LHC Machine Protection Acknowledgments to my colleagues of

LHC Machine Protection Acknowledgments to my colleagues of the MPWG for input and material. J. Wenninger B. . Todd R. Schmidt B. Puccio Rossano Giachino 1 September 2007

Beam 2 4 Beam 1 5 LHC 6 7 3 SPS 2 TI 2 protons LINACS Booster TI 8 8 1 CPS Ions LEIR Linac PSB CPS SPS LHC Top energy/Ge. V Circumference/m 0. 12 30 1. 4 157 26 628 = 4 PSB 450 6’ 911 = 11 x PS 7000 26’ 657 = 27/7 x. SPS Note the energy gain/machine of 10 to 20 – and not more ! The gain is typical for the useful range of magnets !!! 2 2

LHC Powering in 8 Sectors 5 4 Powering Sector: 6 154 dipole magnets & about 50 quadrupoles total length of 2. 9 km Octant DC Power feed 3 DC Power LHC 27 km Circumference 7 Powering Subsectors: 8 2 Sector • long arc cryostats • triplet cryostats • cryostats in matching section 1 3

LHC cycle: charging the magnetic energy beam dump coast energy ramp coast 7 Te. V start of the ramp injection phase preparation and access L. Bottura 450 Ge. V 4

Outline • Energy stored in the LHC magnets • • Energy stored in the LHC beams • • • LHC Dipole Magnets Power Interlock Controllers Quench Protection System LHC Beam Energy Beam Losses and Damage Potential Beam Absorbers, Beam Dump and Collimators Beam Interlock System Conclusion 5

Outline • Energy stored in the LHC magnets • • Energy stored in the LHC beams • • • LHC Dipole Magnets Power Interlock Controllers Quench Protection System LHC Beam Energy Beam Losses and Damage Potential Beam Absorbers, Beam Dump and Collimators Beam Interlock System Conclusion 6

Energy stored in LHC magnets : where Most energy is stored in the magnetic field of the dipoles B = 8. 33 Tesla I = 11800 A L = 0. 108 H 7

Energy stored in LHC magnets Energy is proportional to volume inside magnet aperture and to the square of the magnet field E dipole = 0. 5 L dipole I 2 dipole Energy stored in one dipole is 7. 6 MJoule For all 1232 dipoles in the LHC: 9. 4 GJ 8

The energy stored in the magnets corresponds to. . an aircraft carrier at battle-speed of 55 km/h 9

The energy stored in the magnets corresponds to. . 10 GJoule corresponds to… the energy of 1900 kg TNT the energy of 400 kg Chocolate An important point to determine : How fast can this energy be released? 10

Powering Interlock Controller • PLC-based Powering Interlock Controllers (PIC) are used to manage the interlock signal between the power converters and the quench protection system. • The PIC also interfaces to the Beam Interlock System and will request a beam dump if the electrical circuit that fails is considered to be critical for beam operation. Discharge Switches Cryogenics Quench Protection Power Converters Powering Interlock System AUG UPS 11

Quench A Quench is the phase transition of a super-conducting to a normal conducting state. Quenches are initiated by an energy in the order of m. J • • • Movement of the superconductor by several m (friction and heat dissipation) Beam losses Failure in cooling To limit the temperature increase after a quench • • • The quench has to be detected The energy is distributed in the magnet by force-quenching the coils using quench heaters The magnet current has to be switched off within << 1 second 12

Energy extraction system in LHC tunnel Switches - for switching the resistors into series with the magnets Resistors absorbing the energy 13

If it does not work… During magnet testing the 7 MJ stored in one magnet were released into one spot of the coil (inter-turn short) P. Pugnat 14

Challenges for quench protection • • • Detection of quench for all main magnets • 1600 magnets in 24 electrical circuits • ~800 others Detection of quench across all HTS current leads • 2000 Current Leads Firing heater power supplies, about • 6000 heater units Failure in protection system False quench detection: downtime of some hours Missed quench detection: damage of magnet, downtime 30 days Systems must be very reliable 15

