Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Diagnostics for advanced fusion plasma scenarios
KTH, School of Engineering Sciences (SCI), Physics.
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 [en]
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: urn:nbn:se:kth:diva-4221ISBN: 91-7178-474-8 (print)OAI: oai:DiVA.org:kth-4221DiVA: diva2:11304
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
List of papers
1. First mirror contamination studies for polarimetry motional Stark effect measurements for ITER
Open this publication in new window or tab >>First mirror contamination studies for polarimetry motional Stark effect measurements for ITER
2004 (English)In: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 75, 3446-3448 p.Article in journal (Refereed) Published
Abstract [en]

The motional Stark effect (MSE) diagnostic on the International Thermonuclear Experimental Reactor will need to guide the light through a labyrinth of mirrors to provide neutron shielding. Knowledge of how the mirrors change the polarization is essential for accurate determination of the q profile. The optical properties of the plasma facing mirror are also expected to change with time due to deposition/erosion. For the purpose of examining this experimentally a detector system, identical to the JET MSE system, using twin photoelastic modulators was constructed. Measurements have been performed on freshly prepared mirrors, on mirrors after exposure to plasmas in Tore Supra, and labyrinth designs. The result shows a significant effect on the optical properties and demonstrate the need for in situ monitoring. The measured properties of the labyrinth closely follow the Mueller matrix formalism. With a correct choice of material the angle change introduced by the four mirrors furthest away from the plasma will be below 1 degrees.

National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-6553 (URN)10.1063/1.1779615 (DOI)000224755900020 ()2-s2.0-9944234666 (Scopus ID)
Note
QC 20100906Available from: 2006-12-11 Created: 2006-12-11 Last updated: 2017-12-14Bibliographically approved
2. Accurate polarization measurements with a dual photoelastic modulator
Open this publication in new window or tab >>Accurate polarization measurements with a dual photoelastic modulator
2005 (English)In: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 44, no 28, 5899-5904 p.Article in journal (Refereed) Published
Abstract [en]

Measurements of the polarization effects in multimirror experiments by using a dual photoelastic modulator are described. The effect of single and multiple mirrors in polarization measurements in two and three dimensions is discussed, and experimental results show how symmetrical placement of mirrors in three-dimensional geometry can eliminate changes in the polarization. Calibration procedures for a dual photoelastic modulator and potential error sources such as misalignment of analyzer, signal dc offset, and neglect of aperture size are presented. Mirror-surface evolution and how it can disturb the polarization measurement are also addressed.

National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-6554 (URN)10.1364/AO.44.005899 (DOI)000232186200007 ()2-s2.0-28044470968 (Scopus ID)
Note
QC 20100906Available from: 2006-12-11 Created: 2006-12-11 Last updated: 2017-12-14Bibliographically approved
3. Motional Stark effect diagnostic pilot experiment for MAST
Open this publication in new window or tab >>Motional Stark effect diagnostic pilot experiment for MAST
Show others...
2006 (English)In: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 77, no 10, 10E905- p.Article in journal (Refereed) Published
Abstract [en]

Exploiting the motional Stark effect (MSE) in the low magnetic fields of spherical tokamaks such as MAST is complicated by the Doppler smearing of the relatively closely spaced Stark components. Extensive modeling of MSE spectra and the subsequent polarized fraction (similar to 20%) of spectrally filtered light and signal to noice ratios have been performed taking account of real experimental conditions including neutral beam parameters, port sizes, optical losses, filter characteristics, etc. A design is selected which uses high throughput interference filters (0.1 nm bandpass ) for separation of the spectral components. An accuracy of similar to 0.5 degrees S compared with typically 15 degrees is estimated for field angle measurements. The design allows for early implementation, starting with a pilot two chord system, and for an economic expansion to a multiplicity of chords. Matching the Doppler shifted D-alpha from the beam neutrals will be accomplished by a combination of filter selection and fine-tuning of the beam voltage. Avoiding filter tuning in the design greatly simplifies the diagnostic. Calibration results of the diagnostic support the calculations.

Keyword
Calibration, Doppler effect, Magnetic fields, Optical filters, Signal to noise ratio, Tokamak devices
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-6555 (URN)10.1063/1.2220475 (DOI)000241722800138 ()2-s2.0-33750526497 (Scopus ID)
Conference
Conference: 16th Topical Conference on High-Temperature Plasma Diagnostics. Williamsburg, VA. MAY 07-11, 2006
Note

QC 20100907.

