Intrinsic and extrinsic mechanisms of vortex formation in superfluid3He-B

Abstract

We report on the first comprehensive measurements of critical superJlow velocities in ~He-B which allow diJferent mechanisms of vortex Jormation to be identifi'ed. As a Jimction of temperature T and pressure P, we measure the critical anguhw velocity ~(" T, P) at which vortices start to Jbrm in slowly accelerating rotation in a cylindrical conta#wr fi'llcd with ~He-B. Owing to the long coherence length ~(T, P) ~ 10-100 nm, either trapped remanent vortici O' or #ztrinsie nucleation me O, dominate vortex Jbrmation, depending on the roughness of the contahwr wall and the presence of loaded traps. NMR measurement with a resohztion of one single vortex line allows us to distinguish between diJferent processes: ( 1 ) Three extrinsic mechanisms of vortex Jormation have been observed. One of them is the vortex mill, a continuous periodic source which is activated in a rough-walled container well below the limit Jor intrinsic nuch, ation. (2) In a closed smooth-walled container intrinsic nucleation is the only mechanism available, with a criticalvelocity vJT, P)= g2~(T, P) R, where R is the radius of the container. We find v~(T, P) to be related to the calculated intrinsic stability limit Vcb(T, P) of homogeneous superJlow. The existence of this connection in the form of a scaling law implies that nucleation takes place at an instability, rather than by thermal activation or quantum tunneling which become impossible because of an inaccessibly high energy barrier.

Composite Defect Extends Analogy between Cosmology andH3e

“…The total number of vortex lines accumulated by the end of the irradiation session can be determined by different independent methods. These include (a) measurement of the annihilation threshold, i.e., of the rotation velocity at which vortex lines start to annihilate at the wall of the container during deceleration [19], (b) measurement of the relative heights of the two peaks in the NMR spectrum of Fig. 1, known as the counterflow and Larmor peaks [20], and (c) comparison to measurements at other rotation velocities using an empirically established V dependence of the vortex formation rate [1,8].…”

Quantum turbulence in superfluids with wall-clamped normal component

“…4 is then v s = 0. The formation of quantized vortices "out of nothing" at moderate flow velocities v n ( 1 cm=s is prohibited by a large energy barrier, and thus this metastable vortex-free state can persist for the duration of the experiment in the absence of seed vortices (17). Another state of laminar flow is solid-body rotation of the superfluid component at an angular velocity Ω s : v s = ðΩ sΩ Þ × r. In this state, the sample is filled with rectilinear vortices at a density 2Ω s =κ, aligned along the rotation axis.…”

“…In one of the segments, the Kelvin waves will be properly oriented with respect to the counterflow and the loop will start to grow (iv), repeating the process. Thus, new vortices are created repeatedly without the need for a specially arranged "vortex mill" (17). Eventually the local density of vortices becomes sufficient to start the turbulent burst.…”

Dynamic Remanent Vortices in Superfluid 3He-B

“…N is determined by comparing the NMR line shape to one measured with a known number of vortices (taking into account the tilt angle between axes). 1 Measuring procedure: The measurement is started from a state with large N at Ω 1.7 rad/s which is decelerated at 0.02 rad/s 2 to zero rotation and kept there for a waiting period ∆t. Rotation is then increased (in the same direction) at 0.01 rad/s 2 to Ω f where it is kept constant (see insert in Fig.…”

“…To release a remnant from the trap, the required applied flow velocity is v c ≈ 0.8κ/(2πr o ), if the remnant is modeled as a half circle of radius r o attached at both ends to the cylindrical wall. 1 This measurement is straightforward, but it involves three complications: (i) Remnants can exist on different length scales. The length scale determines the flow velocity at which a particular remnant is inflated out of the pinning trap.…”