hq01 field quality study update
DESCRIPTION
HQ01 field quality study update. F. Borgnolutti , G. Chlachidze , J. DiMarco , H. Felice , P. Ferracin , M. Marchevsky , G.L. Sabbi , E. Todesco, X. Wang HiLumi WP3 meeting on HQ test results August 2, 2012. Topics. Measurement accuracy (probe resolution) - PowerPoint PPT PresentationTRANSCRIPT
HQ01 field quality study update
F. Borgnolutti, G. Chlachidze, J. DiMarco, H. Felice, P. Ferracin, M. Marchevsky, G.L. Sabbi, E. Todesco, X. Wang
HiLumi WP3 meeting on HQ test resultsAugust 2, 2012
2
Topics
28/2/2012
• Measurement accuracy (probe resolution)
• Coil block positioning tolerance
• Static behavior– Main field reproducibility– Geometric and iron saturation
• Dynamic behavior – Eddy current effect and Rc
– Multipole decay as a result of low Rc
3
Measurement accuracy
38/2/2012
0.0001
0.001
0.01
0.1
1
10
3 5 7 9 11 13 15
|bn|
, |an
| (u
nits
at
R.re
f = 2
1.55
mm
)
multipole order
normal
skew
Biot-Savart slope
peak
average
• Plateau of measured multipoles = probe resolution.
• 250 mm long probe: 0.006 units at 14 kA at probe radius (21.55 mm).
4
Resolution at Rref = 40 mm
48/2/2012
100 mm 250 mmn 880 A 14 kA s/n* 880 A 14 kA s/n*3 0.014 0.015 7.0 0.010 0.010 9.64 0.026 0.027 3.8 0.019 0.019 5.25 0.047 0.051 2.0 0.036 0.036 2.86 0.088 0.094 1.1 0.066 0.066 1.57 0.163 0.174 0.6 0.123 0.123 0.88 0.303 0.323 0.3 0.228 0.229 0.49 0.563 0.600 0.2 0.423 0.425 0.2
10 1.045 1.114 0.1 0.785 0.788 0.1
• FNAL working on a new probe.– A factor of ~12.5 increase in resolution for n = 6 with the same radius.
• Scaling from Rref = 21.55 mm to 40 mm.• Target resolution based on CM18 discussion: 0.1 units or better
System meets the minimum requirement up to n = 6
(*) s/n ratios calculated assuming 0.1 units harmonic amplitude.
Coil block positioning tolerance
8/2/2012 5
1.E-03
1.E-02
1.E-01
1.E+00
1 2 3 4 5 6 7 8 9 10
harm
onic
s σ
(uni
ts)
Harmonic order
fit
normal
skew
Rref = 21.55 mm
Best fit obtained with displacement σ=29.6 µm
• Harmonics measured at 12 kA using the 100 mm probe at 3 axial locations. Averaged from up- and down-ramps.
• Match measured σ with the one calculated for random block displacements. Uncertainty on σ is 50% with measurements at 3 locations. Will decrease to 25% with 9 locations (requires ~ 1 m long straight section).
• TQC/TQS coil block positioning σ: 36 µm – 64 µm. [Borgnolutti et al., IEEE TAS 19(3), p.1100, 2009]
• Comparable to the level of current LHC IR quads and main dipoles.
Main field reproducibility
8/2/2012 6
Normalized TF (two meas. shown)
• Two measurements from each probe. Each measurement = Precycle (to 10 kA) + 1 machine cycle (to 14 kA),
10 A/s.
• σ < 10 units below 6 kA (mainly related to “spikes” – much lower at 1.9K)• σ < 2.4 units up to 14 kA (may decrease with larger statistics)• Target: < 1 unit at 7 TeV. [E. Todesco, CM18 presentation, Indico]
σ (b2) of measurements from the same probe
0
2
4
6
8
10
12
0 2 4 6 8 10 12 14 16
Std
dev
of b
2 (u
nit)
Current (kA)
250 mm
100 mm
7
Geometric component and iron saturation
78/2/2012
• Geometric: 12.025 T/m/kA at 2 kA. • Iron saturation at 14 kA: -5.8% with respect to geometric value.
• Some discrepancy between measurement and calculation – Need to incorporate as-built coil geometry and changes due to cool-down and excitation.– Discrepancy changes slope at 10 kA – possibly more than one source.– Iron properties? Other?
11.2
11.3
11.4
11.5
11.6
11.7
11.8
11.9
12.0
12.1
12.2
0 2 4 6 8 10 12 14 16
Tran
sfer
func
tion
(T/
m/k
A)
Current (kA)
up
down
ave. meas.
Roxie
Opera
Rref = 40 mm-0.08
-0.06
-0.04
-0.02
0.00
0.02
0.04
0 2 4 6 8 10 12 14 16
ΔTF
(T/m
/kA
at
R.re
f = 4
0 m
m)
Current (kA)
meas. - calc.