Outline • Energy stored in the LHC magnets • • Energy stored in the LHC beams • • • LHC Dipole Magnets Power Interlock Controllers Quench Protection System LHC Beam Energy Beam Losses and Damage Potential Beam Absorbers, Beam Dump and Collimators Beam Interlock System Conclusion 16

Energy stored in the beams 25 ns Stored beam energy: Proton Energy Number of Bunches Number of protons per bunch Proton Energy: 7 Te. V In order to achieve very high luminosity: Number of bunches per beam: 2808 Number of protons per bunch: 1. 05 × 1011 3× 1014 protons / beam Stored energy per beam: 362 MJoule 17

Stored energy comparison Increase with respect to existing accelerators : • A factor 2 in magnetic field • A factor 7 in beam energy • A factor 200 in stored energy 18

A proton injected into the LHC will end its life… • • • In a collision with an opposing beam proton • The goal of the LHC ! On the LHC beam dump • At the end of a fill, be it scheduled or not. On a collimator or on a protection device/absorber • The collimators must absorb protons that wander off to large amplitudes to avoid quenches. 19

Beam induced damage test The effect of a high intensity beam impacting on equipment is not so easy to evaluate, in particular when you are looking for damage : heating, melting, vaporization … Controlled experiment: § Special target (sandwich of Tin, Steel, Copper plates) installed in an SPS transfer line. § Impact of 450 Ge. V LHC beam (beam size σx/y ~ 1 mm) Beam 25 cm 20 20

Results…. • Melting point of Copper is reached for an impact of 2. 5× 1012 p. • Stainless steel is not damaged, even with 7× 1012 p. • Results agree with simulation A B Shot Intensity / p+ A 1. 2× 1012 B 2. 4× 1012 C 4. 8× 1012 D 7. 2× 1012 D C Based on those results the MPWG has adopted for the LHC a limit for safe beams with nominal emittance @ 450 Ge. V of: 1012 protons ~ 0. 3% of the total intensity Scaling the results yields a limit @ 7 Te. V of: 1010 protons ~ 0. 003% of the total intensity 21

Beam absorber DCCT Dipole Current 1 DCCT Dipole Current 2 RF turn clock Beam Energy Tracking Beam Dumping System • The beam dump block is the ONLY element of the LHC that can safely absorb all the beam! • All other absorbers in the LHC (collimators and protection devices) can only stand partial losses – typically up to a full injected beam, i. e. equivalent to the energy stored in the SPS at 450 Ge. V. 22

LHC Layout IR 3, IR 6 and IR 7 are devoted to protection and collimation ! Beam dump blocks IR 5: CMS experiment IR 4: Radio frequency acceleration IR 3: Momentum Collimation (normal conducting magnets) IR 6: Beam dumping system IR 7: Collimation (normal conducting magnets) IR 8: LHC-B experiment IR 2: ALICE experiment IR 1: ATLAS experiment Injection 23

LHC Layout IR 3, IR 6 and IR 7 are devoted to protection and collimation ! Beam dump blocks IR 5: CMS experiment IR 4: Radio frequency acceleration IR 6: Beam dumping system beam absorber (graphite) about 8 m IR 3: Momentum Collimation (normal conducting magnets) IR 7: Collimation (normal conducting magnets) concrete shielding IR 8: LHC-B experiment IR 2: ALICE experiment IR 1: ATLAS experiment Injection 24

56. 0 mm Collimators at 7 Te. V, squeezed optics 1 mm Ralphs Assmanns EURO +/- 6 sigma = 3. 0 mm Beam +/- 3 sigma Example: Setting of collimators at 7 Te. V - with luminosity optics Very tight settings orbit feedback !! 25

Beam Interlock System and Inputs • • • Protection for the entire machine against beam incidents. Interface to all parties involved in protection, including powering interlock systems and injectors (SPS). Microsecond reaction times. 26

