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Publications (10 of 114) Show all publications
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
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-230495 (URN)10.1103/PhysRevLett.120.225002 (DOI)000433425500007 ()2-s2.0-85047758978 (Scopus ID)
Note

QC 20180614

Available from: 2018-06-14 Created: 2018-06-14 Last updated: 2018-06-19Bibliographically 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: 2017-10-18Bibliographically 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: 2017-11-21Bibliographically approved
Setiadi, A. C., Brunsell, P. & Frassinetti, L. (2016). Improved model predictive control of resistive wall modes by error field estimator in EXTRAP T2R. Plasma Physics and Controlled Fusion, 58(12), Article ID 124002.
Open this publication in new window or tab >>Improved model predictive control of resistive wall modes by error field estimator in EXTRAP T2R
2016 (English)In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 58, no 12, article id 124002Article in journal (Refereed) Published
Abstract [en]

Many implementations of a model-based approach for toroidal plasma have shown better control performance compared to the conventional type of feedback controller. One prerequisite of model-based control is the availability of a control oriented model. This model can be obtained empirically through a systematic procedure called system identification. Such a model is used in this work to design a model predictive controller to stabilize multiple resistive wall modes in EXTRAP T2R reversed-field pinch. Model predictive control is an advanced control method that can optimize the future behaviour of a system. Furthermore, this paper will discuss an additional use of the empirical model which is to estimate the error field in EXTRAP T2R. Two potential methods are discussed that can estimate the error field. The error field estimator is then combined with the model predictive control and yields better radial magnetic field suppression.

Place, publisher, year, edition, pages
Institute of Physics (IOP), 2016
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electrical Engineering
Identifiers
urn:nbn:se:kth:diva-200824 (URN)10.1088/0741-3335/58/12/124002 (DOI)000399802800002 ()2-s2.0-84997606102 (Scopus ID)
Note

QC 20170203

Available from: 2017-02-02 Created: 2017-02-02 Last updated: 2017-05-08Bibliographically approved
Sweeney, R. M., Frassinetti, L., Brunsell, P. R., Fridström, R. & Volpe, F. A. (2016). Local measurement of error field using naturally rotating tearing mode dynamics in EXTRAP T2R. Plasma Physics and Controlled Fusion, 58(12), Article ID 124001.
Open this publication in new window or tab >>Local measurement of error field using naturally rotating tearing mode dynamics in EXTRAP T2R
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2016 (English)In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 58, no 12, article id 124001Article in journal (Refereed) Published
Abstract [en]

An error field (EF) detection technique using the amplitude modulation of a naturally rotating tearing mode (TM) is developed and validated in the EXTRAP T2R reversed field pinch. The technique was used to identify intrinsic EFs of m/n = 1/-12, where m and n are the poloidal and toroidal mode numbers. The effect of the EF and of a resonant magnetic perturbation (RMP) on the TM, in particular on amplitude modulation, is modeled with a first-order solution of the modified Rutherford equation. In the experiment, the TM amplitude is measured as a function of the toroidal angle as the TM rotates rapidly in the presence of an unknown EF and a known, deliberately applied RMP. The RMP amplitude is fixed while the toroidal phase is varied from one discharge to the other, completing a full toroidal scan. Using three such scans with different RMP amplitudes, the EF amplitude and phase are inferred from the phases at which the TM amplitude maximizes. The estimated EF amplitude is consistent with other estimates (e.g. based on the best EF-cancelling RMP, resulting in the fastest TM rotation). A passive variant of this technique is also presented, where no RMPs are applied, and the EF phase is deduced.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2016
Keywords
error field, EXTRAP T2R, plasma, reversed field pinch, tearing mode, tokamak, Amplitude modulation, Magnetoplasma, Modulation, Pinch effect, Plasmas, Tearing modes, Errors
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-202888 (URN)10.1088/0741-3335/58/12/124001 (DOI)000399802800001 ()2-s2.0-84997785038 (Scopus ID)
Note

