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Publications (7 of 7) Show all publications
Lawson, K. D., Bergsåker, H., Bykov, I., Frassinetti, L., Garcia Carrasco, A., Hellsten, T., . . . et al., . (2019). Population modelling of the He II energy levels in tokamak plasmas: I. Collisional excitation model. Paper presented at ARK REH, 1982, ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES, V49, P545. JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS, 52(4), Article ID 045001.
Open this publication in new window or tab >>Population modelling of the He II energy levels in tokamak plasmas: I. Collisional excitation model
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2019 (English)In: JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS, Vol. 52, no 4, article id 045001Article in journal (Refereed) Published
Abstract [en]

Helium is widely used as a fuel or minority gas in laboratory fusion experiments, and will be present as ash in DT thermonuclear plasmas. It is therefore essential to have a good understanding of its atomic physics. To this end He II population modelling has been undertaken for the spectroscopic levels arising from shells with principal quantum number n = 1-5. This paper focuses on a collisional excitation model; ionisation and recombination will be considered in a subsequent article. Heavy particle collisional excitation rate coefficients have been generated to supplement the currently-available atomic data for He II, and are presented for proton, deuteron, triton and alpha-particle projectiles. The widely-used criterion for levels within an n shell being populated in proportion to their statistical weights is reassessed with the most recent atomic data, and found not to apply to the He II levels at tokamak densities (10(18)-10(21) m(-3)). Consequences of this and other likely sources of errors are quantified, as is the effect of differing electron and ion temperatures. Line intensity ratios, including the so-called 'branching ratios' and the fine-structure beta(1), beta(2), beta(3), and gamma ratios, are discussed, the latter with regard to their possible use as diagnostics.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD, 2019
Keywords
He II, population modelling, tokamak plasmas, spectral line intensity ratios
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-243932 (URN)10.1088/1361-6455/aaf703 (DOI)000456847500001 ()
Conference
ARK REH, 1982, ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES, V49, P545
Note

QC 20190212

Available from: 2019-02-12 Created: 2019-02-12 Last updated: 2019-02-12Bibliographically approved
Blanken, T. C., Frassinetti, L., Fridström, R., Garcia-Carrasco, A., Hellsten, T., Jonsson, T., . . . Dori, V. (2019). Real-time plasma state monitoring and supervisory control on TCV. Nuclear Fusion, 59(2), Article ID 026017.
Open this publication in new window or tab >>Real-time plasma state monitoring and supervisory control on TCV
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2019 (English)In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 59, no 2, article id 026017Article in journal (Refereed) Published
Abstract [en]

In ITER and DEMO, various control objectives related to plasma control must be simultaneously achieved by the plasma control system (PCS), in both normal operation as well as off-normal conditions. The PCS must act on off-normal events and deviations from the target scenario, since certain sequences (chains) of events can precede disruptions. It is important that these decisions are made while maintaining a coherent prioritization between the real-time control tasks to ensure high-performance operation. In this paper, a generic architecture for task-based integrated plasma control is proposed. The architecture is characterized by the separation of state estimation, event detection, decisions and task execution among different algorithms, with standardized signal interfaces. Central to the architecture are a plasma state monitor and supervisory controller. In the plasma state monitor, discrete events in the continuous-valued plasma state arc modeled using finite state machines. This provides a high-level representation of the plasma state. The supervisory controller coordinates the execution of multiple plasma control tasks by assigning task priorities, based on the finite states of the plasma and the pulse schedule. These algorithms were implemented on the TCV digital control system and integrated with actuator resource management and existing state estimation algorithms and controllers. The plasma state monitor on TCV can track a multitude of plasma events, related to plasma current, rotating and locked neoclassical tearing modes, and position displacements. In TCV experiments on simultaneous control of plasma pressure, safety factor profile and NTMs using electron cyclotron heating (ECI I) and current drive (ECCD), the supervisory controller assigns priorities to the relevant control tasks. The tasks are then executed by feedback controllers and actuator allocation management. This work forms a significant step forward in the ongoing integration of control capabilities in experiments on TCV, in support of tokamak reactor operation.

