SLAC–WP–035 PSN WE08 May 2003
Magnetic Measurement and Magnet Tutorial, Part 3 ("Lecture 10")*
J. Tanabe Stanford Linear Accelerator Center, Stanford University, Stanford, California 94309
Invited talk presented at 13th International Magnetic Measurement Workshop
Stanford, California
May 19-22, 2003
* Work supported in part by Department of Energy contract DE–AC03–76SF00515.
Lecture 10Jack Tanabe
Santa Barbara, CA
Magnetic Measurements
13th International Magnetic Measurement Workshop, May 19-22, 2003, Stanford, California
1WE08 - Tanabe
Introduction
• Magnetic measurements, like magnet design, is a broad subject. It is the intention of this lecture to cover only a small part of the field, regarding the characterization of the line integral field quality of multipole magnets (dipoles, quadrupoles and sextupoles) using compensated rotating coils. Other areas which are not covered are magnet mapping, AC measurements and sweeping wire measurements.
13th International Magnetic Measurement Workshop, May 19-22, 2003, Stanford, California
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Voltage in a Coil
13th International Magnetic Measurement Workshop, May 19-22, 2003, Stanford, California
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∫
∫
∂∂
=
∂∂
==
dxt
BL
dAt
BVoltageV
y
y
∫=⇒∂∂= dxBA
xA
B yy
( )θLAdxBLVdt y == ∫∫Therefore, substituting;
where A, the vector potential is a function of the rotation angle, θ.
( )sec2
2 ×==×=
××=∫VoltWebersm
mWebers
mTeslamdxBLUnits y
∫∫∫
∫
=∂
∂=
=
dxBL
dxdtt
BL
VoltageIntegratedVdt
y
y
⇒
13th International Magnetic Measurement Workshop, May 19-22, 2003, Stanford, California
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Measurement System Schematic
13th International Magnetic Measurement Workshop, May 19-22, 2003, Stanford, California
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Digital Integrator• The Digital Integrator consists of two
elements.– Voltage to Frequency Converter.– Up-Down (Pulse) Counter.
-15
-10
-5
0
5
10
15
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07
High Voltage
Low Voltage
13th International Magnetic Measurement Workshop, May 19-22, 2003, Stanford, California
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Using an Integrator on a Rotating Coil• Using an integrator simplifies the requirements on the
mechanical system.
radiusdtdB
LradiusdtdB
LV effeffθ
θ∂∂==
radiusdBLVdt eff ×=
( ) radiusBLradiusdBLVdt effeff ×=×= ∫∫ θ
The use of an integrator measures the angular distribution of the integrated field independent of the angular rotation rate of the coil.
13th International Magnetic Measurement Workshop, May 19-22, 2003, Stanford, California
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Theory
( )θLAdxBLVdt y == ∫∫where L is the coil length and A is the vector potential, a function of the rotation angle θ.
The magnetic field can be expressed as a function of a complex variable which can be expressed, in general as ;
( ) ∑=+= nn zCiVAzF
( )( )
( ) ( )[ ]∑∑
∑∑
+++=
=
==+
nnn
n
ninn
innin
nn
ninzC
ezC
ezeCzCzF
n
n
sin cos
ψθψθ
ψθ
θψ
Rewriting;
( )[ ]( )∑ +=
=
nn
n nzC
zFA
cos
Re
ψθThe Vector Potentialis, therefore;
13th International Magnetic Measurement Workshop, May 19-22, 2003, Stanford, California
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( ) ( )∑∫ +== nn
n nzCLLAVdt cos ψθθ
Therefore, when we are measuring the integrated Voltage, we are actually measuring the real part of the function of a complex variable.
We are measuring the rotational distribution of the integrated Vector Potential, AL. We really want to measure the distribution of the Field Integral.