8
Static b6
88/2/2012
• Shift the calculation with +4.5 units to match the measurement between 4 – 8 kA. – Calculation for nominal geometry at warm.
• Some discrepancy between measurement and calculation– Δ = -1.5 units at 14 kA corresponds to ~ 90 µm outward displacement of two mid-plane
blocks under Lorentz forces. – ANSYS shows ~ 30 µm.
-2
-1
0
1
2
3
4
5
6
0 2 4 6 8 10 12 14 16
b6 (u
nit
at R
.ref
= 4
0 m
m)
Current (kA)
Roxie, nominal
shifted
ave. meas.
-1.6
-1.4
-1.2
-1.0
-0.8
-0.6
-0.4
-0.2
0.0
0.2
0.4
0 2 4 6 8 10 12 14 16
Δb6
(uni
t at
R.r
ef =
40
mm
)
Current (A)
meas - calc
9
Dynamic effect
98/2/2012
• Inter-strand eddy current dominates the dynamic effect.– Dynamic field error scales with ramp rate.– Decay time constant on the order of 10 s.
-10
0
10
20
30
40
50
60
70
0 10 20 30 40 50 60
Dyn
amic
sex
tupo
le [m
T]
Ramp rate [A/s]
B2
B3
B6
A3
A6
After subtracting static effectRaw data (static+dynamic component)
10
Calculation of Rc from sensitivity matrix
108/2/2012
• Solve a linear system: e = Sg. – e: field error vector; S: sensitivity matrix; g: conductance vector (g = 1/Rc).
B2 B6 B2 and B6
1=2=3=4 0.40 0.14 -
4=∞1= 2
-0.29
3 0.33
• Using field errors measured at 10 kA, 40 A/s.
• Assuming uniform Rc in block/layer to reduce the number of unknowns. Unique and physical solution not
always available.
Sensitivity factors computed from ROXIE
• Results suggest Rc ~ 0.1 – 0.4 μΩ.
Block Rc (µΩ)
Field error
11
Inverse calculation of Rc
118/2/2012
• Based on method originated from SSC and LHC. [Ogitsu et al., Particle Accelerators, 57, p. 215, 1997; Wolf et al., IEEE TAS 7(2), p. 797, 1997.]
• Error < 3.1% between measured and calculated field errors.• Rc lower in outer layer (0.2 – 0.22 µΩ).
• Goal: to match measured field error of B2 and B6.
12
Inverse calculation to match full error vector
128/2/2012
• Rc ~ 0.1 – 0.4 µΩ. – Error < 5% between calculated and measured dynamic field component.
– Consistent with 0.33 µΩ measured Rc on an HQ prototype cable. [Collings et al., IEEE TAS
21(3), p. 2367, 2011.]
• Top-bottom asymmetry in Rc (two different cables).
• Low Rc accompanied by high AC loss. To compare with loss measurement and quench behavior.
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
0 20 40 60 80 100
Rc (μ
Ω)
Cable number
coil 5
7
8
9
5
8
7
9
13
Multipole decay at different current levels
138/2/2012
• Strong exponential decay in multipoles with τ ranges from 25 to 55 s.
• The decay of inter-strand eddy current due to low Rc.
-70
-60
-50
-40
-30
-20
-10
0
0 50 100 150 200 250 300
ΔTF
(uni
ts)
Time (s)
2 kA
4 kA
6 kA
8 kA
10 kA
12 kA
14 kA
• τ estimated ~ 40 s at 10 kA based on Rc of 0.3 µΩ in block 3 with quadrupole symmetry. [A. P. Verweij, Ph.D. thesis, 1995]
• Expectation with 20 µΩ Rc: τ reduces to the order of 0.1 s and negligible decay.
Rref = 40 mm
14
Conclusions
148/2/2012
• Current probe meets the minimum resolution requirement up to n = 6.• New probe being developed to improve accuracy at the same radius.• Plan to develop larger radius probes and anti-cryostats for future test.
• Coil block positioning error s ~ 30 μm at 12 kA, comparable to current IR quads and LHC main dipoles.
• Main field reproducibility at 14 kA (80% of SSL at 4.4 K) is < 2 units. May improve with larger statistics. Target is < 1 unit at 7 TeV.
• Harmonics as function of current are in general agreement with calculations. • Further analysis is in progress to understand differences up to 0.6% (TF) and 1.5 units
(b6).
• Rc between 0.1 – 0.4 μΩ obtained from direct and inverse calculations.• Consistent with 0.33 μΩ measured on an HQ01 prototype cable. • Responsible for large eddy current effect and multipole decay.• Cored cable was introduced in second generation coils.