QC 20170309

Available from: 2017-03-09 Created: 2017-03-09 Last updated: 2017-05-08Bibliographically approved
Setiadi, A. C., Villone, F., Brunsell, P., Polsinelli, A., Mastrostefano, S. & Frassinetti, L. (2016). Reduced Order Modelling of Resistive Wall Modes in EXTRAP T2R Reversed-Field Pinch. In: 43rd European Physical Society Conference on Plasma Physics, EPS 2016: . Paper presented at 43rd European Physical Society Conference on Plasma Physics, EPS 2016, KU Leuven, Leuven, Belgium, 4 July 2016 through 8 July 2016. European Physical Society
Open this publication in new window or tab >>Reduced Order Modelling of Resistive Wall Modes in EXTRAP T2R Reversed-Field Pinch
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2016 (English)In: 43rd European Physical Society Conference on Plasma Physics, EPS 2016, European Physical Society , 2016Conference paper, Published paper (Refereed)
Abstract [en]

In this paper, we study the Resistive Wall Mode (RWM) instability in the EXTRAP T2R Reversed-Field Pinch. The RWM is a kink-like instability that grows in the time scale of magnetic field diffusion time through the conducting structures. The RWMs are highly affected by the complex three-dimensional conducting structures surrounding the plasma. The first part of the paper will describe the RWM modelling process in EXTRAP T2R using the CarMa computational tool. The code can rigorously take into account the complex geometry of the conducting structures in the solution of the plasma stability problem. The resulting model can be cast into a state space form, with the number of state variables up to several thousands. In the time scale of magnetic field diffusion time, it is possible to stabilize the RWMs by using feedback-controlled external magnetic perturbation to counteract the growing magnetic field caused by the RWMs. Hence, the final suppression level of the RWM is highly dependent on the features of the feedback controller; thus its careful design is needed. Advanced feedback control design method requires an accurate model and the CarMa computational tool can be used in this respect. However, handling such a complex model may pose severe problems both in the design phase and when implemented in real-time due to the computational load. Several model reduction techniques will be employed to address this issue, with the aim of getting to a simpler approximation of RWM response without neglecting the crucial physics information

Place, publisher, year, edition, pages
European Physical Society, 2016
Keywords
Reduced order model, reversed-field pinch, magnetohydrodynamic
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electrical Engineering
Identifiers
urn:nbn:se:kth:diva-200826 (URN)
Conference
43rd European Physical Society Conference on Plasma Physics, EPS 2016, KU Leuven, Leuven, Belgium, 4 July 2016 through 8 July 2016
Note

QC 20170203

Available from: 2017-02-02 Created: 2017-02-02 Last updated: 2018-12-03Bibliographically approved
Frassinetti, L., Sun, Y., Fridström, R., Menmuir, S., Olofsson, K. E., Brunsell, P. R., . . . Drake, J. R. (2015). Braking due to non-resonant magnetic perturbations and comparison with neoclassical toroidal viscosity torque in EXTRAP T2R. Nuclear Fusion, 55(11), Article ID 112003.
Open this publication in new window or tab >>Braking due to non-resonant magnetic perturbations and comparison with neoclassical toroidal viscosity torque in EXTRAP T2R
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2015 (English)In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 55, no 11, article id 112003Article in journal (Refereed) Published
Abstract [en]

The non-resonant magnetic perturbation (MP) braking is studied in the EXTRAP T2R reversed-field pinch (RFP) and the experimental braking torque is compared with the torque expected by the neoclassical toroidal viscosity (NTV) theory. The EXTRAP T2R active coils can apply magnetic perturbations with a single harmonic, either resonant or non-resonant. The non-resonant MP produces velocity braking with an experimental torque that affects a large part of the core region. The experimental torque is clearly related to the plasma displacement, consistent with a quadratic dependence as expected by the NTV theory. The work show a good qualitative agreement between the experimental torque in a RFP machine and NTV torque concerning both the torque density radial profile and the dependence on the non-resonant MP harmonic.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2015
Keywords
NTV, RMP, RFP, braking, EXTRAP T2R, MP
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-180517 (URN)10.1088/0029-5515/55/11/112003 (DOI)000366528700003 ()2-s2.0-84946019106 (Scopus ID)
Note

