Stable Spheromaks Sustained by Neutral Beam Injection

Fowler, T.K.; Jayakumar, R. J.; McLean, H. S.

doi:10.1007/s10894-008-9157-y

Cited by 4 publications

(5 citation statements)

References 18 publications

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“…Neutral beam current drive. Studies [15,16] have primarily focused on using neutral beams as a global, steady-state current drive, concluding that it may be possible to access a q-profile which yields a stable state. In [15] the effect of varying the beam aiming was explored showing an effect on the q-profile, but it did not consider transport.…”

Section: Discussionmentioning

confidence: 99%

“…In [15] the effect of varying the beam aiming was explored showing an effect on the q-profile, but it did not consider transport. Reference [16] concluded that power requirements for a reactor may be satisfactory [37] and that stable profiles may be accessible. Generally, however, the large, energetic-ion orbits [15] make neutral-beam injection useful for affecting the profile across most of the radius but difficult to use for localized MHD-stability control or for control of tearing modes.…”

Section: Discussionmentioning

confidence: 99%

“…The spheromak might be sustained by carefully tailored axisymmetric processes, e.g. using neutral beams [15,16]; but this has neither been addressed experimentally nor modeled in sufficient detail to fully guide experiments. As a result, there is no currently demonstrated means of sustaining a high-temperature spheromak.…”

Section: Introductionmentioning

confidence: 99%

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Physics issues of a spheromak refluxing scenario

Hooper¹

2011

Plasma Phys. Control. Fusion

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The spheromak has a toroidal magnetic fusion geometry embedded in a simply connected flux conserver, which would simplify a reactor design if energy confinement were sufficiently good. Helicity injection is an efficient current-drive mechanism used in many spheromak experiments but has been shown theoretically and computationally to open the magnetic flux surfaces. Experiments are consistent with this: excellent confinement has been demonstrated in slowly decaying spheromaks with good surfaces, but it is poor in driven spheromaks. One option to overcome this limitation is to operate in a 'refluxing' mode in which the current drive and confinement phases of operation are separated in time. After the toroidal current and magnetic field have partially decayed, the current drive would be turned back on to rebuild the magnetic field. The physics of refluxing operation is explored in the resistive-MHD approximation using simulations and an integrated-physics model. The results suggest that sustaining the confinement phase for an extended time will require an auxiliary means of controlling the safety-factor profile.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

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Physics issues of a spheromak refluxing scenario

Hooper¹

2011

Plasma Phys. Control. Fusion

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“…We first consider tearing modes, for which δW in Equation (25) can be simplified as follows. Following Hegna & Callen (1994), applied also in Fowler et al (2009b), we expand k B…”

Section: Jet Stability: Linear Theorymentioning

confidence: 99%

Quasi-Static Model of Magnetically Collimated Jets and Radio Lobes. Ii. Jet Structure and Stability

Colgate

Fowler

et al. 2015

ApJ

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This is the second in a series of companion papers showing that when an efficient dynamo can be maintained by accretion disks around supermassive black holes in active galactic nuclei, it can lead to the formation of a powerful, magnetically driven, and mediated helix that could explain both the observed radio jet/lobe structures and ultimately the enormous power inferred from the observed ultrahigh-energy cosmic rays. In the first paper, we showed self-consistently that minimizing viscous dissipation in the disk naturally leads to jets of maximum power with boundary conditions known to yield jets as a low-density, magnetically collimated tower, consistent with observational constraints of wire-like currents at distances far from the black hole. In this paper we show that these magnetic towers remain collimated as they grow in length at nonrelativistic velocities. Differences with relativistic jet models are explained by three-dimensional magnetic structures derived from a detailed examination of stability properties of the tower model, including a broad diffuse pinch with current profiles predicted by a detailed jet solution outside the collimated central column treated as an electric circuit. We justify our model in part by the derived jet dimensions in reasonable agreement with observations. Using these jet properties, we also discuss the implications for relativistic particle acceleration in nonrelativistically moving jets. The appendices justify the low jet densities yielding our results and speculate how to reconcile our nonrelativistic treatment with general relativistic MHD simulations.

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“…For both approaches, the initial spheromak plasma is formed by CHI. While a spheromak could achieve quasisteady-state operation through external heating and current drive, e.g., neutral beam injection 5 or imposed dynamo current drive, 6 it would increase the size, engineering complexity, and capital costs associated with an experiment. With either approach, significant theoretical, computational, and engineering developments are still required to advance to a full-fledged proof-of-principle device capable of confining fusion plasmas for times long enough to test alpha particle heating and key engineering issues.…”

Section: Introductionmentioning

confidence: 99%

Simulation of multi-pulse coaxial helicity injection in the Sustained Spheromak Physics Experiment

2018

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Nonlinear, numerical computation with the NIMROD code is used to explore magnetic selforganization during multi-pulse coaxial helicity injection in the Sustained Spheromak Physics eXperiment. We describe multiple distinct phases of spheromak evolution, starting from vacuum magnetic fields and the formation of the initial magnetic flux bubble through multiple refluxing pulses and the eventual onset of the column mode instability. Experimental and computational magnetic diagnostics agree on the onset of the column mode instability, which first occurs during the second refluxing pulse of the simulated discharge. Our computations also reproduce the injector voltage traces, despite only specifying the injector current and not explicitly modeling the external capacitor bank circuit. The computations demonstrate that global magnetic evolution is fairly robust to different transport models and, therefore, that a single fluid-temperature model is sufficient for a broader, qualitative assessment of spheromak performance. Although discharges with similar traces of normalized injector current produce similar global spheromak evolution, details of the current distribution during the column mode instability impact the relative degree of poloidal flux amplification and magnetic helicity content.

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Stable Spheromaks Sustained by Neutral Beam Injection

Cited by 4 publications

References 18 publications

Physics issues of a spheromak refluxing scenario

Physics issues of a spheromak refluxing scenario

Quasi-Static Model of Magnetically Collimated Jets and Radio Lobes. Ii. Jet Structure and Stability

Simulation of multi-pulse coaxial helicity injection in the Sustained Spheromak Physics Experiment

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