Operational space and performance limiting events in the first physics campaign of MAST-U

Berkery, J.W.; Sabbagh, S. A.; Kogan, L. A.; Gibson, Sam; Ryan, D. A.; Zamkovska, Veronika; Butt, Jalal; Harrison, James R.; Henderson, S.

doi:10.1088/1361-6587/acb464

Cited by 6 publications

(5 citation statements)

References 36 publications

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“…The diagrams are relatively similar for the two different machines, all showing the Greenwald limit as a rough guide to the operational limit of the machines, and all showing increased disruptivity along the line. The region of increased disruptivity at low measured density but high Greenwald density (high I p , low q) is not due to density limits, but rather low density locked modes [45]. Similar results have been shown in the past for other machines, for example JET [46].…”

Section: Disruptivity Diagramssupporting

confidence: 86%

“…These diagrams, then, do not give a good sense of the total operational time a device spent in a given space. Another type of diagram plotting exactly that is of course possible as well [45], but not shown here. For example in [45], it was seen that in early operation of MAST-U a vast majority of the operation occurred well below the Greenwald limit.…”

Section: Disruptivity Diagramsmentioning

confidence: 95%

“…The DECAF code's many separate physical event modules provide warnings and declare occurrences of certain events leading to disruption. The code also includes the ability to make diagrams showing either the operational space [45] or the probability of a DECAF event occurring within a given parameter space of tokamak operation [22]. Here, each colored square in parameter space is only plotted if at least 10 equilibrium (time) points from the database exist within that space.…”

Section: Disruptivity Diagramsmentioning

confidence: 99%

See 2 more Smart Citations

Density limits as disruption forecasters for spherical tokamaks

Berkery

Sabbagh

Ham

et al. 2023

Plasma Phys. Control. Fusion

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Fusion power output from spherical tokamaks would benefit from increased confined plasma density, but there exists a limit on the density before confinement is lost and the plasma current is disrupted. This density limit has long been characterized by a simple, global Greenwald limit proportional to the plasma current and inversely proportional to the cross sectional area of the plasma. It is shown that in the database of discharges from the NSTX and MAST spherical tokamaks, the likelihood of disruption does increase above the Greenwald limit, and especially in the plasma current rampdown phase. The physics of the density limit has been recently theoretically explored through local criteria. Several of these are tested using the disruption event characterization and forecasting (DECAFTM) code for their potential effectiveness as disruption warning signals. For a limited set of NSTX discharges, a local island power balance criteria was found to be less reliable, presently, than the Greenwald limit. An empirical critical edge line density and a boundary turbulent transport limit were both tested for MAST-U, which has an electron density profile measurement with high spatial resolution in the outer part of the plasma. Both were found to have similar dependencies on key plasma parameters. In a limited set of MAST-U discharges that appear to disrupt due to rising density at values under the Greenwald limit, crossing of the boundary turbulent transport limit occurred close to the time of disruption. Finally, these limits were evaluated for their potential use in real-time, and it was found that with the necessary real-time inputs and with refinement through further testing, these limits could be implemented in a real-time disruption forecasting system.

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Section: Disruptivity Diagramssupporting

confidence: 86%

Section: Disruptivity Diagramsmentioning

confidence: 95%

Section: Disruptivity Diagramsmentioning

confidence: 99%

See 1 more Smart Citation

Density limits as disruption forecasters for spherical tokamaks

Berkery

Sabbagh

Ham

et al. 2023

Plasma Phys. Control. Fusion

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“…Figure 5, upper plots, display three selected diagrams for the MAST-U 2021 database [38]. The DCS trigger event is clustered in the l i (q 95 ) diagram (left) at the stability boundary that was previously observed in [34] in the full-tungsten ASDEX-U device for the high plasma density limit disruptions.…”

Section: Location Of Dec Trigger Events In Plasma Operation Diagramsmentioning

confidence: 89%

DECAF cross-device characterization of tokamak disruptions indicated by abnormalities in plasma vertical position and current

Zamkovska,

Sabbagh,

Tobin

et al. 2024

Nucl. Fusion

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Abnormal (deviating from target) variations in the plasma vertical position Z and current Ip (such as vertical displacements, transient Ip 'spikes' and quenches) constitute common elements of a disruption, a phenomenon that is to be mitigated, or ultimately avoided in future reactor-relevant tokamaks. While those abnormalities are generally recognized cross-shot and cross-device, details in terms of appearance (or not) and order of those abnormalities in disruption event chains is bound with the plasma state at the time of the chain initiation. Detection of those abnormalities is thus indicative not only of the onset of the plasma collapse itself, but also of the disruption driving cause that is promoted at the particular plasma state. Here, occurrence of disruptions, explored via detection of a Ip quench, and analysis of disruption event chains constituted by Ip and Z abnormalities, is reported for in total 7 full years of operation of 3 devices (KSTAR, MAST-U and NSTX-U) using the DECAFTM code expanded tools and capabilities. It is shown that the disruption occurrence depends not only on details of the plasma state, but also on (device-dependent) technical elements of the shot exit scenario. A year-to-year change in main disruption causes and a reduction of the disruptivity rate, bound with device and operation upgrades, are reported. Particular trigger instances of disruption event chains (and the full chains, when applicable) are shown to occupy different parts of the operation space diagrams, in accordance with prior expectation. Plasma elongation is identified as an important factor influencing details of the chains and its role will be further explored.

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“…We speculate that this mode could also be responsible for the internal reconnection events (IREs) observed in MAST-U discharges with rapid current ramp-up rates. 39 In comparing the computational results from Fig. 5 with the experimental MHD signals from Fig.…”

Section: Summary and Discussionmentioning

confidence: 99%

MHD stability of spherical tokamak equilibria with non-monotonic q-profiles

Jardin,

Munaretto,

Ferraro

et al. 2024

Physics of Plasmas

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We use the 3D magnetohydrodynamic (MHD) code M3D-C1 [Jardin et al., Comput. Sci. Discovery 5, 014002 (2012)] to examine the MHD stability and subsequent evolution of NSTX shot 129169. This discharge had a period with a non-monotonic safety factor profile, q (reversed shear), which was terminated by a MHD event that abruptly lowered the central safety factor, q0, and greatly reduced the peakedness of the pressure profile. We show that the equilibrium just before the MHD event occurred was linearly unstable to many pressure-driven infernal modes. Modes with toroidal mode number n≥3 all had rational surfaces very close to the minimum value of q. However, a non-resonant pressure-driven (1, 1) mode was also present, and this dominated the nonlinear evolution. The final state in the simulation, after the MHD activity subsided, had a reduced and flattened pressure profile and a nearly monotonic q-profile, in qualitative agreement with experimental results. The initial state was also unstable to the resistive interchange criteria in the reversed-shear region, but the final state was stable everywhere. The “double tearing mode” (DTM) does not appear to play a role in the MHD activity of this discharge. In Appendix A, we show that in a torus, the DTM is strongly stabilized by pressure, but it is destabilized in cylindrical geometry (which has been the most extensively analyzed in the literature).

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Operational space and performance limiting events in the first physics campaign of MAST-U

Cited by 6 publications

References 36 publications

Density limits as disruption forecasters for spherical tokamaks

Density limits as disruption forecasters for spherical tokamaks

DECAF cross-device characterization of tokamak disruptions indicated by abnormalities in plasma vertical position and current

MHD stability of spherical tokamak equilibria with non-monotonic q-profiles

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