, edition, pages
ELSEVIER SCIENCE SA, 2017
Keywords
Resistive wall mode, Reversed-field pinch, CARIDDI, System identification, Optimal feedback control
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-215807 (URN)10.1016/j.fusengdes.2017.07.011 (DOI)000411550100034 ()2-s2.0-85027698362 (Scopus ID)
Note

QC 20171018

Available from: 2017-10-18 Created: 2017-10-18 Last updated: 2022-06-26Bibliographically approved
Fridström, R., Brunsell, P., Setiadi, A. C. & Frassinetti, L. (2017). Multiple-harmonics RMP effect on tearing modes in EXTRAP T2R. In: : . Paper presented at 44th EPS Conference on Plasma Physics, 26/06/2017 to 30/06/2017, Belfast, Northern Irland. , Article ID P1.137.
Open this publication in new window or tab >>Multiple-harmonics RMP effect on tearing modes in EXTRAP T2R
2017 (English)Conference paper, Published paper (Other academic)
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-218046 (URN)2-s2.0-85055039128 (Scopus ID)
Conference
44th EPS Conference on Plasma Physics, 26/06/2017 to 30/06/2017, Belfast, Northern Irland
Note

QC 20171122

Available from: 2017-11-21 Created: 2017-11-21 Last updated: 2024-03-18Bibliographically approved
Setiadi, A. C., Brunsell, P. R. & Frassinetti, L. (2016). Design and operation of fast model predictive controller for stabilization of magnetohydrodynamic modes in a fusion device. In: Proceedings of the IEEE Conference on Decision and Control: . Paper presented at 54th IEEE Conference on Decision and Control, CDC 2015, 15 December 2015 through 18 December 2015 (pp. 7347-7352). IEEE conference proceedings
Open this publication in new window or tab >>Design and operation of fast model predictive controller for stabilization of magnetohydrodynamic modes in a fusion device
2016 (English)In: Proceedings of the IEEE Conference on Decision and Control, IEEE conference proceedings, 2016, p. 7347-7352Conference paper, Published paper (Refereed)
Abstract [en]

Magnetic confinement fusion (MCF) devices suffer from magnetohydrodynamic (MHD) instabilities. A particular unstable mode, known as the resistive wall mode (RWM), is treated in this work. The RWM perturbs the plasma globally and can degrade the confinement or even terminate the plasma if not stabilized. This paper presents a control design approach to stabilize the RWM in the reversed-field pinch (RFP). The approach consists of: closed-loop system identification of the RFP, design of a fast model predictive controller and experimental validation of the controller. Experimental results shows that the proposed controller manages to stabilize the RWM in plasma.

Place, publisher, year, edition, pages
IEEE conference proceedings, 2016
Keywords
Coils, Control design, Magnetohydrodynamic power generation, Magnetohydrodynamics, Plasmas, Predictive models, Yttrium
National Category
Fusion, Plasma and Space Physics Control Engineering
Identifiers
urn:nbn:se:kth:diva-188273 (URN)10.1109/CDC.2015.7403379 (DOI)000381554507089 ()2-s2.0-84962016878 (Scopus ID)9781479978861 (ISBN)
Conference
54th IEEE Conference on Decision and Control, CDC 2015, 15 December 2015 through 18 December 2015
Note

QC 20160615

Available from: 2016-06-15 Created: 2016-06-09 Last updated: 2024-03-18Bibliographically approved
Fridström, R., Munaretto, S., Frassinetti, L., Chapman, B., Brunsell, P. R. & Sarff, J. (2016). Estimation of anomalous viscosity based on modeling of experimentally observed plasma rotation braking induced by applied resonant magnetic perturbations. In: 43th European Physical Society (EPS) Conference on Plasma Physics. July 4 – July 8, 2016: . Paper presented at 43th European Physical Society (EPS) Conference on Plasma Physics. July 4 – July 8, 2016. European Physical Society (EPS)
Open this publication in new window or tab >>Estimation of anomalous viscosity based on modeling of experimentally observed plasma rotation braking induced by applied resonant magnetic perturbations
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2016 (English)In: 43th European Physical Society (EPS) Conference on Plasma Physics. July 4 – July 8, 2016, European Physical Society (EPS) , 2016Conference paper, Published paper (Refereed)
Place, publisher, year, edition, pages
European Physical Society (EPS), 2016
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-203360 (URN)2-s2.0-85013867240 (Scopus ID)
Conference
43th European Physical Society (EPS) Conference on Plasma Physics. July 4 – July 8, 2016
Note

QC 20170321

Available from: 2017-03-15 Created: 2017-03-15 Last updated: 2024-03-18Bibliographically approved
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Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-5259-0458

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