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IEEE Tr;lns;lctlons on Nucirar Science. Vol. NS-32. No. 5. October 1985
RADIATIUN
3669
EFFECTS OF PROTOW ON SAM.4RIUM-COBALT PERMAIVENT MAGNETS
TKIIJMF,
E .W. Blackmore
Vancouver,
B.C., Canada V6T 2A3
summary
At TRIUMF the use of samarium-cobalt
permanent
magnet quadrupoles
as the first
element
In a secondary
channel
has been studied
as a means of increasing
the
solid
angle acceptance
of the channel.
The high remanent induction
Br and high coercive
force
Mc of rareearth
cobalt
(REC) can be utilized
to produce a highgradient
quadrupole
field
in an extremely
compact
magnet . Although
many properties
of REC material
have
been measured,
little
Ls known about the effect
of
charged particle
radiation
on the magnetic
behaviour.
As the TRIWF applicati.on
requires
the magnets to operate Fn a high radiation
environment
it was considered
essential
to study this effect.
This paper describes
the results
of exposing
samples of samarium-cobalt
and
other
permanent
magnet materials
to a beam of protons.
Introduction
._I____
Since the mid-1960’s
there has been a remarkable
improvement
in the magnetic
quality
of permanent
magnet
initially
with compounds of rare earths,
materials,
1
and more recently
comsuch as samarium,
and cobalt
These materials
neodymium and boron.
pounds of iron,
are characterized
by a high remanent induction
B, of
0.9 to 1.2 T, a high coercivity
H, of 5-10 kOe and an
energy product
(BH),,,
in excess of 200 kJ/m3.
Applications
include
compact dc motors and generators,
electro-mechanical
actuators
such as computer
printers,
magnetic
bearings
for gyros
microphones
and earphones,
field,
magnetic
focussing
and, in the accelerator
devices
for Linear
accelerators
or ion sources
and beam
wigglers
for synchrotron
radiation
sources.
Rare earth
cobalt
magnets are produced
from a
sintered
block of small,
oriented,
highly
anisotropic
crystals
strongLy
magnetized
in the preferred
crystalcustomarily
called
the easy axis.
line
direction,
Different
compositions
are available
commercially
Examples of arrangements
SmCog, SmzColT and SmPrCog.
of these blocks
to produce a quadrupole
field2
are
shown in Fig. 1.
At TRLUMF a high acceptance
surEace muon channel3
has been designed
to utilize
permanent
magnet quadruThe advantage
of these
poles at the front
end.
7
quadrupoles
is that their
compact size and high field
gradients
allow
them to be located
much closer
to rhe
meson production
target
than a conventional
quadrupole
(in this case the front
oE the first
quadrupole
is only
27 cm from the target).
The requirement
oE this
location however is that the magnet must withstand
the high
flux of protons,
neutrons
and secondary
particles
coming from the production
target
without
having
its
magnetic
properties
deteriorate
due to radiation
damage.
Therefore
it was considered
necessary
to
determine
the radiation
effects
of protons
and neutrons
on samarium cobalt
before
installing
quadrupoles
made
from this material
in a high radiation
environment.
A controlled
experiment
was designed
in which a
sample of samarium-cobalt
could be irradiated
directly
in a low intensity
proton
beam, the Intensity
kept low
to minimize
thermal
effects,
and with the capability
of
measuring
the magnetic
field
of the sample remotely
during
the irradiation.
This paper presents
a description of the technique
and the results
of measurements
made on samples of samarium cobalt
and neodymium-ironboron.
Experimental
Arrangement
The experimental
arrangement
Ls shown schenaticala 1.25 cm square by 2.5 cm
ly in Fig. 2.
The sample,
long block magnetized
tn the long direction,
is mounted
in a water cooled copper clamp.
The magnetic
field
is
measured by moving a 50 turn coil
over the sample to
By intejust past the centre
point
of the sample.
grating
the induced
voltage
on the coil
an accurate
measuremen& of the magnetic
flux is obtained.
