1. Simulating Quench Signals in the LHC Superconducting Dipoles
By Andrew Forrester
From California State University, Long Beach
a.k.a. “The Beach”
Today, I’ll be telling you about “Simulating Quench Signals in the LHC Superconducting Dipoles.”
First, let’s look at the LHC and its superconducting dipoles…
CERN Summer Student Program August 2004

2. Problem…
LHC, and…

3. Problem…
along the accelerator there are…

4. Problem… LHC dipole magnet Quench Dipole Magnets Protons at 7 Tev
High Magnetic Fields, ~8.5 T
Low Temp. Superconducting cables -> dipoles
15 meters long
a quench is the process of the superconducting cables in the dipoles becoming normal-conducting, which is a bad thing. …

5. Project Goals 1. Quench Characterization 2. Quench Locationing
Ongoing Dipole Production
R&D: “SC Magnet Science”
Present
Future
More reliability
Fewer rejects
Better technological know-how
Less expensive toys
Feedback …
So, if we care about this quenching phenomena, we’ll have to characterize it somehow.
Luckily the tool for characterization has been invented, and it’s called the LQA, or Local Quench Antenna, but first I should explain what a quench is in more detail so you understand how the LQA works.
---
So somehow we have to gather information about the quench.
Essentially, we’d like to be able to tell where the quenches are originating.
Well, someone invented a detector for this purpose, called the local quench antenna or LQA.

6. Details
Beam Pipes p

7. Details

8. Details I B 12 kA, 8 T field Inner layer, Outer layer
The cables run along the dipole and turn at the ends, connecting and forming big loops.

9. Details I B 12 kA, 8 T field Inner layer, Outer layer
The cables run along the dipole and turn at the ends, connecting and forming big loops. B

10. Details I B 12 kA, 8 T field Inner layer, Outer layer
The cables run along the dipole and turn at the ends, connecting and forming big loops.

11. Details – A Quench LHC dipole magnet Superconducting (SC) cable
Maybe the cables rub together because of the large forces applied on them by the magnetic field… perhaps at this weaker point here…

12. Details – A Quench LHC dipole magnet Superconducting (SC) cable
NC, T>TC

13. Details – A Quench LHC dipole magnet Superconducting (SC) cable
NC, T>TC

14. Details – A Quench LHC dipole magnet Superconducting (SC) cable
NC, T>TC

15. Details – A Quench LHC dipole magnet Superconducting (SC) cable How vq
can this be
measured?
NC, T>TC

16. Quench Measurement Quench Current Redistribution
Change in Magnetic Field
Change in Magnetic Flux
Coil
Voltage Signal
LQA = Local Quench Antenna
Coils of wire

17. Quench Measurement

18. Quench Measurement
The coils, or antennae, pick up change in flux caused by current redistribution…
Model…

19. Model: Cable NC SC LF HF R1 R2 z TC < T < 20 K T < TC z0
BE HERE AT “2 MINUTES”
TC < T < 20 K
T < TC z0
z0(t) = vqt

20. Model: Current Distributionz
(cm)
(kA)
I(z-vqt) NC SC
vq, L, G
R1, R2

21. Model: Current Distributionz NC SC

22. Model: Measurement z
H(z)
LQA
“Coupling Function”
L = 4 cm

23. Model: Measurement z
H(z)
LQA
“Coupling Function”
L = 12 cm

24. Model: Quench Signal   -t (IH)(t) -t [ I(z-vqt) H(z) dz] = -t B
(kA)
I(z-vqt)
H(z)
(cm)
(cm)
Quench Signal? 
-t [ I(z-vqt) H(z) dz] + -
= -t B
V(t)
 -t (IH)(t)
= vq(zI  H)(t)

25. Model: Quench Signal I(z-vqt) H(z) dI/dz (z-vqt) V(t)  (zI  H)(t)
(kA)
I(z-vqt)
H(z)
(cm)
(cm)
dI/dz (z-vqt)
(cm)
(kA/m)
V(t)  (zI  H)(t)

26. Model: Quench Signal I(z-vqt) H(z) dI/dz (z-vqt) V(t)
(kA)
I(z-vqt)
H(z)
(cm)
(cm)
dI/dz (z-vqt)
(cm)
(kA/m)
(ms)
(mV)
V(t)
V(t)  (zI  H)(t)

27. Results – Characterization
Current Distribution
(ms)
(mV)
Quench Signal
(kA) 
(cm)
(ms)
2.5 5
7.5
(mV)
-2.5 -5
-7.5 10  -1
Actual Current
Distribution

28. Results - Locationing
Quench Location
Upper or Lower?
Right or Left?

29. Results - Locationing
Voltage Ratios:
Quench Location
Vac
Vbd

30. Conclusions 1. Quench Characterization 2. Quench Locationing
Ongoing Dipole Production
R&D: “SC Magnet Science”
Present
Future
More reliability
Fewer rejects
Better technological know-how
Less expensive toys
Feedback