Controlled magnetohydrodynamic mode sustainment in the reversed-field pinch: Theory, design and experiments

Olofsson, Erik; Brunsell, Per R.

doi:10.1016/j.fusengdes.2008.11.052

Cited by 24 publications

(54 citation statements)

References 10 publications

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“…Although different in detail RFP and Tokamak RWMs are basically different instances of the same underlying physical principles and T2R is a highly versatile platform for exploring these phenomena. In addition, we speculate that the physics of the elusive tearing-mode (TM) mayhaps can be beneficially studied by employing new dexterous control software features of T2R [14].The project at T2R here outlined nicely fits in the assortment of research cited above. In short, we have used the supposed idealized eigenmode geometry (helical fourier modes) as hinted from the physics of circular cross-section cylindrical plasma curbed by a homogenous resistive thin-wall.…”

mentioning

confidence: 65%

“…Notably, the matrix weight V (i) z implies direct output variance minimization, in essence an intelligent-shell (IS) equivalent [15], [14], [29], [30], whereas weight V (ii) z of (7) is analogous to the ideas of clean-mode control (CMC) as inaugurated in [31].…”

Section: Static Decoupling Discrete-time Fixed-order Controller mentioning

confidence: 99%

“…Matrix M eq is an equalization factor designed to absorb amplifier gain variations [14], r is a reference vector in fourier space for tracking experiments, and finally, tilded vectorsũ,ỹ are actuator and sensor channels respectively.…”

Section: Short Note On Implementationmentioning

confidence: 99%

Section: Introductorymentioning

confidence: 99%

“…Experimentally, they have all been shown to be simultaneously suppressable [12], [13]. More recently, experimental verification of stabilized sustained nonaxisymmetrical perturbations to the plasma column has been produced [14], in essence by merely rehashing and refurbishing the classic active shell algorithm of [15], [16]. The role of this particular work is to carefully develop a fourier mode decoupled plasma control system, yet another recycling of the mode-controller (MC) concept, in a partially automated manner.…”

Section: Introductory Overviewmentioning

confidence: 99%

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Closed-loop identification and controller reconfiguration for EXTRAP T2R reversed-field pinch

Olofsson¹,

Brunsell²

2009

2009 23rd IEEE/NPSS Symposium on Fusion Engineering

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We briefly summarize a supposedly efficient novel method for measuring the external plasma response as applied to the inherently unstable reversed-field pinch EXTRAP T2R. The set of parameters estimated with this particular method is then harvested and fed as input to a discrete-time fixed-order fast fourier transform decoupled multi-input-multi-output controller synthesis. The thus reconfigured feedback system is implemented and experimentally tested on the real plant T2R. A particular and intended behaviour is observed, it seems, from these firstdeployment results. I. INTRODUCTORYOVERVIEW Robust controller synthesis and simulations have been worked out for e.g. the DIII-D Tokamak [1] in the case of RWMs. Apparently, to properly do control system synthesis availability of some plant model is needed. Minimal requirements include (vague) bounds on important parameters in a plausible model structure. There are several studies of external plasma response measurements in the literature [2], [3], [4], [5], [6], and also computational results on the effect of 3D external conducting structures on growth-rates, eddies and eigenmode geometry [7], [8]. Significant efforts and interest is spent on the topic of realistic experimental-conditions MHD dynamics and the associated control issues. Hosted by the Alfvén Laboratory at the Royal Institute of Technology (KTH) in Stockholm, Sweden, the reversed-field pinch (RFP) machine EXTRAP T2R is armed with dense arrays of saddle-shaped coils, both sensors and actuators. Typical parameters for T2R [9] are I p = 100 kA, R = 124 cm and a = 18 cm. A speciality of T2R is feedback control of magnetohydrodynamic (MHD) instabilities including the resistive-wall mode (RWM). Theoretically, given the geometry and dimensions of T2R and the RFP equilibria, the normalmodes spectrum of magnetic perturbations express ∼ 15 unstable solutions [10], [11], [3]. Experimentally, they have all been shown to be simultaneously suppressable [12], [13]. More recently, experimental verification of stabilized sustained nonaxisymmetrical perturbations to the plasma column has been produced [14], in essence by merely rehashing and refurbishing the classic active shell algorithm of [15], [16].The role of this particular work is to carefully develop a fourier mode decoupled plasma control system, yet another recycling of the mode-controller (MC) concept, in a partially automated manner.MHD control research at T2R strives to generate results not only relevant to RFPs, but also to macroscopic plasma dynamics in general with particular focus on Tokamaks. For example, RWMs in Tokamaks are typically more involved than the nonresonant RWM perturbation in RFPs, which for the latter is current-driven and present for all β. Tokamak RWMs in contrast, are resonant and grows while rotating with respect to the vessel, as well as being pressure-driven, i.e. triggered by high-β. Although different in detail RFP and Tokamak RWMs are basically different instances of the same underlying physical principles and T2R is a highly versa...

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mentioning

confidence: 65%

Section: Static Decoupling Discrete-time Fixed-order Controller mentioning

confidence: 99%

Section: Short Note On Implementationmentioning

confidence: 99%

Section: Introductorymentioning

confidence: 99%

Section: Introductory Overviewmentioning

confidence: 99%

See 3 more Smart Citations

Closed-loop identification and controller reconfiguration for EXTRAP T2R reversed-field pinch

Olofsson¹,

Brunsell²

2009

2009 23rd IEEE/NPSS Symposium on Fusion Engineering

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Model based optimal magnetic feedback control of multiple resistive wall modes with discrete coil and sensor arrays

Saad,

Brunsell

2024

Fusion Engineering and Design

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Resonant magnetic perturbation effect on tearing mode dynamics

et al. 2010

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The effect of a resonant magnetic perturbation (RMP) on the tearing mode (TM) dynamics is experimentally studied in the EXTRAP T2R device. EXTRAP T2R is equipped with a set of sensor coils and active coils connected by a digital controller allowing a feedback control of the magnetic instabilities. The recently upgraded feedback algorithm allows the suppression of all the error field harmonics but keeping a selected harmonic to the desired amplitude, therefore opening the possibility of a clear study of the RMP effect on the corresponding TM. The paper shows that the RMP produces two typical effects: (1) a weak oscillation in the TM amplitude and a modulation in the TM velocity or (2) a strong modulation in the TM amplitude and phase jumps. Moreover, the locking mechanism of a TM to a RMP is studied in detail. It is shown that before the locking, the TM dynamics is characterized by velocity modulation followed by phase jumps. Experimental results are reasonably explained by simulations obtained with a model.

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Controlled magnetohydrodynamic mode sustainment in the reversed-field pinch: Theory, design and experiments

Cited by 24 publications

References 10 publications

Closed-loop identification and controller reconfiguration for EXTRAP T2R reversed-field pinch

Closed-loop identification and controller reconfiguration for EXTRAP T2R reversed-field pinch

Model based optimal magnetic feedback control of multiple resistive wall modes with discrete coil and sensor arrays

Resonant magnetic perturbation effect on tearing mode dynamics

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