The
motion of the coil
is achieved
by pivoting
the coil
on
a radial
arm and the voltage
is integrated
using a
The sensicommercial
digital
integrating
voltmeter.
tivity
of this instrument
is 1 mV-s and the typical
signal
level
is about 3,000 DV-s.
A thermocouple
is clamped to the uncooled
end of
the sample to record
the maximum sample temperature.
A
secondary
emission
halo monitor
is mounted in front
of
the sample to centre
the beam and record
the proton
The integrated
beam current
is measured
beam current.
aluminum activation
foils
using three 0.001 in. thick
mounted directly
on the cooled
clamp.
THE SEGMENTED REC OUADRUPOLE
MAGNET
PROTON
TEST ARRANGEMENT
BEAM IRRADIATION
FOR
16 PIECE
8 PIECE
N’,, = 2HC,1y.1 f
ra
WY: omabltl,*lNc
,
: blmrI”WN
: 0.15
0.9,
RIRCI lrn,)
FACTOR
I PXILIGULLI
16 ,DAPIm,DAL
s!ELll
PIKE5
Arrangement
of samarium-cobalt
Fig. 1.
blocks
to produce a quadrupole
field.
0018-9499/85ilooO-369$01.000
Fig.
1985 IEEE
2.
Experimental
arrangement.
3670
A 500 MeV proton
beam from the TRIUMF cyclotron
was used for the irradiation.
The energy loss in
passing
through
the 2.5 cm long sample is approximately
40 MeV. The proton
beam size was adjusted
so that the
FWHM was approximately
the same size as the sample.
For most irradiations
the proton
beam current
was limited to ZOO-300 nA to keep the maximum sample temperature below 120°C.
The magnetic
field
measurement
was
made several
times during
the irradiation
so that the
dependence
on dose level
could be determined.
test
Table I lists
the
samples irradiated
trade names and suppliers
at this time.
Samarium
Trade
the
Composition
Hitachi
Magnetics
Corporation
HICOREX-90B
Hitachi
Magnetlcs
corporation
HICOREX-96B
(SmPr)CoS
Crucible
Magnetics
CRUCORE-18
SnCo5
Crucible
Magnetics
CRUCORE-26
Sm2Co17
NeIGT-27
Neodymium-Iron-Boron
IG Technologies
of Proton
Cobalt
SmCo5
The CRUCORE samples were considerably
more resistant to radiation
with the Sm2Coi, sample being the
most resistant.
To check the reproducibility
of the
measuring
technique
a second sample of CRUCORE-18 was
irradiated
and a comparison
of the two results
is shown
The lines
are least
squares
fits
to the
on Fig. 4.
data.
X
FLUX
LOSS
0 ?,’
”
*‘I
“L’k
-
HICOREX
Studies
of Thermal
0.13
Y2
\
-12
0.45
1.31
!
i
-15
FLUX
0.0-
f
11~1,1111,1111,,11,,1,,,
2
4
6
PROTON
Demagnetization
-0.0388
0.14
0.21
0.99
1.09
CRUCORE-26
-.0318
0.06
0.16
0.34
0.31
10
8
CURRENT
UA-HRS
of REC magnets
due to proton
LOSS
’
o
L
c
”
a
’
s
I
’
b
CRUCORE
m a
B ’
n
B “,
26
-0.8
CRVCORE
CRUCORE-18
906
Ml
\
%
20.03
--
1.48
HICOREX
IRR
INTEGRRTED
9:
%
+0.03*
to.03
__-------
c
i
I
-0.0450
’
9OB
IRR
-9
Fig. 3.
irradiation.
HICOREX-90B
o
\
HICOREX
II
------___--
““I
96B
,
0
%
co .03
I”,
Effects
A similar
arrangement
was used to measure the
temperature
dependence
of the magnetic
field
of the
sample and the onset of an irreversible
loss in magneA resistive
heater
was
tization
with temperature.
mounted on the copper clamp holding
the sample and the
samples heated
to temperatures
of up to 250°C for
The results
are tabulated
in
periods
up to 100 hours.
