LONG
TERM
STABILI'IY
OF
FERMILAB
ENERGY
SAVER
MAGNETS
TM1186
1670,
000
W.
E.
Cooper,
B.
C.
Brown, R.
W.
Hanft,
and E. E. Schmidt
March
1983
*
Fermi
National
Accelerator
Laboratory
,
Batavia,
Illinois
60510
Summary
The quench
and
field
properties
of
Energy
Saver
dipole
and
quadrupole
magnets
are
measured
at
the
Fermilab
Magnet
Test
Facility
shortly
after
the
mag
nets
have
been
produced.
It
is
important
that
magnet
properties
remain
unchanged
with
time.
This
question
has
been
investigated
by
remeasuring
magnets
at
a
later
time
and
comparing
the
two
sets
of
measurements.
Three
sets
of
unbiased
data
are
available:
1)
Fifteen
dipole
magnets
were
remeasured
after
they
. 1
were removed from
the
"Bl2"
cryoloop
test
location.
At
Bl2,
they
were
subjected
to
repeated
thermal
cycles,
quenches
at
high
current,
steady
state
operation
at
high
current,
and
ramping
to
high
current
with
an
accelerator
type
ramp
cycle.
The
average
time
between
the
original
measurement and
the
remeasurement
was
22
months.
2)
Five
standard
length
(66
inch)
quadrupole
magnets
were
remeasured
after
an
elapsed
time
averaging
5
'months.
These
magnets
were
in
storage
during
the
per
iod
between
the
two
sets
of
measurements.
3)
Six
long
(99
inch)
quadrupole
magnets
were
remeas
ured
after
an
average
time
of
12
days.
These
were
also
in
storage.
The
remeasurements
agree
well
with
the
original
mPasurements.
The measurement
techniques
and magnet
properties
obtained
from
the
full
magnet
samples
are
26
described
elsewhere.
Dipole
Magnets
Quench
Results
The
results
of
the
Quench
Test
(quench
on
rising
ramp) and
the
Cycle
Test
(quench
on
flattop
for
an
accelerator
type
ramp
.cycle)
are
shown
in
Figures
la
and
lb.
Table
1
gives
the
average
and
spread
of
the
changes.
The
data
were
taken
at
a
temperature
of
4.61
to
4.69K and
have
not
been
corrected
for
temper
ature
variation.
l"IGU'OE
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00
<i~~
(AMPERES)
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(ORIGllJAI..
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4100
42CX)
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4400
41500
4600
. t
CYCLE
ORIGIN.\L. IAE.\SUREMENT
Table
1.
Change
in
Quench
and
Cycle
results
Average
change
(amp)
Sigma (amp)
Quench
+18 107
Cycle
+22
34
* .
Operated
by
University
Research
Association,
Inc.
under
contract
with
the
U.
S.
Department
of
Ener~y.
The Quench
Test
is
the
only
standard
measurement
which
uses
an
A/D
converter
instead
of
a
DVM
for
cu
rent
measurement.
This
was done
to
ensure
that
the
time
response
would
be
rapid
enough
to
permit
a
study
of
the
development
of
quench
signals.
Unfortunately,
the
AM
502
differential
amplifier
which
precedes
the
A/D
converter
has
a
gain
accuracy
of
only
2%;
this
accounts
for
most,
if
not
all,
of
the
difference
in
spreads
of
the
Quench
Test
and
Cycle
Test.
Harmonics·
The
harmonic'content
of
the
field
is
described
using
a
standard
multipole
expansion
about
the
center:
B +
iB
= B
~
(b
+
ia
)rnein~
y x o n=o n n
·where a
right
handed
coordinate
system
is
used,
the
proton
beam
is
in
the
+z
direction,
the
dipole
field
is
in
the
+y
direction,
and
~
is
measured from
the
+x
axis
with
a
sense
such
that
the
+y
axis
is
at
' =
+1T/2.
The an and bn
are
skew and
normal
multipole
coeffi
cients,
respectively,
where
the
pole
number
is
2(n+l).
We
have
adopted
the
convention
that
1
"standard
unit"
4
n
of
a
or
b
is
10
(inch)
which
gives
a
convenient
n n
scale
for
presentation
of
the
data.
