Optimizing the Design of Single-Stage Power-Factor Correctors
Magnetic Behavior of LHC Correctors: Issues for Machine Operation W. Venturini Delsolaro AT-MTM;...
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Transcript of Magnetic Behavior of LHC Correctors: Issues for Machine Operation W. Venturini Delsolaro AT-MTM;...
Magnetic Behavior of LHC Correctors: Issues for Machine Operation
W. Venturini Delsolaro AT-MTM;
Inputs from A. Lombardi, M. Giovannozzi, S. Fartoukh, J.P. Koutchouk, V. Remondino, R.Wolf
LHC workshop “Chamonix XIV”
January 18-21, 2005
Outline
Magnetic measurements available today Issues on the magnetic behavior
Transfer functions: required accuracy, hysteresis and reproducibility of machine settings
Field quality panorama Cross talks
Plan for the remaining (cold) measurements Conclusions
Corrector Zoo
SHORT SUMMARY OF CORRECTOR MAGNET PARAMETERS. Magnet
Assembly Nr of
correctors Aperture
(mm) number Main
Component Nominal Strength BN or AN
Current (A)
Magn. Length (mm)
MCDO 2 nested
58 1232 B5 B4
1.2 E6 T/m4 8200 T/m3
550 100
66 66
MCS 1 58 2464 B3 1630 T/m2 550 110 MO 2 56 168 B4 6.3 E4 T/m3 550 320
MQT 2 56 160 B2 123 T/m 550 320 MQS 2 56 32 A2 123 T/m 550 320
MSCB 4 56 376 B3, A3 B1, A1
4430 T/m2 2.9 T
550 55
369 647
MQTL 2 56 60 B2 129 T/m 550 1300 MCBC 2 56 84 B1, A1 3.1 T 100 904 MCBY 2 70 38 B1, A1 2.5 T at 4.5K 72 899 MCBX 2
nested 90 18 A1
B1 3.26 T 3.35 T
550 550
480 450
MCBXA =MCBX + MCSTX
4 nested
70 9 A1 B1
B3
B6
3.26 T 3.35 T
52 T/m2 7.22E6T/m5
550 550 50 80
480 450 576 615
MQSX 1 70 9 A2 80.2 T/m 550 223 MCSOX 3
nested 70 9 A4
B4 A3
9666 T/m3 9229 T/m3 377 T/m2
100 100 100
138 137 132
Where we are: summary of cold measurements and c/w campaigns (FQWG 16/11/04)
Corrector type Pre series Series Cold/warm
MCS 10+10 none good
MCDO 10+10 none poor
MO 3 assemblies none 1 mod., fair
MQT/S 3 assemblies 8 modules poor, improving
MCB 1 assembly 2 ass. + 4 mod. good
MS 1 assembly 1 ass. + 3 mod. 1 mod., fair
MCBC 1 assembly 1 module 1 mod., fair
MCBY none none -
MQTL 2 modules - -
MCBX+MCBXA 2 17/25 fair
MQSX+MCSOX 1 8/9 to check
Tolerable uncertainties on the settings of main components (1)
Orbit Correctors in the Arcs (MCB, individually powered):
Closed orbit perturbation from N randomly distributed kicks:
For any given <x>, the tolerable ΔBlrms is found, as a function of
Bρ, and of correction scenario taking <x>rms=2 mm, N=200, the tolerable ΔBlrms at 7 TeV
is
about 4 10-2 Tm, that is 2% of the maximum value (same at injection to get a circulating pilot beam?)
Becomes 1‰, if we take <x>= 0.1 mm (for efficiency of collimation) 1.28 10-4 Tm absolute rms error at injection
0.3% of rms excitation of arc correctors
)(22
)()( 1
QSin
Ns
B
lBsx
Tolerable uncertainties on the settings of main components (2): Tuning Quadrupoles (MQT)
From the operational tolerance on tune shifts (±3 10-3)
At injection, it corresponds to a total integrated MQT field (in Tm at 17 mm) of 5.3 10-3 Tm 6.7 10-4 Tm accuracy
for one single magnet
Figures 10 times lower if we take 10% of the operational tolerance
4
lkQ
)(4 2
ml
Qk
)(4
2 TmQBR
lB ref
From which one gets Q/B2l=0.56/Tm at 17 mm at injection
Tolerable uncertainties (3)… MCS: 1.5 10-4 Tm absolute accuracy at
injection to assure reproducibility of Q’ within 10 units
MS: 7 10-4 Tm absolute accuracy at injection 10 unit of Q’
MO to be determined, not critical: 5% should be OK
IR correctors to be determined, potentially critical
Sample sizes for cold tests
From σ of cold measurements (when available), and required uncertainty u, for a 100(1- α)% confidence interval
Deduce n(u, α) from the usual formula for the estimated standard error of a sample of n units
u= σ t(α, n-1)√(1/n-1/N)
Where t is the Student distr. and N the population number
Different u, σ and N for each corrector type
The problem of hysteresis
Magnetic hysteresis from the superconducting filaments and from the iron affects all the sc correctors
“Likely” settings at injection for some correctors (orbit, tuning, b3 spool pieces) are at very low current
Trims might be numerous and require reversing of current ramps (for example orbit corrections)
As a consequence, hysteresis on the corrector transfer functions results in a “randomization” of the corrector magnetic state (position on the hysteresis loops: upper or lower branch)
Consequences on reproducibility of settings, notably between runs
compare the resulting “uncertainty” to operational optics tolerances
Table of Hysteresis at 0A for some corrector types (Mainly from pre series measurements)
Orbit
Lattice
Multipole
Tm @ 17 mm
Tm @ 17 mm
Tm @ 17 mm
MCB
10-3
MQT
2 10-4
MCS
6 10-5
MCBC
1.3 10-3
MQTL
1.6 10-4
MCD
10-5
MCBY
?
