Скачать презентацию Beam Loss and Collimation at the LHC R Скачать презентацию Beam Loss and Collimation at the LHC R

a0faa587def7481773c92104eacfe6ca.ppt

  • Количество слайдов: 55

Beam Loss and Collimation at the LHC R. Assmann, CERN/AB 15/11/2007 for the Collimation Beam Loss and Collimation at the LHC R. Assmann, CERN/AB 15/11/2007 for the Collimation Team GSI Beschleunigerpalaver RWA, GSI 11/07

What is the LHC Beam? Protons/ions stored in circular accelerator. Top view Particles travel What is the LHC Beam? Protons/ions stored in circular accelerator. Top view Particles travel with light velocity in a 27 km long vacuum tube. Revolution frequency is 11 k. Hz. p Ideally fully stable without any losses. Two beams with opposite travel directions and well defined collision points. 7. 6 cm 0. 2 mm 25 ns RWA, GSI 11/07 25 ns 2

1) Introduction: The LHC Challenge The Large Hadron Collider: Circular particle physics collider with 1) Introduction: The LHC Challenge The Large Hadron Collider: Circular particle physics collider with 27 km circumference. Two colliding 7 Te. V beams with each 3 × 1014 protons. Super-conducting magnets for bending and focusing. Start of beam commissioning: May 2008. LHC nominal parameters Particle physics reach defined from: 1) Center of mass energy 14 Te. V super-conducting dipoles Number of bunches: Bunch population: Bunch spacing: 2808 1. 15 e 11 25 ns Top energy: Proton energy: Transv. beam size: Bunch length: Stored beam energy: 7 Te. V ~ 0. 2 mm 8. 4 cm 360 MJ Injection: 2) Luminosity RWA, GSI 11/07 1034 cm-2 s-1 Proton energy: Transv. Beam size: Bunch length: 450 Ge. V ~ 1 mm 18. 6 cm 3

The LHC SC Magnets RWA, GSI 11/07 4 The LHC SC Magnets RWA, GSI 11/07 4

LHC Luminosity • Luminosity can be expressed as a function of transverse energy density LHC Luminosity • Luminosity can be expressed as a function of transverse energy density re in the beams at the collimators: d = demagnification (bcoll/b*) Np = protons per bunch frev = revolution freq. Eb = beam energy • Various parameters fixed by design, for example: – Tunnel fixes revolution frequency. – Beam-beam limit fixes maximum bunch intensity. – Machine layout and magnets fix possible demagnification. – Physics goal fixes beam energy. • Luminosity is increased via transverse energy density! RWA, GSI 11/07 5

pp, ep, and ppbar collider history Higgs + SUSY + ? ? ? ~ pp, ep, and ppbar collider history Higgs + SUSY + ? ? ? ~ 80 kg TNT 2008 1992 Collimation Machine Protection SC magnets 1971 1987 1981 The “new Livingston plot“ of proton colliders: Advancing in unknown territory! A lot of beam comes with a lot of garbage (up to 1 MW halo loss, tails, backgrd, . . . ) Collimation. Machine Protection.

Proton Losses • LHC: Ideally no power lost (protons stored with infinite lifetime). • Proton Losses • LHC: Ideally no power lost (protons stored with infinite lifetime). • Collimators are the LHC defense against unavoidable losses: – Irregular fast losses and failures: Passive protection. – Slow losses: Cleaning and absorption of losses in super-conducting environment. – Radiation: Managed by collimators. – Particle physics background: Minimized. • Specified 7 Te. V peak beam losses (maximum allowed loss): – Slow: 0. 1% of beam per s for 10 s 0. 5 MW – Transient: 5 × 10 -5 of beam in ~10 turns (~1 ms) 20 MW – Accidental: up to 1 MJ in 200 ns into 0. 2 mm 2 5 TW RWA, GSI 11/07 7