Beam Interlock System and Inputs Beam Current Monitors DCCT Dipole Current 1 DCCT Dipole Current 2 RF turn clock Current Beam Energy Tracking Protection for the entire against Safe LHCmachine. Energy beam incidents. Parameters Energy • Interface to all parties involved in Injection Extraction protection, Energy including powering. SPS interlock Kickers Interlocks systems and injectors Safe. Beam (SPS). Flag • Microsecond reaction times. TL collimators • BLMs aperture Beam Dumping System BLMs arc Access Safety System Discharge Switches Cryogenics Quench Protection Power Converters Collimators / Absorbers Beam Dump Trigger Powering Interlock System BPMs for Beam Dump LHC Beam Interlock System BPMs for dx/dt + dy/dt d. I/dt beam current d. I/dt magnet current essential circuits Screens auxiliary circuits RF + Damper LHC Experiments Vacuum System Operators Software Interlocks AUG UPS NC Magnet Interlocks Timing PM Trigger 27

Architecture of the BEAM INTERLOCK SYSTEM Beam-1 / Beam-2 are Independent! 20 Users per BIC Half maskable Half un-maskable - fast reaction time (~ s) 28

Safe LHC parameters Safe Beam Flags required by • • Beam Interlock Controllers, to permit masking of selected interlock channels, in particular during commissioning Aperture kickers, to disable kickers when there is no “safe” beam Beam Presence Flags required by • SPS extraction, to permit extraction of high intensity beam only when there is circulating beam in the LHC 29

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Outline • Energy stored in the LHC magnets • • Energy stored in the LHC beams • • • LHC Dipole Magnets Power Interlock Controllers Quench Protection System LHC Beam Energy Beam Losses and Damage Potential Beam Absorbers, Beam Dump and Collimators Beam Interlock System Conclusion 31

Conclusions There is no single “Machine Protection System”: LHC Machine Protection relies on several systems working reliably together Safe operation of the LHC start at the SPS, via extraction into TT 40/TI 8 and TI 2, via the transfer lines, via LHC injection etc. Safe operation of the LHC relies not only on the various hardware systems, but also on operational procedures and on the controls system (“software interlocks”) Safe operation of the LHC requires a culture: • as soon as the magnets are powered, there is the risk of damage due to the stored magnet energy • as soon as the beam intensity is above a certain value (…that is much less than 0. 1% of the full 7 Te. V beam), there is the risk of beam induced damage 32

Machine protection at the LHC • Machine protection activities of the LHC are coordinated by the LHC Machine Protection Working Group (MPWG), co-chaired by R. Schmidt & J. Wenninger. http: //lhc-mpwg. web. cern. ch/lhc-mpwg/ • Since 2004 the MPWG is also coordinating machine protection at the SPS (ring & transfer lines). 33

Ramping the current in a string of dipole magnet Power Converter Magnet 1 Magnet 2 Magnet i Magnet 154 • 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) • Note : if you switch off the main dipoles PC, the current decays with a time constant of ~ 6 hours. 34

Summary • The LHC is one of the most complex instruments that has ever been conceived. • The LHC is the first accelerator where the machine protection systems are vital. • LHC commissioning progress will be strongly influenced by the understanding of the components of the protection systems. • The LHC performance will be strongly affected by the protection systems: • due to the large number of interlock channels the reliability of the systems must be very high. • The very tight tolerance on machine parameters and collimation will make LHC operation totally different from SPS or LEP: Play once and the beam is gone ! 35

The price of high fields & high luminosity… When the LHC is operated at 7 Te. V with its design luminosity & intensity, q the LHC magnets store a huge amount of energy in their magnetic fields: per dipole magnet all magnets Estored = 7 MJ Estored = 10. 4 GJ q the 2808 LHC bunches store a large amount of kinetic energy: Ebunch = N x E = 1. 15 x 1011 x 7 Te. V = 129 k. J Ebeam = k x Ebunch = 2808 x Ebunch = 362 MJ To ensure safe operation (i. e. without damage) we must be able to dispose of all that energy safely ! This is the role of Machine Protection ! 36 36

Schematic of the beam interlock system LHC protection systems USER_PERMIT SIGNALS BEAM_PERMIT STATUS SIGNALS LHC Injection System for beam 1 User System #1 UNMASKABLE INPUTS BEAM 1_PERMIT User System #2 for beam 1 SPS Extraction System User System #8 MASKABLE INPUTS User System #9 User System #10 Beam Dumping System PM event Trigger BEAM INTERLOCK CONTROLLER MODULE (BIC) BEAM 2_PERMIT for beam 1 Timing System LHC Injection System for beam 2 Beam Dumping System for beam 2 SPS Extraction System for beam 2 User System #16 Mask Settings Safe Beam Flag to User Systems 37

