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Frequency Transfer Function Measurements during LS1
Emmanuele Ravaioli
Thanks to Arjan Verweij, Zinur Charifoulline, Andrea Musso
MPE-TM
06-12-2012
Unbalanced voltage drop across 2 apertures of some main dipoles
Emmanuele Ravaioli MPE-TM 06-12-2012 2
For more info:• TE-Magnet-Seminary - Circuit simulations of the main LHC dipoles and the case of the 'unbalanced' dipoles – Ravaioli• 5JO-3_Ravaioli_20110916• Modeling of the voltage waves in the LHC main dipole circuits
28 Hz
Why is the impedance of the two apertures different?
28 Hz
Distribution of ΔUpp in S67 (ramp at 2 kA, 10 A/s)
Emmanuele Ravaioli MPE-TM 06-12-2012 3
There is no correlation between ΔUpp and
•Electrical position
•Physical position
•Magnet manufacturer
•Cable manufacturer
•Mechanical parameters (checked with Andrea Musso)
The phenomenon is more evident when the current in the magnets is about 2 kA.
(less amplitude at 6 kA, less amplitude at 1 kA; only present when magnets are ramping)
Why does the phenomenon peak at 2 kA?
Will it be worse at 7 TeV?
28 Hz
Cumulative distribution of ΔUpp in all sectors
Emmanuele Ravaioli MPE-TM 06-12-2012 4
About 50% of the LHC main dipole magnets have a ΔUpp
larger than expected.
Some dipoles have even stranger signals – “Outlier dipoles”
5Emmanuele Ravaioli MPE-TM 06-12-2012
Displayed dipoles•B24L7•B10L7•C27R6•C17R6
FPA at 6 kA @ 10 A/s(S67 20/05/2011 22.00)
• Some dipoles undergo a strange transient after the opening of the switches, lasting about a second• Some magnets in every sector (5-10) present this behavior with different amplitude; in a few cases (a
dozen in the whole LHC) the phenomenon was so significant that the oQPS threshold had to be changed to a higher value (see Zinur’s list).
• The behavior scales up with the current level.• Not related to the DQQDL boards used for the QPS measurements.
What is the origin of the
behavior of the “outlier”
dipoles?
Frequency Transfer Function – AC impedance of a system
6Emmanuele Ravaioli MPE-TM 06-12-2012
Example: L = 2*Laperture = 98 mH C = 2*Cground = 300 nFR = Rparallel = 100 Ω
A fast and practical way to measure the behavior of a complex system at
different frequencies.
Frequency Transfer Function – Setup
7Emmanuele Ravaioli MPE-TM 06-12-2012
Equipment (borrowed from ElQA?)• Gain Phase Analyzer• Amplifier• PCRemarks• Time needed for a measurement (magnet+ 2 apertures + 4 poles) ≈ 10 min• Max current in the magnets < 1 A• If performed after the ‘removal’ of QPS no patches needed(connection to V-taps)
Frequency Transfer Function of dipole apertures in the tunnel
8Emmanuele Ravaioli MPE-TM 06-12-2012
MagnetΔUPP [mV]
ΔZA12
1 240 15.6%
2 26 0.7%
3 172 15.5%
4 90 10.1%
Procedure: EDMS 1180124. Results: EDMS 1193209.
1
2
3
4
Nice correlation!
28 Hz
>15% difference at 28 Hz!
1
2
3
4
Frequency Transfer Function – Tunnel vs SM18
Emmanuele Ravaioli MPE-TM 06-12-2012 9
Reddish → Tunnel
Bluish → SM18
AC impedance measured in the tunnel above ~50 Hz about half of the impedance measured in SM18
Why are the FTF measured in the tunnel different from the
ones in SM18?
Frequency Transfer Function – Tunnel vs SM18 vs Simulation
Emmanuele Ravaioli MPE-TM 06-12-2012 10
Two apertures with different cross-contact resistance, i.e. with different inter-strand coupling losses, have a
dramatically different AC impedance.
In this example: Rc1=100 µΩ, Rc2=25 µΩ
The model can simulate impedance differences between the two apertures in the correct frequency range, but it
cannot simulate the high frequency behavior!
Is there a correlation between AC losses and the measured FTF?
Are inter-strand coupling losses the responsible for the unbalance?
Emmanuele Ravaioli MPE-TM 06-12-2012 11
Why is the impedance of the
two apertures different?
Why does the phenomenon
peak at 2 kA?
