A novel feedback algorithm for simulating controlled dynamics and confinement in the advanced reversed-field pinch

Dahlin, Jon-Erik; Scheffel, Jan

doi:10.1063/1.1924556

Cited by 5 publications

(12 citation statements)

References 16 publications

(15 reference statements)

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“…As has been presented by the authors elsewhere [13,14], the introduction of active feedback of the dynamo field substantially increases energy confinement time and poloidal beta and reduces the radial magnetic field (see figure 1). Tearing modes essentially disappear (the amplitude of the field is reduced by two orders of magnitude) and the fluctuation field E f is virtually eliminated except in the edge region where some activity persists.…”

Section: Effect Of Active Feedback Defined E Amentioning

confidence: 63%

“…To avoid the difficulties associated with optimization of a CPC routine that involves three independent parameters, the development of a numerical model for automatic optimization of the auxiliary field through feedback of the dynamo field has been carried out [13,14]. A general feedback system takes the form…”

Section: Implementation Of a Feedback-defined E Amentioning

confidence: 99%

“…The time scale for the feedback loop is set by the parameter k I , which in principle is a free parameter. As it turns out, however, the final level in confinement is not very sensitive to the value of k I as it merely sets the time scale for the simulation [13]. It should be set high enough to make simulation times realistic and low enough to prevent numerical instabilities but otherwise it does not have to be fine adjusted.…”

Section: Effect Of Allowing a Certain E Fmentioning

confidence: 99%

“…It is shown that active control of the current profile in principle makes it possible to achieve a tearing-mode free RFP, and different variations of the model are discussed in terms of their effect on confinement. The basic model for active feedback CPC that is used to perform the simulations in this paper has been presented earlier [13,14]. The major new results presented here stem from two different variations of the basic concept: the freezing of the dynamic auxiliary field (section 3.2) and the effect of allowing a low level of dynamo fluctuations (section 3.3).…”

Section: Introductionmentioning

confidence: 99%

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Numerical studies of active current profile control in the reversed-field pinch

Dahlin

Scheffel

Anderson

2007

Plasma Phys. Control. Fusion

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Quenching of the reversed-field pinch (RFP) dynamo is observed in numerical simulations using current profile control. A novel algorithm employing active feedback of the dynamo field has been utilized. The quasi-steady state achieved represents an important improvement as compared with earlier numerical work and may indicate a direction for the design of future experiments. Both earlier and the novel schemes of feedback control result in quasi-single helicity states. The energy confinement time and poloidal beta are observed to be substantially increased, as compared with the conventional RFP, in both the cases. Different techniques for experimental implementation are discussed.

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Section: Effect Of Active Feedback Defined E Amentioning

confidence: 63%

Section: Implementation Of a Feedback-defined E Amentioning

confidence: 99%

Section: Effect Of Allowing a Certain E Fmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Numerical studies of active current profile control in the reversed-field pinch

Dahlin

Scheffel

Anderson

2007

Plasma Phys. Control. Fusion

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“…However, the introduction of three free parameters makes optimization of the CPC scheme difficult. Therefore, a parameter-free automatic CPC scheme has been developed by implementing a feedback algorithm [15]. In this paper, an idealized situation is considered where the dynamo action is diminished by applying an arbitrary ad hoc electric field without regard to the actual technology to obtain it, and an optimum configuration is surveyed under certain constraints by minimizing the necessary electric field for eliminating the dynamo action.…”

Section: Introductionmentioning

confidence: 99%

Numerical studies of confinement scalings for the dynamo-free reversed-field pinch

Dahlin

Scheffel

2006

Nucl. Fusion

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In the reversed-field pinch (RFP), tearing modes associated with the dynamo are responsible for reduced energyand particle confinement. In this study, it is observed that by implementing current profile control (CPC) in the RFP, a dynamo-free state can be achieved. The effect of CPC in the RFP is examined by the use of numerical simulations, and scaling laws are presented for confinement parameters. The model is nonlinear MHD in 3D including finite resistivity and pressure. A linear regression analysis is performed on simulation data from a series of computer runs for a set of initial parameter values. Scaling laws are determined for radial magnetic field, energy confinement time, poloidal beta and temperature. Confinement is improved substantially as compared with the conventional RFP-the temperature reaches reactor relevant levels by ohmic heating alone. It is observed that the configuration spontaneously develops into a quasi single helicity state. The CPC scheme is designed to eliminate the fluctuating electric dynamo field E f = − v × B , using feedback of an externally imposed electric field. The focus of this study is on obtaining principal theoretical optimization of confinement in the RFP by implementing CPC and to formulate scaling laws for confinement parameters, thus investigating the reactor viability of the concept.

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Toroidally localized soft x-ray expulsion at the termination of the improved confinement regime in the TPE-RX reversed-field pinch experiment

et al. 2006

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The pulsed poloidal current drive technique reduces the magnetic chaos that characterizes reversed-field pinch configurations and produces a regime with an improved confinement. In this paper, we describe that, in TPE-RX [Y. Yagi et al., Fusion Eng. Des. 45, 409 (1999)], the termination phase of this regime is due to the increase of the slinky structure that creates a stochastic region and produces the expulsion of energy in a localized toroidal position. Before the plasma reaches the improved confinement regime, the slinky distorts the chain of m=0 islands on the reversal surface. During this regime, the magnetic activity and the phase locking decrease, the distortion in the island chain disappears, and the confinement increases. At the termination of this regime the magnetic activity markedly increases, as well as the phase locking, recreating the distortion in the m=0 magnetic island chain. As a consequence, at the position of the distortion the plasma region inside the reversal surface is characterized by a rapid energy loss, and outside the reversal surface a toroidally localized energy expulsion is induced.

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A novel feedback algorithm for simulating controlled dynamics and confinement in the advanced reversed-field pinch

Abstract: Density fluctuation measurements by far-forward collective scattering in the MST reversed-field pincha) Rev. Sci. Instrum. 83, 10E302 (2012); 10.1063/1.4728098Control of ideal and resistive magnetohydrodynamic modes in reversed field pinches with a resistive wall

Cited by 5 publications

References 16 publications

Numerical studies of active current profile control in the reversed-field pinch

Numerical studies of active current profile control in the reversed-field pinch

Numerical studies of confinement scalings for the dynamo-free reversed-field pinch

Toroidally localized soft x-ray expulsion at the termination of the improved confinement regime in the TPE-RX reversed-field pinch experiment

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