1. CAS October 2013 R.Schmidt ● Accidental and continuous beam losses ● Protection of the accelerator from beam losses Machine Protection Rüdiger Schmidt, CERN and ESS CAS Accelerator School October 2013 - Trondheim

2. CAS October 2013 R.Schmidt

3. CERN Rüdiger Schmidt CAS Trondheim 2013page 3 Protection from Energy and Power ● Risks come from Energy stored in a system (Joule), and Power when operating a system (Watt) “Very powerful accelerator” … the power flow needs to be controlled ● An uncontrolled release of the energy, or an uncontrolled power flow can lead to unwanted consequences Damage of equipment and loss of time for operation For particle beams, activation of equipment ● This is true for all systems, in particular for complex systems such as accelerators For the RF system, power converters, magnet system … For particle beams This lecture on Machine Protection is focused on preventing damage caused by particle beams

4. CERN Rüdiger Schmidt CAS Trondheim 2013page 4 Content ● Different accelerator concepts: Examples for ESS and LHC ● Hazards and Risks ● Accidental (uncontrolled) beam losses and consequences ● Accidental (uncontrolled) beam and probability ● Machine Protection Systems For high energy proton synchrotrons (LHC) For high power accelerators (ESS) ● Some principles for protection systems

5. CERN Rüdiger Schmidt CAS Trondheim 2013page 5 LHC pp and ions 7 TeV/c – up to now 4 TeV/c 26.8 km circumference Energy stored in one beam 362 MJ Switzerland Lake Geneva LHC Accelerator (100 m down) SPS Accelerator CMS, TOTEM ALICELHCbATLAS CERN Proton collider LHC – 362 MJ stored in one beam

6. CERN Rüdiger Schmidt CAS Trondheim 2013page 6 LHC pp and ions 7 TeV/c – up to now 4 TeV/c 26.8 km Circumference Energy stored in one beam 362 MJ Switzerland Lake Geneva LHC Accelerator (100 m down) SPS Accelerator CMS, TOTEM ALICELHCbATLAS CERN Proton collider LHC – 362 MJ stored in one beam If something goes wrong, the beam energy has to be safely deposited

7. CERN Rüdiger Schmidt CAS Trondheim 2013page 7 ESS Lund / Sweden – 5 MW beam power Power of 5000 kW Drift tube linac with 4 tanks Low energy beam transport Medium energy beam transport Super-conducting cavities High energy beam transport Operating with protons Operation with beam pulses at a frequency of 14 Hz Pulse length of 2.86 ms Average power of 5 MW Peak power of 125 MW RFQ 352.2 MHz 75 keV 3 MeV 78 MeV200 MeV628 MeV2500 MeV Source LEBT RFQ MEBT DTL Spokes High β Medium β HEBT & Upgrade Target 2.4 m4.0 m 3.6 m32.4 m 58.5 m 113.9 m 227.9 m 352.21 MHz704.42 MHz As an example for a high intensity linear accelerator (similar to SNS and J-PARC) ~ 500 m

8. CERN Rüdiger Schmidt CAS Trondheim 2013page 8 Power of 5000 kW Drift tube linac with 4 tanks Low energy beam transport Medium energy beam transport Super-conducting cavities High energy beam transport Operating with protons Operation with beam pulses at a frequency of 14 Hz Pulse length of 2.86 ms Average power of 5 MW Peak power of 125 MW RFQ 352.2 MHz 75 keV 3 MeV 78 MeV200 MeV628 MeV2500 MeV Source LEBT RFQ MEBT DTL Spokes High β Medium β HEBT & Upgrade Target 2.4 m4.0 m 3.6 m32.4 m 58.5 m 113.9 m 227.9 m 352.21 MHz704.42 MHz As an example for a high intensity linear accelerator (similar to SNS and J-PARC) ~ 500 m ESS Lund / Sweden – 5 MW beam power If something goes wrong, injection has to be stopped

9. CERN Rüdiger Schmidt CAS Trondheim 2013page 9 Energy stored in beam and magnet system Factor ~200

10. CERN Rüdiger Schmidt CAS Trondheim 2013page 10 What does it mean ……… MJoule ? 360 MJ: the energy stored in one LHC beam corresponds approximately to… 90 kg of TNT 8 litres of gasoline 15 kg of chocolate It matters most how easy and fast the energy is released !! The energy of an 200 m long fast train at 155 km/hour corresponds to the energy of 360 MJ stored in one LHC beam. 860 litres H 2 O from 0 0 C to 100 0 C

11. CERN Rüdiger Schmidt CAS Trondheim 2013page 11 Consequences of a release of 600 MJ at LHC Arcing in the interconnection 53 magnets had to be repaired The 2008 LHC accident happened during test runs without beam. A magnet interconnect was defect and the circuit opened. An electrical arc provoked a He pressure wave damaging ~600 m of LHC, polluting the beam vacuum over more than 2 km. Over-pressure Magnet displacement

12. CERN Rüdiger Schmidt CAS Trondheim 2013page 12 Energy and Power density Many accelerators operate with high beam intensity and/or energy ● For synchrotrons and storage rings, the energy stored in the beam increased with time (from ISR to LHC) ● For linear accelerators and fast cycling machines, the beam power increases The emittance becomes smaller (down to a beam size of nanometer) ● This is important today, and even more relevant for future projects, with increased beam power / energy density (W/mm 2 or J/mm 2 ) and increasingly complex machines Even a small amount of energy can lead to some (limited) damage ● Can be an issue for sensitive equipment

13. CERN Rüdiger Schmidt CAS Trondheim 2013page 13 Hazards and Risks

14. CERN Rüdiger Schmidt CAS Trondheim 2013page 14 Hazard and Risk for accelerators ● Hazard: a situation that poses a level of threat to the accelerator. Hazards are dormant or potential, with only a theoretical risk of damage. Once a hazard becomes "active“: incident / accident. Consequences and possibility of an incident interact together to create RISK, can be quantified: RISK = Consequences ∙ Probability Related to accelerators ● Consequences of an uncontrolled beam loss ● Probability of an uncontrolled beam loss ● The higher the RISK, the more Protection is required

15. CERN Rüdiger Schmidt CAS Trondheim 2013page 15 Example for ESS ● Bending magnet in an accelerator deflecting the beam ● Assume that the power supply for the bend in HEBT-S2 fails and the magnets stops deflecting the beam Probability: MTBF for power supply is 100000 hours = 15 years ● The beam is not deflected and hits the vacuum chamber Consequences: what is expected to happen? Damage of magnet, vacuum pipe, possibly pollution of superconducting cavities ● Detect failure and stop beam 5 MW Beam ~ 160 m following the sc cavities HEBT-S2

