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Experimental studies of confinement in the EXTRAP T2 and T2R reversed field pinches
KTH, Superseded Departments, Alfvén Laboratory.
2003 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

The confinement properties of fusion plasmas are affected bymagnetic and electrostatic fluctuations. The determination ofthe plasma confinement properties requires the measurement ofseveral global and local quantities such as the ion andelectron temperatures, the electron and neutral densityprofiles, the radiation emissivity profiles, the ohmic inputpower and the particle and heat diffusivities. The focus ofthis thesis is the study of the plasma confinement propertiesbased on measurements of these quantities under differentexperimental conditions.

The studies have been carried out on the reversed fieldpinch experiments EXTRAP T2 and T2R at the AlfvénLaboratory, Royal Institute of Technology (KTH) in Stockholm.Studies carried out in EXTRAP T2 were focused on dynamoactivity and on the effect of phase alignment and locking tothe wall of magnetic instabilities. These were observed with adedicated imaging system. The experimental studies in EXTRAPT2R were focused on the measurement of the confinementproperties of different configurations. To this aim, a set ofdiagnostics were used some of which were upgraded, such as theinterferometer, while others were newly installed, such as aneutral particle energy analyser and a bolometer array.

The dynamo, which is responsible for the plasma sustainment,involves resistive magnetohydrodynamic instabilities thatenhance stochastic transport. Furthermore, the plasmaconfinement properties are in general improved in the presenceof mode rotation. The possibility of reducing the stochastictransport and thereby further improving the confinement hasbeen demonstrated in a current profile control experiment.These results indicate that long pulse operations with aresisitive shell and current profile control are indeedfeasible.

KeywordsEXTRAP T2, T2R, reversed field pinch, dynamo,energy confinement time, transport, CCD, bolometer,interferometer, neutral particle energy analyser, PPCD, MonteCarlo

Place, publisher, year, edition, pages
Stockholm: KTH , 2003. , x, 135 p.
Keyword [en]
extap t2, extrap t2r, reversed field pinch
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:kth:diva-3468ISBN: 91-7283-417-X (print)OAI: oai:DiVA.org:kth-3468DiVA: diva2:9270
Public defence
2003-01-31, 00:00 (English)
Note
QC 20100524Available from: 2003-02-06 Created: 2003-02-06 Last updated: 2010-05-24Bibliographically approved
List of papers
1. Locked modes and plasma-wall interaction in a reversed-field pinch with aresistive shell and carbon first wall
Open this publication in new window or tab >>Locked modes and plasma-wall interaction in a reversed-field pinch with aresistive shell and carbon first wall
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1999 (English)In: Proceedings of the 17th International Conference on Fusion Energy, Vienna: International Atomic Energy Agency , 1999Conference paper, Published paper (Other academic)
Place, publisher, year, edition, pages
Vienna: International Atomic Energy Agency, 1999
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-13010 (URN)
Conference
17th Fusion Energy Conference
Note
QC 20100524Available from: 2010-05-24 Created: 2010-05-24 Last updated: 2010-05-24Bibliographically approved
2. Self-organisation and intermittent coherent oscillations in the EXTRAP T2 reversed field pinch
Open this publication in new window or tab >>Self-organisation and intermittent coherent oscillations in the EXTRAP T2 reversed field pinch
2002 (English)In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 65, no 1, 69-75 p.Article in journal (Refereed) Published
Abstract [en]

Many reversed-field pinch (RFP) experiments exhibit a coherent oscillatory behaviour that is characteristic of discrete dynamo events and is associated with intermittent current profile self-organisation phenomena. However, in the vast majority of the discharges in the resistive shell RFP experiment EXTRAP T2, the dynamo activity does not show global, coherent oscillatory behaviour, The internally resonant tearing modes are phase-aligned and wall-locked resulting in a large localised magnetic perturbation. Equilibrium and plasma parameters have a level of high frequency fluctuations but the average values are quasi-steady. For some discharges, however, the equilibrium parameters exhibit the oscillatory behaviour characteristic of the discrete dynamo events. For these discharges, the trend observed in the tearing mode spectra, associated with the onset of the discrete relaxation event behaviour, is a relative higher amplitude of m = 0 mode activity and relative lower amplitude of the m = 1 mode activity compared with their average values. Global plasma parameters and model profile calculations for sample discharges representing the two types of relaxation dynamics are presented.

Place, publisher, year, edition, pages
Stockholm: ROYAL SWEDISH ACAD SCIENCES, 2002
Keyword
LOCKED MODES, MAGNETIC RECONNECTION, NONLINEAR DYNAMICS, RELAXATION, PLASMA, CONFINEMENT, GENERATION, FLUCTUATIONS, MECHANISM, BEHAVIOR
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-13014 (URN)10.1238/Physica.Regular.065a00069 (DOI)000173243200009 ()
Note
QC 20100524Available from: 2010-05-24 Created: 2010-05-24 Last updated: 2017-12-12Bibliographically approved
3. Initial results from the rebuilt EXTRAP T2R RFP device
Open this publication in new window or tab >>Initial results from the rebuilt EXTRAP T2R RFP device
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2001 (English)In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 43, no 11, 1457-1470 p.Article in journal (Refereed) Published
Abstract [en]

