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Reversed field pinch operation with intelligent shell feedback control in EXTRAP T2R
KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.ORCID iD: 0000-0002-5259-0458
KTH, School of Engineering Sciences (SCI), Physics.
KTH, School of Engineering Sciences (SCI), Physics.
KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
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2006 (English)In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 46, no 11, 904-913 p.Article in journal (Refereed) Published
Abstract [en]

Discharges in the thin shell reversed field pinch (RFP) device EXTRAP T2R without active feedback control are characterized by growth of non-resonant m = 1 unstable resistive wall modes (RWMs) in agreement with linear MHD theory. Resonant m = 1 tearing modes (TMs) exhibit initially fast rotation and the associated perturbed radial fields at the shell are small, but eventually TMs wall-lock and give rise to a growing radial field. The increase in the radial field at the wall due to growing RWMs and wall-locked TMs is correlated with an increase in the toroidal loop voltage, which leads to discharge termination after 3-4 wall times. An active magnetic feedback control system has been installed in EXTRAP T2R. A two-dimensional array of 128 active saddle coils (pair-connected into 64 independent m = 1 coils) is used with intelligent shell feedback control to suppress the m = 1 radial field at the shell. With feedback control, active stabilization of the full toroidal spectrum of 16 unstable m = 1 non-resonant RWMs is achieved, and TM wall locking is avoided. A three-fold extension of the pulse length, up to the power supply limit, is observed. Intelligent shell feedback control is able to maintain the plasma equilibrium for 10 wall times, with plasma confinement parameters sustained at values comparable to those obtained in thick shell devices of similar size.

Place, publisher, year, edition, pages
2006. Vol. 46, no 11, 904-913 p.
Keyword [en]
Correlation methods; Feedback control; Perturbation techniques; Pinch effect; Plasma confinement; Resonance; Rotation; Discharge termination; Perturbed radial fields; Reversed field pinch operation; Tearing modes (TM); Shells (structures)
National Category
Fusion, Plasma and Space Physics
Identifiers
URN: urn:nbn:se:kth:diva-6558DOI: 10.1088/0029-5515/46/11/004ISI: 000242664000006Scopus ID: 2-s2.0-33846062292OAI: oai:DiVA.org:kth-6558DiVA: diva2:11303
Note
QC 20100810Available from: 2006-12-11 Created: 2006-12-11 Last updated: 2012-03-22Bibliographically approved
In thesis
1. Diagnostics for advanced fusion plasma scenarios
Open this publication in new window or tab >>Diagnostics for advanced fusion plasma scenarios
2006 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Over the past decade, fusion research has showed the potential of being a main candidate for energy production for future generations. Further advances in improved fusion performance are therefore vital. This thesis focuses on advanced fusion plasma scenarios and their diagnostic requirements. In particular the design of a motional Stark effect (MSE) diagnostic at the MAST spherical tokamak and the analysis of magneto-hydrodynamic mode feedback control and pulsed poloidal current drive (PPCD) at the reversed field pinch (RFP) experiment EXTRAP T2R are discussed.

The MSE diagnostic is important for the determination of the plasma current profile, information that is necessary for studies in advanced confinement scenarios like reversed shear profiles or current holes. The MAST MSE system has two channels and selects the spectral components using 1Å FWHM interference filters. The diagnostic has been commissioned during the fall of 2006 and the results show the feasibility of the technique with rms-noise ~0.5° using a time resolution of 1 ms. Investigations of mirror labyrinths for the future ITER MSE diagnostic highlight the need for careful calibration considerations.

Feedback control and PPCD are techniques for improved confinement. Feedback control dramatically decreases impurity influx at the end of discharges while transport in the bulk plasma is largely unaffected. During PPCD the transport is seen to decrease and it is demonstrated that PPCD and feedback control can be employed simultaneously.

New and innovative techniques for fusion spectroscopy are furthermore described. This includes the use of correlations in line integrated signals to determine ion emission profiles in poloidally symmetric environments. Good agreement with other diagnostic methods is obtained. The assessment of electron temperature profiles using measured differences between Thomson scattering and vacuum ultra-violet spectroscopy is also shown.