13th International Magnetic Measurement Workshop, May 19-22, 2003, Stanford, California
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Field Integral
( )( ) ( )( )nn nin
nnini
n
nn
nn
ezCinezeCin
zinCzCdzd
iziFB
111
1'*
ψθθψ +−−−
−
==
===
( )( ) ( )( )[ ]( )( ) ( )( )[ ]n
nn
nn
nyx
ninnzCn
ninnzCiniBBB
1cos 1sin
1sin 1cos*1
1
ψθψθ
ψθψθ
+−++−−=
+−++−=−=−
−
( )( )( )( )
+−+−
−=
−
n
nnn
y
x
nn
zCnLLBB
1cos 1sin1
ψθψθEquating the real
and imaginary parts of the expression;
Let us take just one term of the infinite series.
13th International Magnetic Measurement Workshop, May 19-22, 2003, Stanford, California
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• In order to fully characterize the line integral of the magnetic field distribution, we need to obtain only |Cn| and ψn from the measurement data.
( ) ( )nn
n nzCLLAVdt cos ψθθ +==∫
-2.0
-1.5
-1.0
-0.5
0.0
0.5
0 45 90 135 180 225 270 315 360
Angle (deg.)
The graph illustrates the output from a quadrupole measurement. The integrator is zeroedbefore the start of measurement and the graph displays the result of a linear drift due to DC voltage generated in the coil.
13th International Magnetic Measurement Workshop, May 19-22, 2003, Stanford, California
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Fourier Analysis• In principal, it is possible to mathematically characterize
the measured data by performing a Fourier analysis of the data. – The Fourier Analysis is performed after the linear portion of the
curve is subtracted from the data.
∑∫ += θθ nbnaVdt nn sin cos
( )
( )∑
∑∫−=
+=
nnn
nn
nn
nn
nnzCL
nzCLVdt
sin sin cos cos
cos
ψθψθ
ψθ
nn
nn
nn
nn
zCLb
zCLa
sin
cos
ψ
ψ
−=
=Equating common terms,
13th International Magnetic Measurement Workshop, May 19-22, 2003, Stanford, California
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22
22
nnn
neff
NNN
Neff
bazCL
bazCL
+=
+=
−=
−=
−
−
Nab
ab
nn
N
NN
1
1
tan
tan
ψ
ψ
n
n
n
nn a
b−== cos sin
tanψψψ
−= −
n
nn a
b1tan ψor, finally,
Separately, for the fundamental and error terms;
13th International Magnetic Measurement Workshop, May 19-22, 2003, Stanford, California
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Fundamental and Error Fields• In general, the Fourier analysis of measurement data will
include as many terms as desired. The number of terms is only limited by the number of measurement points. – Earlier, we introduced the concept of the fundamental and error
fields. The Vector potential can be expressed in these terms.
( )
( ) ( )∑
∑
≠
+++=
+=
Nnn
nnN
NN
nn
nn
nzCNzC
nzCA
cos cos
cos
ψθψθ
ψθ
[ ]( ) ( )∑
∫
≠
+++=
=
Nnn
nnN
NN nzCLNzCL
LAVdt
cos cos ψθψθ
θ
13th International Magnetic Measurement Workshop, May 19-22, 2003, Stanford, California
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Compensated (Bucked) Coil• The multipole errors are usually very small
compared to the amplitude of the fundamental field. Typically they are < 10-3 of the fundamental field at the measurement radius. – The accuracy of the measurement of the multipole
errors is often limited by the resolution of the voltmeter or the voltage integrator.
• Therefore, a coil system has been devised to nullthe fundamental field, that is, to measure the error fields in the absence of the large fundamental signal.
13th International Magnetic Measurement Workshop, May 19-22, 2003, Stanford, California
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• Consider the illustrated coil. r1
r2
r3
r4
M inner turnsM inner turns M outer turnsM outer turns
( ) ( ) ( )∑∫ +−=n
nnn
noutereffouternrrCMLVdt cos31 ψθ
Two sets of nested coils with Mouter and Minner number of turns to increase the output voltage for the outer and inner coils, respectively, are illustrated.
( ) ( ) ( )∑∫ +−=n
nnn
ninnereffinnernrrCMLVdt cos42 ψθ
13th International Magnetic Measurement Workshop, May 19-22, 2003, Stanford, California
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Compensated Connection• The two coils are connected in series opposition.
