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Патент USA US3021468

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` Feb. 13,> 1962
B, w, MANLEY ETAL
3,021,458
PERMANENT MAGNET SYSTEMS
Filed April 1o, 1959
7
'
`
2 sheets-sheet 1
FIG.1.
,
AGENT
Feb. 13, 1962
y
B. w. MANLEY ETAL
3,021,458
PERMANENT MAGNET SYSTEMS
Filed Aprily l0, 1959
2 Sheets-Sheet 2
FIG.3.
INVENTORS
BRIAN w. MANLEY
B
.- BERNARD T. MURPHY
Y
United States Patent O
,
3,021,458
Patented Feb. ~13, A1962
2 l
1
3,021,458
connecting supports 6 which unite the two assemblies of
shells and pole-pieces into a unit and which at the same
‘ Murphy, Salfords, England, assiguors to North Ameri
thepole-pieces 2 are inwardly directed towards a common
axis passing through the shells in a direction substantially
time act as return paths for the llux. It will be seen that
PERMANENT MAGNET SYSTEMS
Brian William Manley, Horley, and Bernard Thomas
can Philips Company, Inc., New York, N.Y.
at right angles to the axis. l The pole-piece 5 is extended
inwardly of the shell 1 so as to form an inner coaxial
shell which is spaced from the pole-piece 2 so as to pro
,
6 Claims. (Cl. 317-200)
'
vide an air gap. From the above it will now be seen that
rThe present invention relates to permanent magnet 10 there are three air gaps two of which are subsidiary gaps
Filed Apr. 10, 1959, Ser. No. 805,515
yClaims priority, application Great Britain May 13, 1958
systems.
between the pole-pieces of each individual shell whereas
'
the main gap extends between the two shells 1. Preferably
the centre gap is twice the length of each of »the subsidi
According to the present invention, Ia permanent magnet j
system for focusing a beam of charged particles comprises
a series of apertured pole-pieces, the aperture boundaries
ary gaps.
'
series of magnets, the magnets and the pole-pieces being
In >order to assist in obtaining the correct flux ñow the
innerk ends of the outer shells 1 are curved slightly inward
so associated that along the common axis is provided al
field of substantially uniform ñux the sense of‘which is
strength, a coil is wound externally of the shells, this being
being figures of revolution about a common axis, and a 15
ly as shown. In order to provide fine control of the flux ~
connected, in operation, to an external source of current
reversed in adjacent sections and the reversals being
(not shown). The coil is shown divided into two parts
7 which may be connected in series.`
Ideally, the ñux reversals are sharply defined. In prac- ~`
tice, however, the abruptness of ythe reversals are limited
in any particular case, by considerations of undesirable
abrupt.
The system may comprise a pair of opposed magnets,
each of which is a substantially cylindrical or a substan
tially frusto-conical shell of magnetic material, secured
in position with the -aid of supports providing an external
ilux path for the magnets, the shells being spaced apar-t
25
from one another along, and co-axial about, the common
axis and each having pole-pieces at each end.
The pole-piece at one end of each magnet may extend
inwardly of the magnet shell to form a co-axial inner
shell and the pole-piece at the other end of said magnet 30
leakage ñux which would -be produced by over-saturation
of the pole-pieces. The pole-pieces 2 are shown as thin
ner towards the axis to provide a reasonably abrupt ñux
reversal with material sufficient to carry the ñux towards
the axis. FIGURE 3 shows the main flux ñow and
illustrates the opposing considerationsy discussed above.
The size of the central aperture is determined by the
device with which it is intended the system is to be used
and in any case the maximum size will be determined by
the common axis with the ñrst mentioned pole-piece.
the beam constants of the beam of charged particles pro
Each pole-piece extending inwardly to form an inner
shell may be secured to that end of the associated magnet 35 duced in normal operation- in the said device.
