Integrated shell approach to vertical position control on PBX-M

Hatcher, R.; Okabayashi, M.

doi:10.2172/32583

Cited by 4 publications

(8 citation statements)

References 3 publications

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“…The top and bottom members of the inner shell plates Nos 1, 2 and 3 are saddle connected, and function as an y1 = 0 stabilizing system. The passive plates Nos 5 with the 10 midplane electrical jumpers also serve as a stabilizer for n = 0 vertical motion by allowing a distributed saddle current [27],…”

Section: Pbx-m Conducting Shellmentioning

confidence: 99%

“…The eddy current through the midplane jumpers, l e d d y ( $ j , t ) , where $j, j = 1, 2, ..., 10, is the toroidal angle of the jumpers, is decomposed into toroidal eigenmodes with n = 1, 2, 3. For an mln = 311 helical filament located at rlu = 0.7, the n = 1 eigenmode decay constant is between 30 and 40 ms, and for an m/n = 211 filament the time constant is between 20 and 40 ms [27].…”

Section: Pbx-m Conducting Shellmentioning

confidence: 99%

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Role of the stabilizing shell in high- beta , low-q disruptions in PBX-M

et al. 1996

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The characteristics of high+, low-q disruptions have been studied in PBX-M, a device with a nearby conducting shell. The coupling between the wall and the plasma was varied by choosing different plasma shapes, including nearly circular plasmas, D-shaped plasmas and bean-shaped plasmas (indented on the midplane), and by increasing the effective coverage of the plasma by the shell. Disruption precursors were observed to have a strong dependence on the coupling between the plasma and the shell. Measured mode growth times vary from between several times the AlfvCn time-scale (-100 p s ) to the LIR time-scale of the wall (-20 ms). The behaviour of observed disruption precursors is interpreted in terms of the resistive wall mode theory of ideal plasmas, and a detailed calculation of the stability of a strongly coupled bean configuration using the NOVA-W linear stability code is presented. The experimental observations are in good agreement with the theoretical predictions.

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Section: Pbx-m Conducting Shellmentioning

confidence: 99%

Section: Pbx-m Conducting Shellmentioning

confidence: 99%

Role of the stabilizing shell in high- beta , low-q disruptions in PBX-M

et al. 1996

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“…In the SC scheme, which is equivalent to Bishop's intelligent shell scheme [13], the sensor signal is the shell eddy current, I 2 , representing the flux loss due to the finite resistivity of the shell. This scheme has been implemented successfully for n = 0 vertical position control in PBX-M [8] and is shown here to be an attractive scheme for n = 1 kink mode control. In the TF and FRS schemes the sensor signal is the total perturbed flux, which depends on I 1 , I 2 and I 3 .…”

Section: Introductionmentioning

confidence: 92%

“…Feedback on I 1 is equivalent to feedback on I plasma δz for the n = 0 mode. Such a feedback scheme has been implemented for n = 0 control in most shaped tokamak experiments [1][2][3][4][5][6][7][8]. Although direct measurement of I 1 is probably not practical for n ≥ 1 kink mode control because of the difficulty in accurately distinguishing this plasma perturbation from contributions due the eddy currents in the passive shell, a discussion of this scheme provides a useful means for comparing the relative merits of the SC, TF and FRS feedback schemes and for comparing these schemes with known features of n = 0 control.…”

Section: Explicit Displacement Feedbackmentioning

confidence: 99%

“…The ability to control the n = 0 vertical position instability in tokamaks with a shaped cross-section has been crucial to the success of modern tokamak fusion research [1][2][3][4][5][6][7][8]. The key to the success of vertical position control is the integration of a passive stabilizing system that slows the vertical growth rate from an ideal time-scale (∼ microseconds) to a resistive wall time-scale (∼ milliseconds), and an active feedback system which controls the measured amplitude of the instability.…”

Section: Introductionmentioning

confidence: 99%

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Circuit equation formulation of resistive wall mode feedback stabilization schemes

1998

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Recently, various schemes for controlling the resistive wall mode have been proposed. Here, the problem of resistive wall mode feedback control is formulated utilizing concepts from electrical circuit theory. Each of the coupled elements (the perturbed plasma current, the poloidal passive shell system and the active coil system) is considered as lumped parameter electrical circuits obeying the usual laws of linear circuit theory. A dispersion relation is derived using different schemes for the feedback logic. The various schemes differ in the choice of sensor signal, which is determined by some combination of the three independent circuit currents. Feedback schemes are discussed which can, ideally, completely stabilize the kink mode. These schemes depend, for their success, on a suitable choice for the location of the sensors. A feedback scheme based on sensing the passive shell eddy current is discussed which seeks to drive the feedback system response to a point of marginal stability. For realizable feedback gain factors, this feedback system can suppress the kink mode amplitude for times that are very long compared with the L/R time-scale of the passive shell system. The circuit equation approach discussed provides a useful means for comparing various control strategies for n ⩾ 1 kink mode control, and allows useful analogies to be drawn between kink mode control and the control of n = 0 vertical position instabilities.

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