16. CERN Rüdiger Schmidt CAS Trondheim 2013page 16 Example for LHC: SPS, transfer line and LHC 1 km Beam is accelerated in SPS to 450 GeV (288 bunches, stored energy of 3 MJ) Beam is transferred from SPS to LHC Beam is accelerated in LHC to high energy (stored energy of 362 MJ) Transfer line 3 km LHC SPS 6911 m 450 GeV 3 MJ transfer to LHC IR8 Fast extraction kicker Injection kicker Transfer line Injection kicker IR2 Fast extraction kicker

17. CERN Rüdiger Schmidt CAS Trondheim 2013page 17 Protection at injection LHC circulating beam Circulating beam in LHC LHC vacuum chamber Transfer line vacuum chamber

18. CERN Rüdiger Schmidt CAS Trondheim 2013page 18 LHC circulating beam Beam injected from SPS and transfer line Protection at injection Beam from SPS Injection Kicker LHC injected beam

19. CERN Rüdiger Schmidt CAS Trondheim 2013page 19 LHC circulating beam Kicker failure (no kick) Protection at injection Beam from SPS Injection Kicker Major damage to sc magnets, vacuum pipes, possibly LHCb / Alice experiments

20. CERN Rüdiger Schmidt CAS Trondheim 2013page 20 LHC circulating beam Beam absorbers take beam in case of kicker misfiring Transfer line collimators ensure that incoming beam trajectory is ok Protection at injection Beam from SPS Injection Kicker Set of transfer line collimators (TCDI) ~5σ Injection absorber (TDI) ~7σ phase advance 90 0

21. CERN Rüdiger Schmidt CAS Trondheim 2013page 21 LHC circulating beam Beam absorbers take beam in case of kicker misfiring on circulating beam Protection at injection Injection Kicker Injection absorber (TDI) ~7σ Circulating beam – kicked out phase advance 90 0 LHC circulating beam Set of transfer line collimators (TCDI) ~5σ This type of kicker failure happened several times: protection worked

22. CERN Rüdiger Schmidt CAS Trondheim 2013page 22 (Accidental) beam loss and consequences

23. CERN Rüdiger Schmidt CAS Trondheim 2013page 23 Beam losses and consequences ● Charged particles moving through matter interact with the electrons of atoms in the material, exciting or ionizing the atoms => energy loss of traveling particle described by Bethe-Bloch formula. ● If the particle energy is high enough, particle losses lead to particle cascades in materials, increasing the deposited energy the maximum energy deposition can be deep in the material at the maximum of the hadron / electromagnetic shower ● The energy deposition leads to a temperature increase material can vaporise, melt, deform or lose its mechanical properties risk to damage sensitive equipment for less than one kJ, risk for damage of any structure for some MJ (depends on beam size) superconducting magnets could quench (beam loss of ~mJ to J) superconducting cavities performance degradation by some 10 J activation of material, risk for hand-on-maintenance

24. CERN Rüdiger Schmidt CAS Trondheim 2013page 24 Energy loss: example for one proton in iron (stainless steel, copper very similar) Low energy few MeV, beam transport, RFQ for many machines SNS - ESS 1 – 3 GeV LHC 7 TeV From Bethe- Bloch formula.

25. CERN Rüdiger Schmidt CAS Trondheim 2013page 25 Beam losses and consequences

26. CERN Rüdiger Schmidt CAS Trondheim 2013page 26 Heating of material with low energy protons (3 MeV)

27. CERN Rüdiger Schmidt CAS Trondheim 2013page 27 Heating of material with high energy protons (> GeV) Nuclear inelastic interactions (hadronic shower) Creation of pions when going through matter Causes electromagnetic shower through decays of pions Exponential increase in number of created particles Final energy deposition to large fraction done by large number of electromagnetic particles Scales roughly with total energy of incident particle Energy deposition maximum deep in the material Energy deposition is a function of the particle type, its momentum and parameters of the material (atomic number, density, specific heat) No straightforward expression to calculate energy deposition Calculation by codes, such as FLUKA, GEANT or MARS http://williamson-labs.com/ltoc/cbr-tech.htm

28. CERN Rüdiger Schmidt CAS Trondheim 2013page 28 Copper graphite Damage of a pencil 7 TeV proton beam (LHC) copper graphite

29. CERN Rüdiger Schmidt CAS Trondheim 2013page 29 Beam losses and consequences ● Calculate the response of the material (deformation, melting, …) to beam impact (mechanical codes such as ANSYS, hydrodynamic codes such as BIG2 and others) ● Beams at very low energy have limited power…. however, the energy deposition is very high, and can lead to (limited) damage in case of beam impact issue at the initial stage of an accelerator, after the source, low energy beam transport and RFQ limited impact (e.g. damaging the RFQ) might lead to long downtime, depending on spare situation ● Beams at very high energy can have a tremendous damage potential for LHC, damage of metals for ~10 10 protons one LHC bunch has about 1.5∙10 11 protons, in total up to 2808 bunches in case of catastrophic beam loss, possibly damage beyond repair

30. CERN Rüdiger Schmidt CAS Trondheim 2013page 30 Controlled SPS experiment ● 8  10 12 protons clear damage ● beam size σ x/y = 1.1mm/0.6mm above damage limit for copper stainless steel no damage ● 2  10 12 protons below damage limit for copper 6 cm 25 cm 0.1 % of the full LHC 7 TeV beams factor of three below the energy in a bunch train injected into LHC damage limit ~200 kJoule V.Kain et al A B D C SPS experiment: Damage with 450 GeV protons

31. CERN Rüdiger Schmidt CAS Trondheim 2013page 31 Vacuum chamber in SPS extraction line, 2004 ● 450 GeV protons, 2 MJ beam in 2004 ● Failure of a septum magnet ● Cut of 25 cm length, groove of 70 cm ● Condensed drops of steel on other side of the vacuum chamber ● Vacuum chamber and magnet needed to be replaced

32. CERN Rüdiger Schmidt CAS Trondheim 2013page 32 Collimator in Tevatron after, 2003 ● A Roman pot (movable device) moved into the beam ● Particle showers from the Roman pot quenched superconducting magnets ● The beam moved by 0.005 mm/turn, and touched a collimator jaw surface after about 300 turns ● The entire beam was lost, mostly on the collimator Observation of HERA tungsten collimators: grooves on the surface when opening the vacuum chamber were observed. No impact on operation.