( ) ( ) ( )[ ] ( )∑∫ +−−−=n
nnn
innernn
outerndcompensatenrrMrrMCLVdt cos4231 ψθ
Define the following parameters:
1
31 r
r≡β2
42 r
r≡β1
2
rr≡ρ
outer
inner
MM≡µand
( ) ( )( ) ( )( )[ ] ( )∑∫ +−−−−−=n
nnnnn
noutereffdcompensatenrCMLVdt cos 1 1 211 ψθβρµβ
( )( ) ( )( )nnnns 1 1 21 βρµβ −−−−−≡We define the coil sensitivities;
( ) ( )∑∫ +=n
nnn
nouterdcompensatensrCLMVdt cos1 ψθthen,
13th International Magnetic Measurement Workshop, May 19-22, 2003, Stanford, California
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Compensation (Bucking)
• The sensitivities for the fundamental (n=N) and the multipole one under the fundamental (n=N-1) are considered.
( )( ) ( )( )NNNNs 1 1 21 βρµβ −−−−−=
Why one under the fundamental?
( )( ) ( )( )22
2212 1 1 βρµβ −−−−−=sConsider the
quadrupole, N=2
( )( ) ( )( )12
111 1 1 −−
− −−−−−= NNNNs βρµβ
( )( ) ( )( ) 1 1 211 βρµβ −−−−−=s
13th International Magnetic Measurement Workshop, May 19-22, 2003, Stanford, California
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• The classical geometry which satisfies the conditions fornulling the N=2 and N=1 field components in the compensated mode have the following geometry.
2= 0.625,= ,2. ,5.0 21 µρββ ==
Homework, show that s1 and s2 are zero for these values, compute the balance of the sensitivities and compare with the graph.
Quadrupole Coil Sensitivities
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1 3 5 7 9
11
13
15
17
19
21
Multipole Index
Qsens
13th International Magnetic Measurement Workshop, May 19-22, 2003, Stanford, California
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Compensated Measurements• Quadrupole measurements using the coil in the
compensated configuration are typically as illustrated in the figure.
-3.5
-3.0
-2.5
-2.0
-1.5
-1.0
-0.5
0.0
0.5
0 45 90 135 180 225 270 315 360
Angle (deg.)
13th International Magnetic Measurement Workshop, May 19-22, 2003, Stanford, California
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Bucking Ratio• In the illustrated example of the compensated
measurements, two properties can be readily seen.– The drift is present. Usually, it is a larger portion of the
signal than in the uncompensated measurements. This is because the DC voltage, usually due to thermocouple effects, is a larger fraction of the small compensated coil measurements.
– The signal is dominated by a quadrupole term. This is because of coil fabrication errors so that the quadrupole sensitivity is only approximately zero. The quality of the compensation is measured as a bucking ratio.
( )( )
buckedNN
unbuckedNN
ba
baBucking
22
22
Ratio +
+=
Achieving a Bucking Ratio > 100 indicates a well fabricated coil.
13th International Magnetic Measurement Workshop, May 19-22, 2003, Stanford, California
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Uncompensated Measurements• The magnet is also measured with the rotating coil
wired in the uncompensated condition to measure the fundamental field integral and the multipole one below the fundamental.
( ) ( )( ) ( )∑∫ +−−=n
nnn
noutereffteduncompensanrCMLVdt cos 1 11 ψθβ
( )( )nnS 1 1 β−−=
Where the sensitivities in the uncompensated condition are designated by capital S.