BIS reaction times USER_PERMIT signal changes from TRUE to FALSE a failure has been detected… beam dump request User System process Signals send to LBDS Beam Interlock system process Beam Dumping System waiting for beam gap ~70μs max. > 10μs t 1 89μs max t 2 Kicker fired all bunches have been extracted ~ 89μs t 3 t 4 Achievable response time ranges between 100 s and 270 s (between the detection of a dump request and the completion of a beam dump) 38

User system detects failure Core of the Machine Protection System Beam dump request to Beam Interlock System Beam dump request to Beam Dumping System Fire kicker magnets Protection for powering operation • Quench Protection System (4000 channels) • Power Interlocking Controller (36 crates for 800 electrical circuits) Protection for beam operation • Beam Loss Monitors System (3500 channels) • Special beam instrumentation (few channels) • Beam Interlock System (16 crates for 150 user connections) • Beam Dumping System (2 complex systems) dump beam 39

Prototype collimators Robustness maximized with C-C jaws and water cooling! 40

Robustness test at SPS Test condition: • 450 Ge. V SPS LHC beam • 3× 1013 protons • 2 MJ • 1 mm 2 beam area • equivalent to: Full Tevatron beam ½ kg TNT each jaw hit 5 times! C-C jaw TED Dump C jaw No sign of jaw damage! (but some deformation was observed on the supporting structures) 41

Beam collimation (cleaning) The very high stored energy, combined with a very low thresholds for quench requires a complex two-stage cleaning system: • • • Large amplitude protons are scattered by the primary collimator (closest to the beam). The scattered particles impact on the secondary collimators that should absorb them. The efficiency of the collimation must be larger than 99. 9% to be able to run under reasonable conditions, i. e. with lifetimes that can drop down to less than 1 hours from time to time… This requires settings tolerance of < 0. 1 mm. 60 collimators/beam! 42

Quench - transition from superconducting state to normalconducting state - Emergency discharge of energy Power Converter Discharge resistor Magnet 1 Magnet 2 Magnet 154 Magnet i To limit the temperature increase after a quench • The quench has to be detected : use voltage increase over coil • The energy is distributed in the magnet by force-quenching using quench heaters • The current in the quenched magnet decays is < 200 ms • The current of all other magnets flows through the bypass diode (triggered by the voltage increase over the magnet) that can stand the current for 100 -200 s. • The current of all other magnets is dischared inot the dump resistors 43

‘Unscheduled’ beam loss due to failures Two main classes for failures (with more subtle sub-classes): Passive protection Beam loss over a single turn • Avoid such failures (high reliability systems) during injection, beam dump or any other fast ‘kick’. • Rely on collimators and beam absorbers Active Protection Beam loss over multiple turns • Failure detection (from beam monitors due to many types of failures and / or equipment monitoring) • Fire Beam Dump In case of any failure or unacceptable beam lifetime, the beam must be dumped immediately, safely into the beam dump block 44

Requirements for a clean dump • Strength of kicker and septum magnets must match the beam energy: • Very safe beam measurement based on the current of the magnets ! • Dump kickers must be synchronized to the « Particle free gap » : • Accurate and reliable synchronization. • Abort gap must be free of particles: gap cleaning with damper. Large graphite absorbers in the beam dump area protect downstream elements (including dump septa themselves) against badly ‘kicked’ particles. 45

Powering superconducting magnets Water cooled copper cables Cryostat 2. 7 -4. 5 K Cryostat DFB HTS Current Leads Power Converter 46 46

Operational margin of a superconducting magnet Applied Field [T] Bc critical Bc field quench with fast loss of ~5× 106 protons ~ 0. 00001% total no. protons/beam 8. 3 T QUENCH quench with fast loss of ~5× 109 protons 0. 54 T 1. 9 K Temperature [K] Tc critical temperature Tc 9 K 47