The LHC Collimators… • Collimators must intercept any losses of protons such that the The LHC Collimators… • Collimators must intercept any losses of protons such that the rest of the machine is protected („the sunglasses of the LHC“): > 99. 9% efficiency! Top view • To this purpose collimators insert diluting and absorbing materials into the vacuum pipe. • Material is movable and can be placed as close as 0. 25 mm to the circulating beam! • Nominal distance at 7 Te. V: ≥ 1 mm. • Presently building/installing phase 1! RWA, GSI 11/07 8

Preventing Quenches • Shock beam impact: 2 MJ/mm 2 in 200 ns (0. 5 Preventing Quenches • Shock beam impact: 2 MJ/mm 2 in 200 ns (0. 5 kg TNT) • Maximum beam loss at 7 Te. V: 1% of beam over 10 s 500 000 W • Quench limit of SC LHC magnet: 8. 5 W/m RWA, GSI 11/07 9

Machine Protection • There a number of LHC failure scenarios which lead to beam Machine Protection • There a number of LHC failure scenarios which lead to beam loss. • No discussion of machine protection details here. However, comments on collimator role in machine protection. R. Schmidt is Project Leader for MP. • Slow failures: – First losses after >10 -50 turns appear at collimators as closest aperture restrictions. – Beam loss monitors detect abnormally high losses and dump the beam within 1 -2 turns. • Fast failures (dump and injection kicker related): – Sensitive equipment must be passively protected by collimators. • In all cases, the exposed collimators must survive the beam impact: up to 2 MJ in 200 ns (0. 5 kg TNT) RWA, GSI 11/07 10

2) LHC Collimation Basics Beam axis Beam propagation Impact parameter Core CFC RWA, GSI 2) LHC Collimation Basics Beam axis Beam propagation Impact parameter Core CFC RWA, GSI 11/07 e p Shower CFC e Absorber Secondary p halo p Shower p W/Cu Multi-Stage Cleaning Tertiary halo p Superconducting magnets Absorber Unavoidable losses Secondary collimator Impact parameter ≤ 1 mm Particle Primary collimator Primary halo (p) Collimator SC magnets and particle physics exp. W/Cu 11

“Phase 1” System Design Momentum Collimation Betatron Collimation “Final” system: Layount is 100% frozen! “Phase 1” System Design Momentum Collimation Betatron Collimation “Final” system: Layount is 100% frozen! RWA, GSI 11/07 C. Bracco 12

A Virtual Visit to IR 7 RWA, GSI 11/07 13 A Virtual Visit to IR 7 RWA, GSI 11/07 13

LHC Collimator Gaps Collimator settings: 5 - 6 s (primary) 6 - 9 s LHC Collimator Gaps Collimator settings: 5 - 6 s (primary) 6 - 9 s (secondary) s ~ 1 mm (injection) s ~ 0. 2 mm (top) Small gaps lead to: 1. Surface flatness tolerance (40 mm). 2. Impedance increase. 3. Mechanical precision demands (10 mm). RWA, GSI 11/07 14

Required Efficiency Allowed intensity Quench threshold (7. 6 × 106 p/m/s @ 7 Te. Required Efficiency Allowed intensity Quench threshold (7. 6 × 106 p/m/s @ 7 Te. V) Illustration of LHC dipole in tunnel Cleaning inefficiency = Beam lifetime (e. g. 0. 2 h minimum) Dilution length Number of escaping p (>10 s) Number of impacting p (6 s) (~10 m) Collimation performance can limit the intensity and therefore LHC luminosity RWA, GSI 11/07 15

Intensity Versus Cleaning Efficiency For a 0. 2 h minimum beam lifetime during the Intensity Versus Cleaning Efficiency For a 0. 2 h minimum beam lifetime during the cycle. 99. 998 % per m efficiency RWA, GSI 11/07 16