( ) ( )222
122 2cos ψθ +=∫ SrCMLVdt outereff
( ) ( )11121 cos ψθ +=∫ SrCMLVdt outereff
For the Quadrupole;
13th International Magnetic Measurement Workshop, May 19-22, 2003, Stanford, California
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• Recalling the expression for the magnetic field components,
( )( )( )( )
+−+−
−=
−
n
nnneffeff
y
x
nn
zCnLLBB
1cos 1sin1
ψθψθ
the amplitude of the fundamental field is,
11
22 −=+= NneffNyNxeffN rCNLBBLB
( ) ( )21 2cos ψθ +=∫ NN
NoutereffNSrCMLVdt
NN
NoutereffNNN
SrCMLbaVdt 122 =+=∫
NN
outereff
NNN SrML
baC
1
22 +=Solving,
13th International Magnetic Measurement Workshop, May 19-22, 2003, Stanford, California
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• Substituting into the expression for the fundamental amplitude;
NN
outereff
NNN
effNNeffeffN
SrML
barNLrCNLLB
1
22111
1
+==
−−
Tmm
Webersmeter
VoltSrMbaN
LBNouter
NN
reffN ==−=+
= .sec
1
22
@ 1
13th International Magnetic Measurement Workshop, May 19-22, 2003, Stanford, California
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Normalized Field Errors• The separate multipole field errors, normalized to the
fundamental field amplitude can be computed from the measurement data.
nn
noutereffnnn
srCMLbaVdt 122 =+=∫
nouter
nn
reffn srMban
LB1
22
@ 1
+=
22
22
@ 1 NNn
nnN
reffN
effn
baNs
banSLBLB
+
+=
an and bn are from the compensated measurements and aN and bN are from the uncompensated measurements.
13th International Magnetic Measurement Workshop, May 19-22, 2003, Stanford, California
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Reference Radius
• The expression for the normalized error multipole is evaluated at the outside radius of the inner coil, r1. This radius is limited by measurement coil fabrication constraints and, in general, is substantially smaller than the pole radius and generally smaller than the desired radius of the good field region, which might be > 80% of the pole radius. Therefore, the expression for the normalized error multipole is re-evaluated at a reference radius, r0.
13th International Magnetic Measurement Workshop, May 19-22, 2003, Stanford, California
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• The figure illustrates a 35 mm. pole radius quadrupole with a compensated rotating coil installed in the gap. The coil housing is < 35 mm. so that it will fit between the four poles. A half cylinder sleeve is placed around the housing to center the coil. As a result of these mechanical constraints, the maximum coil radius is < 27 mm.
13th International Magnetic Measurement Workshop, May 19-22, 2003, Stanford, California
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• The desired good field radius is 32 mm., the maximum 10 σ beam radius. Therefore, in order to compute the field quality at this radius, the normalized field errors are recomputed at the required r0.
1 −∝ nn rB 1 −∝ N
N rBand
NnN
n
N
n rrr
BB −
−
−
=∝ 1
1
Therefore,
andNn
NNn
nnN
reffN
effn
rr
baNs
banSLBLB
−
×+
+=
1
0
22
22
@ 0
13th International Magnetic Measurement Workshop, May 19-22, 2003, Stanford, California
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Dipole Measurements
• The quadrupole coil configuration can also be used to measure a dipole magnet. Since the coil has no quadrupole sensitivity in the buckedconfiguration, a quadrupole error must be evaluated using the unbucked configuration. Since a quadrupole multipole is not an allowed multipole for a symmetric dipole magnet, this does not usually present a serious problem. However, if the dipole design constraints requires that the symmetry conditions be violated (ie. a “C” shaped dipole), the evaluation of the small quadrupole error present in this geometry may be marginal.
13th International Magnetic Measurement Workshop, May 19-22, 2003, Stanford, California
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Sextupole Measurements• For sextupole measurements, it is desirable to
make s3 and s2=0 for the compensated coil.
( ) ( )( ){ }( )
( ) ( )( ){ }( ) 0 1 1
1 1
0 1 1
1 1
22
221
22
2212
32
331
32
3313
=−−−=−−−−−=
=+−+=
−−−−−=
βρµββρµβ
βµρβ
βρµβ
s
s
This set of equations is difficult to solve algebraically. Therefore, the equations are solved transcendentally.
13th International Magnetic Measurement Workshop, May 19-22, 2003, Stanford, California
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• One of many solutions to these equations are, 2= 0.77987,= ,83234.0 ,79139.0 21 µρββ ==
The compensated sensitivities for these parameters are illustrated.