The EXTRAP T2R thin shell reversed-field pinch (RFP) device has recently resumed operation after a major rebuild including the replacement of the graphite armour with molybdenum limiters, a fourfold increase of the shell time constant, and the replacement of the helical coil used for the toroidal field with a conventional solenoid-type coil. Wall-conditioning using hydrogen glow discharge cleaning was instrumental for successful RFP operation. Carbon was permanently removed from the walls during the first week of operation. The initial results from RFP operation with relatively low plasma currents in the range I-p = 70-100 kA are reported. RFP discharges are sustained for more than three shell times. Significant improvements in plasma parameters are observed, compared to operation before the rebuild. There is a substantial reduction in the carbon impurity level. The electron density behaviour is more shot-to-shot reproducible. The typical density is n(e) = 0.5-1 x 10(19) m(-3). Monitors of H-alpha line radiation indicate that the plasma wall interaction is more toroidally symmetric and that there is less transient gas release from the wall. The minimum loop voltage is in the range V-t = 28-35 V, corresponding to a reduction by a factor of two to three compared to the value before the rebuild.

Place, publisher, year, edition, pages
BRISTOL. ENGLAND: IOP PUBLISHING LTD, 2001
Keyword
REVERSED-FIELD PINCH, RESISTIVE-SHELL, TOROIDAL PINCH, FLUCTUATIONS, WALL
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-13016 (URN)000172457100003 ()
Note
QC 20100524 QC 20120206Available from: 2010-05-24 Created: 2010-05-24 Last updated: 2017-12-12Bibliographically approved
4. Total radiation losses studies in EXTRAP T2R
Open this publication in new window or tab >>Total radiation losses studies in EXTRAP T2R
2001 (English)In: Proceedings of the 28th European Physical Society Conference on Controlled Fusion and Plasma Physics, Madeira, 2001Conference paper, Published paper (Other academic)
Place, publisher, year, edition, pages
Madeira: , 2001
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-13018 (URN)
Conference
28th European Physical Society Conference on Controlled Fusion and Plasma Physics
Note
QC 20100524Available from: 2010-05-24 Created: 2010-05-24 Last updated: 2010-05-24Bibliographically approved
5. Electron density and transport in EXTRAP T2R
Open this publication in new window or tab >>Electron density and transport in EXTRAP T2R
2002 (English)In: Proceedings of the 29th European Physical Society Conference on ControlledFusion and Plasma Physics, Montreux, 2002Conference paper, Published paper (Other academic)
Place, publisher, year, edition, pages
Montreux: , 2002
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-13020 (URN)
Conference
29th European Physical Society Conference on Controlled Fusion and Plasma Physics
Note
QC 20100524Available from: 2010-05-24 Created: 2010-05-24 Last updated: 2010-05-24Bibliographically approved
6. Study of the confinement properties in a reversed-field pinch with mode rotation and gas fuelling
Open this publication in new window or tab >>Study of the confinement properties in a reversed-field pinch with mode rotation and gas fuelling
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2002 (English)In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 44, no 8, 1625-1638 p.Article in journal (Refereed) Published
Abstract [en]

An extensive investigation of the global confinement properties in different operating scenarios in the rebuilt EXTRAP T2R reversed-field pinch (RFP) experiment is reported here. In particular, the role of a fast gas puff valve system, used to control plasma density, on confinement is studied. Without gas puffing, the electron density decays below 0.5 x 10(19) M-3. The poloidal beta varies between 5% and 15%, decreasing at large I/N. The energy confinement time ranges from 70 to 225 mus. With gas puffing, the density is sustained at n(e) approximate to 1.5 x 10(19) m(-3). However, a general slight deterioration of the plasma performances is observed for the same values of I/N: the plasma becomes cooler and more radiative. The poloidal beta is comparable to that in the scenarios without puff but the energy confinement time drops ranging from 60 to 130 mus. The fluctuation level and the energy confinement time have been found to scale with the Lundquist number as S-0.05+/-0.07 and S0.5+/-0.1, respectively. Mode rotation is typical for all the discharges and rotation velocity is observed to increase with increasing electron diamagnetic velocity.

Place, publisher, year, edition, pages
BRISTOL, ENGLAND: IOP PUBLISHING LTD, 2002
Keyword
POLOIDAL CURRENT DRIVE, ENERGY CONFINEMENT, RFX, FLUCTUATIONS, VUV
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-13022 (URN)10.1088/0741-3335/44/8/314 (DOI)000178020200016 ()
Note
QC 20100524Available from: 2010-05-24 Created: 2010-05-24 Last updated: 2017-12-12Bibliographically approved
7. Current profile control experiments in EXTRAP T2R
Open this publication in new window or tab >>Current profile control experiments in EXTRAP T2R
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(English)Manuscript (preprint) (Other academic)
National Category
Natural Sciences
Identifiers
urn:nbn:se:kth:diva-13023 (URN)
Note
QC 20100524Available from: 2010-05-24 Created: 2010-05-24 Last updated: 2010-05-24Bibliographically approved

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