Dendritic flux avalanches in superconducting Nb3Sn films

Abstract

The penetration of magnetic flux into a thin superconducting film of Nb3Sn with critical temperature 17.8K and critical current density 6MA/cm^2 was visualized using magneto-optical imaging. Below 8 K an avalanche-like flux penetration in form of big and branching dendritic structures was observed in response to increasing perpendicular applied field. When a growing dendritic branch meets a linear defect in the film, several scenarios were observed: the branch can turn and propagate along the defect, continue propagation right through it, or "tunnel" along a flux-filled defect and continue growth from its other end. The avalanches manifest themselves in numerous small and random jumps found in the magnetization curve.Comment: 3 pages, 4 figures, submitted to Cryogenics. Revision: M(H) data adde

Ultrafast magnetic flux dendrite propagation into thin superconducting films

“…A wealth of recent experiments convincingly demonstrate that a propagating dendritic flux pattern driven by the flux jumping instability is a general phenomenon typical for Bean's-type critical state [13,14,15,22,23,24,25]. Indeed, the flux dendrites were observed under a wide variety of conditions in superconducting films of Nb [13,14,22], YBa 2 Cu 3 O 7−δ [13,15,23], Nb 3 Sn [24], and MgB 2 [25].…”

“…Indeed, the flux dendrites were observed under a wide variety of conditions in superconducting films of Nb [13,14,22], YBa 2 Cu 3 O 7−δ [13,15,23], Nb 3 Sn [24], and MgB 2 [25].…”

Nanosecond voltage pulses from dendritic flux avalanches in superconducting NbN films

“…2,3 It can take place in bulk samples, wires, and tapes, but in thin films subjected to a perpendicular magnetic field, the instability takes a most spectacular form of dendritic avalanches propagating at ultra-fast speeds. The phenomenon has been reported to occur in a large number of materials important for practical applications, such as Nb, 4 NbN, 5 Nb 3 Sn, 6 and MgB 2 . 7 The avalanches are expected to generate strong electromagnetic noise and even destroy superconducting equipment.…”

“…7 The avalanches are expected to generate strong electromagnetic noise and even destroy superconducting equipment. 8 Whereas flux structures frozen in superconducting films after such events are routinely observed by magneto-optical imaging (MOI), [4][5][6][7] experiments providing insight to the time-resolved behavior of these ultrafast avalanches are extremely few. Previous work on films of YBa 2 Cu 3 O x has combined MOI and a femtosecond pulsed laser technique, where an avalanche was triggered by a laser-generated hot spot, and a few nanoseconds later laser light was used to record a snapshot of the evolving flux distribution.…”

Avalanches injecting flux into the central hole of a superconductingMgB2ring

“…Such avalanches were first observed in YBa 2 Cu 3 O x , where they must be triggered by a sudden point-like heatpulse 1,2 . Since then spontaneous dendritic avalanches have been observed 3,4,5,6,7 in Nb, Nb 3 Sn, YNi 2 B 2 C and NbN, as well as in patterned Pb thin films 8 . The recent interest in the phenomenon was largely triggered by the discovery 9 that in MgB 2 films the avalanches are ubiquitous below a threshold temperature T th ∼ 10 K. The dendrites disrupt electrical current flow and limit the overall current capacity of superconductors, 10 and are thus harmful for prospective applications.…”