Sextupole Coil Sensitivities
-1.2
-0.8
-0.4
0.0
0.4
0.8
1.2
1 3 5 7 9
11 13 15 17 19 21
Multipole Index
Ssens
13th International Magnetic Measurement Workshop, May 19-22, 2003, Stanford, California
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Relative Phase• The calculation of the phase angles is based on an
arbitrary mechanical angular shaft encoder zero datum, adjusted by aligning the measurement coil. Therefore, a phase of the fundamental field, ψN, is always present. This angular offset can introduce large errors since small angular offsets between this datum and the zero phase of the fundamental field can result in large errors in the relative phase of the multipole error with respect to the quadrupole zero datum. Therefore, one normally computes a relative phase with respect to a zero phase for the fundamental field.
index field lfundamenta=index multipoleerror =
where= measured measured corrected Nn
Nn
Nnn ψλλ −
( )o063 , modPhase Rel. corrected nλ=
13th International Magnetic Measurement Workshop, May 19-22, 2003, Stanford, California
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A one page summary of the multipoles for 15Q-001 measured at approximately 81 Amps is reproduced in the table. These measurements were made at IHEP in the PRC.
Magnet ID: 15Q-001 Polarity: DFile Name: a150181t2
Norm.I(A): 81
n PHI[n] Angle PHI[n]/PHI[2] Coil Coef.[n] B[n]/B[2] Rel Phase(*10E-08 V.S) (dgr.)
u1 311879.602 297.248 4.1040E-02 1.0400E-01 4.2581E-031 1831.573 296.431
u2 7599033.299 181.496 1.0000E+00 1.0000E+00 1.0000E+002 52902.217 143.7273 3341.497 3.276 4.3973E-04 7.6002E-01 3.3420E-04 914 375.048 167.623 4.9355E-05 2.4505E+00 1.2094E-04 1655 252.797 260.508 3.3267E-05 1.6031E+00 5.3329E-05 1676 195.521 335.883 2.5730E-05 3.3999E+00 8.7479E-05 1517 202.765 89.396 2.6683E-05 3.2245E+00 8.6041E-05 1748 29.374 268.986 3.8655E-06 5.5016E+00 2.1266E-05 2639 127.338 104.702 1.6757E-05 6.0269E+00 1.0099E-04 8
10 1004.305 5.026 1.3216E-04 9.0748E+00 1.1993E-03 17811 32.07 268.79 4.2203E-06 1.0631E+01 4.4866E-05 35112 2.155 74.915 2.8359E-07 1.4855E+01 4.2128E-06 6613 10.023 258.199 1.3190E-06 1.7978E+01 2.3713E-05 15814 49.045 2.676 6.4541E-06 2.4003E+01 1.5492E-04 17215 4.321 62.461 5.6862E-07 2.9496E+01 1.6772E-05 14116 2.354 168.007 3.0978E-07 3.8279E+01 1.1858E-05 15617 8.098 115.978 1.0657E-06 4.7340E+01 5.0449E-05 1318 80.486 6.305 1.0592E-05 6.0330E+01 6.3899E-04 173
Sample Quadrupole
Measurements
13th International Magnetic Measurement Workshop, May 19-22, 2003, Stanford, California
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• Two measurements are made at each current, one with the coil connected in the uncompensated mode and one in the compensated mode. The integrated voltage for each magnet is Fourier analyzed and the amplitudes of each coefficient are listed. The u1 and u2 amplitudes (PHI[n] in 10E-8 V-sec.) are the amplitudes of the coefficients for the cos θ and cos 2 θ terms from the uncompensated measurements.
• The balance of the amplitudes are the coefficients of the cos n θ terms from the compensated coil measurements.
13th International Magnetic Measurement Workshop, May 19-22, 2003, Stanford, California
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• The next four columns include measured and computed values. – Angle The absolute phase angle of the nth Fourier
term with respect to the shaft encoder zero datum. The same datum is used for both the uncompensated and compensated measurements.
– PHI[n]/PHI[2] The ratio of the compensated nth Fourier coefficient to the uncompensated 2nd Fourier coefficient.
– Coil Coef.[n] The coil sensitivities computed from the design radii of the various measurement coil wire bundles.
