Powering the LHC Magnets markus.zerlauth@cern.ch 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

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

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)

Interconnection between a quadrupole and a dipole

Interconnecting busbars

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

LHC Powering in 8 Sectors 5 (+) 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

Arc cryostat with string of dipole magnets LHC powered in eight sectors, each with 154 dipole magnets Time for the energy ramp is about 20-30 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

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

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

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

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)

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

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

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

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

CERN - Eine Einführung

Superconducting Magnet Units

Standard FODO cell = 2 electrical ‘half’-cell

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

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

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 10.000 superconducting magnets in the LHC http://edms.cern.ch/cedar/plsql/navigation.tree?top=1459088716 23