Theory of Diamagnetic Signal in Current-Free Stellarators

Pustovitov, V. D.

doi:10.1585/pfr.5.s2054

Cited by 5 publications

(21 citation statements)

References 23 publications

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“…where δ means the difference of the final and initial values, ( ) β a J is the 'poloidal beta' defined by ( 3) and calculated for a plasma within a toroidal tube = a const, and b is the plasma minor radius. If the wall of minor radius a w acts as a perfect conductor, the net plasma column shift ∆ b must vary as [52][53][54]…”

Section: Simulation Resultsmentioning

confidence: 99%

Local and integral forces on the vacuum vessel during thermal quench in the ITER tokamak

Khayrutdinov

Lukash

Pustovitov

2016

Plasma Phys. Control. Fusion

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The forces arising during an early stage of disruption in tokamaks are studied here. The analysis is based on DINA calculations and comparison with recent analytical predictions (Pustovitov 2015 Plasma Phys. Rep. 41 952). One such prediction was that a large radial force on the vacuum vessel wall can be generated by a thermal quench (TQ) alone, even before the plasma current is changed. The numerical results presented here confirm this and provide precise quantitative characteristics. The calculations are performed for the International Thermonuclear Experimental Reactor (ITER) geometry by using the DINA code. It is shown, in particular, that the TQ-produced radial force in ITER can reach ~70 MN. Its poloidal distribution has a peak ~2.8 times larger than the average. The relevant details of physics models are also presented.

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Section: Simulation Resultsmentioning

confidence: 99%

Local and integral forces on the vacuum vessel during thermal quench in the ITER tokamak

Khayrutdinov

Lukash

Pustovitov

2016

Plasma Phys. Control. Fusion

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“…found in [9] between the diamagnetic β values calibrated by the new method based on 3D magnetohydrodynamic (MHD) equilibrium calculations and that from a conventional method under the cylindrical and large aspect ratio plasma model. This discrepancy remains mysterious, and it looks even more puzzling in view of earlier analytical [16] and numerical [17] predictions that, for stellarators, higher order corrections to the diamagnetic flux in (1) would be small, in qualitative agreement with the statements on the toroidal corrections in [1].…”

Section: Introductionmentioning

confidence: 89%

“…In addition, the problem of δS pl detection as a quantity related to diamagnetic measurements was never addressed in theory (except several papers, see [21,32]) and experiments. However, recent studies [18] of the LHD plasma boundary change with β have demonstrated that the related δS pl (though of a different origin from that we discuss in this section) can be large enough to be detected.…”

Section: Flux-conserving Plasma Evolution and Diamagnetic Measurementsmentioning

confidence: 99%

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Diamagnetic measurements and plasma energy in toroidal systems

Pustovitov¹

2010

Plasma Phys. Control. Fusion

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Sensitivity of the diamagnetic signal to several operational and geometrical factors is analysed. Among them are the flux conservation in the plasma, eddy currents induced in the outer structures at fast processes, toroidal shift and deformation of the plasma boundary due to its energy change, and inhomogeneity of the confining magnetic field. It is shown that in each case, under proper experimental circumstances, the contribution, unaccounted in the traditional theory of diamagnetic measurements, can reach a level compared to β (ratio of the volumeaveraged plasma pressure to the magnetic field pressure). The approach is fully analytical with all relevant dependencies shown explicitly, allowing easy estimates and suggesting a resolution of the problem in order to restore the accuracy of finding β from diamagnetic measurements. This essentially extends the analysis [1] of possible measures to improve separation of the useful fraction of the measured diamagnetic signal. The approach is aimed to explanation of the discrepancies between model estimates and experimental results, unification of a knowledge obtained in separate numerical studies, extending a theoretical basis of magnetic diagnostics and uncovering potential dangers in interpretations. This is also an essential step from traditional cylindrical theory to analytical derivations in the toroidal geometry. The results are equally applicable to tokamaks and stellarators.Interpretation of diamagnetic measurements in tokamaks and stellarators is based on a simple formuladerived for a circular plasma cylinder more than 50 years ago, or its modifications. HereΦ is the flux of the magnetic field through the diamagnetic loop and ΔΦ is the difference between the current state and initial state when, B is the magnetic field, v B is the vacuum magnetic field (assumed unchanged in this case),

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“…Part of these additional terms related to the toroidal plasma current can be minimised by arranging the DL perpendicular to the plasma axis and thus in leading order perpendicular to a possible toroidal plasma current. A detailed derivation of all these terms can be found in [12].…”

Section: Diamagnetic Loopsmentioning

confidence: 99%

Engineering design for the magnetic diagnostics of Wendelstein 7-X

Endler

Brucker

Bykov

et al. 2015

Fusion Engineering and Design

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The magnetic diagnostics foreseen for the Wendelstein 7-X (W7-X) stellarator are diamagnetic loops to measure the plasma energy, Rogowski coils to measure the toroidal plasma current, saddle coils to measure the Pfirsch-Schlüter currents, segmented Rogowski coils (poloidal magnetic field probes) to add information on the distribution of the plasma current density, and Mirnov coils to observe magnetohydrodynamic modes. All these magnetic field sensors were designed as classical pick-up coils, after the time integration of induced signals for 1/2 hour had been successfully demonstrated.The long-pulse operation planned for W7-X causes nevertheless significant challenges to the design of these diagnostics, in particular for the components located inside the plasma vessel, which may be exposed to high levels of microwave (electron cyclotron resonance) stray radiation and thermal radiation. This article focuses on the tests and modelling performed during the development of the magnetic diagnostics and on the design solutions adopted to meet the conflicting requirements. * Corresponding author, email: endler@ipp.mpg.de 1 All pick-up coils foreseen for the initial operation phase of W7-X and their signal cable sections inside the plasma vessel and the cryostat are now installed, and their electronics and data acquisition are under preparation.

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Theory of Diamagnetic Signal in Current-Free Stellarators

Cited by 5 publications

References 23 publications

Local and integral forces on the vacuum vessel during thermal quench in the ITER tokamak

Local and integral forces on the vacuum vessel during thermal quench in the ITER tokamak

Diamagnetic measurements and plasma energy in toroidal systems

Engineering design for the magnetic diagnostics of Wendelstein 7-X

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