Power into superconducting cable after a quench 48

Full LHC beam deflected into copper target 2808 bunches Copper target 2 m Energy density [Ge. V/cm 3] on target axis vaporisation melting The beam will drill a hole along the target axis … Target length [cm] N. Tahir (GSI) et al. 49

Powering superconducting magnets q The magnet is cooled down to 1. 9 K or 4. 5 K – Installed in a cryostat. q The magnet must be powered – Room temperature power converters supply the current. q The magnet must be connected – By superconducting cables inside the cryostat. – By normal conducting cables outside the cryostat. q The superconducting cables must be connected to normal conducting cables – Connection via current leads inside special cryostat (DFB) Cryostat DFB HTS Current Leads Power Converter 50 50

Powering from room temperature source… 6 k. A power converter Water cooled 13 k. A Copper cables ! Not superconducting ! 51 51

…to the cryostat Feedboxes (‘DFB’) : transition from Copper cable to super-conductor Cooled Cu cables 52 52

…to the cryostat Feedboxes (‘DFB’) : transition from Copper cable to super-conductor Cryostat DFB HTS Current Leads Power Converter 53 53 53

Comparison… The energy of an A 380 at 700 km/hour corresponds to the energy stored in the LHC magnet system : Sufficient to heat up and melt 12 tons of Copper!! The energy stored in one LHC beam corresponds approximately to… • 90 kg of TNT • 8 litres of gasoline • 15 kg of chocolate It’s how ease the energy is released that matters most !! 54 54

Schematic layout of beam dump system in IR 6 Septum magnet deflecting the extracted beam Beam 1 Q 5 L H-V kicker for painting the beam Beam Dump Block Q 4 L about 700 m 15 kicker magnets Q 4 R about 500 m Q 5 R Beam 2 55

Beam interlock system BIS Beam ‘Permit’ Dump kicker User permit signals Hardware links and systems Actors and signal exchange for the beam interlock system: • ‘User systems’ : systems that survey equipment or beam parameters and that are able to detect failures and send a HW signal to the beam interlock system. • Each user system provides a HW status signal, the user permit signal. • The beam interlock system combines the user permits and produces the beam permit. • The beam permit is a HW signal that is provided to the dump kicker (also injection or extraction kickers) : absence of beam permit dump triggered ! 56

Interlock systems of the LHC The LHC is protected by 2 distinct, but coupled interlock systems : • Powering interlock systems § Protection of the SC magnets. § Sectorized to allow independent operation of different cryostats & circuits. § Interface to power converters, quench protection, energy extraction and beam interlock system. § Millisecond reaction time. • Beam interlock system § Protection for the entire machine against beam incidents. § Interface to all parties involved in protection, including powering interlock systems and injectors (SPS). § Microsecond reaction times. 57

LHC cycle – charging the beam energy 7 Te. V injection phase 12 batches from the SPS (every 20 sec) one batch 216 / 288 bunches 450 Ge. V L. Bottura 58

Dump resistors Those large air-cooled resistors can absorb the 1 GJ stored in the dipole magnets (they heat up to few hundred degrees Celsius). 59 59

Machine protection systems Beam Current Monitors Current Safe LHC Parameters Energy DCCT Dipole Current 1 DCCT Dipole Current 2 RF turn clock Beam Energy Tracking Injection Kickers BPMs for Beam Dump NC Magnet Interlocks BPMs for dx/dt + dy/dt d. I/dt beam current d. I/dt magnet current RF + Damper LHC Experiments auxiliary circuits Vacuum System Screens Operators AUG UPS Collimators / Absorbers LHC Beam Interlock System essential circuits Powering Interlock System TL collimators BLMs arc Beam Dump Trigger Cryogenics SPS Extraction Interlocks BLMs aperture Discharge Switches Power Converters Safe. Beam Flag Beam Dumping System Access Safety System Quench Protection Energy Timing Software Interlocks