MS
10-3
MCO
10-4
MCBX
6 10-3
MO
4.6 10-4
Hysteresis of orbit corrections Compare kick at injection due to hysteresis
to some tolerance on CO displacement….
10-3 Tm at injection randomly distributed amongst 200 MCB 782 μm rms on CO
1) Reproducibility at 100 μm level not to be obtained if hysteresis is ignored
2) May have an influence on the convergence of correction algorithms
Hysteresis of tune corrections
Taking ΔQ/ΔB2l=0.56/Tm at injection,
the hysteresis width of a single MQT corresponds to ΔQ=1.1 10-4
For one circuit of 8 MQT 9 10-4 ,
Remember the tolerance on ΔQ=±3 10-3
Considering 8 circuits 7 ·10-3 (!)
Consequence on tune corrections at injection From cold measurement of MQT-MA-003
2.0E-02
3.0E-02
4.0E-02
5.0E-02
6.0E-02
7.0E-02
8.0E-02
9.0E-02
1.0E-01
1 1.2 1.4 1.6 1.8 2
Current in 8 MQT circuits [A]
Q
ΔI to cross the loop is related to re-penetration of filaments plus iron hysteresis: Hp =30 mT (1 A for the MQT)
7 10-3
MA-E-0001, Coil 0607, 1.8K
-0.08
-0.06
-0.04
-0.02
0
0.02
0.04
0.06
0.08
-600 -400 -200 0 200 400 600
Current [A]
B3 @
r=
17m
m [T
m]
-6.E-05
-5.E-05
-4.E-05
-3.E-05
-2.E-05
-1.E-05
0.E+00
1.E-05
2.E-05
3.E-05
4.E-05
5.E-05
B3 d
evi
atio
n @
r=17m
m [T
m]
Corresponds to a jump in Q’ of 3.8 units
Excitation curve of a pre series MCS
Hysteresis of Lattice Sextupoles
0.E+00
2.E-04
4.E-04
6.E-04
8.E-04
1.E-03
1.E-03
1.E-03
0 50 100 150 200 250 300 350
Current [A]
Wid
th o
f B
3 h
yste
resi
s lo
op
(T
m @
17
mm
)
-0.06
-0.04
-0.02
0
0.02
0.04
0.06
-30 -10 10 30Current (A)
B3
(Tm
@ 1
7 m
m)
Corresponds to
more than 10 units of Q’
Field quality panorama
Warm measurements: the emerging spikes
-45-40-35-30-25-20-15-10
-505
1015202530354045
0 2 4 6 8 10 12 14
FQWG target
mec. target
measured
MQT modules: systematic vs
b1 b2 b3 b4 b5 b6 b7 b8 b9 b10 b11 b12 b13 b14
0
2
4
6
8
10
12
-50 -40 -30 -20 -10 0 10 20
Mean= -40.281Standard deviation=2.003Target value= 0
freq
ue
[units]
b3
b3=-40 units in MCBC
b6=-10 units and b10=-15 units in MQT, and… MQTL!
Field quality at warm and at 1.9 K of the first 2 MQTL modules (pre series)
-20
-18
-16
-14
-12
-10
-8
-6
-4
-2
0
2
4
6
8
10
12
14
16
18
20
b3 a3 b4 a4 b5 a5 b6 a6 b7 a7 b8 a8 b9 a9 b10 a10
Harmonic No.
Un
its
@ r
=1
7 m
m
MQTL1_COLD_avg100A
MQTL1_WARM_bench2
MQTL2_COLD_avg100A
MQTL2_WARM_bench2
Likely field quality of Q6 in IR3 and IR7, done with 6 MQTL
Series MCBC module measured
at warm and at 1.9 K
MCBC 35 (August 2004)
-60.00
-50.00
-40.00
-30.00
-20.00
-10.00
0.00
10.00
warm
cold at 100 A
Cross talks
Between apertures at high field (MSCB, MQTL) Checked for 2 MSCB variants and found to be
negligible (order of 10-4 Tm between the MCB) Effects foreseen for the MQTL assemblies
In nested magnets (MCDO, Inner Triplet correctors) Very few measurements, to be completed with
extended programs on the spare units
Cross talk effects in nested magnets (MCBX)
-0.0015
-0.001
-0.0005
0
0.0005
0.001
0.0015
-0.3 -0.2 -0.1 0 0.1 0.2 0.3B1 (T )
T @
17
mm
B 3
A 3
B1
A1
Proposal for minimal cold measurements plan
Corrector type TF Hysteresis measurement
setting up cycle
MCS 10+10 (1%) yes
MCDO 10+10 (1%) ?
MO 9 no
MQT/S 9 yes
MSCB 12 yes
MCBC 9 yes
MCBY 9 yes
MQTL 4 yes
MCBX+MCBXA - yes
MQSX+MCSOX - yes
Conclusions The knowledge of the transfer functions with 10-3
accuracy would be needed to set some corrections. Transfer functions are not linear.
Very few measurements so far. Sample sizes not defined The hysteresis of main components is an issue. Set up
cycles will have to be defined, in particular for nested magnets. Refined measurements and models may be needed for operation
Field quality of MQTL and MCBC is at the limit of tolerance Plan for the cold series measurements must provide
sufficient experimental data for modeling work
Thanks to
L. Bottura,
A. Lombardi,
S. Fartoukh,
M. Giovannozzi,
J. P. Koutchouk,
V. Remondino,
L. Walckiers
R. Wolf