arXiv subjects

S. Inagaki

Publications and source records attributed to S. Inagaki.

6 recordsLinked to original sources

arXiv2026

Sensitivity of a low-shear heliotron configuration to localised ferrite perturbations

The influence of ferritic steel on low-shear stellarator/heliotron magnetic configurations is investigated for the Heliotron J device using a point dipole magnetisation model. By numerically evaluating ferritic steel plates assumed at several locations inside the Heliotron J vacuum vessel, the changes in the rotational transform and magnetic island width are shown to be sensitive to the installation location. This sensitivity arises from the coupling between the background nonaxisymmetric field and ferrite perturbation, rather than being determined solely by the perturbation amplitude. Ferritic steel plates placed on the outer side of a straight section produce the most significant changes in the magnetic topology and exhibit the highest sensitivity to violations of the $M = 4$ toroidal periodicity. Additionally, we show that appropriate arrangements of passive magnetic dipoles can reduce the effective helical ripple while preserving the vacuum magnetic well depth in Heliotron J, and can induce stellaratorasymmetric boundary perturbation in low-field experiments near the ferrite saturation threshold.

physics.plasm-ph↗

arXiv2013

Dynamics of the fast component of nano-confined water under electric field

We report the diffusion of water molecules confined in the pores of folded silica materials (FSM-12 with average pore diameter of $\sim$ 16 Å), measured by means of quasielastic neutron scattering using the cold neutron chopper spectrometer (CNCS). The goal is to investigate the effect of electric field on the previously observed fast component of nano-confined water. The measurements were taken at temperatures between 220 K and 245 K, and at two electric field values, 0 kV/mm and 2 kV/mm. Similar to the recently observed electric field induced enhancement of the slow translational motion of confined water, there is a an equally important impact of the field on the faster diffusion.

cond-mat.soft↗

arXiv2012

Phases of Superfluid Helium in Smooth Cylindrical Pores

Two different microscopic phases have been observed via inelastic neutron scattering for superfluid helium confined within highly monodisperse, smooth, and unidimensional silica pores. When the helium forms a thin film on the pore walls, it supports a dramatically modified phonon-roton spectrum as well as a 2D surface roton. The energies of these modified phonon-roton modes are consistent with predictions for a dilute, low-density film, while the energy of the 2D surface roton corresponds to that of a dense film. The relatively smooth and weak surface potential of the substrate permits the formation of a film with large dilute regions and only small compressed regions. When the pores are saturated with liquid, the modified phonon-roton spectrum disappears, and bulk-like modes coexist with the 2D surface roton. Presumably, bulk-like liquid occupies the core volume of the pores and high density liquid layers are present at the liquid-solid interface. These findings clearly connect the nature of the excitations to the local density of the liquid.

cond-mat.other↗

arXiv2007

Compensation of the Crossing Angle with Crab Cavities at KEKB

Crab cavities have been installed in the KEKB B--Factory rings to compensate the crossing angle at the collision point and thus increase luminosity. The beam operation with crab crossing has been done since February 2007. This is the first experience with such cavities in colliders or storage rings. The crab cavities have been working without serious issues. While higher specific luminosity than the geometrical gain has been achieved, further study is necessary and under way to reach the prediction of simulation.

physics.ins-det↗

arXiv2006

Reorganization of a 2D disordered granular medium due to a small local cyclic perturbation

We measure experimentally the rearrangements due to a small localized cyclic displacement applied to a packing of rigid grains under gravity in a 2D geometry. We analyze the evolution of the response to this perturbation by considering the individual particle displacement and the coarse grained displacement field, as well as the mean packing fraction and coordination number. We find that the displacement response is rather long ranged, and evolves considerably with the number of cycles. We show that a small difference in the preparation method (induced by tapping the container) leads to a significant modification in the response though the packing fraction changes are minute. Not only the initial response but also its further evolution change with preparation, demonstrating that the system still retains a memory of the initial preparation after many cycles. Nevertheless, after a sufficient number of cycles, the displacement response for both preparation methods converges to a nearly radial field with a 1/r decay from the perturbation source. The observed differences between the preparation methods seem to be related to the changes in the coordination number (which is more sensitive to the evolution of the packing than the packing fraction). Specifically, it may be understood as an effect of the breaking of local arches, which affects the lateral transmission of forces.

cond-mat.soft↗

arXiv1997

Evolution of Tidally Truncated Globular Clusters with Anisotropy

The evolution of tidally truncated globular clusters is investigated by integrating two-dimensional Fokker-Planck equation that allows the development of velocity anisotropy. We start from the isotropic Plummer model with tidal cut off and followed the evolution through the corecollapse. The heating by three-binary is included to obtain the evolution past the corecollapse. The anisotropy in velocity dispersion develops during the precollapse evolution. However, the anisotropy becomes highly depressed during the post-collapse evolution because of rapid loss of radial orbits. Maximum radial anisotropy appears just after the beginning of the expansion, and degree of anisotropy decreases slowly as the total mass of the cluster decreases. Thus it may be possible to determine the evolutionary status of a cluster if the velocity anisotropy can be measured in the sense that the postcollapse clusters always have very little degree of anisotropy. The structure of the post-collapse cluster can be well fitted to King models because the degree of anisotropy is rather small.

astro-ph↗