Makoto Tsubota

Spin relaxation in U2D23He

The spin relaxation in the U2D2 phase of solid3He is investigated theoretically. Following the procedure similar to the spin-wave theory of the electronic anti-ferromagnetic resonance, the multimagnon Hamiltonian is derived with the use of the Holstein-Primakoff method. We calculate the spin-relaxation rate due to three- and four-magnon processes that dominate at low temperatures and compare it with the linewidth of cw-NMR measured by Sasaki et al.

Relaxation of Brinkman-Smith Mode in Superfluid 3He–B between Parallel Plates

The relaxation of the Brlnkman-Smlth (B–S) mode in superfluld 3He–B placed between parallel plates is considered. It Is known that the Leggett-Takagi mechanism does not lead to relaxation of the B–S mode In bulk 3He–B. In the presence of the boundaries, however, the B–S mode relaxes due to the surface torque, since this torque generates time dependent spatial variation of the texture which makes the Leggett-Takagi mechanism operative. Assuming that the perturbation due to the surface is small, we have calculated the recovery of the magnetization as a function of time. The result is compared with the data obtained by the pulsed N.M.R. experiment of Ishikawa et al., presented in this Conference.

Dynamics of quantized vortices in rotating superfluid

Dynamics of interactive quantized vortices in rotating superfluid is studied theoretically. This work considers the basic system where superfluid is contained in a cylindrical vessel that rotates about its axis at an angular velocity. Although two-dimensional equilibrium patterns of vortex arrays are understood fairly well at present, there has been only a little amount of information on the dynamical aspects. Thus this work studies some typical dynamical problems, i.e., formation of vortex array and spin-down process. We describe also three-dimensional analysis which is much more troublesome than two-dimensional one.

High-speed fluid phenomena caused by laser beam focusing in liquid nitrogen

The high-speed phenomena caused by the focusing of a pulsed laser beam in liquid nitrogen is studied experimentally with an image converter camera. The focusing of a laser beam elevates the energy density at the focus. When the energy density exceeds a critical value necessary for optical breakdown, there appears luminous plasma, and a shock wave is emitted from the plasma into the bulk liquid. The initial shape of the vapor bubble and the shock front is nonspherical because of reflecting that of plasma. While the plasma relaxes to a vapor bubble, however, several compression waves are emitted following the preceding shock wave, so that both the bubble and the shock front become spherical. The resulting spherical bubble grows under the dominant effect of liquid inertia, and collapses after reaching a maximum size. The high vapor pressure retards the collapse process from the growth and makes the bubble surface rough. While the bubble repeats the growth and collapse processes a few times, that distribution over its surface is amplified through every rebound, eventually breaking up the bubble itself.

Dynamics of two quantized vortices on a pinning site

Abstract Following our preceding paper, this describes the interactive motion of two quantized vortices trapped by a pinning site. When they are antiparallel, they reconnect with each other to leave the pinning site. On the other hand, two parallel vortices relax to a stationary configuration on the pinning site because of mutual friction. The critical depinning superflow velocity is smaller than that for only one.

Capture of two quantized vortices by a pinning site

Abstract The capture process of two interactive quantized vortices by a pinning site in superfluid 4 He is studied numerically. The present paper discusses whether one vortex can be attracted by a pinning site that has already captured another.

Interaction of two close quantized vortices in superfluid4He

The three-dimensional dynamics of two interacting quantized vortex filaments is studied. The equations of motion and the method of numerical calculation follow Schwarz. Whether two approaching filaments reconnect or not depends on their arrangement before approach. When a ring moves toward a line from a distance, only within a critical initial distance they can reconnect. The critical distance is minimized when their circulations are parallel at the closest place, while it increases as their circulations begin to deviate from being parallel. Hence the reconnection probability can be less than unity.

High-Speed Phenomena Induced by Laser Focusing in Liquid Nitrogen.

The dynamics of high-speed phenomena induced by focusing of pulsed laser beam in liquid nitrogen is studied experimentally. Before the growth of a spherical bubble, a series of nonspherical phenomena is observed. The laser-induced breakdown creates luminous plasma around the point of focus. When the pulsed laser beam is switched off, the relaxing plasma and the resulting gas form a nonspherical bubble, which emits a nonspherical shock wave. Then several compression waves following the preceding shock wave are emitted from the bubble. As they overtake the shock wave, they make both the shock wave and the bubble spherical. A possible mechanism for these phenomena is considered.

Three-dimensional growth of quantized vortices in rotating superfluid

This work studies numerically three-dimensional growth of small quantized vortices from the vessel boundary in rotating superfluid.

Three-dimensional dynamics of a vortex array in rotating superfluid

This work studies numerically three-dimensional formation of a vortex array in a rotating cylindrical vessel. The formation process and the resulting equilibrium pattern are affected by pinning sites on the vessel’s bottom.