Multi-mode error field correction on the DIII-D tokamak

Scoville, J. T.; Haye, R. J. La

doi:10.1088/0029-5515/43/4/305

Cited by 113 publications

(143 citation statements)

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“…Over the last 15 years an extensive set of resonant magnetic perturbation experiments have been carried out in DIII-D using a variety of non-axisymmetric coil sets including the original n = 1 coil used to study the effect of field-errors [27], the field-error correction coil i.e., the C-coil [23] and the internal I-coil [22] designed to provide resistive wall mode stabilization in DIII-D. Of the various coils used, only the I-coil is capable of producing the type of mode spectrum needed to control the pedestal i.e., the spectrum shown in Fig A closer look at the detailed evolution of the pedestal parameters in this 7.9 MW discharge is of interest for understanding how the transport is affected by the edge RMP. This may imply that the particle transport is responding to changes other than an increase in the effectiveness of the open field stochastic layer.…”

Section: Resultsmentioning

confidence: 99%

“…In this paper we describe results from edge resonant magnetic perturbation (RMP) experiments in low e,neo * = 0.12 0.04 plasmas where both the DIII-D I-coil [22], configured for n = 3 toroidal mode number perturbations, and the DIII-D correction coil (C-coil) operated in n = 1 field-error feedback mode [23] were used simultaneously. The plasmas used in these experiments are configured for strong lower single null divertor pumping, as shown in Fig.…”

Section: Experimental Overviewmentioning

confidence: 99%

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The physics of edge resonant magnetic perturbations in hot tokamak plasmas

et al. 2006

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Small edge resonant magnetic perturbations are used to control the pedestal transport and stability in low electron collisionality ( e * ), ITER relevant, poloidally diverted plasmas. The applied perturbations reduce the height of the density pedestal and increase its width while increasing the height of the electron pedestal temperature and its gradient.The effect of the perturbations on the pedestal gradients is controlled by the current in the perturbation coil, the poloidal mode spectrum of the coil, the neutral beam heating power and the divertor deuterium fueling rate. Large pedestal instabilities, referred to as edge as an array of higher frequency electromagnetic waves and turbulence [7]. Outside the plasma, sources such as field-errors from asymmetries in toroidal and poloidal magnetic field coils, magnetic materials, vacuum vessel image and return currents [8], external control coils used to stabilize plasma modes, and correction coils [9] used to minimize perturbations from known field-errors on low integer rational surfaces all contribute to the structure of the magnetic field in which the plasma resides. At the edge of the plasma where the safety factor [ q ( ) defined as the rate of change in toroidal magnetic flux with poloidal magnetic flux ] increases rapidly, all of these perturbations contribute to the creation of closely spaced resonant magnetic islands which may result in the formation of edge stochastic layers. In a poloidally diverted tokamak, the high magnetic shear q across the edge of the plasma results in an increased density of island states and a significantly higher probability of forming open stochastic layers that connect magnetic field lines to plasma facing material surfaces [10]. Thus, the edge plasma is immersed in a dynamically complex magnetic topology over the same region where substantial radial flows of mass and energy, driven by large gradients, compete with strong turbulent transport in highly sheared toroidal and poloidal plasma flow fields. Large radial gradients in the plasma pressure are often established by a strong reduction in turbulent 4 transport due to sheared plasma flow. The large edge gradients are a key factor in the establishment of good confinement levels that make the tokamak the leading candidate for fusion reactors. However, they also lead to the instabilities known as ELMs which drive impulsive energy losses that can be detrimental to plasma facing surfaces. It is easy to understand why the development of tools to control the pedestal transport and stability is a compelling issue for improving the performance and operational safety of high energy density tokamak based fusion confinement systems.A strong motivation for understanding the physics of edge stochastic layers is to enable the development of predictable and reliable tools for controlling key fusion plasma pedestal processes such as: the plasma temperature and pressure at the top of the pedestal, the size and frequency of ELMs, the energy and particle exhaust rate in steady-state cond...

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Section: Resultsmentioning

confidence: 99%

Section: Experimental Overviewmentioning

confidence: 99%

The physics of edge resonant magnetic perturbations in hot tokamak plasmas

et al. 2006

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“…However, a significant degradation of performance in tokamak plasmas are observed for nonaxisymmetric magnetic perturbations as small as δB/B 0 ∼ 10 −4 . [1][2][3][4][5][6]. Tokamaks are difficult to build without such small errors.…”

Section: Introductionmentioning

confidence: 99%

Importance of plasma response to nonaxisymmetric perturbations in tokamaks

et al. 2009

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Tokamaks are sensitive to deviations from axisymmetry as small as δB/B 0 ∼ 10 −4 . These non-axisymmetric perturbations greatly modify plasma confinement and performance by either destroying magnetic surfaces with subsequent locking or deforming magnetic surfaces with associated non-ambipolar transport. The Ideal Perturbed Equilibrium Code (IPEC) calculates ideal perturbed equilibria and provides important basis for understanding the sensitivity of tokamak plasmas to perturbations. IPEC calculations indicate that the ideal plasma response, or equivalently the effect by ideally perturbed plasma currents, is essential to explain locking experiments on National Spherical Torus eXperiment (NSTX) and DIII-D. The ideal plasma response is also important for Neoclassical Toroidal Viscosity (NTV) in non-ambipolar transport. The consistency between NTV theory and magnetic braking experiments on NSTX and DIII-D can be improved when the variation in the field strength in IPEC is coupled with generalized NTV theory. These plasma response effects will be compared with the previous vacuum superpositions to illustrate the importance. However, plasma response based on ideal perturbed equilibria is still not sufficiently accurate to predict the details of NTV transport, and can be inconsistent when currents associated with a toroidal torque become comparable to ideal perturbed currents.

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“…These toroidal asymmetries are often responsible for the creation of magnetic islands inside the plasma and locked modes [8,9,10,11,12,13] and therefore reduction of the plasma confinement. During the breakdown, breaking of the toroidal symmetry leads to a reduction of the connection length of the magnetic field lines and the probability to obtain a stable and reproducible breakdown is therefore decreased.…”

Section: Introductionmentioning

confidence: 99%

Measurement of the magnetic field errors on TCV

Piras

Moret

Rossel

2010

Fusion Engineering and Design

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A set of 24 saddle loops is used on the Tokamakà Configuration Variable (TCV) to measure the radial magnetic flux at different toroidal and vertical positions. The new system is calibrated together with the standard magnetic diagnostics on TCV. Based on the results of this calibration, the effective current in the poloidal field coils and their position is computed. These corrections are then used to compute the distribution of the error field inside the vacuum vessel for a typical TCV discharge.Since the saddle loops measure the magnetic flux at different toroidal positions, the non-axisymmetric error field is also estimated and correlated to a shift or a tilt of the poloidal field coils.

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Multi-mode error field correction on the DIII-D tokamak

Cited by 113 publications

References 18 publications

The physics of edge resonant magnetic perturbations in hot tokamak plasmas

The physics of edge resonant magnetic perturbations in hot tokamak plasmas

Importance of plasma response to nonaxisymmetric perturbations in tokamaks

Measurement of the magnetic field errors on TCV

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