Table II.
These results
show that for the samarium
cobalt
samples the loss in magnetization
after
100
hours at temperatures
of 125°C is less than 1X. This
was the maximum temperature
which was allowed
during
the irradiations
which typically
took 30-75 hours.
Table
Irradiation
The demagnetization
of the samarium cobalt
nagnets
due to proton
irradiation
is shown in Fig. 3 for the
HICOREX samples and in Fig. 4 for the CRUCORE
samples.
The integrated
proton
pA-h in each case was determined
ed by measuring
the 22Na activity
within
the 1.25 cm x
1.25 cm area of the aluminum activation
foil
adjacent
to the sample.
The interim
readings
were determined
by
integrating
the beam current
during
the irradiation
and
scaling
to the total
reading.
After
the irradiation
of
the HICOREX-90B sample,
the sample was placed in an
external
magnetic
field
of 2.5 T and remagnetized.
The
field
returned
to slightly
above its original
level
prior
to irradiation.
This sample was then irradiated
again and demagnetized
at a higher
rate than during
the
original
irradiation
as shown in the figure.
Table
---.---l_Supplier
I
--Name
of
Results
-
-1.2
CRUCORE
IRR
18
18
#2
-1.6
___
---
---__----
Ne LGT-2 7
*Manufacturers
-0.13”
__---
< 3*
INTEGRRTED
specifications
Fig. 4.
irradiation.
Demagnetization
PROTON
CURRENT
of REC magnets
UR-WRS
due to proton
I
3671
The measured demagnetization
obtained
CRUCORE-26 sample at a temperature
of
period
of LOO h is also shown.
by heating
the
125°C Ear a
DOSE (lOgRAD)
0.0
Neodymium-Iron-Boron
_____-__
The samples of neodymium-iron-boron
were in blocks
1.25 cm square by 0.5 cm long . Five of these blocks
were stacked
together
for the irradiation.
The beam
current
was kept intentionalLy
low so that the maxiaum
temperature
during
the first
irradiation
was less than
70°C.
The first
magnetic
field
measurement
taken after
an irradiation
of .124 PA-h indicated
that the field
had dropped to 3% of its original
value.
A second
irradiation
was carried
out on a new sanple
of the same
material.
In this case the current
was reduced by a
factor
of 25 so that the maximum temperature
rise over
ambient was 3°C.
The field
after
an irradiation
of
only 7.0 nA-h reduced by 55.4%.
This sample was able
to be remagnetized
in an external
magnetic
field
to its
original
value.
Discussion
-~--
KRUPP
-5.0
z
2
TRIUMF
O---
CERN
2
I?
8 -10.0
of Results
160
Using the conversion
factor
1 rad = 6.24~10’
MeV/g
a proton
irradiation
of 1 PA-h at 500 MeV corresponds
to an average
dose of 4.5x10*
rads to the sample. The
peak dose due to the non-uniform
irradiation
across
the
sample is approximately
2 times the average
dose or
9x10* rads per 1 uA-h.
The conclusions
of this
series
of measurements
can be summarized
as follows:
1. Samarium-cobalt
permanent
significant
demagnetizatfon
proton
beam at dose levels
effect
cannot be explained
macroscopic
scale.
o--
magnets exhibit
a
when irradiated
in a
of 10q-lO1o
rads.
This
by thermal
heating
on the
2. Samples from different
manufacturers
exhibit
large
differences
in the demagnetization
as a function
of
dose.
This could be due to a diEferent
production
process
or the presence
of different
impurities.
3. The sample of neodymium-iron-boron
proved to be
extremely
sensitive
to ionizing
radiation
losing
essentially
all of its magnetization
at a dose of
7x10’ rads and over 50% at 4~10~ rads.