The LHC Phase 1 Collimation • Low Z materials closest to the beam: – The LHC Phase 1 Collimation • Low Z materials closest to the beam: – Survival of materials with direct beam impact – Improved cleaning efficiency – High transparency: 95% of energy leaves jaw • Distributing losses over ~250 m long dedicated cleaning insertions: – Average load ≤ 2. 5 k. W per m for a 500 k. W loss. – No risk of quenches in normal-conducting magnets. – Hot spots protected by passive absorbers outside of vacuum. • Capturing residual energy flux by high Z absorbers: – Preventing losses into super-conducting region after collimator insertions. – Protecting expensive magnets against damage. • No shielding of collimators: – As a result radiation spread more equally in tunnel. – Lower peak doses. – Fast and remote handling possible for low weight collimators. RWA, GSI 11/07 17

3) Collimator Hardware RWA, GSI 11/07 18 3) Collimator Hardware RWA, GSI 11/07 18

Hardware: Water Cooled Jaw Up to 500 k. W impacting on a jaw (7 Hardware: Water Cooled Jaw Up to 500 k. W impacting on a jaw (7 k. W absorbed in jaw)… Advanced material: Fiber-reinforced graphite (CFC) RWA, GSI 11/07 19

The LHC “TCSG” Collimator Resea rch top Advan ic: ced m echan ical engin The LHC “TCSG” Collimator Resea rch top Advan ic: ced m echan ical engin eering 1. 2 m 3 mm beam passage with RF contacts for guiding image currents Designed for maximum robustness: Advanced CC jaws with water cooling! Other types: Mostly with different jaw materials. Some very different with 2 beams! 360 MJ proton beam RWA, GSI 11/07 20

Robustness Test with Beam TED Dump 450 Ge. V 3 1013 p 2 MJ Robustness Test with Beam TED Dump 450 Ge. V 3 1013 p 2 MJ 0. 7 x 1. 2 mm 2 Microphone ~ Tevatron beam Fiber-reinforced graphite (CFC) C jaw Resea rch top Advan ic: ced m ateria extrem ls and e shoc k wav es Graphite C-C jaw ~ ½ kg TNT RWA, GSI 11/07 21

Operational Control RWA, GSI 11/07 22 Operational Control RWA, GSI 11/07 22

Using Sensors to Monitor LHC Jaw Positions Side view at one end Resea CFC Using Sensors to Monitor LHC Jaw Positions Side view at one end Resea CFC Vacuum tank Microphone rch top ic: Precis ion re Movement mote for spare contro and su l surface rvey mechanism Temperature sensors (1 motor, 2 switches, 1 LVDT) Reference Motor Sliding table Gap opening (LVDT) Resolver Gap position (LVDT) + switches for IN, OUT, ANTI-COLLISION RWA, GSI 11/07 23

Collimator Controls S. Redaelli et al Collimator Beam-Based Alignment Successful test of LHC collimator Collimator Controls S. Redaelli et al Collimator Beam-Based Alignment Successful test of LHC collimator control architecture with SPS beam (low, middle, top level) RWA, GSI 11/07 24

Position Measurement and Reproducibility 20 µm ~ 25 µm mechanical play • R. Losito Position Measurement and Reproducibility 20 µm ~ 25 µm mechanical play • R. Losito et al Measured during test in TT 40 (Oct. 31 st) in remote!!!! RWA, GSI 11/07 25

Compatibility with LHC UHV Resea Energ rch top ic: y abso rption Ultra H Compatibility with LHC UHV Resea Energ rch top ic: y abso rption Ultra H in igh Va cuum J-P. BOJON, J. M. JIMENEZ, D. LE NGOC, B. VERSOLATTO Conclusion: Graphite-based jaws are compatible with the LHC vacuum. The outgassing rates of the C jaws will be optimized by material and heat treatment under vacuum, an in-situ bake-out and a proper shape design No indication that graphite dust may be a problem for the LHC. RWA, GSI 11/07 26