– B[n]/B[2] The computed (using the coil sensitivities) absolute value of the ratio of the multipole amplitude to the quadrupole field amplitude, evaluated at 32 mm.
13th International Magnetic Measurement Workshop, May 19-22, 2003, Stanford, California
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Multipole Spectrum15Q-001 Multipoles @ 81 Amps
1.E-06
1.E-05
1.E-04
1.E-03
1.E-02
3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
Multipole Index
|Bn
/B2|
@ 3
2 m
m.
13th International Magnetic Measurement Workshop, May 19-22, 2003, Stanford, California
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Multipole Errors as VectorsQ15-001 Multipole Vectors
-0.0005
0
0.0005
0.001
0.0015
-0.0015 -0.001 -0.0005 0 0.0005
Re Bn/B2 @ 32 mm.
Ske
w B
n/B
2 @
32
mm
.
y3
y4
y5
y6
y7
y8
y9
y10
y11
y12
y13
y14
y15
y16
y17
y18
13th International Magnetic Measurement Workshop, May 19-22, 2003, Stanford, California
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Distribution of n=6 Multipole ErrorsQ-15 n=6 Multipoles
1.E-05
1.E-04
1.E-03
1.E-02
15Q
-001
15Q
-002
15Q
-003
15Q
-004
15Q
-005
15Q
-006
15Q
-007
15Q
-008
15Q
-009
15Q
-010
15Q
-010
15Q
-012
15q-
013
15Q
-014
15Q
-015
15Q
-016
15Q
-017
15Q
-018
15Q
-019
15Q
-020
15Q
-021
15q-
022
15Q
-023
15Q
-024
15Q
-025
15Q
-026
15Q
-027
15Q
-028
15Q
-029
15q-
030
Magnets
|B6/
B2|
@ 3
2 m
m.
at 81A
at 89A
13th International Magnetic Measurement Workshop, May 19-22, 2003, Stanford, California
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Distribution of n=10 Multipole ErrorsQ-15 n=10 Multipols
1.E-05
1.E-04
1.E-03
1.E-02
15Q
-001
15Q
-002
15Q
-003
15Q
-004
15Q
-005
15Q
-006
15Q
-007
15Q
-008
15Q
-009
15Q
-010
15Q
-010
15Q
-012
15q-
013
15Q
-014
15Q
-015
15Q
-016
15Q
-017
15Q
-018
15Q
-019
15Q
-020
15Q
-021
15q-
022
15Q
-023
15Q
-024
15Q
-025
15Q
-026
15Q
-027
15Q
-028
15Q
-029
15q-
030
Magnets
|B10
/B2|
@ 3
2 m
m.
at 81A
at 89A
13th International Magnetic Measurement Workshop, May 19-22, 2003, Stanford, California
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Distribution of n=3 First Random Multipole Errors
Q-15 n=3 Multipoles
-5.E-04
-4.E-04
-3.E-04
-2.E-04
-1.E-04
0.E+00
1.E-04
2.E-04
3.E-04
4.E-04
15Q
-001
15Q
-002
15Q
-003
15Q
-004
15Q
-005
15Q
-006
15Q
-007
15Q
-008
15Q
-009
15Q
-010
15Q
-010
15Q
-012
15q-
013
15Q
-014
15Q
-015
15Q
-016
15Q
-017
15Q
-018
15Q
-019
15Q
-020
15Q
-021
15q-
022
15Q
-023
15Q
-024
15Q
-025
15Q
-026
15Q
-027
15Q
-028
15Q
-029
15q-
030
Magnets
B3/
B2
@ 3
2 m
m. (
Rea
l and
Ske
w)
Re3
Im3
13th International Magnetic Measurement Workshop, May 19-22, 2003, Stanford, California
40WE08 - Tanabe
Iso-Errors
• The normalized multipole errors and their phases provide information regarding the Fourier components of the error fields. Often, however, one wants to obtain a map of the field error distribution within the required beam aperture. This analog picture of the field distribution can be obtained by constructing an iso-error map of the field error distribution. This map can be reconstructed from the normalized error Fourier coefficients and phases.