Place, publisher, year, edition, pages
Institute of Physics (IOP), 2019
Keywords
real-time control, supervisory control, control of tokamak plasmas
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-242971 (URN)10.1088/1741-4326/aaf451 (DOI)000455823900003 ()
Note

QC 20190212

Available from: 2019-02-12 Created: 2019-02-12 Last updated: 2019-02-12Bibliographically approved
Tierens, W., Frassinetti, L., Hellsten, T., Petersson, P., Fridström, R., Garcia Carrasco, A., . . . et al., . (2019). Validation of the ICRF antenna coupling code RAPLICASOL against TOPICA and experiments. Nuclear Fusion, 59(4), Article ID 046001.
Open this publication in new window or tab >>Validation of the ICRF antenna coupling code RAPLICASOL against TOPICA and experiments
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2019 (English)In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 59, no 4, article id 046001Article in journal (Refereed) Published
Abstract [en]

In this paper we validate the finite element code RAPLICASOL, which models radiofrequency wave propagation in edge plasmas near ICRF antennas, against calculations with the TOPICA code. We compare the output of both codes for the ASDEX Upgrade 2-strap antenna, and for a 4-strap WEST-like antenna. Although RAPLICASOL requires considerably fewer computational resources than TOPICA, we find that the predicted quantities of experimental interest (including reflection coefficients, coupling resistances, S- and Z-matrix entries, optimal matching settings, and even radiofrequency electric fields) are in good agreement provided we are careful to use the same geometry in both codes.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD, 2019
Keywords
ICRF, finite elements, simulation
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-243928 (URN)10.1088/1741-4326/aaf455 (DOI)000456197200001 ()
Note

QC 20190212

Available from: 2019-02-12 Created: 2019-02-12 Last updated: 2019-02-12Bibliographically approved
Dumont, R. J., Mailloux, J., Aslanyan, V., Baruzzo, M., Challis, C. D., Coffey, I., . . . Weisen, H. (2018). Scenario development for the observation of alpha-driven instabilities in JET DT plasmas. Nuclear Fusion, 58(8), Article ID 082005.
Open this publication in new window or tab >>Scenario development for the observation of alpha-driven instabilities in JET DT plasmas
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2018 (English)In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 58, no 8, article id 082005Article in journal (Refereed) Published
Abstract [en]

In DT plasmas, toroidal Alfven eigenmodes (TAEs) can be made unstable by the alpha particles resulting from fusion reactions, and may induce a significant redistribution of fast ions. Recent experiments have been conducted in JET deuterium plasmas in order to prepare scenarios aimed at observing alpha-driven TAEs in a future JET DT campaign. Discharges at low density, large core temperatures associated with the presence of internal transport barriers and characterised by good energetic ion confinement have been performed. ICRH has been used in the hydrogen minority heating regime to probe the TAE stability. The consequent presence of MeV ions has resulted in the observation of TAEs in many instances. The impact of several key parameters on TAE stability could therefore be studied experimentally. Modeling taking into account NBI and ICRH fast ions shows good agreement with the measured neutron rates, and has allowed predictions for DT plasmas to be performed.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD, 2018
Keywords
JET, alphas, instabilities, TAEs, scenario, DT plasmas
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-232387 (URN)10.1088/1741-4326/aab1bb (DOI)000436930000002 ()2-s2.0-85050403274 (Scopus ID)
Note

QC 20180727

Available from: 2018-07-27 Created: 2018-07-27 Last updated: 2018-10-16Bibliographically approved
Sharapov, S. E., Garcia-Munoz, M., Van Zeeland, M. A., Bobkov, B., Classen, I. G., Ferreira, J., . . . Vallejos, P. (2018). The effects of electron cyclotron heating and current drive on toroidal Alfven eigenmodes in tokamak plasmas. Plasma Physics and Controlled Fusion, 60(1), Article ID 014026.
Open this publication in new window or tab >>The effects of electron cyclotron heating and current drive on toroidal Alfven eigenmodes in tokamak plasmas
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2018 (English)In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 60, no 1, article id 014026Article in journal (Refereed) Published
Abstract [en]

