1. Powering the LHC Magnets
July 2015
LHC Layout, Optics and naming conventions
Electrical circuits and Powering Subsectors
Power Converters, Cables, QPS, Energy Extraction,…
Magnet/Circuit Protection
Operation of magnet powering system

2. How to achieve a collision energy of 7TeV in the LHC?
LHC Layout
eight sectors
eight arcs
eight long straight sections (insertions) about 700 m long
Beam dump blocks
IR5:CMS
IR4: RF + Beam instrumentation
IR6: Beam dumping system
IR3: Momentum Cleaning (warm)
IR7: Betatron Cleaning (warm)
Main dipole magnets: making the circle
IR8: LHC-B
IR2:ALICE
IR1: ATLAS
Injection
Injection 2

3. LHC arcs: dipoles and short straight sections
1232 superconducting dipoles magnets
magnetic field 8.3T (7Tev), each magnet 15m long, operating at 1.9K
Deflection of all man dipoles: 2 , in total 19 km main dipole magnets
Arc length ~21 km (dipoles + short straight sections + interconnects)

4. Interconnection between a quadrupole and a dipole

5. Interconnecting busbars

6. Bus bar interconnections right of point 8 (19/3/2007)
600 A bus bars (Nline)
6 kA bus bars

7. LHC Powering in 8 Sectors5
(+) Less energy & voltage per circuit
(+) For superconducting magnets, no DC powering across IPs
(+) Commissioning possible for each sector, independent of other sectors 4 6
DC Power feed
(o) Main DC power feed at even points (MB, MQ)
(o) Some DC power feed at odd points
Octant 3
DC Power 7
arc cryostat
LHC Sector 2 8
(-) Higher complexity, i.e. more powering equipment needed (converters, DFBs,…)
(-) More complex circuit tracking between circuits
Sector 1

8. Arc cryostat with string of dipole magnets
LHC powered in eight sectors, each with 154 dipole magnets
Time for the energy ramp is about min (Energy from the grid)
Time for discharge is about the same (Energy back to the grid)
DFB
DFB
Magnet 2
Magnet 4
Magnet 152
Magnet 154
Magnet 1
Magnet i
Magnet 153
Magnet 3
Energy Extraction: switch closed
Energy Extraction: switch closed
Power Converter

9. Main dipoles: quench of a magnet
Quench in one magnet: Resistance and voltage drop across quenches zone
Quench is detected: Voltage across magnet exceeds 100 mV
DFB
DFB
Magnet 2
Magnet 4
Magnet 152
Magnet 154
Magnet 1
Magnet i
Magnet 153
Magnet 3
Energy Extraction: switch closed
Energy Extraction: switch closed
Quench
Detector
Power Converter

10. Main dipoles: magnet protection
Quench heaters warm up the entire magnet coil: energy stored in magnet dissipated inside the magnet (time constant of 200 ms)
Diode in parallel becomes inductive: current of other magnets goes through diode
Resistance is switched into the circuit: energy of 153 magnets is dissipated into the resistance (time constant of 100 s for main dipole magnets)
DFB
DFB
Magnet 2
Magnet 4
Magnet 152
Magnet 154
Magnet 1
Magnet i
Magnet 153
Magnet 3
Energy Extraction: switch open
Energy Extraction: switch open
Quench
Detector
Quench
Heater PS
Power Converter

11. Magnet current after a quench
Current in a dipole magnets after a quench, when heaters are fired (7 TeV / 8.3 Tesla) - 7 MJ within 200 ms into magnet
Current after quench
Gaussian approximation

12. Circuit Protection
Protection of superconducting circuits is a function of stored energy (and complexity) of the circuit
Main concern is with fast extraction of energy from circuit and avoidance of quenches (mechanical stress, downtime to recover,..)
Quench Protection system to detect quenches, mitigation through
Quench heaters (spread out energy dissipation in whole volume)
Parallel protection through diode or resistor (bypass the quenching magnet)
Energy Extraction system and crow-bars (forced extraction of energy from magnet chain)

13. QPS Installations II MB protection rack Protection unit Q4.L8 & D2.L8
Quench heater power supplies Q4.L8
Quench heater connection Q5.L8

14. QPS Installations III 13 kA EE systems 13 kA protection diode
13 kA EE extraction resistors RB
600 A EE systems

15. LHC Hardware Commissioning
nominal
6kA
4kA
EE, free-wheel +
2kA
EE, free-wheel +
Injection level
Splice
Measurements
Splice
Measurements
Power Converter
Setup
Interlock
tests
Splice
Measurements
Splice
Measurements

16. Putting it all together: The LHC operational cycle
beam dump
energy ramp (30mn)
Physic run (10 to 12h)
coast
2000
4000
6000
8000
10000
12000
-4000
-2000
time from start of injection (s)
dipole current (A)
7 TeV
start of the ramp
injection phase
preparation and access
450 GeV

17. CERN - Eine Einführung

18. Superconducting Magnet Units

19. Standard FODO cell = 2 electrical ‘half’-cell

20. Circuit Types defined for HWC and operation
60A (752 orbit corrector circuits)
80-120A (~ 284 LSS and DS orbit correctors)
600A EE (202 x 600A correctors with Energy Extraction System)
600A no EE (72 x 600A correctors without Energy Extraction)
600A no EE crowbar (136 x 600A correctors without EE, but crowbar)
IPQ (~ 6kA) (78 x Individually powered quads, Q4-Q10)
IPD (~ 6kA) (16 x Separation and re-combination dipoles)
IT (~ 8kA) (8x Main Inner Triplet Circuits)
Main Dipole and Quadrupoles (~ 12kA) x 24
WARM x40
Total of 1612 electrical circuits

21. Electrical half-cells - Electrical Circuits & connections
Line N
Majority of magnets in the arc of a given family connected in SERIES
…why not in the whole machine…?
Main Busbars +
Spool-pieces

22. Magnet inventory
1232 main dipole magnets powered in series with the same strength
to make it around the LHC
752 orbit corrector magnets powered individually
to ensure that the beam follows the design orbit (within about 0.5 mm),
392 Focusing and defocusing quadrupole magnets powered in series
to keep beam size limited
Lattice sextupole magnets powered in series
to correct the trajectories for off-energy particles,
Multipole-corrector magnets (sextupoles, decapoles, octupoles, ...)
to correct field imperfections, to suppress instabilities, etc., powered in series
Corrector magnets to adjust essential beam parameters (quadrupoles)
Insertion dipole and quadrupole magnets
to ensure beam crossing / increase the interbeam distance / focus beams for experiments etc.
Total of more than superconducting magnets in the LHC 23