Correcting for background fields and multipole field errors in the localization of the magnetic axis in quadrupole magnets

2018 ◽  
Vol 895 ◽  
pp. 112-119
Author(s):  
Pasquale Arpaia ◽  
Domenico Caiazza ◽  
Carlo Petrone ◽  
Stephan Russenschuck
Keyword(s):  
Magnetic Axis ◽  
Multipole Field ◽  
Background Fields ◽  
Field Errors

scholarly journals Figures of merit for stellarators near the magnetic axis

2021 ◽  
Vol 87 (1) ◽  
Author(s):  
Matt Landreman
Keyword(s):  
Magnetic Field ◽  
Field Strength ◽  
Magnetic Axis ◽  
Configuration Design ◽  
New Paradigm ◽  
First Order ◽  
Figures Of Merit ◽  
Minor Radius ◽  
Error Field ◽  
Quantities Of Interest

A new paradigm for rapid stellarator configuration design has been recently demonstrated, in which the shapes of quasisymmetric or omnigenous flux surfaces are computed directly using an expansion in small distance from the magnetic axis. To further develop this approach, here we derive several other quantities of interest that can be rapidly computed from this near-axis expansion. First, the $\boldsymbol {\nabla }\boldsymbol {B}$ and $\boldsymbol {\nabla }\boldsymbol {\nabla }\boldsymbol {B}$ tensors are computed, which can be used for direct derivative-based optimization of electromagnetic coil shapes to achieve the desired magnetic configuration. Moreover, if the norm of these tensors is large compared with the field strength for a given magnetic field, the field must have a short length scale, suggesting it may be hard to produce with coils that are suitably far away. Second, we evaluate the minor radius at which the flux surface shapes would become singular, providing a lower bound on the achievable aspect ratio. This bound is also shown to be related to an equilibrium beta limit. Finally, for configurations that are constructed to achieve a desired magnetic field strength to first order in the expansion, we compute the error field that arises due to second-order terms.

scholarly journals Direct construction of optimized stellarator shapes. Part 3. Omnigenity near the magnetic axis

2019 ◽  
Vol 85 (6) ◽  
Author(s):  
Gabriel G. Plunk ◽  
Matt Landreman ◽  
Per Helander
Keyword(s):  
Numerical Method ◽  
Plasma Phys ◽  
Magnetic Axis ◽  
Direct Construction ◽  
Numerical Construction ◽  
First Order

The condition of omnigenity is investigated, and applied to the near-axis expansion of Garren & Boozer (Phys. Fluids B, vol. 3 (10), 1991a, pp. 2805–2821). Due in part to the particular analyticity requirements of the near-axis expansion, we find that, excluding quasi-symmetric solutions, only one type of omnigenity, namely quasi-isodynamicity, can be satisfied at first order in the distance from the magnetic axis. Our construction provides a parameterization of the space of such solutions, and the cylindrical reformulation and numerical method of Landreman & Sengupta (J. Plasma Phys., vol. 84 (6), 2018, 905840616); Landreman et al. (J. Plasma Phys., vol. 85 (1), 2019, 905850103), enables their efficient numerical construction.

scholarly journals Effect of magnetic field on the burning of a neutron star

2018 ◽  
Vol 27 (10) ◽  
pp. 1850083 ◽  
Author(s):  
Ritam Mallick ◽  
Amit Singh
Keyword(s):  
Magnetic Field ◽  
Neutron Star ◽  
Initial Density ◽  
Considerable Effect ◽  
Magnetic Axis ◽  
Small Window ◽  
Exothermic Process ◽  
Text Density ◽  
The Magnetic Field ◽  
Observational Aspect

In this paper, we present the effect of a strong magnetic field in the burning of a neutron star (NS). We have used relativistic magneto-hydrostatic (MHS) conservation equations for studying the PT from nuclear matter (NM) to quark matter (QM). We found that the shock-induced phase transition (PT) is likely if the density of the star core is more than three times nuclear saturation ([Formula: see text]) density. The conversion process from NS to quark star (QS) is found to be an exothermic process beyond such densities. The burning process at the star center most likely starts as a deflagration process. However, there can be a small window at lower densities where the process can be a detonation one. At small enough infalling matter velocities the resultant magnetic field of the QS is lower than that of the NS. However, for a higher value of infalling matter velocities, the magnetic field of QM becomes larger. Therefore, depending on the initial density fluctuation and on whether the PT is a violent one or not the QS could be more magnetic or less magnetic. The PT also have a considerable effect on the tilt of the magnetic axis of the star. For smaller velocities and densities the magnetic angle are not affected much but for higher infalling velocities tilt of the magnetic axis changes suddenly. The magnetic field strength and the change in the tilt axis can have a significant effect on the observational aspect of the magnetars.

scholarly journals ON TARGET SPACE DUALITY IN p-BRANES

1995 ◽  
Vol 10 (05) ◽  
pp. 441-450 ◽  
Author(s):  
R. PERCACCI ◽  
E. SEZGIN
Keyword(s):  
Dimensional Space ◽  
Target Space ◽  
Field Equations ◽  
Parameter Group ◽  
Duality Transformations ◽  
World Volume ◽  
The World ◽  
Dimensional Space Time ◽  
Background Fields ◽  
Two Parameter

We study the target space duality transformations in p-branes as transformations which mix the world volume field equations with Bianchi identities. We consider an (m+p+1)-dimensional space-time with p+1 dimensions compactified, and a particular form of the background fields. We find that while a GL (2) = SL (2) × R group is realized when m = 0, only a two-parameter group is realized when m > 0.

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