33. CERN Rüdiger Schmidt CAS Trondheim 2013page 33 Beam Current Monitors (BCM) measure current pulse at different locations along the linac. About 16 µsec of beam lost in the superconducting part of linac 680 µs of beam before sc linac 664 µs of beam after sc linac 16 µs of beam lost in the sc linac Beam energy in 16 µs End of DTL = 30 J End of CCL = 66 J End of SCL = 350 J Beam losses in SNS linac M.Plum / C.Peters

34. CERN Rüdiger Schmidt CAS Trondheim 2013page 34 Beam loss with low energy deposition ● Beam might hit surface of HV system (RFQ, kicker magnets, cavities) ● Surfaces with HV, after beam loss performance degradation might appear (not possible to operate at the same voltage, increased probability of arcing, …) ● SNS: errant beam losses led to a degradation of the performance of superconducting cavity Bam losses likely to be caused by problems in ion source, low energy beam transfer and normal conducting linac Cavity gradient needs to be lowered, conditioning after warm-up helps in most cases Energy of beam losses is about 100 J Damage mechanisms not fully understood, it is assumed that some beam hitting the cavity desorbs gas or particulates (=small particles) creating an environment for arcing M.Plum / C.Peters

35. CERN Rüdiger Schmidt CAS Trondheim 2013page 35 Accidental beam loss and probability

36. CERN Rüdiger Schmidt CAS Trondheim 2013page 36 Beam losses mechanisms In accelerators, particles are lost due to a variety of reasons: beam gas interaction, losses from collisions, losses of the beam halo, … ● Continuous beam losses are inherent during the operation of accelerators Taken into account during the design of the accelerator ● Accidental beam losses are due to a multitude of failures mechanisms ● The number of possible failures leading to accidental beam losses is (nearly) infinite

37. CERN Rüdiger Schmidt CAS Trondheim 2013page 37 Continuous beam losses: Collimation prevents too high beam losses around the accelerator (beam cleaning) A collimation system is a (very complex) system with (massive) material blocks close to the beam installed in an accelerator to capture halo particles Such system is also called (beam) Cleaning System Accidental beam losses: “Machine Protection” protects equipment from damage, activation and downtime Machine protection includes a large variety of systems, including collimators (or beam absorbers) to capture mis-steered beam Machine Protection Beam Cleaning Beam losses, machine protection and collimation

38. CERN Rüdiger Schmidt CAS Trondheim 2013page 38 Regular and irregular operation Failures during operation Beam losses due to failures, timescale from nanoseconds to seconds Machine protection systems Collimators Beam absorbers Regular operation Many accelerator systems Continuous beam losses Collimators for beam cleaning Collimators for halo scraping Collimators to prevent ion-induced desorption

39. CERN Rüdiger Schmidt CAS Trondheim 2013page 39 Continuous beam losses: Collimation Continuous beam with a power of 1 MW and more (SNS, JPARC, PSI) A loss of 1% corresponds to 10 kW – not to be lost along the beam line to avoid activation of material, heating, quenching, … Assume a length of 200 m: 50 W/m, not acceptable Plans for accelerators of 5 MW (ESS), 10 MW and more Limitation of beam losses is in order of 1 W/m to avoid activation and still allow hands-on maintenance Avoid beam losses – as far as possible Define the aperture by collimators Capture continuous particle losses with collimators at specific locations LHC stored beam with an energy of 360 MJ Assume lifetime of 10 minutes corresponds to beam loss of 500 kW, not to be lost in superconducting magnets Reduce losses by four orders of magnitude ….but also: capture fast accidental beam losses

40. CERN Rüdiger Schmidt CAS Trondheim 2013page 40 RF contacts for guiding image currents Beam spot 2 mm View of a two sided collimator for LHC about 100 collimators are installed in LHC Ralph Assmann, CERN length about 120 cm

41. CERN Rüdiger Schmidt CAS Trondheim 2013page 41 Accidental beam losses: Machine Protection Single-passage beam loss in the accelerator complex (ns -  s) transfer lines between accelerators or from an accelerator to a target station (target for secondary particle production, beam dump block) failures of kicker magnets (injection, extraction, special kicker magnets, for example for diagnostics) failures in linear accelerators, in particular due to RF systems too small beam size at a target station Very fast beam loss (ms) e.g. multi turn beam losses in circular accelerators due to a large number of possible failures, mostly in the magnet powering system, with a typical time constant of ~1 ms to many seconds Fast beam loss (some 10 ms to seconds) Slow beam loss (many seconds)

42. CERN Rüdiger Schmidt CAS Trondheim 2013page 42 Classification of failures ● Type of the failure hardware failure (power converter trip, magnet quench, AC distribution failure such as thunderstorm, object in vacuum chamber, vacuum leak, RF trip, kicker magnet misfires,.…) controls failure (wrong data, wrong magnet current function, trigger problem, timing system, feedback failure,..) operational failure (chromaticity / tune / orbit wrong values, …) beam instability (due to too high beam / bunch current / e-clouds) ● Parameters for the failure time constant for beam loss probability for the failure damage potential defined as risk

43. CERN Rüdiger Schmidt CAS Trondheim 2013page 43 Probability of a failure leading to beam loss ● Experience from LHC (…..the most complex accelerator) When the beam are colliding, the optimum length of a store is in the order of 10-15 hours, then ended by operation Most fills (~70 %) are ended by failures, the machine protection systems detect the failure and dump the beams MTBF of about 6 h ● Other large accelerators (SNS, plans for ESS, synchrotron light sources) MTBF between 20 h and up to several 100 h (…. more accurate numbers are appreciated) ● At high power accelerators, most failures would lead to damage if not mitigated = > the machine protection system is an essential part of the accelerator

44. CERN Rüdiger Schmidt CAS Trondheim 2013page 44 Machine Protection

45. CERN Rüdiger Schmidt CAS Trondheim 2013page 45 Example for Active Protection - Traffic ● A monitor detects a dangerous situation ● An action is triggered ● The energy stored in the system is safely dissipated

46. CERN Rüdiger Schmidt CAS Trondheim 2013page 46 Example for Passive Protection The monitor fails to detect a dangerous situation The reaction time is too short Active protection not possible – passive protection by bumper, air bag, safety belts

47. CERN Rüdiger Schmidt CAS Trondheim 2013page 47 Strategy for protection and related systems ● Avoid that a specific failure can happen