Other collimator features • In-situ spare concept by moving the whole tank (move to Other collimator features • In-situ spare concept by moving the whole tank (move to fresh surface if we scratch the surface with beam) • Direct measurements of jaw positions and absolute gap (we always know where the jaws are) • Precision referencing system during production • Measurements of jaw temperature • Radiation impact optimization: Electrical and water quick plug-ins, quick release flanges, ceramic insulation of cables, . . . • RF contacts to avoid trapped modes or additional impedance C. Rathjen, AT/VAC RWA, GSI 11/07 27

Collimator Deliveries Production deadline for initial installation Initial 7 Te. V installation Industry: 87% Collimator Deliveries Production deadline for initial installation Initial 7 Te. V installation Industry: 87% of production for 7 Te. V initial ring installation has been completed (66/76). All collimators for first run should be at CERN by end of the year. Total production should be completed in April. RWA, GSI 11/07 28

4) Tunnel Installations (vertical and skew shown) Water Connections Vacuum pumping Modules Collimator Tank 4) Tunnel Installations (vertical and skew shown) Water Connections Vacuum pumping Modules Collimator Tank (water cooled) Quick connection flanges A. Bertarelli RWA, GSI 11/07 BLM Beam 2 29

Tunnel Preparations IR 7 Cable routing from top (radiation) Water connection Cable trays Pumping Tunnel Preparations IR 7 Cable routing from top (radiation) Water connection Cable trays Pumping domes RWA, GSI 11/07 Series of collimator plug-in supports 30

Collimator Installation Quick plug-in support (10 min installation) RWA, GSI 11/07 31 Collimator Installation Quick plug-in support (10 min installation) RWA, GSI 11/07 31

Installed Collimator on Plug-In Collimator Upper plug-in Lower plug-in Base support RWA, GSI 11/07 Installed Collimator on Plug-In Collimator Upper plug-in Lower plug-in Base support RWA, GSI 11/07 32

Remote Train Resea rch top ic: Remo te han dling radioa in ctive e Remote Train Resea rch top ic: Remo te han dling radioa in ctive e nviron ment RWA, GSI 11/07 33

Remote Survey RWA, GSI 11/07 34 Remote Survey RWA, GSI 11/07 34

4) Collimation Performance Simulations: 5 million halo protons 200 turns realistic interactions in all 4) Collimation Performance Simulations: 5 million halo protons 200 turns realistic interactions in all collimator-like objects LHC aperture model Multi-turn loss predictions RWA, GSI 11/07 35

Efficiency in Capturing Losses Local inefficiency [1/m] Resea Efficiency 99. 998 % per m Efficiency in Capturing Losses Local inefficiency [1/m] Resea Efficiency 99. 998 % per m TCDQ rch top 7 Te. V Beam 1, ic: Halo a Betatron cleaning nd co performance Ideal llimati on mode l. Quench limit ing (nominal I, t=0. 2 h) Beam 2, 7 Te. V Efficiency 99. 998 % per m TCDQ Betatron cleaning Ideal performance Quench limit (nominal I, t=0. 2 h) 99. 998 % needed Local inefficiency: #p lost in 1 m over total #p lost = leakage rate RWA, GSI 11/07 99. 995 % predicted 36

Problem: Beam loss tails? Resea rch top ic: Halo b eam d ynami and Problem: Beam loss tails? Resea rch top ic: Halo b eam d ynami and d cs iffusio n theo ry Observation of BLM signal tails: BLM team: team RWA, GSI 11/07 Up to 10 -20 seconds in length Many measurements Beam related true signal! signal 37

Collimation for Ions Different physics! Two-stage b cleaning not working! Limitation to ~50% of Collimation for Ions Different physics! Two-stage b cleaning not working! Limitation to ~50% of Resea nominal ion intensity. rc Ion co llimati h topic : G. Bellodi et al Power load [W/m] on an d ion losses Loss predictions used for allocation of additional BLM’s for ions! ions RWA, GSI 11/07 38

K. Tsoulou et al Energy Deposition (FLUKA) Resea rch top ic: Energ y depo K. Tsoulou et al Energy Deposition (FLUKA) Resea rch top ic: Energ y depo sition FLUKA team RWA, GSI 11/07 39

