Imposed-dynamo current drive

Jarboe, T. R.; Victor, B.S.; Nelson, B. A.; Hansen, Chris; Akçay, C.; Ennis, D.A.; Hicks, N.; Hossack, Aaron; Marklin, G.J.; Smith, Roger

doi:10.1088/0029-5515/52/8/083017

Cited by 32 publications

(22 citation statements)

References 23 publications

(40 reference statements)

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“…A simulated version of this discharge shows similar results [52]. This suggests a large-scale transition between the inner and outer regions of the plasma, perhaps contributing to a shear layer such as that expected with impose-dynamo current drive [36]. This phase shift occurs at R ≈ 0.8 − 0.9 m, close to the closed flux surfaces in the plasma.…”

Section: Sparsity-promoting Dmd: First Injector Harmonicsupporting

confidence: 63%

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Characterizing magnetized plasmas with dynamic mode decomposition

et al. 2020

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Accurate and efficient plasma models are essential to understand and control experimental devices. Existing magnetohydrodynamic or kinetic models are nonlinear, computationally intensive, and can be difficult to interpret, while often only approximating the true dynamics. In this work, data-driven techniques recently developed in the field of fluid dynamics are leveraged to develop interpretable reduced-order models of plasmas that strike a balance between accuracy and efficiency. In particular, dynamic mode decomposition (DMD) is used to extract spatio-temporal magnetic coherent structures from the experimental and simulation datasets of the HIT-SI experiment. Three-dimensional magnetic surface probes from the HIT-SI experiment are analyzed, along with companion simulations with synthetic internal magnetic probes. A number of leading variants of the DMD algorithm are compared, including the sparsity-promoting and optimized DMD. Optimized DMD results in the highest overall prediction accuracy, while sparsity-promoting DMD yields physically interpretable models that avoid overfitting. These DMD algorithms uncover several coherent magnetic modes that provide new physical insights into the inner plasma structure. These modes were subsequently used to discover a previously unobserved three-dimensional structure in the simulation, rotating at the second injector harmonic. Finally, using data from probes at experimentally accessible locations, DMD identifies a resistive kink mode, a ubiquitous instability seen in magnetized plasmas.

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Section: Sparsity-promoting Dmd: First Injector Harmonicsupporting

confidence: 63%

“…The higher harmonics of the injector frequency are f inj 2 , f inj 3 , and so on. A description of the equilibrium profile and postulated current drive mechanism during sustainment can be found in previous work [36]. The sustainment period of each experimental discharge, indicated by the vertical black lines, is illustrated in Fig.…”

Section: Methodsmentioning

confidence: 98%

Characterizing magnetized plasmas with dynamic mode decomposition

et al. 2020

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“…A time-smoothed trace of n e from shot 122385 is included in Figure 2 of Ref. 28. n e ¼ 1:5 Â 10 19 m À3 was chosen for the simulations.…”

Section: Resultsmentioning

confidence: 99%

“…The recently discovered imposed dynamo current drive (IDCD) theory explains how HIT-SI plasmas can be sustained stably by the injector-imposed fluctuations with the possibility of current profile control. 28 The present numerical implementation of SIHI is an extension of the original work by Izzo and Jarboe, who ran the first MHD simulations of HIT-SI with NIMROD. 20 The helicity injectors required for current drive are modeled as oscillating normal magnetic and tangential electric field boundary conditions (BCs).…”

Section: Introductionmentioning

confidence: 99%

Validation of single-fluid and two-fluid magnetohydrodynamic models of the helicity injected torus spheromak experiment with the NIMROD code

Akçay

Kim²,

Victor

et al. 2013

Physics of Plasmas

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We present a comparison study of 3-D pressureless resistive MHD (rMHD) and 3-D presureless two-fluid MHD models of the Helicity Injected Torus with Steady Inductive helicity injection (HIT-SI). HIT-SI is a current drive experiment that uses two geometrically asymmetric helicity injectors to generate and sustain toroidal plasmas. The comparable size of the collisionless ion skin depth d i to the resistive skin depth predicates the importance of the Hall term for HIT-SI. The simulations are run with NIMROD, an initial-value, 3-D extended MHD code. The modeled plasma density and temperature are assumed uniform and constant. The helicity injectors are modeled as oscillating normal magnetic and parallel electric field boundary conditions. The simulations use parameters that closely match those of the experiment. The simulation output is compared to the formation time, plasma current, and internal and surface magnetic fields. Results of the study indicate 2fl-MHD shows quantitative agreement with the experiment while rMHD only captures the qualitative features. The validity of each model is assessed based on how accurately it reproduces the global quantities as well as the temporal and spatial dependence of the measured magnetic fields. 2fl-MHD produces the current amplification I tor I inj and formation time s f demonstrated by HIT-SI with similar internal magnetic fields. rMHD underestimates I tor I inj and exhibits much a longer s f . Biorthogonal decomposition (BD), a powerful mathematical tool for reducing large data sets, is employed to quantify how well the simulations reproduce the measured surface magnetic fields without resorting to a probe-by-probe comparison. BD shows that 2fl-MHD captures the dominant surface magnetic structures and the temporal behavior of these features better than rMHD. V C 2013 AIP Publishing LLC. [http://dx.

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“…While this method offers the potential for steady-state current drive, and was initially tested on NSTX [5] it was found that discharges generated using this approach could not be successfully coupled to subsequent inductive drive, because of an influx of low-Z impurities. The method is being further developed on smaller machines, including novel approaches that drive steady-state current using a method that relies on steady-state inductive drive [6]. In the second approach, known as Transient CHI, the current on the openfield lines is rapidly reduced on the time scales it takes for the open-field line plasma discharge to fill the vessel.…”

Section: Introductionmentioning

confidence: 99%

Design description of the coaxial helicity injection (CHI) system on NSTX-U

Raman

Jarboe

Nelson

et al. 2013

2013 IEEE 25th Symposium on Fusion Engineering (SOFE)

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Elimination of the central solenoid would simplify the engineering design of a Fusion Nuclear Science Facility (FNSF) and tokamak based devices. The method of Transient Coaxial Helicity Injection (CHI) has successfully demonstrated formation of a high-quality closed flux plasma in NSTX and will be used as the front end of the start-up method for a full demonstration of non-inductive current start-up, followed by non-inductive current ramp-up using neutral beams in the NSTX-U device that is now under construction at the Princeton Plasma Physics Laboratory (PPPL). CHI is implemented by driving current along open field lines that connect the lower inner and outer divertor plates of a Spherical Torus (ST). The engineering system requirements and the design of the CHI system on NSTX-U are described.

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Imposed-dynamo current drive

Cited by 32 publications

References 23 publications

Characterizing magnetized plasmas with dynamic mode decomposition

Characterizing magnetized plasmas with dynamic mode decomposition

Validation of single-fluid and two-fluid magnetohydrodynamic models of the helicity injected torus spheromak experiment with the NIMROD code

Design description of the coaxial helicity injection (CHI) system on NSTX-U

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