48. CERN Rüdiger Schmidt CAS Trondheim 2013page 48 Strategy for protection and related systems ● Avoid that a specific failure can happen ● Detect failure at hardware level and stop beam operation ● Detect initial consequences of failure with beam instrumentation ….before it is too late… ● Stop beam operation inhibit injection extract beam into beam dump block stop beam by beam absorber / collimator ● Elements in the protection systems equipment monitoring and beam monitoring beam dump (fast kicker magnet and absorber block) chopper to stop the beam in the low energy part collimators and beam absorbers beam interlock systems linking different systems

49. CERN Rüdiger Schmidt CAS Trondheim 2013page 49 Beam instrumentation for machine protection ● Beam Loss Monitors stop beam operation in case of too high beam losses monitor beam losses around the accelerator (full coverage!) could be fast and/or slow (LHC down to 40  s) ● Beam Position Monitors ensuring that the beam has the correct position in general, the beam should be centred in the aperture ● Beam Current Transformers if the current difference between two locations of the accelerator is too high (=beam lost somewhere): stop beam operation if the beam lifetime is too short: dump beam ● Beam Size Monitors if beam size is too small could be dangerous for windows, targets, …

50. CERN Rüdiger Schmidt CAS Trondheim 2013page 50 Ionization chambers to detect beam losses: Reaction time ~ ½ turn (40  s) Very large dynamic range (> 10 6 ) There are ~3600 chambers distributed over the ring to detect abnormal beam losses and if necessary trigger a beam abort ! LHC Beam Loss Monitors

51. CERN Rüdiger Schmidt CAS Trondheim 2013page 51 Layout of beam dump system in IR6 51 LHC Layout eight arcs (sectors) eight long straight section (about 700 m long) IR6: Beam dumping system IR4: RF + Beam instrumentation IR5:CMS IR1: ATLAS IR8: LHC-B IR2: ALICE Injection IR3: Moment Beam Clearing (warm) IR7: Betatron Beam Cleaning (warm) Beam dump blocks Detection of beam losses with >3600 monitors around LHC Signal to kicker magnet Beams from SPS

52. CERN Rüdiger Schmidt CAS Trondheim 2013page 52 LHC: Continuous beam losses during collisions CMS Experiment ATLAS Experiment LHC Experiment ALICE Experiment Momentum Cleaning RF and BI Beam dump Betatron Cleaning

53. CERN Rüdiger Schmidt CAS Trondheim 2013page 53 LHC: Accidental beam losses during collisions CMS Experiment ATLAS Experiment LHC Experiment ALICE Experiment Momentum Cleaning RF and BI Beam dump Betatron Cleaning

54. CERN Rüdiger Schmidt CAS Trondheim 2013page 54 LHC: Accidental beam losses during collisions

55. CERN Rüdiger Schmidt CAS Trondheim 2013page 55 Beam 2 Beam dump block Kicker magnets to paint (dilute) the beam about 700 m about 500 m 15 fast ‘kicker’ magnets deflect the beam to the outside When it is time to get rid of the beams (also in case of emergency!), the beams are ‘kicked’ out of the ring by a system of kicker magnetsd send into a dump block ! Septum magnets deflect the extracted beam vertically quadrupoles The 3  s gap in the beam gives the kicker time to reach full field. Ultra-high reliable system !! R.Schmidt HASCO 201355 CERN Layout of LHC beam dumping system in IR6

56. CERN Rüdiger Schmidt CAS Trondheim 2013page 56 Beam dumping system line for LHC

57. CERN Rüdiger Schmidt CAS Trondheim 2013page 57 LHC Beam dump ● Screen in front of the beam dump block ● Each light dot shows the passage of one proton bunch traversing the screen ● Each proton bunch has a different trajectory, to better distribute the energy across a large volume 50 cm

58. CERN Rüdiger Schmidt CAS Trondheim 2013page 58 High power accelerators … ● Operate with beam power of 1 MW and more ● SNS – 1 MW, PSI cyclotron – 1.3 MW, ESS – planned for 5 MW, FRIB (ions) – planned for 0.4 MW ● ESS (4 % duty cycle): in case of an uncontrolled beam loss during 1 ms, the deposited energy is up to 130 kJ, for 1 s it is up to 5 MJ ● It is required to inhibit the beam after detecting uncontrolled beam loss – how fast? ● The delay between detection and “beam off” to be considered

59. CERN Rüdiger Schmidt CAS Trondheim 2013page 59 Example for ESS source dT = dT_detect failure + dT_transmit signal + dT_inhibit source + dT_beam off inhibit beam interlock signal Example: After the DTL normal conducting linac, the proton energy is 78 MeV. In case of a beam size of 2 mm radius, melting would start after about 200 µs. Inhibiting beam should be in about 10% of this time. L.Tchelidze Time to melting point

60. CERN Rüdiger Schmidt CAS Trondheim 2013page 60 Some design principles for protection systems ● Failsafe design detect internal faults possibility for remote testing, for example between two runs if the protection system does not work, better stop operation rather than damage equipment ● Critical equipment should be redundant (possibly diverse) ● Critical processes not by software (no operating system) no remote changes of most critical parameters ● Demonstrate safety / availability / reliability use established methods to analyse critical systems and to predict failure rate ● Managing interlocks disabling of interlocks is common practice (keep track !) LHC: masking of some interlocks possible for low intensity / low energy beams

61. CERN Rüdiger Schmidt CAS Trondheim 2013page 61 Accelerators that require protection systems I ● Hadron synchrotrons with large stored energy in the beam Colliders using protons / antiprotons (TEVATRON, HERA, LHC) Synchrotrons accelerating beams for fixed target experiments (SPS) ● High power accelerators (e.g. spallation sources) with beam power of some 10 kW to above 1 MW Risk of damage and activation Spallation sources, up to (and above) 1 MW quasi-continuous beam power (SNS, ISIS, PSI cyclotron, JPARC, and in the future ESS, FRIB, MYRRHA and IFMIF) ● Synchrotron light sources with high intensity beams and secondary photon beams ● Energy recovery linacs Example of Daresbury prototype: one bunch train cannot damage equipment, but in case of beam loss next train must not leave the (injector) station

62. CERN Rüdiger Schmidt CAS Trondheim 2013page 62 Accelerators that require protection systems II ● Linear colliders / accelerators with very high beam power densities due to small beam size High average power in linear accelerators: FLASH 90 kW, European XFEL 600 kW, JLab FEL 1.5 MW, ILC 11 MW One beam pulse can lead already to damage “any time interval large enough to allow a substantial change in the beam trajectory of component alignment (~fraction of a second), pilot beam must be used to prove the integrity” from NLC paper 1999 ● Medical accelerators: prevent too high dose to patient Low intensity, but techniques for protection are similar ● Very short high current bunches: beam induces image currents that can damage the environment (bellows, beam instruments, cavities, …)

63. CERN Rüdiger Schmidt CAS Trondheim 2013page 63 For future high intensity machines Machine protection should always start during the design phase of an accelerators ● Particle tracking to establish loss distribution with realistic failure modes accurate aperture model required ● Calculations of the particle shower (FLUKA, GEANT, …) energy deposition in materials activation of materials accurate 3-d description of accelerator components (and possibly the tunnel) required ● Coupling between particle tracking and shower calculations ● From the design, provide 3-d model of all components

64. CERN Rüdiger Schmidt CAS Trondheim 2013page 64 Summary Machine protection ● is not equal to equipment protection ● requires the understanding of many different type of failures that could lead to beam loss ● requires comprehensive understanding of all aspects of the accelerator (accelerator physics, operation, equipment, instrumentation, functional safety) ● touches many aspects of accelerator construction and operation ● includes many systems ● is becoming increasingly important for future projects, with increased beam power / energy density (W/mm 2 or J/mm 2 ) and increasingly complex machines ● I find it a fascinating topic ……… at least until nothing breaks

65. CERN Rüdiger Schmidt CAS Trondheim 2013page 65 Acknowledgements to many colleagues from CERN and to the authors of the listed papers ● R.F.Koontz, Multiple Beam Pulse of the SLAC Injector, PAC 1967 ● R.Bacher et al., The HERA Quench Protection System, a Status Report, EPAC 1996 ● C.Adolphsen et al., The Next Linear Collider Machine Protection System, PAC 1999 ● M.C.Ross et al., Single Pulse Damage in Copper, LINAC 2000 ● C.Sibley, Machine Protection Strategies for High Power Accelerators, PAC 2003 ● C.Sibley, The SNS Machine Protection System: Early Commissioning Results and Future Plans, PAC 2005 ● S.R.Buckley and R.J.Smith, Monitoring and Machine Protection Designs for the Daresbury Laboratory Energy Recovery Linac Prototype, EPAC 2006 ● L.Fröhlich et al., First Operation of the FLASH Machine Protection System with long Bunch Trains, LINAC 2006 ● L.Fröhlich et al., First Experience with the Machine Protection System of FLASH, FEL 2006 ● N.V.Mokhov et al., Beam Induced Damage to the TEVATRON Components and what has been done about it, HB2006 ● M.Werner and K.Wittenburg, Very fast Beam Losses at HERA, and what has been done about it, HB2006 ● S.Henderson, Status of the Spallation Neutron Source: Machine and Experiments, PAC 2007 ● H.Yoshikawa et al., Current Status of the Control System for J-PARC Accelerator Complex, ICALEPCS 2007 ● L.Froehlich, Machine Protection for FLASH and the European XFEL, DESY PhD Thesis 2009 ● A.C.Mezger, Control and protection aspects of the megawatt proton accelerator at PSI, HB2010 ● Y.Zhang, D.Stout, J.Wei, ANALYSIS OF BEAM DAMAGE TO FRIB DRIVER LINAC, SRF 2012

66. CERN Rüdiger Schmidt CAS Trondheim 2013page 66 CERN and LHC ● R.B.Appleby et. al., Beam-related machine protection for the CERN Large Hadron Collider experiments, Phys. Rev. ST Accel. Beams 13, 061002 (2010) ● R.Schmidt et al., Protection of the CERN Large Hadron Collider, New Journal of Physics 8 (2006) 290 ● R.Schmidt, Machine Protection, CERN CAS 2008 Dourdan on Beam Diagnostics ● N.Tahir et al., Simulations of the Full Impact of the LHC Beam on Solid Copper and Graphite Targets, IPAC 2010, Kyoto, Japan, 23 - 28 May 2010 Theses ● Verena Kain, Machine Protection and Beam Quality during the LHC Injection Process, CERN-THESIS- 2005-047 ● G.Guaglio, Reliability of the Beam Loss Monitors System for the Large Hadron Collider at CERN /, CERN-THESIS-2006-012 PCCF-T-0509 ● Benjamin Todd, A Beam Interlock System for CERN High Energy Accelerators, CERN-THESIS-2007-019 ● A. Gomez Alonso, Redundancy of the LHC machine protection systems in case of magnet failures / CERN-THESIS-2009-023 ● Sigrid Wagner, LHC Machine Protection System: Method for Balancing Machine Safety and Beam Availability /, CERN-THESIS-2010-215 ● Roderik Bruce, Beam loss mechanisms in relativistic heavy-ion colliders, CERN-THESIS-2010-030 Acknowledgements to many colleagues from CERN and to the authors of the listed papers

67. CERN Rüdiger Schmidt CAS Trondheim 2013page 67 ● L.Tchelidze, In how long the ESS beam pulse would start melting steel/copper accelerating components? ESS AD Technical Note, ESS/AD/0031, 2012 ● Conference reports in JACOW, keywords: machine protection, beam loss Acknowledgements to many colleagues from CERN and to the authors of the listed papers

68. CERN Rüdiger Schmidt CAS Trondheim 2013page 68 68 Example for LHC Collimation and Machine Protection during operation Assume that two 100 MJoule beams (=25 kg TNT) are circulating with the speed of light through the 56 mm diameter vacuum chamber and 2 mm wide collimators 1. Suddenly the AC distribution for CERN fails – no power! 2. An object falls into the beam 3. The betatron tune is driven right onto a 1/3 order resonance

69. CERN Rüdiger Schmidt CAS Trondheim 2013page 69 LHC from injection to collisions 3.5 TeV / 100 MJoule 0.45 TeV / 13 MJoule Energy ramp Luminosity: start collisions Injection of 1380 bunches per beam About 2 hours

70. CERN Rüdiger Schmidt CAS Trondheim 2013page 70 Orbit for last 1000 turns before power cut

71. CERN Rüdiger Schmidt CAS Trondheim 2013page 71 Continuous beam losses

72. CERN Rüdiger Schmidt CAS Trondheim 2013page 72 Total power cut atLHC - 18 August 2011, 11:45

73. CERN Rüdiger Schmidt CAS Trondheim 2013page 73 1.Suddenly the AC distribution for CERN fails – no power for LHC!

74. CERN Rüdiger Schmidt CAS Trondheim 2013page 74

75. CERN Rüdiger Schmidt CAS Trondheim 2013page 75 LHC from injection to collisions: beam loss

76. CERN Rüdiger Schmidt CAS Trondheim 2013page 76 …zoom - going into collisions

77. CERN Rüdiger Schmidt CAS Trondheim 2013page 77 Beam cleaning system captures beam losses ● In case protons are lost because of low lifetime ● In case of protons are lose when colliding beams, and scattering of protons during the collisions that would be lost around the LHC ● In case of protons outside the RF bucket – losing slowly energy – are captured by collimators in the Momentum Cleaning Insertion Questions ● How to stop high energy protons? ● Why so many collimators? ● Why carbon composite or graphite used for most collimators?

78. CERN Rüdiger Schmidt CAS Trondheim 2013page 78 Collimator material ● Metal absorbers would be destroyed ● Other materials for injection absorber preferred, graphite or boron nitride for the injection absorber ● In case of a partial kick (can happen), the beam would travel further to the next collimators in the cleaning insertions P.Sievers / A.Ferrari / V. Vlachoudis 7 TeV, 2  10 12 protons For collimators close to the beam, metal absorbers would be destroyed Other materials for collimators close to the beam are preferred (carbon – carbon)

79. CERN Rüdiger Schmidt CAS Trondheim 2013page 79 Collimation ● For a circular accelerator, the transverse distribution of beams is in general Gaussian, or close to Gaussian (beams can have non- Gaussian tails) ● In general, particles in these tails cause problems when they might touch the aperture Background Quenches in magnets (for accelerators with sc magnets) For high intensity machines, possible damage of components ● Nearly all particles that are in the centre go first through the tails before getting lost (except those that do a inelastic collision with gas molecules) ● Tails are scraped away using collimators

80. CERN Rüdiger Schmidt CAS Trondheim 2013page 80 Phase space and collimation x’ x Starting with a Gaussian beam profile

81. CERN Rüdiger Schmidt CAS Trondheim 2013page 81 Phase space and collimation x’ x Collimator outside the beam

82. CERN Rüdiger Schmidt CAS Trondheim 2013page 82 82 Phase space and collimation: multi turn x’ x Collimator driven into the beam tail: loss of particles

83. CERN Rüdiger Schmidt CAS Trondheim 2013page 83 83 Phase space and collimation: multi turn x’ x Collimator again outside the beam – beam size reduction (for proton synchrotrons)

84. CERN Rüdiger Schmidt CAS Trondheim 2013page 84 84 Phase space and collimation: single turn x’ x Collimator in a transfer line or linac: cuts only part of the beam

85. CERN Rüdiger Schmidt CAS Trondheim 2013page 85 85 Phase space and collimation: single turn x’ x Collimator in a transfer line or linac: cuts only part of the beam

86. CERN Rüdiger Schmidt CAS Trondheim 2013page 86 86 Phase space and collimation: single turn x’ x Collimator in a transfer line or linac: several collimators are required

87. CERN Rüdiger Schmidt CAS Trondheim 2013page 87 87 Phase space and collimation: single turn x’ x Collimator in a transfer line or linac: several collimators are required …. at different betatron phases 90 degrees further down

88. CERN Rüdiger Schmidt CAS Trondheim 2013page 88 Gaussian beam not collimated

89. CERN Rüdiger Schmidt CAS Trondheim 2013page 89 Gaussian beam collimated at 4 sigma N = 0.999 (number of protons ) L = 0.999 (luminosity )

90. CERN Rüdiger Schmidt CAS Trondheim 2013page 90 Gaussian beam collimated at 3 sigma N= 0.987 L = 0.992

91. CERN Rüdiger Schmidt CAS Trondheim 2013page 91 Gaussian beam collimated at 2 sigma N= 0.863 L = 0.866

92. CERN Rüdiger Schmidt CAS Trondheim 2013page 92 Collimation: why so many? Answer A: ● For a transfer line or a linear accelerator, many collimators are required to take out particles at all phases Answer B: ● Cite: “It is not possible to stop a high energy proton, it is only possible to make them mad” ● Collimators cannot stop a high energy proton ● The particle impact on a collimator jaw is very small, in the order of microns or even less ● Particles scatter….. depends on particle type, energy and impact on collimator jaw ● Staged collimation system in a ring and in a transfer line

93. CERN Rüdiger Schmidt CAS Trondheim 2013page 93 Betatron beam cleaning Cold aperture Cleaning insertion Arc(s)IP Circulating beam Illustration drawing Arc(s) Primary collimator Secondary collimators Tertiary beam halo + hadronic showers Shower absorbers Tertiary collimators SC Triplet

94. CERN Rüdiger Schmidt CAS Trondheim 2013page 94 Measurement: 500kJ losses at primary collimators (loss rate: 9.1e11 p/s) – IR7 Daniel Wollmann 94 TCP: ~505 kJ Q8L7: ~335 J Q11L7: ~35 J Q19L7: ~4.7 J Q8L7:  ~ 6.7e-4 Lower limit: R q L dil ~ 1.22e9 p/s (with c resp = 2 ) Lost energy over 1 s

95. CERN Rüdiger Schmidt CAS Trondheim 2013page 95 Film from Alessandro

96. CERN Rüdiger Schmidt CAS Trondheim 2013page 96 173 bunches grazing incident on injection absorber Upstream of IP2 Beam 1 Downstream of IP2 Beam 1 Insertion losses: 3 magnets quenched (D1.L2, MQX.L2, D2.R2) TDI Losses starting at TDI, no injection loss signature  only circulating beam kicked by MKI In comparison to flashover event of April 18 th in P8 (LMC 20/04/11), cleaner in arc less magnet quenches (3), ALICE SDD permanent effect, open MCSOX.3L2 circuit C.Bracco

97. CAS October 2013 R.Schmidt97 Is protection required?

98. CAS October 2013 R.Schmidt98 Protection for beam transfer from SPS to LHC A signal “extraction permit” is required to extract beam from SPS and another signal “injection permit“ to inject beam into LHC After extraction the trajectory is determined by the magnet fields: safe beam transfer and injection relies on correct settings –orbit bump around extraction point in SPS during extraction with tight tolerances verified with BPMs –correct magnet currents (slow pulsing magnets, fast pulsing magnets) –position of vacuum valves, beam screens,… must all be OUT –energy of SPS, transfer line and LHC must match –LHC must be ready to accept beam Verifying correct settings just before extraction and injection The kicker must fire at the correct time with the correct strength Position of collimators and beam absorbers in SPS, transfer line and LHC injection region to protect from misfiring

99. CAS October 2013 R.Schmidt99 Case studies The principles of machine protection are illustrated with examples from different accelerators

100. CAS October 2013 R.Schmidt100 Example: SNS normal conducting linac superconducting linac accumulator ring transfer lines target station beam power on target 1.4 MW beam pulse length 1 ms repetition rate 60 Hz (more or less) continuous beam to above 1 MW –the deposited energy is proportional to the time of exposure –the risk (possible damage) increases with time Protection by detecting the failure and stopping injection and acceleration

101. CAS October 2013 R.Schmidt101 SNS damage limits Damage of a copper cavity: Time to reach the thermal stress limit for copper assuming a beam size of 2 mm, a current of 36 mA and an energy density of 62 J/gm as maximum permitted energy deposition (from C.Sibley, PAC 2003) The SNS MP system uses inputs from BLMs, beam current monitors, RF, power supplies, vacuum system, kickers, etc.

102. 102 Radiation Damage to Undulator Magnets Nd 2 Fe 14 B magnets lose magnetization when irradiated literature: relative demagnetization rate 10 −8 /Gy (gammas) — 10 −4 /Gy (fast neutrons) hybrid magnet structure Nd 2 Fe 14 B permanent magnets soft magnetic pole pieces Lars Froehlich, DESY and Uni Hamburg, Machine Protection Machine Protection for FLASH and the European XFEL

103. 103 Conclusion Superconducting linacs can transport dangerously powerful beams Permanent magnet undulators are among the most vulnerable components Beam losses must be controlled tightly (FLASH design: 3∙10 −8 ) Dark current can be problematic Good passive & active protection is required FLASH machine protection system is fully functional & reliable XFEL machine protection system will be more complex, but concepts & first prototypes are ready Lars Froehlich, DESY and Uni Hamburg, Machine Protection Machine Protection for FLASH and the European XFEL

104. CAS October 2013 R.Schmidt104 Machine Protection during all phases of operation The LHC is the first accelerator with the intensity of the injected beam already far above threshold for damage, protection during the injection process is mandatory At 7 TeV, fast beam loss with an intensity of about 5% of one single “nominal bunch” could damage equipment (e.g. superconducting coils) The only component that can stand a loss of the full beam is the beam dump block - all other components would be damaged The LHC beams must ALWAYS be extracted into the beam dump blocks –at the end of a fill –in case of failure During powering, about 10 GJ is stored in the superconducting magnets, quench protection and powering interlocks must be operational long before starting beam operation

105. CAS October 2013 R.Schmidt105 Multiturn beam losses Consequence of a magnet powering failure –Closed orbit grows and moves everywhere the ring or downstream the linac (follows free betatron oscillation with one kick) –Beam size explodes –Can happen very fast (for example, if a normal conducting magnet trips or after a magnet quench) –Can be detected around the entire accelerator Local orbit bump –Can be generated due to BPM offset –Needs several magnets to fail and cannot happen very fast –Might be detected only locally Protection: Detect failure and dump beam Detection by equipment monitoring and beam monitoring

106. CAS October 2013 R.Schmidt106 Failure of normal conducting magnets After about 13 turns 3·10 9 protons touch collimator, about 6 turns later 10 11 protons touch collimator V.Kain / O.Bruning “Dump beam” level 10 11 protons at collimator

107. CAS October 2013 R.Schmidt107 Fast Magnet Current change Monitors (initial development for HERA, upgrade for LHC in collaboration with DESY) Several FMCMs are installed on critical magnets Tested using steep reference changes to trigger FMCM. The trigger threshold and the magnet current (resolution one ms) Beam tests confirmed these results Reference PC current time (ms) I (A) FMCM trigger  0.1% drop ! time (ms) I (A) 10 ms FMCM triggers @ 3984.4 <10 3

108. CAS October 2013 R.Schmidt

109. 109 Principle of LHC / SPS Beam Interlock Systems BIS LHC Dump kicker Beam ‘Permit’ User permit signals ‘User systems’ survey equipment or beam parameters, detect failures and send a hardwired signal to the beam interlock system (user permit) The BIS combines user permits and produces beam permit The beam permit is a hardwired signal to injection / extraction kickers : LHC ring: absence of beam permit  dump triggered ! LHC injection: absence of beam permit  no injection ! SPS: absence of beam permit  no extraction ! Hardware links /systems, fully redundant SPS Extraction kicker LHC Injection kicker SPS Dump kicker

110. CAS October 2013 R.Schmidt110 Machine Protection and Controls Software Interlock Systems (SIS) provides additional protection for complex but also less critical conditions –Surveillance of magnet currents to avoid certain failures (local bumps) that would reduce the aperture –The reaction time of those systems will be at the level of a few seconds –The systems rely entirely on the computer network, databases, etc – clearly not as safe as HW systems! Sequencer: program to execute defined procedures –To execute defined well-tested procedures for beam operation Logging and PM systems: recording of data – continuous logging and for transients (beam dump, quench, …) –Very important to understand what happened

111. CAS October 2013 R.Schmidt111 P.Sievers / A.Ferrari / V. Vlachoudis Beryllium Accidental kick by the beam dump kicker at 7 TeV part of beam touches collimators (about 2  10 12 from 3  10 14 )

112. CAS October 2013 R.Schmidt112 Target length [cm] vaporisation melting N.Tahir (GSI) et al. Copper target 2 m Energy density [GeV/cm 3 ] on target axis 2808 bunches 7 TeV 350 MJoule Full LHC beam deflected into copper target

113. CAS October 2013 R.Schmidt113 LHC circulating beam Injection absorbers (TCLI) ~7σ n·180 +/- 20 degrees Beam absorbers take beam in case of kicker wrong strength Protection at injection Beam from SPS Injection Kicker Set of transfer line collimators (TCDI) ~5σ Injection absorber (TDI) ~7σ Circulating beam – kicked out Injection kicker – wrong strength phase advance 90 0 LHC circulating beam

114. CAS October 2013 R.Schmidt114 LHC circulating beam Injection Kicker Injection absorber TDI ~7σ Injection absorbers TCLI ~7σ Only when beam is circulating in the LHC, injection of high intensity beam is permitted – verification of LHC magnet settings Probe Beam: Replacing low intensity beam by a full batch from SPS Set of transfer line collimators TCDI ~5σ Beam from SPS

115. CAS October 2013 R.Schmidt115 Active and passive protection Start operation with low intensity beam (“pilot beam”) Active protection Detect failure Turn off the beam as fast as possible (e.g. source, RF, …) Only permit beam injection into the next part of the accelerator complex in case of positive confirmation that all parameters are within predefined limits Abort the beam from a storage ring / accumulator ring Passive protection Install collimators and beam absorbers, in particular if active protection is not possible

116. CAS October 2013 R.Schmidt116 Active protection Monitoring of the beam detects a failure and allows to switch off the beam before damage Stored beam in a circular accelerator –multi turn beam losses –monitor beam losses, and dump the beam if losses exceed threshold “Continuous” beam in linacs of other accelerators –continuous: if the time constant for a failure is such that the source can be switched off in time There is a large number of possible failures, mostly in the magnet powering system, with a typical time constant of ms to many seconds

117. CAS October 2013 R.Schmidt Cold aperture Primary beam halo Primary collimator Secondary collimators Tertiary beam halo + hadronic showers Secondary beam halo + hadronic showers Shower absorbers Cleaning insertion Tertiary collimators SC Triplet Arc(s)IP Protection devices Circulating beam Illustrative scheme

118. CAS October 2013 R.Schmidt118

119. CAS October 2013 R.Schmidt119 Failure of a kicker magnet 1 km Extraction kicker magnet: wrong pulse strength wrong timing Injection kicker magnet: wrong pulse strength wrong timing Transfer line LHC SPS 6911 m 450 GeV / 400 GeV 3 MJ Acceleration cycle of 10 s CNGS Target IR8 Switching magnet Fast extraction kicker Injection kicker Transfer line Injection kicker IR2 Fast extraction kicker

120. CAS October 2013 R.Schmidt120 Failure in the transfer line (magnet, other element) 1 km Wrong setting of magnets Object in the transfer line blocks beam passage Transfer line LHC SPS 6911 m 450 GeV / 400 GeV 3 MJ Acceleration cycle of 10 s CNGS Target IR8 Switching magnet Fast extraction kicker Injection kicker Transfer line Injection kicker IR2 Fast extraction kicker

121. CAS October 2013 R.Schmidt M.Jonker Beam damage capabilities

122. CERN Rüdiger Schmidt CAS Trondheim 2013page 122 Accidental beam losses: Risks and protection ● Protection is required since there is some risk ● Risk = probability of an accident (in number of accidents per year)  consequences (in Euro, downtime, radiation dose to people) ● Probability of an accidental beam loss What are the failure modes the lead to beam loss into equipment (there is an practical infinite number of mechanisms to lose the beam)? What is the probability for the most likely failures? ● Consequences of an accidental beam loss Damage to equipment Downtime of the accelerator for repair (spare parts available?) Activation of material, might lead to downtime since access to equipment is delayed ● The higher the risk, the more protection becomes important

123. CERN Rüdiger Schmidt CAS Trondheim 2013page 123 Damage of LHC during the 2008 accident Accidental release of an energy of 600 MJoule stored in the magnet system - no beam in LHC

124. CERN Rüdiger Schmidt CAS Trondheim 2013page 124 Energy loss: example for protons in Aluminium

125. CERN Rüdiger Schmidt CAS Trondheim 2013page 125 Heating of material with low energy protons

126. CERN Rüdiger Schmidt CAS Trondheim 2013page 126 Strategy for Machine Protection Beam Interlock System Collimator and Beam Absorbers Early detection of failures for equipment acting on beams and generating beam abort request (inhibit injection, dump beam). Active monitoring of the beams detects abnormal beam conditions and generates beam abort request. Reliable transmission of beam abort requests to beam stop system. Active signal required for operation, absence of signal is considered as beam abort request and injection inhibit. Reliable operation of beam abort system. Passive protection by beam absorbers and collimators for specific failure cases.

127. CERN Rüdiger Schmidt CAS Trondheim 2013page 127 LHC: Strategy for machine protection ● Definition of aperture by collimators. Beam Cleaning System Beam Loss Monitors Other Beam Monitors Beam Interlock System Powering Interlocks Fast Magnet Current change Monitor Beam Dumping System Collimator and Beam Absorbers Early detection of failures for equipment acting on beams generates dump request, possibly before the beam is affected. Active monitoring of the beams detects abnormal beam conditions and generates beam dump requests down to a single machine turn. Reliable transmission of beam dump requests to beam dumping system. Active signal required for operation, absence of signal is considered as beam dump request and injection inhibit. Reliable operation of beam dumping system for dump requests or internal faults, safely extract the beams onto the external dump blocks. Passive protection by beam absorbers and collimators for specific failure cases.

128. CERN Rüdiger Schmidt CAS Trondheim 2013page 128 Beam losses and consequences ● Equipment becomes activated due to beam losses (acceptable is ~1 W/m, but must be “As Low As Reasonably Achievable – ALARA” )

129. CERN Rüdiger Schmidt CAS Trondheim 2013page 129 Energy deposition and temperature increase

130. CERN Rüdiger Schmidt CAS Trondheim 2013page 130 Energy deposition and temperature increase

131. CERN Rüdiger Schmidt CAS Trondheim 2013page 131 Energy deposition and temperature increase ● There is no straightforward expression for the energy deposition ● The energy deposition is a function of the particle type, its momentum, and the parameters of the material (atomic number, density, specific heat) ● Programs such as FLUKA, MARS, GEANT and others are being used for the calculation of energy deposition and activation ● Other programs are used to calculate the response of the material (deformation, melting, …) to beam impact (mechanical codes such as ANSYS, hydrodynamic codes such as BIG2 and others) Question: what is dangerous (stored beam energy, beam power)?

132. CERN Rüdiger Schmidt CAS Trondheim 2013page 132 What parameters are relevant? ● Momentum of the particle ● Particle type Activation is mainly an issue for hadron accelerators ● Time structure of beam ● Energy stored in the beam one MJoule can heat and melt 1.5 kg of copper one MJoule corresponds to the energy stored in 0.25 kg of TNT ● Beam power one MWatt during one second corresponds to a MJoule ● Beam size ● Beam power / energy density (MJoule/mm 2, MWatt/mm 2 ) Consequences for an accident with 360 MJ beam can be catastrophic (LHC damage beyond repair) Delicate components can be damaged already with some Joule (e.g. RFQ) Machine protection becomes very important if beam energy > 0.1 – 1 MJ