13th International Magnetic Measurement Workshop, May 19-22, 2003, Stanford, California
41WE08 - Tanabe
( )1
00
−
∆=∆
n
rnn rz
BB ⇒
( )[ ]
( )[ ]n
n
rnny
n
n
rnnx
nrz
BB
nrz
BB
1sin
1cos
1
0
1
0
0
0
ψθ
ψθ
+−∆=∆
+−∆=∆
−
−
where is the phase angle of the multipole error with respect to the zero phase for the fundamental (quadrupole) field.
n ψ
Therefore, 0
220 r
zBB
r=
( )[ ]
( )[ ]n
n
r
nny
n
n
r
nnx
nrz
BB
B
B
nrz
BB
BB
1sin
1cos
2
022
2
022
0
0
ψθ
ψθ
+−∆
=∆
+−∆
=∆
−
−
13th International Magnetic Measurement Workshop, May 19-22, 2003, Stanford, California
42WE08 - Tanabe
( )[ ]
( )[ ] 2
18
3
2
02
18
3 22
1
18
3
2
02
18
3 22
1sin
1cos
0
0
Σ
Σ
=+−∆
=∆
=∆
=+−∆
=∆
=∆
∑∑
∑∑
=
−
=
=
−
=
nn
n
r
n
n
nxy
nn
n
r
n
n
nxx
nrz
BB
BB
B
B
nrz
BB
BB
BB
ψθ
ψθ
∑∑ +=∆ 2
221
2BB
and 0
22
0 ryx
rz +
=xy1tan −=θWhere
13th International Magnetic Measurement Workshop, May 19-22, 2003, Stanford, California
43WE08 - Tanabe
The computationsand contour mapare programmed using MatLab.
15Q01 at 81 Amps.
-40 -30 -20 -10 0 10 20 30 40
-30
-20
-10
0
10
20
30
x (mm)
y
15Q001 DB/B2 (X104) at 81 Amps
0.1
0.5
0.5
0.5 0.5
0.5
0.5
1
1
11
11
1
1
1
1
2
22
2
2
2
2
2
2
2
55
5
5
5
5
5
5
5
10
10
10
10
10
10
10
10
13th International Magnetic Measurement Workshop, May 19-22, 2003, Stanford, California
44WE08 - Tanabe
• The iso-error plot isreplotted for only the allowed multipoles (n=6, 10, 14 and 18) and the first threeunallowed multipoles (n=3,4 and 5). It can be seen that it is virtually identical with the previous plot, indicating that theunallowed multipole errors > 6 are not important.
-40 -30 -20 -10 0 10 20 30 40
-30
-20
-10
0
10
20
30
x (mm)
y
15Q001 DB/B2 (X104) at 81 Amps
0.1
0.5
0.5
0.5
0.5
0.5
0.5
11
1 1
11
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
5
5
5
5
5
5 5
5
5
5
10
10
10
10
10
10
10
10
15Q001 at 81 Amps
13th International Magnetic Measurement Workshop, May 19-22, 2003, Stanford, California
45WE08 - Tanabe
• When the iso-error curve is replotted with theunallowed multipole errors reduced to zero and the allowed multipole phases adjusted to eliminate the skew terms, the ∆B/B <1x10-4 region is dramatically increased. This illustrates the importance of the first three unallowedmultipole errors which are primarily the result of magnet fabrication and assembly errors.
15Q01 at 81 Amps. Unallowed multipole errors = 0. No skew phases for allowed multipoles.
-40 -30 -20 -10 0 10 20 30 40
-30
-20
-10
0
10
20
30
x (mm)
y
15Q001 DB/B2 (X104) at 81 Amps
0.1
0.1
0.1
0.10.1
0.1
0.10.1
0.50.5 0.5
0.50.50.5
1
11
1
1
1
1
2
22
2
222
5
5
5 5
5
555
5
10
10
10
10
10
10
10
10
13th International Magnetic Measurement Workshop, May 19-22, 2003, Stanford, California
46WE08 - Tanabe