An apparatus which enables the establishment of a magnetic field in air that has the same intensity as the ones in ferromagnetic materials is described. The apparatus is comprised of a core of ferromagnetic material and is surrounded by a cylinder made of a material that has superconducting properties when cooled below a critical temperature. A method is provided for producing a magnetic field through the ferromagnetic core. The core can also be split and pulled apart when it is required that the center of the cavity be left empty

Elleman, D. D.

Hildebrandt, A. F.

Whitmore, F. C.

English

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https://ntrs.nasa.gov/search.jsp?R=19730019978 2020-03-17T09:20:53+00:00Z
Aug. 3, 1965 A. F. HILDEBRANDT ETAL. 3,198,994
SUPERCONDUCTIVE MAGNETIC-r'IELD-TRAFFING DEVICE
. FUed Nov. 29. 1961
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3,198,994
SUPERCONDUCTIVE MAGNETIC-FIELD-
TRAPPING DEVICE
Alvin F. Hildebrandt, La Crescents, Daniel D. Elleman,
La Canada, and .7rank C. Whitmore, Altadena, Calif.,
assignors to California Institute Research Foundation,
Pasadena, Calif., a corporation of California
Filed Nov. 29, 1961, Ser. No. 155,595
1 Claim. (CI. 317—158)
This invention relates to magnetic-field-trapping de-
vices. The invention described herein was made in the
perf jrmance of work under a NASA contract and is sub-
ject to the provisions of the National Aeronautics and
Space Act of 1958, Public Law 85-568 (72 Stat. 426;
42 U.S.C. 2451), as amended.
This invention relates to apparatus for establishing a
magnetic field and, more particularly, to improvements
therein;
There are many scientific and technological operations,
and there are many pieces of apparatus which require the
establishment of a large magnetic field. Experiments
with plasma use magnetic fields. Magnetic fields are
used in magnetometer calibration; electronic and nuclear
apparatus employ magnetic fields; motors, generators, and
dynamos employ magnetic fields. There also are bio-
logical applications of magnetic fields. The apparatus
for generating magnetic fields is well known and will not
be set forth here. However, it is also known that a mag-
netic field which is established in air is not as intense as
a magnetic field which exists within ferromagnetic ma-
terial occupying the same space. Since any operations
which are required to be performed within a magnetic
field take place within air, it will be appreciated that if
it were possible to transfer a magnetic field of a given
intensity which exists within iron into air, both the limit
of magnetic-field intensity obtainable in air today would
be extended and, also much less energy would be ex-
pended for achieving a magnetic field in air of the same
intensity as exists in iron.
An object of this invention is to provide apparatus
which enables the establishment of a magnetic field in
air having the same intensity as that existing within a
ferromagnetic material.
Another object of this invention is the provision of
apparatus for establishing a magnetic field in air which
has the same intensity as that in a ferromagnetic material
using only the energy required to establish the field in a
ferromagnetic material.
Yet another object of the present invention is the pro-
vision of a novel, useful, and simple arrangement for
establishing a magnetic field in air of a predetermined
intensity employing less energy than thought required
heretofore. -
These and other objects of the invention are achieved
in an arrangement wherein a core of ferromagnetic ma;
terial is surrounded by a cylinder made of a material that
has the property of superconductivity when it is cooled
below a critical temperature. The core effectively is
split so that it may be pulled apart when required to leave
the center of the cylinder empty. Means are provided
for establishing a magnetic field through the ferromag-
netic mtal core. Thereafter, the cylinder of supercon-
ductive material is cooled below the critical temperature.
The means for establishing a magnetic field is de-acti-
vated.. However, because of infinite conductivity of the
superconductive cylinder, the magnetic flux which was
established when the winding was excited remains trapped
by reason of currents flowing on the walls. The core
may then be removed from the cylinder, which still re-
tains the trapped field. However, the trapped field now
exists in air and has substantially the same intensity as it
had in the presence of the core.
The novel features that are considered characteristic of
.Jis invention are set forth with particularity in the ap-
pended claim. The invention itself, both as to its or-
ganization and method of operation, as well as additional
objects and advantages thereof, will best be understood
from the following description whe:i read in connection
with the accompanying drawings, in which.
10 FIGURE 1 is a view in elevation of an embodiment of
the invention; and
•FIGURE 2 is a cross-sectional view of the embodiment
of the invention.
