Adaptive feedback control of rotating external kink modes in HBT-EP

Rath, N.; Byrne, P.J.; Levesque, J.P.; Angelini, Sarah; Bialek, J.; DeBono, B.; Hughes, Paul E.; Mauel, M. E.; Navratil, G.A.; Peng, Qian; Rhodes, Dov; Stoafer, C.C.

doi:10.1088/0029-5515/53/7/073052

Cited by 7 publications

(19 citation statements)

References 28 publications

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“…Previous success using this feedback system before installing the ferric wall was given in Ref. 18, where a 60% reduction in mode amplitude was seen at the dominant frequency.…”

Section: Magnetic Feedbackmentioning

confidence: 99%

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Active and passive kink mode studies in a tokamak with a movable ferromagnetic walla)

et al. 2015

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High-resolution active and passive kink mode studies are conducted in a tokamak with an adjustable ferromagnetic wall near the plasma surface. Ferritic tiles made from 5.6 mm thick Hiperco V R 50 alloy have been mounted on the plasma-facing side of half of the in-vessel movable wall segments in the High Beta Tokamak-Extended Pulse device [D. A. Maurer et al., Plasma Phys. Controlled Fusion 53, 074016 (2011)] in order to explore ferritic resistive wall mode stability. Low-activation ferritic steels are a candidate for structural components of a fusion reactor, and these experiments examine MHD stability of plasmas with nearby ferromagnetic material. Plasma-wall separation for alternating ferritic and non-ferritic wall segments is adjusted between discharges without opening the vacuum vessel. Amplification of applied resonant magnetic perturbations and plasma disruptivity are observed to increase when the ferromagnetic wall is close to plasma surface instead of the standard stainless steel wall. Rapidly rotating m=n ¼ 3=1 external kink modes have higher growth rates with the nearby ferritic wall. Feedback suppression of kinks is still as effective as before the installation of ferritic material in vessel, in spite of increased mode growth rates. V C 2015 AIP Publishing LLC. [http://dx.

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“…Previous success using this feedback system before installing the ferric wall was given in Ref. 18, where a 60% reduction in mode amplitude was seen at the dominant frequency.…”

Section: Magnetic Feedbackmentioning

confidence: 99%

“…Section V presents observations of the plasma resonant response to applied magnetic perturbations, which show enhanced plasma response relative to previous observations without ferritic material. 19 Section VI illustrates the successful application of HBT-EP's active feedback control system 18 …”

Section: Introductionmentioning

confidence: 99%

Active and passive kink mode studies in a tokamak with a movable ferromagnetic walla)

et al. 2015

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“…SOLCs will be driven in limited and diverted plasmas to test the effects on modes and disruptions. Coupling of this 'virtual SOL coil' to kink modes will be compared to results from existing RMP and feedback control experiments [40,41].…”

Section: Diagnostic and Control Upgradementioning

confidence: 99%

Measurement of scrape-off-layer current dynamics during MHD activity and disruptions in HBT-EP

et al. 2017

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We report scrape-off layer (SOL) current measurements during magnetohydrodynamic (MHD) mode activity, resonant magnetic perturbations (RMPs), and disruptions in the High Beta Tokamak-Extended Pulse (HBT-EP) device. Currents are measured via segmented plasma current Rogowski coils, jumpers running toroidally between otherwise-isolated vessel sections, and a grounded electrode in the scrape-off layer. These currents strongly depend on the plasma's major radius, and amplitude and phase of non-axisymmetric field components. SOL currents connecting through the vessel are seen to reach ∼0.2-0.5% of the plasma current during typical kink activity and RMPs. Plasma current asymmetries and scrape-off-layer currents generated during disruptions, which are commonly called halo currents, reach ∼4% of I p . Asymmetric toroidal currents between vessel sections rotate at tens of kHz through most of the current quench, then symmetrize once I p reaches ∼30% of its pre-disruptive value. Toroidal jumper currents oscillate between co-and counter-I p , with co-I p being dominant on average during disruptions. A relative increase in local plasma current measured by a segmented I p Rogowski coil correlates with counter-I p current in the nearest toroidal jumper. Measurements are interpreted in the context of two models that produce contrary predictions for the toroidal vessel current polarity during disruptions. Plasma current asymmetry measurements are consistent with both models, and SOL currents scale with plasma displacement toward the vessel wall. The design of an upcoming SOL current diagnostic and control upgrade is also briefly presented.

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“…In order to evaluate performance and usability in an experimental setting, the proposed DSP platform has been connected to HBT-EPs magnetic sensors and actuators and an appropriate feedback control algorithm was implemented for the GPU. The details of the algorithm are described in more detail in Rath et al 22,23 In order to control the plasma, HBT-EP uses 40 "saddle" control coils and 40 poloidal magnetic sensors (cf. Figure 9).…”

Section: A External Kink Mode Control At Hbt-epmentioning

confidence: 99%

Fast, multi-channel real-time processing of signals with microsecond latency using graphics processing units

Rath

Kato

Levesque

et al. 2014

Review of Scientific Instruments

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Fast, digital signal processing (DSP) has many applications. Typical hardware options for performing DSP are field-programmable gate arrays (FPGAs), application-specific integrated DSP chips, or general purpose personal computer systems. This paper presents a novel DSP platform that has been developed for feedback control on the HBT-EP tokamak device. The system runs all signal processing exclusively on a Graphics Processing Unit (GPU) to achieve real-time performance with latencies below 8 μs. Signals are transferred into and out of the GPU using PCI Express peer-to-peer direct-memory-access transfers without involvement of the central processing unit or host memory. Tests were performed on the feedback control system of the HBT-EP tokamak using forty 16-bit floating point inputs and outputs each and a sampling rate of up to 250 kHz. Signals were digitized by a D-TACQ ACQ196 module, processing done on an NVIDIA GTX 580 GPU programmed in CUDA, and analog output was generated by D-TACQ AO32CPCI modules.

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Adaptive feedback control of rotating external kink modes in HBT-EP

Cited by 7 publications

References 28 publications

Active and passive kink mode studies in a tokamak with a movable ferromagnetic walla)

Active and passive kink mode studies in a tokamak with a movable ferromagnetic walla)

Measurement of scrape-off-layer current dynamics during MHD activity and disruptions in HBT-EP

Fast, multi-channel real-time processing of signals with microsecond latency using graphics processing units

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