Figures
2a

2h
show
the
remeasurements
versus
the
original
measurements
for
the
lowest
eight
harmonic
coefficients.
Figure
3 shows
the
normal
18
pole
for
the
two
sets
of
measurements.
The normal 18
pole
is
relatively
insensitive
to
magnet
construction
and
coil
motion
so
its
stability
provides
a
check
that
the
measurements
are
correct.
The
average
and
spread
in
the
change
of
coefficients
are
given
in
Table
2.
One
magnet
for
which
the
original
harmonic
measurements
were
not
available
has
been
omitted
from
the
sample.
Figure
2.
Harmonic
coefficients
at
4000
amperes
~~
~a
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•
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ORIGINAL
MEASUREMENT
Table
2.
Change
in
harmonic
coefficients
at
4000
amperes
(standard
units)
Average change Sigma
al
+o.31
0.80
bl
0.14
0.53
a2
+o.11
0.18
b2
0.14
0.78
83
0.04
0.29
b3
0.11
0.24
a·
4
0.06
0.13
b4
0.04
o.
22
b8
+o.18
0.17
The two
sets
of
measurements
agree
well
with
one
exception:
ont' mngnet
11how11
n
decr<'ARP
:In
h
2
of
2.fl
units.
No
fault
can
be found
in
the
<lata
for
this
TM1186
magnet.
If
this
magnet
is
omitted
from
the b
2
distri
bution,
the
average
change
in
b
2
becomes
+o.06
and
the
sigma becomes
0.16.
Then
the
averages
and sigmas
of
the
changes
are
within
the
absolute
measurement
accur
acy
of
about
0.3
unit
except
for
a
1
and b
1
• These
two
coefficients
show
small
changes
but
remain
well
within
the
design
window
of
± 2
.5
units.
Field
Integral
The
field
integral
is
obtained
directly
using
stretched
wire
techniques.
The measurement
depends
on
shunt
calibrations
which
have
been
maintained
by
comparing
NMR
measurements
of
remeasured
magnets
not
included
in
this
sample.
It
also
depends
on
reliably
knowing
the
stretched
wire
loop
width
which was
not
measured
for
every
magnet
but
which
was
studied
exten
sively
during
two
time
periods.
These
studiPS
indicate
that
tl•e magnet
effective
l~ngth
is
independent
of
mag
net
number.
This
information
has
been
used
to
correct
for
changes
in
loop
width
during
periods
when
it
was
not
.routinely
measured.
NMR
measurements
were
made
over
most
of
the
magnet
length.
These
are
proportional
to
the
field
integral
if
the
magnet
effective
length
remains
unchanged.
The
data
are
shown
in
Figures
4a
and
4b.
The
remeasurements
show
a
decrease
in
average
field
integ
4 .
ral
of
3.9
parts
in
10 and
in
NMR
transfer
function
5
(=
field
I
current)
of
3.9
parts
in
10
with
sigmas
for
the
changes
of
4.6
parts
in
10
4
and
2.3
parts
in
10
4
,
respectively.
The
data
shown
were
taken
at
2000
amperes.
The
NMR
measurement
is
inherently
more
accurate
;md
avoids
the
uncertainty
in
loop
width
cor
rections.
Limits
on
changes
set
by
either
technique
are
acceptable.
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Field
Angle
The
field
angle
is
determined
by
measuring
the
com
ponent
of
the
field
passing
through
a
stretched
wire
loop
oriented
in
the
vertical
plane.
Knowing
the
field
integral
permits
one
to
calculate
the
field
angle
with
respect
to
vertical.
ntis
angle
is
encoded
in
magnet
reference
"lugs"
which
can
be
used
to
mount
the
magnet
with
a known
field
direction
at
a
later
time.
nte
remeasurements
were made
with
the
lugs
in
a
horizontal
plane.
in
which
case
one
expects
to
obtain
a
field
angle
of
zero.
A
single
turn
''Kaiser
coil"
embedded
in
the
magnet
yoke
laminations
provides
an
independent
monitor
of
field
angle
changes
with
respect
to
the
outer
magnet
iron.