What we claim is:
shell which is remote from the air gap between the pair
1. A permanent magnet system for focussing a beam
of magnets'.
of charged particles, comprising, in order, four coaxial,
The supports may be secured to extensions of the in
towards and transversely of the common -axis into over
lapping spaced relationship in the direction transverse to
axially-spaced -pole pieces having aligned central openings
wardly extending pole-pieces.
A coil may be provided for ñne electro-magnetic adjust 40 and defining between them three air-gaps, the portions of
the pole pieces bounding their openings being symmetrical
men-t of the ñux. The coil may be in one or a plurality of
sections.
'
ly disposed about the axis, two spaced hollow permanent
y
magnets both magnetized axially and in the same sense,
one of said magnets being disposed between the first
The reversing flux provided by the system according
to the present invention, may be used ito focus an electron
beam, for example, in a klystron or a travelling-wave tube. 45 and second pole pieces and being magnetically coupled
thereto, the other of said magnets being disposed between
By dividing up the magnetic ñeld into the series of re
the third and fourth pole pieces »and being magnetically
coupled thereto, and means for maintaining said magnets
and said pole pieces in assembled relationship to provide
said system with three regions along the axis in the air
gaps between the pole pieces of substantially uniform
versed sections less magnetic material isY required for a
desired substantially uniform flux field. This is important
for example where use in aircraft is envisaged.
In order that the present invention may be more readily 50
understood and carried into effect, one embodiment there
flux that is in opposite directions in adjacent regions.
of will now be described, by way of example, with refer
2. A system as set forth in claim 1 wherein two coils
ence to the accompanying diagrammatic drawings in
are
provided each coaxial with and adjacent to one of the
which:
.
’ FIGURE l shows 4a part sectional view in elevation;
FIGURE 2 shows an external plan view; and
FIGURE 3 shows, on a reduced scale, a diagrammatic"
view of a magnet system according to the present invention
and showing the ñux distribution (lwkage ñux being ne
glected).
The system shown in FIGURE 1 comprises two perm
anent magnet shells 1, of substantially cylindrical shape
and coaxially disposed with respect to each other, having
pole-pieces 2 and 3 secured together by screws 4. The
` pole-pieces 3 have extensions 5 which are bored to receive
55 permanent magnets for providing fine electro-magnetic
adjustment of the flux.
`
3. A permanent magnet system for focussing a beam `
of charged particles, comprising, inorder, four coaxial,
axially-spaced pole pieces having aligned central openings
60
and defining between them three air-gaps, Ithe portions
` of the pole pieces bounding their openings being sym
metrical-ly disposed about the axis, two spaced hollow, sub
stantiall'y cylindrical permanent magnets both magnetized
axially and in the same sense and coaxially aligned with the
65 pole pieces, one of said magnets being disposed between
3,021,458
4
and contacting the first and second pole pieces and sur
rounding the air~gap therebetween, the other of said
magnets being disposed between and contacting `the third
and fourth pole pieces and surrounding Ithe air-gap there
5'. A system as set forth in claim 3 wherein the ñrst
and fourth pole pieces each have `a cylindrical projection
extending within the adjacent magnet toward the adjacent
pole piece.
between, and magnetic means outside yof the magnets and
providing `a return ñux path and maintaining the magnets
and pole pieces in assembled relation, said system pro
ducing three regions along the axis in the air-gaps between
the pole pieces of substantially uniform ñux that is in op
posite directions in adjacent regions.
4. A system as set forth in claim 3 wherein the main
taining magnetic means are secured to lateral extensions
of the ñrst and fourth pole pieces, and means are provided
6. A system s set forth in claim 5 wherein the second
and third pole pieces comprise plate-like members extend
ing `transverse to the axis.
10
for securing the magnets and second 'and third pole pieces
to the first and fourth pole pieces.
15
References Cited in the file of this patent
UNITED STATES PATENTS
2,797,360
2,8'7Í’aA-13»r
2,940,020
Rogers et a1. __-; _____ __ June 25, 1957
Reynst ______________ __ Feb. 10, 1959
Muller ______________ .__ June 7, 1960
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