Other
laboratorfes
have been making similar
At LAMPF4 samples of HICOREX
measurements
in parallel.
YOB and HICOREX 96B have been exposed to spallation
The -axineutrons
at the LAMPF irradtation
facility.
A decrease
of
mum exposure
was l.lxtOLs
neutron/cm2.
l-Z% was measured but attributed
to a thermal
effect
At CERNS a number of
rather
than radiation
damage.
magnets have been irradiated
in the 400 GeV proton
beam
of these measurements
are
of the SPS. A selection
shown in Fig. 5 together
with the TRIUHF data indiTo achieve
the necessary
dose
cating
similar
results.
the CERN irradiations
took approximately
50 days
exposure
as compared with several
days at TRIUMF.
At
KFA-Julich6
a number of magnets have been irradiated
in
a reactor
at neutron
fluxes
up to 8x101g neutrons/cm2
10 Less
(O<E<7 MeV).
Sm2Co17 was found to be a factor
sensitive
to neutron
irradiation
than SmCoS, a result
consistent
with our data.
The radiatfon
damage mechanism is not understood
at this time although
it appears
to be similar
to a
thermal
heating
of the sample at elevated
temperatures.
It is possible
to remagnetize
the demagnetized
samples
to their
original
value indicating
that there
is no
permanent
damage to the crystallographic
strtucture.
There is a correlation
between the temperature
dependence of both the reversibLe
and irreversible
demagneCRUCORE-26
tization
and the sensitivity
to radiation.
demagnetizes
a factor
3-4 less on heating
to 250°C than
-15.0
RECOMi
20
(1:5)
\
\
\
Fig.
5. Comparison
of TRIUMF and CERN data.
HICOREX 90-B and is much less sensitive
to radiation.
Neodymium-iron-boron
has a much lower Curie temperature
of 310°C compared with 710°C for samarium cobalt
which
probably
accounts
for its sensitivity
to radiation.
As a result
of this
study two permanent
magnet
quadrupoles
of bore 10.7 cm diam and gradient
x
effective
length
of 6.2 kG and 3.7 kG have been
fabricated
from CRUCORE-26
material
and installed
as
the first
two elements
of beamline
Ml5 at TRIUMF.
This
beamline
has been operating
successfully
for six
months.
Acknowledgements
The irradiations
and thermal
measurements
have
been carried
out with the assistance
of the TRIUMF
Operations
Group, A. Hurst and summer students
G. Stuart,
8. McKinney and N. Evans.
Other
acknowledgements
are to la. Moritz
for the activation
analysis,
A. Otter, and A. Arrott
for discussions
on
permanent
magnets and special
thanks to the suppliers
of the magnet samples.
References
~__
[l]
K.J. Strnat,
C.I. HoEfer,
Techn. Report
AFML-TR-65-446,
Wright-Patterson
Air Force Base
(1966).
(21 K. Halbach,
“Strong
Rare Earth Cobalt
Quadrupoles,”
IEEE Trans.
on Nucl.
Sci. NS-26 (197Y),
3882.
[3] J. Doornbos,
“M15, A Dedicated
Surface
Muon
Channe 1, ” TRI-DN-82-8,
May 1982.
[4] R.D. Brown, E.D. Bush, W.T. Hunter,
“Radiation
Effects
on Samarium-Cobalt
Permanent Magnets,”
LA-9437-MS,
July L982.
[5] F. Coninckx,
W. Naegele,
El. Reinharz,
H. Schoenbacher,
P. Seraphin,
“Radiation
Effects
on
Rare-Earth
Cobalt
Permanent Magnets,”
CERN/SPS
TIS-RP/IR/83-07.
“Magnetisierungsverlust
van
[6] II. Spitzer,
A. Weller,
Samarium-Kobalt
Permanentmagneten
in hohen
SNQI.V/BH 22 05 84.
Neutronenfeldern,