Theoretical Principles of the Plasma-Equilibrium Control in Stellarators

Pustovitov, V. D.

doi:10.1007/978-1-4615-4309-1_1

Cited by 19 publications

(5 citation statements)

References 178 publications

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“…The ellipticity κ is about 2. This is consistent with the study in [6]. On the other hand, for the HE configuration, a clear figure-eight separatrix does not exist inside flux surfaces and the O-point outside of the torus degenerates to the X-point.…”

Section: Doublet-like Configurations In Lhdsupporting

confidence: 92%

“…In heliotron plasmas, when the shape of flux surfaces is elongated vertically (horizontally), the following characteristics are predicted by numerical [4,5] and analytical [6] analyses based on the stellarators expansions [7]: (i) the rotational transform on the axis is decreased, (ii) the Pfirsch-Schlüter current is suppressed (enhanced) and (iii) the Shafranov shift towards the outside of the torus is small (large). If the elongation produced by the quadrupole field is increased further, the rotational transform crosses zero and the magnetic shear is reversed.…”

Section: Introductionmentioning

confidence: 99%

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Theoretical considerations of doublet-like configuration in LHD

Suzuki¹,

Yamada

Nakajima

et al. 2005

Nucl. Fusion

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In order to investigate the separatrix structure inside the plasma, the magnetohydrodynamic (MHD) equilibrium and the high-energy particle orbit are studied for the Large Helical Device plasmas with two magnetic axes located within the two lobes of a figure-eight magnetic separatrix. Magnetic axes are split for strongly elongated cross section by the external quadrupole field. MHD equilibria without assuming existence of nested flux surfaces are obtained from the HINT code. For the vertical elongation, the figure-eight structure evolves due to the finite beta effect and the structure of magnetic field lines outside the separatrix is ergodized. For the horizontal elongation, the Shafranov shift is very large Δ/a > 0.5. To see MHD equilibrium beta limit, high beta equilibrium (∼5%) is studied. The magnetic axis shifts extremely to the outside of the torus and a new figure-eight separatrix appears. The particle orbit on the separatrix is studied by solving the guiding-centre drift equation on the rectangular grid. If the reflecting point of the trapped particle is close to the separatrix, the banana width is very large implying large, nonlocal neoclassical transport.

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Section: Doublet-like Configurations In Lhdsupporting

confidence: 92%

Section: Introductionmentioning

confidence: 99%

Theoretical considerations of doublet-like configuration in LHD

Suzuki¹,

Yamada

Nakajima

et al. 2005

Nucl. Fusion

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“…Note that these line densities include the information outside the LCFS (called ergodic region), and therefore, κ eff is an approximation of κ. Both in helical plasmas and tokamaks, κ is controlled by the quadrupole magnetic field B Q [1]. In the standard configurations of LHD, the quadrupole component generated by two helical coils is 100% cancelled by the quadrupole field generated by poloidal coils and therefore κ = 1.…”

Section: Plasma Shape Control By the Quadrupole Magnetic Fieldmentioning

confidence: 99%

“…This is called the Shafranov shift. Since the PS current is proportional to the pressure gradient, ∆ is determined by the central plasma beta β 0 [1]. Especially in helical plasmas, a large Shafranov shift exceeding a half of the plasma minor radius a for example, may cause destruction of magnetic surfaces leading to loss of confinement.…”

Section: Introductionmentioning

confidence: 99%

Abrupt Flushing of High-Density Core in Internal Diffusion Barrier Plasmas and its Suppression by Plasma Shape Control in LHD

Miyazawa

Sakamoto

Ohdachi

et al. 2008

Plasma and Fusion Research

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Abrupt flushing of central density occurs in internal diffusion barrier (IDB) plasmas in the Large Helical Device (LHD), where a super dense core (SDC) of the order of 10 20 m −3 is formed inside; this event is called "core density collapse (CDC)." CDC must be suppressed as further increase of the central pressure is inhibited. Since CDC is always accompanied by a large Shafranov shift of the plasma center, it has been supposed that mitigation of the Shafranov shift might affect CDC. Vertical elongation of the plasma shape (κ > 1) is effective in mitigating the Shafranov shift, and κ can be controlled with the quadrupole magnetic field B Q . To examine the impact of plasma shape control on CDC, B Q scan experiment has been performed in the LHD. The large Shafranov shift in IDB plasmas is mitigated by increasing κ. As a result, CDC is suppressed and high central β values of approximately 7% have been achieved in vertically elongated plasmas. The optimum κ varies with the magnetic configuration. Beta gradients greater than those at CDC in the κ = 1 configuration are observed without CDC in vertically elongated plasmas.

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“…This result was already found in previous studies and interpreted as a near-wall mobility effect. 62 This phenomenon is caused by the SEE and its effect on the averaged mobility is stronger than that of the drop of electron temperature. Consequently, the values of electron mobility measured from the PIC simulation data and predicted by equation (6) are higher in case 1 than in cases 2 and 3.…”

Section: B Role Of the Wall Propertiesmentioning

confidence: 99%

The effect of alternative propellants on the electron drift instability in Hall-effect thrusters: Insight from 2D particle-in-cell simulations

et al. 2018

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Hall-effect thrusters (HETs) operated with xenon are one of the most commonly used electric propulsion technologies for a wide range of space missions, including drag compensation in low Earth orbit, stationkeeping, and orbital insertion, as access to space becomes more affordable. Although anomalous electron transport, the electron drift instability (EDI), and secondary electron emission (SEE) have been studied experimentally and numerically in xenon-based HETs, the impact of alternative propellants is still poorly characterized. In this work, a two-dimensional particle-in-cell/Monte Carlo collision (PIC/MCC) code is used to model the (r − θ) plane of a HET operated separately with four different noble gases: xenon, krypton, argon, and helium. Models for electron induced secondary electron emission (SEE) and dielectric walls are implemented in order to investigate the coupling between the propellant choice and the radial thruster walls. For all conditions and propellants studied, an EDI and enhanced electron cross-field transport are observed. The frequency of the instability, as well as the electron mobility, are compared with analytical expressions from a recently developed kinetic theory. Confirming this theory, it is shown that while the frequency of the EDI depends on the propellant mass, the electron mobility appears to be almost independent of the propellant choice.

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Theoretical Principles of the Plasma-Equilibrium Control in Stellarators

Cited by 19 publications

References 178 publications

Theoretical considerations of doublet-like configuration in LHD

Theoretical considerations of doublet-like configuration in LHD

Abrupt Flushing of High-Density Core in Internal Diffusion Barrier Plasmas and its Suppression by Plasma Shape Control in LHD

The effect of alternative propellants on the electron drift instability in Hall-effect thrusters: Insight from 2D particle-in-cell simulations

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