Machine Protection Systems and (HW) Interfaces Beam Current Monitors Current Safe LHC Parameters Energy DCCT Dipole Current 1 DCCT Dipole Current 2 RF turn clock Beam Energy Tracking Injection Kickers Powering Interlock System Collimators / Absorbers BPMs for Beam Dump LHC Beam Interlock System NC Magnet Interlocks BPMs for dx/dt + dy/dt d. I/dt beam current d. I/dt magnet current essential circuits Screens auxiliary circuits RF + Damper LHC Experiments Vacuum System Operators Software Interlocks AUG UPS TL collimators BLMs arc Beam Dump Trigger Cryogenics SPS Extraction Interlocks BLMs aperture Discharge Switches Power Converters Safe. Beam Flag Beam Dumping System Access Safety System Quench Protection Energy Timing PM Trigger 61

Powering superconducting magnets q The magnet is cooled down to 1. 9 K or 4. 5 K – Installed in a cryostat. q The magnet must be powered – Room temperature power converters supply the current. q The magnet must be connected – By superconducting cables inside the cryostat. – By normal conducting cables outside the cryostat. q The superconducting cables must be connected to normal conducting cables – Connection via current leads inside special cryostat (DFB) Cryostat DFB HTS Current Leads Power Converter 62 62

Powering superconducting magnets Water cooled copper cables Cryostat DFB HTS Current Leads 6 k. A power converter Power Converter 63 63

Outline • Energy stored in the LHC magnets • • Protecting Against Damage • • LHC Beam Energy What is a “Safe Beam”? Injection into an empty machine Protecting Against Damage • • • Quench Protection Energy stored in the LHC beams • • LHC Dipole Magnets Magnet Powering LHC Magnetic Cycle Beam Dumps / Absorbers and Collimation Interlock Systems and Active Protection Summary 64

Outline • Energy stored in the LHC magnets • • Protecting Against Damage • • LHC Beam Energy What is a “Safe Beam”? Injection into an empty machine Protecting Against Damage • • • Quench Protection Energy stored in the LHC beams • • LHC Dipole Magnets Magnet Powering LHC Magnetic Cycle Beam Dumps / Absorbers and Collimation Interlock Systems and Active Protection Summary 65

Outline • Energy stored in the LHC magnets • • Protecting Against Damage • • LHC Beam Energy What is a “Safe Beam”? Injection into an empty machine Protecting Against Damage • • • Quench Protection Energy stored in the LHC beams • • LHC Dipole Magnets Magnet Powering LHC Magnetic Cycle Beam Dumps / Absorbers and Collimation Interlock Systems and Active Protection Summary 66

Outline • Energy stored in the LHC magnets • • Protecting Against Damage • • LHC Beam Energy What is a “Safe Beam”? Injection into an empty machine Protecting Against Damage • • • Quench Protection Energy stored in the LHC beams • • LHC Dipole Magnets Magnet Powering LHC Magnetic Cycle Beam Dumps / Absorbers and Collimation Interlock Systems and Active Protection Summary 67

Outline • Energy stored in the LHC magnets • • Protecting Against Damage • • LHC Beam Energy What is a “Safe Beam”? Injection into an empty machine Protecting Against Damage • • • Quench Protection Energy stored in the LHC beams • • LHC Dipole Magnets Magnet Powering LHC Magnetic Cycle Beam Dumps / Absorbers and Collimation Interlock Systems and Active Protection Summary 68

Beam loss into material • • • Proton losses lead to particle cascades in materials The energy deposition leads to a temperature increase The temperature increase may lead to damage : melting, vaporisation, pressure waves… Magnets could quench…. . • beam lost - re-establish condition will take hours The material could be damaged…. . • melting • losing performance (mechanical strength) Repair could take several weeks or years ! From SPS we (OP) know by experience that ~ 1013 protons at 450 Ge. V (1 MJ) we can damage equipment ! 69

Beam induced damage : SPS experiment Beam 25 cm Controlled experiment: • • Special target installed in the TT 40 transfer line Impact of 450 Ge. V LHC beam (beam size σx/y = 1. 1 mm/0. 6 mm) 70

Energy stored in LHC magnets Approximation: energy is proportional to volume inside magnet aperture and to the square of the magnet field about 5 MJ per magnet Accurate calculation with the magnet inductance: E dipole = 0. 5 L dipole I 2 dipole Energy stored in one dipole is 7. 6 MJoule For all 1232 dipoles in the LHC: 9. 4 GJ 71