Why are the FTF measured in
the tunnel different from the
ones in SM18?
What is the origin of the
behavior of the “outlier”
dipoles?
Will it be worse at 7 TeV?
What about quadrupoles?
And what about other
magnets?
Is there a correlation
between AC losses and
the measured FTF?
Are inter-strand coupling
losses the responsible for
the unbalance?
Effects of currents to ground?
Phenomenon realated to
superconductivity effect or not?
We need to know
more about the AC
impedance of the
LHC magnets at
different
frequencies
Test Proposal – Frequency Transfer Function
12Emmanuele Ravaioli MPE-TM 06-12-2012
# What Where When Time Motivation I need help!
1
FTF of 15 to-be-replaced dipoles (2372, 2373, 2377, 2395, 2387, 2413, 2336, 2353, 2357, 2438, 2252, 2138, 1007, 2007)
S12, S45, S78, etc
Start of LS1 3 hCompare FTF from tunnel and SM18 (1007↔2431, 2007↔3128, 2373↔2868)
2 FTF of 30 more dipoles (60?) S67? Start of LS1 6 h- More statistics- Look for outliers
3FTF of 10 “outlier” dipoles (22 non-conformities)
Mostly S78
Start of LS1 2 h Better understanding
4FTF of 4 dipoles moving the grounding point of the chain
S67? Start of LS1 2 hAsses influence of paths to ground
ElQA
5 FTF of 10 main quadrupoles Any S Start of LS1 2 h V-taps?
6 FTF of 1 MQXA, MQXB Any S Start of LS1 1 h V-taps?
7 FTF of 1 MQM, MQMC, MQML Any S Start of LS1 1 h V-taps?
Start of LS12
days?
8 FTF of 4 dipoles at 20 K S23During CSCM
time-frame1 h
Assess impact of superconductivity effects
9FTF of 15 (5?) to-be-replaced dipoles at warm
After cooling down
2 hAssess impact of superconductivity effects
10FTF of 2 to-be-replaced dipoles(+AC loss measurements)
SM181
month?
- Compare FTF from tunnel and SM18- Relate FTF and AC loss
SM18 team
11 FTF of 15 replaced dipolesS12, S45, S78, etc
End of LS1 3 h- Compare FTF from tunnel and SM18
New QPS?
Annex
13Emmanuele Ravaioli MPE-TM 06-12-2012
Distribution of ΔUpp in S12 (ramp at 2 kA and at 6 kA, 10 A/s) -1
Emmanuele Ravaioli MPE-TM 06-12-2012 14
Why does the phenomenon peak at 2 kA?
Will it be worse at 7 TeV?
Distribution of ΔUpp in S12 (ramp at 2 kA and at 6 kA, 10 A/s) -2
Emmanuele Ravaioli MPE-TM 06-12-2012 15
Why does the phenomenon peak at 2 kA?
Will it be worse at 7 TeV?
RB.A78: 30/06/2008
7500A
5000A
3000A2000A
Top 10 magnets:A16L8 – 3504B17L8 – 2006B30R7 – 1007 *B8R7 – 1031C28R7 – 2011B29L8 – 1009A15R7 – 3020B29R7 – 1013A21R7 – 3014A22R7 – 1023
Threshold changed to 264mV!
Emmanuele Ravaioli Special TE-MPE-TM 28-03-2011 16
Outlier dipoles – Past observations -1 From MPP meeting (16/07/2008) Zinour CharifoullineNote: Data acquired when the value
of the extraction resistor was halved
Emmanuele Ravaioli Special TE-MPE-TM 28-03-2011 17
Outlier dipoles – Past observations -2From Zinour Charifoulline
Dipoles high ΔUpp for several seconds
18Emmanuele Ravaioli MPE-TM 06-12-2012
Displayed dipoles•B28L7•A27L7•A28L7•B32R6
FPA at 6 kA @ 10 A/s(S67 20/05/2011 22.00)
•Some dipoles present a voltage difference larger than normal after the opening of the switches; such a behavior lasts for many seconds (during the whole discharge?). After the first switch opening, the voltage difference of these dipoles is about half of that measured after the second switch opening
•A few magnets in every sector (5-10) present this behavior
•This phenomenon was found to be related to electronics (Board A and B give different results!)
Frequency Transfer Function – Four poles of an unbalanced dipole
Emmanuele Ravaioli MPE-TM 06-12-2012 19
Frequency Transfer Function – Modeled AC impedance
Emmanuele Ravaioli MPE-TM 06-12-2012 20