Figure
5 shows
the
remeasured
field
angle
versus
the
change
in
Kni.sl"r
coil
aignnl
st
n mngnl"t
current
of
2000
amperes.
llle
line
is
the
Kaiser
coil
calibration
cih
tnined
from
other
mngnf'ta. The change
in
field
angle
hnA
nn
nv<'r11p,r
or
0.07. mllllr1111ln11"
nnil
n
11ly,mn
of
0.42
millirndians.
One
of
the
magnets (shown
as
x
in
2
Figure
5)
is
known
to
have had a
defective
anchor
support
and
is
not
included
in
the
average
or
sigma.
This
defect
was
the
result
of
an
early
procedure
which
affected
five
magnets,
a~~
of
which
are
well
identi
fied.
The
field
angle
stability
is
significantly
better
than
the
1.0
milliradian
stability
sought.
1.0
o.<o
·0.4
·1.0
0.4
0.(e
KAl~ER
COIL
•
~EMEASUREMEIJ"'I'
)
MINUS ORIGINAL
MEASURe:MENT
(VOi.
I'S)
Quadrupole
Magnets
The
data
for
66
inch
and
99
inch
quadrupoles
agree
well
and
have
been
combined
for
all
measurements
except
field
angle
to
give
a
larger
statistical
sample.
Quench
Results
The Quench
Test
and
Cycle
Test
currents
increased
by 21
and
8
amperes,
respectively,
with
sigmas
for
the
distributions
of
9
3.
and 28
amperes.
These
results
agree
well
with
those
obtained
for
dipoles.
The
data
are
shown
in
Figures
6a
and
6b.
REMl!:A~EIJT
FIGUF>lt
C.A
J:
QUl!:NC.M
(..•)
•
4000
..
"°°
'""°°
ORIGl'AAL
""~e:..rT
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4400
4900
ORIGllJAL
MEASUREMElolT
TM1186
Harmonics
Harmonics
are
expressed
using
the
same
conventions
as
for
dipoles
except
that
for
quadrupole
magnets
bl
is
defined
to
be
1.0
and B
is
adjusted
to
give
the
cor
o
rect
quadrupole
field.
Remeasured
harmonics
are
avail
able
on
eight
of
the
magnets.
Table
3 shows
the
change
in
the
lowest
8
coefficients.
No
significant
changes
have
occurred
between
the
two
sets
of
measurements.
Table
3.
Changes
in
harmonic
coefficients
at
2000
amperes
(standard
units)
Average
change
Sigma
a2
+o.35
o.
76
b2
0.22
0.55
a3
+o.09
0.40
b3
+o.11
0.41
a4
0.07
0.37
b4
o.oo
0.18
a5
0.06
0.49
b5
+o.12
0.40
Integral
Field
The
integrated
field
gradient
is
measured
using
four
wire
stretched
wire
techniques.
At
2000
amperes,
the
average
integrated
field
decreased
by
0.036%
with
a sigma
for
the
change
of
0.101%.
The
change and
sig
ma
are
consistent
with
the
0.1% measurement
accuracy.
Field
Angle
The
field
angle
is
expected
to
be
zero
upon
re
measurement
for
magnets
levelled
from
lugs
set
after
a
previous
measurement.
The
only
unbiased
sample
available
consists
of
the
five
standard
length
quadrupoles.
At
4000
amperes,
these
had a mean
field
_angle
of
+o.10
milliradians
and a sigma
of
the
distri
bution
of·0.57
milliradians
upon
remeasurement.
1.
2.
3.
4.
s.
6.
References
K.
Koepke and
P.
Martin,
Fermilab
Internal
Report
UPC155
(1982).
B. C.
Brown
et
al.,
Report
on
the
Production
Magnet
Measurement
System
for
the
Fermilab
Energy
Saver
Superconducting
Dipoles
and
Quadrupoles,
this
conference,
R.
Hanft
et
al.,
Magnetic
Field
Properties
of
Fermilab
Energy
Saver
Dipoles,
this
conference.
E. E. Schmidt
et
al.,
Magnetic
Field
Data
on
Fermi
lab
Energy
Saver
Quadrupoles,
this
conference.
F.
Turkot
et
al.,
Maximum
Field
Capabilities
of
Energy
Saver
Superconducting
Magnets,
this
conference.
W.
E. Cooper
et
al.,
Cryogenic
System
for
Testing
and
Measurement
of
Fermilab
Energy
Saver
Super.
conducting
Magnets,
this
conference.