Available from: 2006-12-11 Created: 2006-12-11 Last updated: 2017-12-14Bibliographically approved
4. Measurements and modeling of transport and impurity radial profiles in the EXTRAP T2R reversed field pinch
Open this publication in new window or tab >>Measurements and modeling of transport and impurity radial profiles in the EXTRAP T2R reversed field pinch
Show others...
2006 (English)In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 13, no 9, 092506- p.Article in journal (Refereed) Published
Abstract [en]

Radial impurity profiles of oxygen in the rebuilt reversed field pinch EXTRAP T2R [P. R. Brunsell , Plasma Phys. Control. Fusion 43, 1457 (2001)] have been measured with a multichannel spectrometer. Absolute ion densities for oxygen peak between 1-4x10(10) cm(-3) for a central electron density of 1x10(13) cm(-3). Transport simulations with the one-dimensional transport code STRAHL with a diffusion coefficient of 20 m(2) s(-1) yield density profiles similar to those measured. Direct measurement of the ion profile evolution during pulsed poloidal current drive suggests that the diffusion coefficient is reduced by a factor similar to 2 in the core but remains unaffected toward the edge. Core transport is not significantly affected by the radial magnetic field growth seen at the edge in discharges without feedback control. This indicates that the mode core amplitude remains the same while the mode eigenfunction increases at the edge.

Keyword
Carrier concentration; Diffusion; Eigenvalues and eigenfunctions; Feedback control; Magnetic fields; Radial flow; Spectrometers; Diffusion coefficients; Multichannel spectrometers; Radial impurity; Impurities
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-7661 (URN)10.1063/1.2349304 (DOI)000240877800033 ()2-s2.0-33749334196 (Scopus ID)
Note
QC 20100810. Titel ändrad, tidigare titel: "Measurements and modelling of transport and impurity profiles in the EXTRAP T2R reversed field pinch" 20100810.Available from: 2007-11-20 Created: 2007-11-20 Last updated: 2017-12-14Bibliographically approved
5. Method for measuring radial impurity emission profiles using correlations of line integrated signals
Open this publication in new window or tab >>Method for measuring radial impurity emission profiles using correlations of line integrated signals
Show others...
2006 (English)In: Review of scientific instruments, ISSN 0034-6748, Vol. 77, no 4, 043508- p.Article in journal (Refereed) Published
Abstract [en]

A method of determining radial impurity emission profiles is outlined. The method uses correlations between line integrated signals and is based on the assumption of cylindrically symmetric fluctuations. Measurements at the reversed field pinch EXTRAP T2R show that emission from impurities expected to be close to the edge is clearly different in raw as well as analyzed data to impurities expected to be more central. Best fitting of experimental data to simulated correlation coefficients yields emission profiles that are remarkably close to emission profiles determined using more conventional techniques. The radial extension of the fluctuations is small enough for the method to be used and bandpass filtered signals indicate that fluctuations below 10 kHz are cylindrically symmetric. The novel method is not sensitive to vessel window attenuation or wall reflections and can therefore complement the standard methods in the impurity emission reconstruction procedure.

Keyword
reversed-field pinch, density-fluctuations, transport, plasma, system
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-6557 (URN)10.1063/1.2195122 (DOI)000237136500018 ()2-s2.0-33646428654 (Scopus ID)
Note

QC 20150727

Available from: 2006-12-11 Created: 2006-12-11 Last updated: 2015-07-27Bibliographically approved
6. Reversed field pinch operation with intelligent shell feedback control in EXTRAP T2R
Open this publication in new window or tab >>Reversed field pinch operation with intelligent shell feedback control in EXTRAP T2R
Show others...
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.

Keyword
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:nbn:se:kth:diva-6558 (URN)10.1088/0029-5515/46/11/004 (DOI)000242664000006 ()2-s2.0-33846062292 (Scopus ID)
Note
QC 20100810Available from: 2006-12-11 Created: 2006-12-11 Last updated: 2017-12-14Bibliographically approved

Open Access in DiVA

fulltext(2728 kB)1073 downloads
File information
File name FULLTEXT01.pdfFile size 2728 kBChecksum MD5
e28ad2746903ffa2993ec211b55da7c777f86efe9c4b166f6e5fae559d734050c9cc6db5
Type fulltextMimetype application/pdf

Search in DiVA

By author/editor
Kuldkepp, Mattias
By organisation
Physics
Atom and Molecular Physics and Optics

Search outside of DiVA

GoogleGoogle Scholar
Total: 1073 downloads
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

isbn
urn-nbn

Altmetric score

isbn
urn-nbn
Total: 735 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf