Rüdiger Schmidt1 The LHC collider project II Rüdiger Schmidt - CERN SUSSP Sumer School St.Andrews Challenges LHC accelerator physics LHC technology Operation and protection

Rüdiger Schmidt2 summarising constraints and consequences…. Centre-of-mass energy must well exceed 1 TeV, LHC installed into LEP tunnel: l Colliding protons, and also heavy ions l Magnetic field of 8.3 T with superconducting magnets l Large amount of energy stored in magnets Luminosity of : l Need for “two accelerators” in one tunnel with beam parameters pushed to the extreme – with opposite magnetic dipole field l Large amount of energy stored in beams Economical constraints and limited space: l Two-in-one superconducting magnets

l Accelerator Physics: An Introduction Why protons? Why in the LEP tunnel? Why superconducting magnets? Why “two” accelerators in one tunnel? l LHC Layout l The quest for high luminosity and the consequences l Beam-Beam interaction l Crossing angle and insertion layout l Wrapping up: LHC Parameters l The CERN accelerator complex: injectors and transfer l LHC technology l LHC operation and machine protection l Conclusions Outline

Rüdiger Schmidt4 Getting beam into the LHC Beam size of protons decreases with energy:  2 = 1 / E l Beam size large at injection l Beam fills vacuum chamber at 450 GeV If the energy would be lower... l larger vacuum chamber and larger magnets – increased cost l magnets and power converter limitations (dynamic effects, stability, …) l issues of beam stability Injection from the SPS at 450 GeV, via two transfer lines, into the LHC

Rüdiger Schmidt5 LHC injector complex - pre-accelerators exist

Rüdiger Schmidt6 Injector Complex l Pre-injectors: Linac, PS Booster and Proton Synchrotron deliver protons at 26 GeV to the SPS l The SPS accelerates protons from 26 GeV to 450 GeV l Both, the pre-injectors and the SPS were upgraded for the operation with nominal LHC beam parameters l Already today, beams are available close to the nominal beam parameters required for the LHC

Transfer Lines SPS - LHC Two new transfer line tunnels from SPS to LHC are being built. The beam lines use normal conducting magnets. Length of each line: about 2.8 km Magnets are all available, made by BINP / Novosibirsk Commissioning of the first line for 2004 Dipole magnets waiting for installation

Rüdiger Schmidt8 LHC accelerator in the tunnel

Rüdiger Schmidt9 LHC Technology …in particular superconducting dipole magnets LHC Technology …in particular superconducting dipole magnets Challenges: Superconducting magnets Cryogenics Vacuum system Powering (industrial use of High Temperature Superconducting material)

Rüdiger Schmidt main dipoles multipole corrector magnets 392 main quadrupoles corrector magnets Regular arc: Magnets

Rüdiger Schmidt11 Regular arc: Cryogenics Supply and recovery of helium with 26 km long cryogenic distribution line Static bath of superfluid helium at 1.9 K in cooling loops of 110 m length Connection via service module and jumper

Rüdiger Schmidt12 Insulation vacuum for the cryogenic distribution line Regular arc: Vacuum Insulation vacuum for the magnet cryostats Beam vacuum for Beam 1 + Beam 2

Rüdiger Schmidt13 Regular arc: Electronics Along the arc about several thousand electronic crates (radiation tolerant) for: quench protection, power converters for orbit correctors and instrumentation (beam, vacuum + cryogenics)

Rüdiger Schmidt Dipolmagnets Length about 15 m Magnetic Field 8.3 T Two beamtubes with an opening of 56 mm Dipole magnets for the LHC

Coils for Dipolmagnets

Rüdiger Schmidt16 Dipole field – approximate cosine teta current distribution In practice the above current distributions are approximated by real conductors, so the field contains also higher order harmonics (see later). Intersecting ellipses generate uniform field. Two intersecting ellipses, rotated of 90 , generate a perfect quadrupole fields:. Such configuration follows: J s = J  cos(  )

Rüdiger Schmidt17 Superconducting cable for 12 kA 15 mm / 2 mm Temperature 1.9 K cooled with Helium Force on the cable: F = B * I0 * L with B = 8.33 T I0 = Ampere L = 15 m F = 165 tons 56 mm

Rüdiger Schmidt18

Rüdiger Schmidt19 Two - in One Magnet

Rüdiger Schmidt20 Beam tubes Supraconducting coil Nonmagetic collars Ferromagnetic iron Steelcylinder for Helium Insulationvacuum Supports Vacuumtank

The Dipolmagnet in a cryostat

Rüdiger Schmidt22 Discovery of superconductivity Kamerlingh Onnes liqufies Helium R-T for Mercury ? "…. Mercury has passed into a new state, which on account of its extraordinary electrical properties may be called the superconductive state …." Copyright A.Verweij

Rüdiger Schmidt23 Magnetic field - current density - temperature Superconducting material determines: Tc critical temperature Bc critical field Production process: Jc critical current density Bc Tc Lower temperature  increased current density Typical for NbTi: K, 6T Für 10 T, Operation less than 1.9 K required Copyright A.Verweij

Rüdiger Schmidt24 Typical Supraconductors The high critical field of supraconductor type II allows the construction of high field magnets – commerically available supraconducting wires Niobium-Titan (NbTi) Charactersisation of superconductors: Temperature Magnetic Field Current density Copyright A.Verweij

Rüdiger Schmidt25 Helium: Phasediagram T>T : He I T<T : He II (superfluid Helium) T =2.17 K LHC: T=1.9 K P  1.2 bar Copyright A.Verweij

Rüdiger Schmidt26 Helium Parameter T Specific heat of Helium as function of T Phasetransition at 2.18 Kelvin Superfluid Helium (He II) Copyright A.Verweij

Rüdiger Schmidt27 Supraconducting wire  1 mm  6  m Typical value for operation at 8 T and 1.9 K: 800 A Copyright A.Verweij Rutherford cable width 15 mm

Rüdiger Schmidt28 Fabrication of superconducting dipoles Dipole assembly in industry

Rüdiger Schmidt29 Snapshot at industry L.Rossi

Rüdiger Schmidt30 Cryostating and measurements (main dipoles and other magnets) SMA18 cryostating hall at CERN for installing dipole magnets into cryostats SM18: 12 measurement stations are prepared for cold tests of possibly all superconducting magnets

31 Challenges for dipole production l The magnets must reach without quenching a field of at least 8.3 Tesla, and possibly 9 Tesla l The field quality must be excellent (relative field errors much less than 0.1 %, positioning of collars to some 10  m) l The geometry must be respected – and the magnet must be correctly bent l All magnets must be produced in time, delivered to CERN, installed in the cryostats, cold tested, and finally installed into the LHC tunnel

Rüdiger Schmidt32 LHC Progress Dashboard - on the WEB

Rüdiger Schmidt33 Operation and machine protection

34 Outline l Energy stored in the LHC magnets and beams l Charging the energy l LHC dipole magnets - discharging the energy irregular discharge - magnet quenches l LHC Beams - discharging the energy regular and irregular discharge l Magnets facing Beams l Strategy for Protection of the LHC machine

Rüdiger Schmidt35 Energy stored in LHC magnets Approximation: energy is proportional to volume inside magnet aperture and to the square of the magnet field l 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

Rüdiger Schmidt36 What does this mean? 10 GJoule…… l corresponds to the energy of 1900 kg TNT l corresponds to the energy of 400 kg Chocolate l corresponds to the energy for heating and melting kg of copper l corresponds to the energy produced by of one nuclear power plant during about 10 seconds Could this damage equipment: How fast can this energy be released?

37 Outline l Energy stored in the LHC magnets and beams l Charging the energy l LHC dipole magnets - discharging the energy irregular discharge - magnet quenches l LHC Beams - discharging the energy regular and irregular discharge l Magnets facing Beams l Strategy for Protection of the LHC machine

Rüdiger Schmidt38 energy ramp preparation and access beam dump injection phase coast LHC magnetic cycle L.Bottura 450 GeV 7 TeV start of the ramp

Rüdiger Schmidt39 injection phase 12 batches from the SPS (every 20 sec) one batch 216 / 288 bunches LHC magnetic cycle - Beam injection L.Bottura 450 GeV 7 TeV

Rüdiger Schmidt40 Sector 1 5 DC Power feed 3 DC Power LHC 27 km Circumference LHC Powering in 8 Sectors Powering Subsectors allow for progressive Hardware Commissioning - starting two years before beam P.Proudlock Powering Sector Powering Subsectors: triplet cryostats cryostats in matching section long arc cryostats

Rüdiger Schmidt41 Ramping the current in a string of dipole magnet Magnet 1Magnet 2 Power Converter Magnet 154Magnet i l LHC powered in eight sectors, each with 154 dipole magnets l Time for the energy ramp is about min (Energy from the grid) l Time for discharge is about the same (Energy back to the grid)

42 Outline l Energy stored in the LHC magnets and beams l Charging the energy l LHC dipole magnets - discharging the energy irregular discharge - magnet quenches l LHC Beams - discharging the energy regular and irregular discharge l Magnets facing Beams l Strategy for Protection of the LHC machine

Rüdiger Schmidt43 Operational margin of a superconducting magnet Bc Tc 9 K Applied Magnetic Field [T] Bc critical field 1.9 K quench with fast loss of ~5 · 10 9 protons quench with fast loss of ~5 · 10 6 protons 8.3 T 0.54 T QUENCH Tc critical temperature

Rüdiger Schmidt44 Power into superconducting cable after a quench

Rüdiger Schmidt45 Quench - transition from superconducting state to normalconducting state Quenches are initiated by an energy in the order of mJ (corresponds to the energy of 1000 protons at 7 TeV) l Movement of the superconductor by several  m (friction and heat dissipation) l Beam losses l Failure in cooling To limit the temperature increase after a quench l The quench has to be detected l The energy is distributed in the magnet by force-quenching the coils using quench heaters l The magnet current has to be switched off within << 1 second

Gaussian approximation Current after quench Current in a dipole magnets after a quench, when heaters are fired (7 TeV) - 7 MJ within 200 ms into magnet

Rüdiger Schmidt47 Quench - Emergency discharge of energy … Magnet 1Magnet 2 HTS leads 1HTS leads 2 Power Converter Magnet 154Magnet i l assume one magnet quenches l assume the magnets in the string have to be discharged in, say, 200 ms Discharge with about 1 MV: not possible

Rüdiger Schmidt48 …..and how it being done in the LHC Magnet 1Magnet 2 Power Converter Magnet 154 Magnet i l when one magnet quenches, quench heaters are fired for this magnet l the current in the quenched magnet decays in about 200 ms l the current in all other magnets flows through the bypass diode that can stand the current for about seconds

Bypass Diode … l installed in 1.9 K system (not accessible) l needs to carry 12 kA during the exponential discharge for about 150 seconds l needs to be radiation tolerant l need to be very reliable (all diodes tested at cold before installation) l one diode for each dipole magnet l two diodes for each arc quadrupole magnets F.Rodriguez-Mateos, D.Hagedorn

F.Rodriguez-Mateos, K.Dahlerup-Petersen Energy extraction system in LHC tunnel Resistors absorbing the energy Switches - for switching the resistors into series with the magnets

51 Outline l Energy stored in the LHC magnets and beams l Charging the energy l LHC dipole magnets - discharging the energy irregular discharge - magnet quenches l LHC Beams - discharging the energy regular and irregular discharge l Magnets facing Beams l Strategy for Protection of the LHC machine

Rüdiger Schmidt52 Regular (very healthy) operation Assuming that the beams are colliding at 7 TeV Single beam lifetime larger than 100 hours….. corresponds to a loss of about 1 kW / beam far below the cooling power of the cryogenic system, even if all particles would be lost at 1.9 K losses should be either distributed across the machine or captured in the warm cleaning insertions Collision of beams with a luminosity of cm -2 s -1 lifetime of the beam can be be dominated by collisions 10 9 protons / second lost per beam / per experiment (in IR 1 and IR 5 - high luminosity insertions) - this is about 1.2 kW large heat load to close-by superconducting quadrupoles heavy shielding around the high luminosity IPs

Rüdiger Schmidt53 Regular operation: some challenges High radiation environment close to interaction point Moderate radiation load in the arcs (in the order of 1 Gy / year) Even less radiation dose in tunnel enlargements (about factor of 10 less compared to the tunnel - to be reviewed) A large fraction of the electronics for quench protection, beam monitoring, vacuum monitoring, cryogenics and powering is located in areas with some radiation Single Event Upsets (for example bit flips by radiation) introduce failures of the electronics Development and qualification of radiation tolerant electronics since several years in many groups

Rüdiger Schmidt54 End of data taking in normal operation l Luminosity lifetime estimated to be approximately 10 h (after 10 hours only 1/3 of initial luminosity) l Beam current somewhat reduced - but not much l Energy per beam still about MJ l Beams are extracted in beam dump blocks l The only component that can stand a fast loss of the full beam at top energy is the beam dump block - all other components would be damaged l At 7 TeV, fast beam losses with an intensity of about 5% of a “nominal bunch” could damage superconducting coils

Rüdiger Schmidt55 LHC ring: 3 insertions for machine protection systems Beam Cleaning IR3 (Momentum) Beam Cleaning IR7 (Betatron) Beam dump system IR6 RF+ Beam monitors IR4

Rüdiger Schmidt56 Beam losses into material l Proton losses lead to particle cascades in materials l The energy deposition leads to a temperature increase l For the maximum energy deposition as a function of material there is no straightforward expression l Programs such as FLUKA are being used for the calculation of the energy deposition Magnets could quench….. beam lost - re-establish condition will take hours The material could be damaged….. melting losing their performance (mechanical strength) Repair could take several weeks

Rüdiger Schmidt57 Damage of material for impact of a pencil beam copper graphite

Rüdiger Schmidt58 Schematic layout of beam dump system in IR6 Q5R Q4R Q4L Q5L Beam 2 Beam 1 Beam Dump Block Septum magnet deflecting the extracted beam H-V kicker for painting the beam about 700 m AB - Beam Transfer Group about 500 m Fast kicker magnet

Rüdiger Schmidt59 Beam Dump Block - Layout about 8 m L.Bruno concrete shielding beam absorber (graphite)

Rüdiger Schmidt60 Beam on Beam Dump Block about 35 cm M.Gyr initial transverse beam dimension in the LHC about 1 mm beam is blown up due to long distance to beam dump block additional blow up due to fast dilution kickers: painting of beam on beam dump block beam impact within less than 0.1 ms

Rüdiger Schmidt61 L.Bruno: Thermo-Mechanical Analysis with ANSYS Temperature of beam dump block at 80 cm inside up to 800 C

Rüdiger Schmidt62 L.Bruno: Thermo-Mechanical Analysis with ANSYS Hydrostatic stress after beam deposition

Rüdiger Schmidt63 Beam dump must be synchronised with particle free gap Strength of kicker and septum magnets must match energy of the beam « Particle free gap » must be free of particles Requirement for clean beam dump

64 Outline l Energy stored in the LHC magnets and beams l Charging the energy l LHC dipole magnets - discharging the energy irregular discharge - magnet quenches l LHC Beams - discharging the energy regular and irregular discharge l Magnets facing Beams l Strategy for Protection of the LHC machine

Lifetime of the beam with nominal intensity at 7 TeV Beam lifetime Beam power into equipment (1 beam) Comments 100 h1 kWHealthy operation 10 h10 kWOperation acceptable, collimation must absorb large fraction of beam energy (approximately beam losses = cryogenic cooling power at 1.9 K) 0.2 h500 kWOperation only possibly for short time, collimators must be very efficient 1 min6 MWEquipment or operation failure - operation not possible - beam must be dumped << 1 min> 6 MWBeam must be dumped VERY FAST Failures will be a part of the regular operation and MUST be anticipated

Rüdiger Schmidt  ~5 mm Beam +/- 3 sigma 56.0 mm Beam in vacuum chamber with beam screen at 450 GeV

Rüdiger Schmidt  ~1.3 mm Beam +/- 3 sigma 56.0 mm Beam in vacuum chamber with beam screen at 7 TeV

Rüdiger Schmidt68 Beam+/- 3 sigma 56.0 mm 1 mm +/- 8 sigma = 4.0 mm Example: Setting of collimators at 7 TeV - with luminosity optics Beam must always touch collimators first ! R.Assmanns EURO Collimators at 7 TeV, squeezed optics

Rüdiger Schmidt69 Jaws (blocks of solid materials such as copper, graphite, ….) very close to the beam to absorb more than 99.9 % of protons that would be lost Primary collimators:Intercept primary halo Impact parameter: ~ 1  m Scatter protons of primary halo Convert primary halo to secondary off-momentum halo Secondary collimators:Intercept secondary halo Impact parameter: ~ 200  m Absorb most protons Leak a small tertiary halo Particles Beam axis Impact parameter Collimator jaw Basic concept of two stage collimation R.Assmann / J.B.Jeanneret

Rüdiger Schmidt70 Accidental kick by the beam dump kicker at 7 TeV part of beam touches collimators (about 20 bunches from 2800) P.Sievers / A.Ferrari / V.Vlachoudis circulating beam

Rüdiger Schmidt71 Accidental kick by the beam dump kicker at 7 TeV part of beam touches collimators (about 20 bunches from 2800) P.Sievers / A.Ferrari / V. Vlachoudis Beryllium

Rüdiger Schmidt72 Half gap b [m] LHC impedance without collimators Typical collimator half gap at 7 TeV: 1.5 mm F.Ruggiero, L.Vos Impedance for different materials as a function of collimator half gap

Rüdiger Schmidt73 Optimisation of Cleaning system l Requirements for collimation system take into account failure scenarios and imperfect operation Worst case is the impact of about 20 bunches on the collimator due to pre-firing of one dump kicker module l Material for collimator is being reconsidered - low Z material is favoured l Impedance to be considered - conducting material is favoured l more exotic materials are considered: copper loaded graphite, beryllium, partially plated copper ….

74 Outline l Energy stored in the LHC magnets and beams l Charging the energy l LHC dipole magnets - discharging the energy irregular discharge - magnet quenches l LHC Beams - discharging the energy regular and irregular discharge l Magnets facing Beams l Strategy for Protection of the LHC machine

Multiple turn beam loss due to many types of failures Passive protection l Avoid such failures (high reliability systems - work is ongoing to better estimate reliability) l Rely on collimators and beam absorbers Active Protection l Failure detection (from beam monitors and / or equipment monitoring) l Issue beam abort signal l Fire Beam Dump Single turn beam loss during injection and beam dump In case of any failure or unacceptable beam lifetime, the beam must be dumped immediately, safely into the beam dump block

Rüdiger Schmidt76 Beam Loss Monitors Primary strategy for protection: Beam loss monitors at collimators and other aperture limitations continuously measure beam losses l Beam loss monitors indicate increased losses => MUST BE FAST When beam losses exceed threshold: l Beam loss monitors break Beam Permit Loop l Beam dump sees “No Beam Permit” => dump beams

Rüdiger Schmidt77 B.Dehning Dynamic Range of 10 8 Beam loss monitors: quench levels as function of loss duration BLMCs at aperture limitations and Collimator ms BLMAs in arcs 2.5 ms 450 GeV 7 GeV

Rüdiger Schmidt78 Beam loss monitors: Ideas for realisation ionisation chamber gas N 2 normal pressure 800 to 1800 V # of electron / ion pairs: MIP / cm Current to frequency converter first stage (input cable length up to 400 m) dynamics about 10 7 input current: 30 pA to 50 mA output frequency: 0.05 Hz to several MHz second stage (optical fibre length up 1.5 km) every channel with micro controller (FPGA) several mean loss values in parallel energy tracking chamber B.Dehning

Rüdiger Schmidt79 Architecture of the BEAM INTERLOCK SYSTEM

Rüdiger Schmidt80 Electron Cloud

Rüdiger Schmidt81 Electron cloud: bunch train coming in T = t 0 proton emits a photon (synchrotron radiation)

Rüdiger Schmidt82 Electron cloud: photon creates electron T = t 1 photon hits vacuum chamber and creates electron

Rüdiger Schmidt83 Electron cloud: more secondary electrons T = t 2 electron accelerated by the potential of the next bunch, then hits vacuum chamber, and generates more electrons

Rüdiger Schmidt84 Electron cloud: many bunches to come... T = t 3 electrons accelerated by the potential of the next bunch, hit vacuum chamber, and generates more electrons

Rüdiger Schmidt85 Effects from the electron cloud l Several nasty effects Vacuum degradation Heat load in cryogenics system Beam instability l Has been obseved at several accelerators with intense bunch trains B-factories SPS as injector for LHC l Depends on many parameters Bunch distance and intensity Surface of vacuum chamber (cleanliness, coefficient for desorption) l Cures Special surface materials for vacuum chamber Avoid too close bunch distance (LHC: 75 ns should be ok) “Beam Scrubbing” to clean surfaces

Rüdiger Schmidt86 LHC: From today to colliding beams Spring: Start of installation of general services (electricity, ventilation,....) 2003 – July: Start of installation of the cryogenic distribution line 2004 – Spring: Start of magnet installation 2005: Hardware commissioning of first LHC sector 2006: First beam test – injection from SPS through 1/8 of the LHC (to be confirmed soon) 2007: Finish installation and hardware commissioning 2007 : Commissioning with two beams and first proton proton collision

From the summary of the Large Hadron Collider Machine Advisory Committee in March 2002 l The LHC is a global project with the world-wide high- energy physics community devoted to its progress and results l As a project, it is much more complex and diversified than the SPS or LEP or any other large accelerator project constructed to date The Status and the complexity of the LHC is documented in more than 80 papers at this conference (EPAC 2002) - this talk is considered as a very brief overview Machine Advisory Committee, chaired by Prof. M. Tigner, March 2002

Rüdiger Schmidt88 Acknowledgement The LHC accelerator is being realised by CERN in collaboration with institutes from many countries over a period of more than 20 years Main contribution come from the USA, Russia, India, Canada, special contributions from France and Switzerland Industry plays a major role in the construction of the LHC Thanks for the material from: R.Assmann, L.Bottura, L.Bruno, R.Denz, A.Ferrari, B.Goddard, M.Gyr, D.Hagedorn, J.B.Jeanneret, P.Proudlock, B.Puccio, F.Rodriguez-Mateos, F.Ruggiero, L.Rossi, S.Russenschuck, P.Sievers, G.Stevenson, A.Verweij, V.Vlachoudis, L.Vos

Rüdiger Schmidt89 …….and thanks to the organisers of SUSSP for inviting me giving this presentation

Rüdiger Schmidt90 Some references (...more in write-up) Accelerator physics l Proceedings of CERN ACCELERATOR SCHOOL (CAS), In particular: 5th General CERN Accelerator School, CERN 94-01, 26 January 1994, 2 Volumes, edited by S.Turner Superconducting magnets / cryogenics l Superconducting Accelerator Magnets, K.H.Mess, P.Schmüser, S.Wolff, World Scientific 1996 l Superconducting Magnets, M.Wilson, Oxford Press l Superconducting Magnets for Accelerators and Detectors, L.Rossi, CERN-AT MAS (2003) LHC l Technological challenges for the LHC, CERN Academic Training, 5 Lectures, March 2003 (CERN WEB site) l Beam Physics at LHC, L.Evans, CERN-LHC Project Report 635, 2003 l Status of LHC, R.Schmidt, CERN-LHC Project Report 569, 2003 l...collimation system.., R.Assmann et al., CERN-LHC Project Report 640, 2003 l LHC Design Report 1995 l LHC Design Report in preparation