CERN Mechanical Simulations Displacement analysis – Nominal conditions (100 k. W) – Load Case CERN Mechanical Simulations Displacement analysis – Nominal conditions (100 k. W) – Load Case 2 Resea 10 s Transient (500 k. W) – Loss rate 4 x 1011 p/s (Beam Lifetime 12 min) rc Initial loss 8 e 10 p/s Max. deflect. ~20 mm h topic Advan : ced th ermo mecha nical m odelin g Transient loss 4 e 11 p/s during 10 s Max deflect. -108 mm Back to 8 e 10 p/s situation! RWA, GSI 11/07 A. Bertarelli & A. Dallochio 40

Local Activation • Losses at collimators generate local heating and activation. • Local heating: Local Activation • Losses at collimators generate local heating and activation. • Local heating: On average 2. 5 k. W/m. • Activation: Up to 20 m. Sv/h on contact (better not touch it). tion im pact Fast handling implemented. Remote handling being developed. • Resea Radia rch top ic: Residual dose rates One week of cooling S. Roesler et al RWA, GSI 11/07 41

Kurchatov Collaboration Studies of CFC Material Used in LHC Collimators Resea rch top ic: Kurchatov Collaboration Studies of CFC Material Used in LHC Collimators Resea rch top ic: Radia tion d amage accele in rator m ateria ls A. Ryazanov Working on understanding radiation damage to LHC collimators from 1016 impacting protons of 7 Te. V per year. Also with BNL/LARP… … in addition shock wave models… RWA, GSI 11/07 42

Impedance Problem • Several reviews of LHC collimator-induced impedance (originally not thought to be Impedance Problem • Several reviews of LHC collimator-induced impedance (originally not thought to be a problem). • Surprise in 2003: LHC impedance driven by collimators, even metallic collimators. • LHC will have an impedance that depends on the collimator settings! • Strong effort to understand implications… Third look at impedance in Feb 03 revealed a problem: Resea rch top ic: Imped ance F. Ruggiero RWA, GSI 11/07 43

Transverse Impedance [MΩ/m] First Impedance Estimates 2003 Typical collimator half gap 104 103 102 Transverse Impedance [MΩ/m] First Impedance Estimates 2003 Typical collimator half gap 104 103 102 LHC impedance without collimators 10 1 10 -1 0 2 4 6 Half Gap [mm] RWA, GSI 11/07 8 10 F. Ruggiero, L. Vos 44

Impedance and Chromaticity E. Metral et al RWA, GSI 11/07 45 Impedance and Chromaticity E. Metral et al RWA, GSI 11/07 45

2006 Collimator Impedance Measurement Improved controls in 2006: • Possibility of automatic scan in 2006 Collimator Impedance Measurement Improved controls in 2006: • Possibility of automatic scan in collimator position. • Much more accurate and complete data set in 2006 than in 2004! R. Steinhagen et al E. Metral et al RWA, GSI 11/07 46

Summary: The Staged LHC Path Energy density at collimators Stored energy in beams Number Summary: The Staged LHC Path Energy density at collimators Stored energy in beams Number of collimators (nominal 7 Te. V) State-of-the-art in SC colliders (TEVATRON, 1 MJ/mm 2 2 MJ Phase 1 LHC Collimation 400 MJ/mm 2 150 MJ * 88 Nominal LHC 1 GJ/mm 2 360 MJ 122 Ultimate & upgrade scenarios ~4 GJ/mm 2 ~1. 5 GJ ≤ 138 Limit (avoid damage/quench) ~50 k. J/mm 2 ~10 -30 m. J/cm 3 HERA, …) RWA, GSI 11/07 * Limited by cleaning efficiency (primary) and impedance (secondary) 47

