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 16 August 2004

Problem… LHC, and…

Problem… along the accelerator there are…

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. …

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.

Details Beam Pipes p

Details

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.

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

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.

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…

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

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

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

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

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

Quench Measurement

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

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

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

Model: Current Distribution z NC SC

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

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

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)

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)

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)

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

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

Results - Locationing Voltage Ratios: Quench Location Vac Vbd

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