Place, publisher, year, edition, pages
Stockholm: KTH, 2006. xiv, 84 p.
Series
Trita-FYS, ISSN 0280-316X ; 2006:64
Keyword
MSE, PEM, mirror evolution, fusion, diagnostics, plasma spectroscopy, reversed field pinch, spherical tokamak, intelligent shell, PPCD, MAST, ITER
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-4221 (URN)91-7178-474-8 (ISBN)
Public defence
2006-12-15, Sal F3, KTH, Lindstedtsvägen 26, Stockholm, 09:00
Opponent
Supervisors
Note
QC 20100907Available from: 2006-12-11 Created: 2006-12-11 Last updated: 2010-09-07Bibliographically approved
2. Visible spectroscopic diagnostics: application and development in fusion plasmas
Open this publication in new window or tab >>Visible spectroscopic diagnostics: application and development in fusion plasmas
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Diagnostic measurements play a vital role in experiments. Without them we would be in the dark with no way of knowing what was happening; of understanding the processes and behaviour occurring; or even of judging the success or failure of our experiments. The development of fusion plasma devices is no different. In this thesis we concentrate on visible spectroscopy based diagnostics: examining the techniques for measurement and analysis; the breadth of plasma parameters that can be extracted from the spectroscopic data; and how the application of these diagnostic techniques gives us a broader picture of the plasma and the events taking place within. Techniques are developed and applied to plasmas in three fusion experiments, EXTRAP T2R, ASDEX Upgrade and JET. The diagnostic techniques exploit different features of the measurements of the emitted photons to obtain various useful plasma parameters.

Determination of the ion temperature and rotation velocity of oxygen impurity ions in the EXTRAP T2R plasma is achieved through measurement and analysis of, respectively, the Doppler broadening and the Doppler wavelength shift of visible wavelength atomic spectral lines. The evolution of the temperature and rotation is studied as a function of the discharge parameters, in particular looking at the effect of applying active feedback control schemes to the resistive wall modes and/or pulsed poloidal current drive. Measurements of multiple ionisation stages are used to estimate radial profiles of the toroidal rotation and the ion temperature and correlations between the ion rotations and the rotation velocities of tearing modes are also established.

Radial profiles of the emissivity and density (or concentration) of the oxygen ions are obtained by means of measurements of the spectral line intensities on a small array of linesof- sight through the plasma. Changes to the profiles for different plasma schemes and the implications for particle transport are investigated. The derived emissivity profiles are used in the analysis for some of the other spectroscopic diagnostics. Spectral line intensity measurements (in this case of neutral ions) are also the basis for calculations of both the electron temperature and the particle fluxes at the plasma edge. The latter is an indicator of the degree and type of interaction between the plasma and the surrounding surfaces. Particle fluxes of the operating gas hydrogen and of chromium and molybdenum impurities are investigated in EXTRAP T2R for different operating scenarios, in particular changes in the metallic influx with the application of active feedback mode control are examined along with the correspondence between spectroscopic and collector probe results. In the ASDEX Upgrade divertor estimates of the particle flux of the deuterium operating gas are also made through analysis of spectral intensities. Molecular D2 band structure is explored in addition to the Balmer Dα spectral line intensity to acquire both atomic and molecular particle fluxes, investigate the contribution of the dissociating D2 to the Dα line and study the effect of changes in the divertor.

Analysis of the D2 molecular band structure (the relative intensities of the rotational lines and vibrational bands) also enables calculation of the upper state rotational and ground state vibrational temperatures. The locations of emitting atomic ions in JET are estimated from Zeeman splitting analysis of the structure of their spectral lines.

The measurement and analysis of visible wavelength light is demonstrated to be a sensitive diagnostic tool in the quest for increased knowledge about fusion plasmas and their operating scenarios.

Place, publisher, year, edition, pages
Stockholm: KTH, 2007. x, 52 p.
Series
Trita-FYS, ISSN 0280-316X ; 2007:72
Keyword
visible spectroscopy, fusion, Doppler shift, Doppler broadening
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-4541 (URN)978-91-7178-771-2 (ISBN)
Public defence
2007-12-07, Sal FB42, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20100810Available from: 2007-11-20 Created: 2007-11-20 Last updated: 2010-08-10Bibliographically approved

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Brunsell, Per R.Rachlew, Elisabeth

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