Dedicated studies performed for toroidal Alfven eigenmodes (TAEs) in ASDEX-Upgrade (AUG) discharges with monotonic q-profiles have shown that electron cyclotron resonance heating (ECRH) can make TAEs more unstable. In these AUG discharges, energetic ions driving TAEs were obtained by ion cyclotron resonance heating (ICRH). It was found that off-axis ECRH facilitated TAE instability, with TAEs appearing and disappearing on timescales of a few milliseconds when the ECRH power was switched on and off. On-axis ECRH had a much weaker effect on TAEs, and in AUG discharges performed with co- and counter-current electron cyclotron current drive (ECCD), the effects of ECCD were found to be similar to those of ECRH. Fast ion distributions produced by ICRH were computed with the PION and SELFO codes. A significant increase in T-e caused by ECRH applied off-axis is found to increase the fast ion slowing-down time and fast ion pressure causing a significant increase in the TAE drive by ICRH-accelerated ions. TAE stability calculations show that the rise in T-e causes also an increase in TAE radiative damping and thermal ion Landau damping, but to a lesser extent than the fast ion drive. As a result of the competition between larger drive and damping effects caused by ECRH, TAEs become more unstable. It is concluded, that although ECRH effects on AE stability in present-day experiments may be quite significant, they are determined by the changes in the plasma profiles and are not particularly ECRH specific.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD, 2018
Keywords
energetic particles, Alfven eigenmodes, ECRH, ECCD, ICRH
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-217926 (URN)10.1088/1361-6587/aa90ee (DOI)000414369100001 ()
Note

QC 20171121

Available from: 2017-11-21 Created: 2017-11-21 Last updated: 2017-11-24Bibliographically approved
Vallejos, P., Johnson, T. & Hellsten, T. (2016). An iterative method to include spatial dispersion for waves in nonuniform plasmas using wavelet decomposition. Paper presented at 29 August 2016 through 2 September 2016. Journal of Physics, Conference Series, 775(1), Article ID 012016.
Open this publication in new window or tab >>An iterative method to include spatial dispersion for waves in nonuniform plasmas using wavelet decomposition
2016 (English)In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 775, no 1, article id 012016Article in journal (Refereed) Published
Abstract [en]

A novel method for solving wave equations with spatial dispersion is presented, suitable for applications to ion cyclotron resonance heating. The method splits the wave operator into a dispersive and a non-dispersive part. The latter can be inverted with e.g. finite element methods. The spatial dispersion is evaluated using a wavelet representation of the dielectric kernel and added by means of iteration. The method has been successfully tested on a low frequency kinetic Alfvén wave with second order Larmor radius effects in a nonuniform plasma slab.

Keywords
Cyclotron resonance, Finite element method, Fusion reactions, Iterative methods, Wave equations, Wavelet decomposition, Ion cyclotron resonance heating, Larmor radius effects, Nonuniform plasma, Second orders, Solving wave equations, Spatial dispersion, Wave operators, Wavelet representation, Dispersion (waves)
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-201866 (URN)10.1088/1742-6596/775/1/012016 (DOI)2-s2.0-85009809630 (Scopus ID)
Conference
29 August 2016 through 2 September 2016
Note

QC 20170308

Available from: 2017-03-08 Created: 2017-03-08 Last updated: 2017-11-29Bibliographically approved
Hellsten, T., Johnson, T. & Vallejos, P. (2014). An iterative method for including Doppler shift in global wave solvers using FEM decomposition. Paper presented at Joint Varenna-Lausanne International Workshop on the Theory of Fusion Plasmas, SEP 01-05, 2014, Varenna, ITALY. Journal of Physics: Conference series, 561
Open this publication in new window or tab >>An iterative method for including Doppler shift in global wave solvers using FEM decomposition
2014 (English)In: Journal of Physics: Conference series, ISSN 1742-6596, Vol. 561Article in journal (Refereed) Published
Abstract [en]

A method for calculating the wave field for spatial dispersive media is proposed suitable for FEM. The method is based on operator splitting by separating the induced current and wave field calculations, and solving the system by means of iterations. In order to take into account several coexisting waves with different poloidal mode numbers when calculating the induced current the wave field is decomposed into wavelets, for which the current is calculated assuming the plasma to be weakly non-uniform.

Place, publisher, year, edition, pages
Institute of Physics (IOP), 2014
Keywords
Dispersive media, Non-uniform, Operator-splitting, Poloidal mode numbers, Wavefields
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-159055 (URN)10.1088/1742-6596/561/1/012010 (DOI)000346423600010 ()2-s2.0-84919343559 (Scopus ID)
Conference
Joint Varenna-Lausanne International Workshop on the Theory of Fusion Plasmas, SEP 01-05, 2014, Varenna, ITALY
Note

QC 20150122

Available from: 2015-01-22 Created: 2015-01-20 Last updated: 2016-12-15Bibliographically approved
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Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0003-4343-6325

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