8 research outputs found
Magnetic fields and currents for two current-carrying parallel coplanar superconducting strips in a perpendicular magnetic field
Abstract We present general solutions for the Meissner-state magnetic-field and current-density distributions for a pair of parallel, coplanar superconducting strips carrying arbitrary but subcritical currents in a perpendicular magnetic field. From these solutions we calculate (a) the inductance per unit length when the strips carry equal and opposite currents, (b) flux focusing in an applied field-how much flux per unit length is focused into the slot between the two strips when each strip carries no net current, (c) the current distribution for the zero-flux quantum state when the strips are connected with superconducting links at the ends and (d) the current and field distributions around both strips when only one of the strips carries a net current. The solutions are closely related to those found recently for the magnetic-field and current-density distributions in a thin, bulk-pinning-free, type-II superconducting strip with a geometrical barrier when the strip carries a current in a perpendicular applied field
Self-field effects upon the critical current density of flat superconducting strips
We develop a general theory to account self-consistently for self-field
effects upon the average transport critical current density Jc of a flat
type-II superconducting strip in the mixed state when the bulk pinning is
characterized by a field-dependent depinning critical current density Jp(B),
where B is the local magnetic flux density. We first consider the possibility
of both bulk and edge-pinning contributions but conclude that bulk pinning
dominates over geometrical edge-barrier effects in state-of-the-art YBCO films
and prototype second-generation coated conductors. We apply our theory using
the Kim model, JpK(B) = JpK(0)/(1+|B|/B0), as an example. We calculate Jc(Ba)
as a function of a perpendicular applied magnetic induction Ba and show how
Jc(Ba) is related to JpK(B). We find that Jc(Ba) is very nearly equal to
JpK(Ba) when Ba > Ba*, where Ba* is the value of Ba that makes the net flux
density zero at the strip's edge. However, Jc(Ba) is suppressed relative to
JpK(Ba) at low fields when Ba < Ba*, with the largest suppression occurring
when Ba*/B0 is of order unity or larger.Comment: 9 pages, 4 figures, minor revisions to add four reference
Magnetic-field and current-density distributions in thin-film superconducting rings and disks
We show how to calculate the magnetic-field and sheet-current distributions
for a thin-film superconducting annular ring (inner radius a, outer radius b,
and thickness d<<a) when either the penetration depth obeys lambda < d/2 or, if
lambda > d/2, the two-dimensional screening length obeys Lambda = 2 lambda^2/d
<< a for the following cases: (a) magnetic flux trapped in the hole in the
absence of an applied magnetic field, (b) zero magnetic flux in the hole when
the ring is subjected to an applied magnetic field, and (c) focusing of
magnetic flux into the hole when a magnetic field is applied but no net current
flows around the ring. We use a similar method to calculate the magnetic-field
and sheet-current distributions and magnetization loops for a thin,
bulk-pinning-free superconducting disk (radius b) containing a dome of magnetic
flux of radius a when flux entry is impeded by a geometrical barrier.Comment: 10 pages, 13 figure
Magnetic-field dependence of the critical currents in a periodic coplanar array of narrow superconducting strip
We calculate the magnetic-field dependence of the critical current due to
both geometrical edge barriers and bulk pinning in a periodic coplanar array of
narrow superconducting strips. We find that in zero or low applied magnetic
fields the critical current can be considerably enhanced by the edge barriers,
but in modest applied magnetic fields the critical current reduces to that due
to bulk pinning alone.Comment: 23 pages, 7 figure
Hysteretic characteristics of a double stripline in the critical state
Analytical investigations of the critical state are carried out for a
superconducting stripline consisting of two individual coplanar strips with an
arbitrary distance between them. Two different cases are considered: a
stripline with transport current and strips exposed to a perpendicular magnetic
field. In the second case, the obtained solutions correspond to "fieldlike"
(for unclosed strips) and "currentlike" (for a long rectangular superconducting
loop) states in an isolated strip to which both a transport current and a
magnetic field are applied with constant ratio.Comment: 8 pages, 6 figures. accepted by SS