Electricity: magnetically operated switches – magnets – and electr – Magnets and electromagnets – Superconductive type
Reexamination Certificate
2002-10-25
2004-07-13
Donovan, Lincoln (Department: 2832)
Electricity: magnetically operated switches, magnets, and electr
Magnets and electromagnets
Superconductive type
Reexamination Certificate
active
06762664
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a method for the pulsed magnetization of a high temperature superconductive (HTS) kryomagnet, which is operated below its transient temperature, and which consists of discs stacked along an axis and comprising each n annular or polygon-shaped concentric conductor elements of superconductive material with n−1 annular gaps formed between the n concentric conductor elements.
HTS massive material capable of carrying high currents can be used for kryomagnets as long as, after the magnetization, it is maintained at an operating temperature T below the transient temperature T
c
, that is, T<T
c
. Then the kryomagnet becomes, in effect, a permanent magnet. Its field is frozen. Fields of >14 Tesla have been demonstrated to exist after magnetization by large superconductive magnet coils by way of the “Field-Cooled” procedure. The procedure is, in principle, as follows:
Within the initially time-wise constant outer field of for example a superconductive coil, the HTS is cooled to a temperature T<T
c
. At this temperature, the magnetic flux is frozen or captured. Then the outer magnetic field is reduced slowly that is on a scale of minutes and hours, whereby superconductive currents are induced in the HTS which substantially maintain the field in the HTS and which render the HTS in effect permanent magnetic that is, they form a kryomagnet.
The magnetization of HTS bodies capable of carrying high currents when installed in an electric machine cannot be performed by the use of a large superconductive coil but must be done by way of a pulsed magnetization using for example a Cu coil. In contrast to the above “field-cooled” procedure the superconductor is cooled by the so-called “zero field-cooled” process without outer field to a temperature <T
c
and is then subjected to a short magnetic field pulse. With sufficiently strong magnetic fields, magnetic flux can be frozen in the superconductor also with this process. The magnetization may also occur in successive magnetization steps by multiple successive pulsing of the magnetizing magnet. Multipurpose processes with pulse durations of several ms have been found to be advantageous in this connection in order to freeze magnetic fields of up to 3 Tesla.
Pulsed magnetizing processes using CU coils without coupled current pulses [I, II, III] as well as shaping and connecting techniques for HTS solid material [IV], HTS ring structures and their magnetic characterization [V] as well as mechanical reinforcements for accommodating the high forces [VI] generated by the strong magnetic fields and effective on the HTS, are known.
The saturation magnetization of a shaped body, that is, the maximum field H* that can be frozen is determined by the shape of the sample and by the critical current density thereof. As a general rule, with the field-cooled method the field of the coil must be at least 1×H* in order to fully magnetize the probe. With a pulsed magnetization however, that is, the zero field-cooled” procedure, typically a magnetic field of a pulse height 2×H* is necessary. The reason is that shielding currents are generated in the probe in the area of the rising flank of the magnetizing pulse,.
These shielding currents induced with the increasing flank of the magnetizing current pulse and the pulse fields of 3-6 Tesla maximally achievable with the installed Cu coils determine consequently the practical limits for frozen feeds maximally achievable.
If the induced shielding currents could be limited, ideally to zero, such a situation, which is comparable to the “field-cooled” process would not be reached. If furthermore the individual shaped bodies could be separately magnetized the fields generated by the individual segments would add up and, altogether fields could be obtained which are higher than those generated by the Cu coil.
It is therefore the object of the present invention to provide a magnetizing procedure for a kryo-HTS magnet whereby high magnetic fields can be frozen at temperatures below the transient temperature T
c
and to provide a kryomagnet which can be effectively magnetized in by this procedure.
SUMMARY OF THE INVENTION
In a method and a kryomagnet for the pulsed magnetization of the kryomagnet which comprises discs stacked on top of one another, with each disc including concentric annular conductor elements arranged in axially spaced relationship and each conductor element having two contact points forming two arms between the contact points for their energization, a transport current impulse is applied to each conductor element which pulse is divided in each conductor element into first and second partial currents I
1
and I
2
to flow through the two arms from one of the contact points, in an opposite sense, to the other contact point, wherein one arm has a length of maximally 35% of the circumference of the conductor element, the transport current having a polarity such that the larger partial current flowing through the shorter arm while the transport current is increasing flows in all the conductor elements in the same direction.
For a better understanding of the method, first the design specifically of the kryomagnet is shortly, described: The kryomagnet consists of m discs in a stack with the centers of the dics being all disposed on an axis. Each disc comprises n circular or polygonal conductor elements which are disposed concentrically in a plane and form therebetween n−1 annular gaps, m and n being natural numbers ≧1. The conductor elements consist of superconductive, or more specifically, high temperature superconductive material.
Each of the n conductor elements has two contact points by way of which it is energized during the magnetizing procedure below the lowest transient temperature T
c
of the respective used superconductive materials.
To each of the n conductor elements, a transport current impulse I pulse of a predetermined polarity strength and pulse form is supplied by way of its two contact points. From one contact point to the other of an energized conductor element, the transport current I pulse is separated into two partial currents I
1
through one arm of the conductor element to the other contact point and I
2
through the other contact arm of the conductor element to the other contact point. The two contact points are so arranged that the length of the connecting path therebetween that is, the length of the shorter of the two arms, comprises maximally 35% of the total circumference of the conductor element. In this way, a current asymmetry I
1
≠I
2
is established. The current flowing in the longer arm will be designated I
2
.
The m, n conductor elements are geometrically arranged and electrically so interconnected that the transport current impulse I
puls
introduced into each of the n conductor elements has such a polarity that the partial current I
1
has, in the area of the rising flank of the transport current impulse I
pulse
, with respect to a predetermined sense the same direction in all n conductor elements. With the use of several discs, the transport current impulse I
pulse
supplied to the conductor elements is so selected that the partial current I
1
flowing during the increasing flank of the transport current pulse I
puls
has, with respect to a predetermined sense, in all discs the same direction.
Preferably, the transport current impulse is adjusted in all m, n conductor elements in such a way that the respective maximum value I
puls,mzx
is the same in each conductor element. The largest part of the length of the shorter arm of the full circumference of the closed conductor loop is designated for all m, n conductor elements with A
max
. As critical current I
c
of a superconductive conductor element, the current is designated which generates in the superconductor a voltage drop of 10
−6
V/cm. Currents >I
c
lead to a buildup of an ohmic resistance in the superconductor. The largest critical current of all the m, n conductor elements is desi
Bach Klaus J.
Donovan Lincoln
Forschungszentrum Karlsruhe GmbH
Rojas Bernard
LandOfFree
HTS cryomagnet and magnetization method does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with HTS cryomagnet and magnetization method, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and HTS cryomagnet and magnetization method will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3237056