QC 20160118

Available from: 2016-01-18 Created: 2016-01-14 Last updated: 2017-11-30Bibliographically approved
Fridström, R., Frassinetti, L. & Brunsell, P. R. (2015). Hysteresis in the tearing mode locking/unlocking due to resonant magnetic perturbations in EXTRAP T2R. Plasma Physics and Controlled Fusion, 57(10), Article ID 104008.
Open this publication in new window or tab >>Hysteresis in the tearing mode locking/unlocking due to resonant magnetic perturbations in EXTRAP T2R
2015 (English)In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 57, no 10, article id 104008Article in journal (Refereed) Published
Abstract [en]

The physical mechanisms behind the hysteresis in the tearing mode locking and unlocking to a resonant magnetic perturbation (RMP) are experimentally studied in EXTRAP T2R reversed-field pinch. The experiments show that the electromagnetic and the viscous torque increase with increasing perturbation amplitude until the mode locks to the wall. At the wall-locking, the plasma velocity reduction profile is peaked at the radius where the RMP is resonant. Thereafter, the viscous torque drops due to the relaxation of the velocity in the central plasma. This is the main reason for the hysteresis in the RMP locking and unlocking amplitude. The increased amplitude of the locked tearing mode produces further deepening of the hysteresis. Both experimental results are in qualitative agreement with the model in Fitzpatrick et al (2001 Phys. Plasmas 8 4489)

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2015
Keywords
EXTRAP T2R, hysteresis, locking unlocking, resonant magnetic perturbation, reversed-field pinch, tearing modes, Magnetic resonance, Magnetism, Pinch effect, Wave plasma interactions, Resonant magnetic perturbations, Reversed field pinch, Locks (fasteners)
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-177743 (URN)10.1088/0741-3335/57/10/104008 (DOI)000366679100009 ()2-s2.0-84940838273 (Scopus ID)
Note

QC 20151130

Available from: 2015-11-30 Created: 2015-11-25 Last updated: 2017-12-01Bibliographically approved
Setiadi, A. C., Brunsell, P. & Frassinetti, L. (2015). Implementation of model predictive control for resistive wall mode stabilization on EXTRAP T2R. Plasma Physics and Controlled Fusion, 57(10), Article ID 104005.
Open this publication in new window or tab >>Implementation of model predictive control for resistive wall mode stabilization on EXTRAP T2R
2015 (English)In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 57, no 10, article id 104005Article in journal (Refereed) Published
Abstract [en]

A model predictive control (MPC) method for stabilization of the resistive wall mode (RWM) in the EXTRAP T2R reversed-field pinch is presented. The system identification technique is used to obtain a linearized empirical model of EXTRAP T2R. MPC employs the model for prediction and computes optimal control inputs that satisfy performance criterion. The use of a linearized form of the model allows for compact formulation of MPC, implemented on a millisecond timescale, that can be used for real-time control. The design allows the user to arbitrarily suppress any selected Fourier mode. The experimental results from EXTRAP T2R show that the designed and implemented MPC successfully stabilizes the RWM.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2015
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-168631 (URN)10.1088/0741-3335/57/10/104005 (DOI)000366679100006 ()2-s2.0-84940854105 (Scopus ID)
Note

Updated from manuscript to article.

QC 20151127

Available from: 2015-06-05 Created: 2015-06-05 Last updated: 2017-12-04Bibliographically approved
Brunsell, P., Frassinetti, L., Volpe, F., Olofsson, E., Fridström, R. & Setiadi, A. C. (2014). Resistive Wall Mode Studies utilizing External Magnetic Perturbations. In: Proceeding of the 25th IAEA Fusion Energy Conference: . Paper presented at 25th IAEA Fusion Energy Conference, St. Petersburg, Russian Federation, 2014. , Article ID Paper EX/P4-20.
Open this publication in new window or tab >>Resistive Wall Mode Studies utilizing External Magnetic Perturbations
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2014 (English)In: Proceeding of the 25th IAEA Fusion Energy Conference, 2014, article id Paper EX/P4-20Conference paper, Published paper (Other academic)
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-200835 (URN)
Conference
25th IAEA Fusion Energy Conference, St. Petersburg, Russian Federation, 2014
Note

QC 20170202

Available from: 2017-02-02 Created: 2017-02-02 Last updated: 2017-02-02Bibliographically approved
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Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-5259-0458

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