arXiv subjects

T. Maekawa

Publications and source records attributed to T. Maekawa.

5 recordsLinked to original sources

arXiv2022

Solenoid-free current drive via ECRH in EXL-50 spherical torus plasmas

As a new spherical tokamak (ST) designed to simplify engineering requirements of a possible future fusion power source, the EXL-50 experiment features a low aspect ratio (A) vacuum vessel (VV), encircling a central post assembly containing the toroidal field coil conductors without a central solenoid. Multiple electron cyclotron resonance heating (ECRH) resonances are located within the VV to improve current drive effectiveness. Copious energetic electrons are produced and measured with hard X-ray detectors, carry the bulk of the plasma current ranging from 50kA to 150kA, which is maintained for more than 1s duration. It is observed that over one Ampere current can be maintained per Watt of ECRH power issued from the 28-GHz gyrotrons. The plasma current reaches Ip>80kA for high density (>5e18me-2) discharge with 150kW ECHR heating. An analysis was carried out combining reconstructed multi-fluid equilibrium, guiding-center orbits of energetic electrons, and resonant heating mechanisms. It is verified that in EXL-50 a broadly distributed current of energetic electrons creates smaller closed magnetic-flux surfaces of low aspect ratio that in turn confine the thermal plasma electrons and ions and participate in maintaining the equilibrium force-balance.

physics.plasm-ph↗

arXiv2004

Computational Topology for Regular Closed Sets

The Boolean algebra of regular closed sets is prominent in topology, particularly as a dual for the Stone-Cech compactification. This algebra is also central for the theory of geometric computation, as a representation for combinatorial operations on geometric sets. However, the issue of computational approximation introduces unresolved subtleties that do not occur within "pure" topology. One major effort towards reconciling this mathematical theory with computational practice is our ongoing I-TANGO project. The acronym I-TANGO is an abbreviation for "Intersections - Topology, Accuracy and Numerics for Geometric Objects". The long-range goals and initial progress of the I-TANGO team in development of computational topology are presented.

math.GN↗

arXiv2002

On relation between unitary gauge and gauge given by $ξ$-limiting process

It is shown that in general the gauge given by the limit of $ξ\to 0$ in $R_ξ$ gauge does not necessarily agree with the unitary gauge by examining the symmetry breaking of two steps from ${\rm SU(3) \otimes U(1)}_N$ to ${\rm SU(2) \otimes U(1)}_Y$ and then to ${\rm U(1)}_{em}$.

hep-ph↗

arXiv2002

Note on Triangle Anomalies and Assignment of Singlet in 331-like Model

It is pointed out that in the $331-$like model which uses both fundamental and complex conjugate representations for an assignment of the representations to the left-handed quarks and the scalar representation to their corresponding right-handed counterparts, the nature of the scalar should be taken into account in order to make the fermion triangle anomalies in the theory anomaly-free, i.e. renormalizable in a sense with no anomalies, even after the spontaneous symmetry breaking.

hep-ph↗

arXiv2002

On Nature of Right-Handed Singlet in 331 Model and Anomalies before and after SSB

The gauge invariant and anomaly-free 331 model is studied with $R_ξ$ gauges in order to see which of the right-handed singlet between the case (i), assigning the bosonic singlet to the counterpart of 3 and $\bar 3$ representations, and the case (ii), assigning fermionic siglet to the counterpart of the left-handed 3 representation and assigning the antifermionic singlet to that of the left-handed $\bar 3$ representaion, should be assigned in physics but not mathematics to the counterparts of the left-handed fundamental 3 representation and the left-handed complex conjugate $\bar 3$ representation. It is shown that through an effect on the Yukawa interaction of the transformation property of the singlet it depends on the choices of the case (i) or the case (ii) whether the anomaly coefficients even after the spontaneous symmetry breaking (SSB) vanish or not, and the coefficients vanish only in the case (ii) but do not in the case (i). Furthermore, it is pointed out that the BRS invariance after the SSB holds for the case (ii) and (i-b) of two possibilities in the choice for the mass eigenstates in the case (i) and thus the BRS invariance does not necessarily ensure renormalizability of the theory though the inverse of it holds.

hep-ph↗