It is known that when certain metals are cooled below
15 a very low characteristic temperature they exhibit prop-
erties such as substantially infinite electrical conductivity
and an almost perfect diamagnetism—Meissner effect.
The material also has the property that a current,.once
started, continues to flow, so that if a magnetic field is
20 Created and a closed circuit of superconductive material
.s established in the magnetic field, when the magnetic
field is removed a current is induced in the closed circuit
of supercondrctive material, which re-establishes and pre-
serves the magnetic field. This is known as the flux-
25 trapping property of the material.
Referring now to the drawings, FIGURE 1 is a view
in elevation, and FIGURE 2 is a cross-sectional view of
an embodiment of the invention. A cylinder 10 of the
superconducting material is placed in a circular cryostat
30 12-—that is, one having, when the cover 14 is in position,
the appearance of two concentric tubes. These will in-
clude an outer tube 16, having double walls from within
which air has been evacuated. The inner tube 18 also
has double walls, from which air has been evacuated. The
35 cylinder 10 is placed within the inner tube. When re-
quired for reducing the temperature of the cylinder 10,
nitrogen may be placed in the space between the inner and
outer tubes 16, 18 and helium may be placed within the
inner tube 18.
40 A yoke, consisting of two parts, respectively 20A, 203,
has a core or central section 22A, 22B, which fills the
central space of the cylindrical outer tube 16 and has leg
portions, respectively 24A, 24B, which are also split and
which aie positioned outside of the outer tube walls 16.
4;i Two coiJs, respectively 26A, 26B, are fitted on the outer
legs 24A, 24B. The coils are connected to a source of
potential 28 through a switch 30.
The yoke has the opposing surfaces of the two halves
thereof ground flat, so that they may intimately engage
50 one another when the yoke is in the closed position shown
in FIGURE 2. Initially, the cylinder 10 is maintained
above the critical temperature. If desired, a first cooling
liquid may be poured in the cryostat space between the
inner and outer tubes 18, 16. The switch 30 is closed,
55 whereby the coils 26A, 26B are energized. This estab-
lishes flux having a desired intensity through the core
sections 22A, 22B. In an embodiment of the invention,
a flux field on the order of 35,000 gauss can be obtained
in the iron. A second cooling liquid may then be poured
00 into the inner tube 18, whereupon the cylindrical shell
of superconducting material 10 is reduced in temperature
below the critical value. The magnetic field is then re-
duced to zero and the magnetic yoke 20A, 20B is then
pulled apart and removed. As a result, a flux field is
05 trapped within the cavity of the cylinder of superconduct-
ing material 10, which field is equal to the original flux
in the iron divided by the crocs-sectional, area, n-R2, of
the cylinder of superconducting material. The field may
be employed for any desired purpose at this time. The
70 cylinder 10 may be of niobium metal or lead, or any
other superconducting material.
There has accordingly been described and shown here-
3,108,994
in a novel and useful arrangement for establishing in air
a magnetic field having substantially the intensity obtain-
able in ferromagnetic material for the same magnetizing
force. The existing magnetic field may be established in
other v ays than by electromagnetic excitation, such as
by a permanent magnet, and other shapes for the super-
conductor than a hollow cylinder may be used without
departing from the spirit and scope of this invention.
We claim:
Apparatus for establishing a magnetic field at a desired
 10
region comprising a cylinder -which is hollow having walls
made of i material having the property of superconduc-
tion when said material is cooled below a critical tempera-
ture, a- yoke comprising a central core and an outer-leg
portion, said yoke and outer-leg portion being split where-
 15
two portions thereof may be fitted together, said
two portions being inserted and fitted together with said
core inserted within the center of said cylinder and with
said outer leg portion and enclosing said cylinder, means
for applying a magnetomotive force to a leg 'Of said yoke
for establishing a magnetic field through said core with
the lines of flux parallel to the axis of said cylinder, means
for cooling said cylinder walls below said critical tem-
perature, and means for discontinuing the application of
said magnetomotive force whereby a magnetic field is
trapped within the center of said cylinder, and when the
por'ons of said yoke are pulled apart and ren;oved from
said cylinder the magnetic field remains behind.
References Cited by the Examiner
UNITED STATES PATENTS
?.,916,615 12/59 Lundburg 340-^173.1
2,946,030 7/60 Slade 336—155
JOHN F. BURNS, Primary Examiner.
E. JAMES SAX, Examiner.


Superconductive magnetic-field-trapping device

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