Frequency Transfer Function Measurements during LS1 Emmanuele Ravaioli Thanks to Arjan Verweij, Zinur Charifoulline, Andrea Musso MPE-TM 06-12-2012

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)


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


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


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


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


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


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


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?


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?


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


# 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


Distribution of ΔUpp in S12 (ramp at 2 kA and at 6 kA, 10 A/s) -1




Distribution of ΔUpp in S12 (ramp at 2 kA and at 6 kA, 10 A/s) -2




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


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


Frequency Transfer Function – Modeled AC impedance


Documents

Frequency Transfer Function Measurements during LS1 Emmanuele Ravaioli Thanks to Arjan Verweij, Zinur Charifoulline, Andrea Musso MPE-TM 06-12-2012