5) Beyond Phase 1 • The LHC phase 1 system is the best system 5) Beyond Phase 1 • The LHC phase 1 system is the best system we could get within the available 4 -5 years. • Phase 1 is quite advanced and powerful already and should allow to go a factor 100 beyond HERA and TEVATRON. • Phase 2 R&D for advanced secondary collimators starts early to address expected collimation limitations of phase 1. • Phase 2 collimation project was approved and funded (CERN white paper). Starts Jan 2008. Should aim at complementary design compared to SLAC. • Collaborations within Europe through FP 7 and with US through LARP are crucial components in our plans and address several possible problems. • We also revisit other collimation solutions, like cryogenic collimators, crystals, magnetic collimators, non-linear schemes. RWA, GSI 11/07 48

LHC Phase 2 Cleaning & Protection Beam axis Beam propagation Impact parameter Core Particle LHC Phase 2 Cleaning & Protection Beam axis Beam propagation Impact parameter Core Particle Unavoidable losses CFC & RWA, GSI 11/07 Crystal CFC Phase 2 material 2. Crystals AP under study (surface effects, dilution, absorption of extracted halo). Shower p e W/Cu Tertiary halo p Superconducting magnets Absorber p Shower Phase 2 materials for system improvement. Absorber e Hybrid Collimator TCSM Primary collimator Crystal Impact parameter ≤ 1 mm 1. Secondary p halo p Phase 1 Colli- 1 Collimator TCSG Primary halo (p) Collimator SC magnets and particle physics exp. W/Cu Low electrical resistivity, good absorption, flatness, cooling, radiation, 49 …

 September workshop provided important input and support… RWA, GSI 11/07 50 September workshop provided important input and support… RWA, GSI 11/07 50

Draft Work Packages White Paper (WP), Europe (FP 7), US (LARP) WP 1 (FP Draft Work Packages White Paper (WP), Europe (FP 7), US (LARP) WP 1 (FP 7) – Management and communication WP 2 (WP, FP 7, LARP) – Collimation modeling and studies WP 3 (WP, FP 7, LARP) – Material & high power target modeling and tests WP 4 (WP, FP 7, LARP) – Collimator prototyping & testing for warm regions Task 1 – Scrapers/primary collimators with crystal feature Task 2 – Phase 2 secondary collimators WP 5 (FP 7) – Collimator prototyping & testing for cryogenic regions WP 6 (FP 7) – Crystal implementation & engineering RWA, GSI 11/07 51

SLAC Collimator Design and Prototyping: Rotatable LHC Collimator for Upgrade Strong SLAC commitment and SLAC Collimator Design and Prototyping: Rotatable LHC Collimator for Upgrade Strong SLAC commitment and effort: Design with 2 rotatable Cu jaws Theoretical studies, mechanical design, prototyping. New full time mechanical engineer hired. Looking for SLAC post-doc on LHC collimation! RWA, GSI 11/07 First prototype with helical cooling circuit (SLAC workshop) 52

Working Together to Develop Solutions… • Many if not most new accelerators are loss-limited Working Together to Develop Solutions… • Many if not most new accelerators are loss-limited in one way or another! • Collimation has become a core requirement for success. The LHC success upgrade program is or will be just one example. • Collimation is so challenging in modern accelerators that it warrants a full collaborative approach to extend the present technological limits. • Collaborations exist or are under discussion with presently 17 partners: partners Alicante University, Austrian Research Center, BNL, EPFL, FNAL, GSI, IHEP, INFN, JINR Dubna, John Adams Institute, Kurchatov Institute, Milano University, Plansee company, Protvino, PSI, SLAC, Turin Polytechnic • The importance and intellectual challenge is reflected by the strong support from the international community • Operational and design challenges impose fascinating technological and physics R&D. RWA, GSI 11/07 53

6) Conclusion • LHC advances the accelerator field into a new regime of high 6) Conclusion • LHC advances the accelerator field into a new regime of high power beams with unprecedented stored energy (and destructive potential). • The understanding of beam halo and collimation of losses at the 10 -5 level will be crucial for its success (high luminosity)! • LHC collimation will be a challenge and a learning experience! • Collimation is a surprisingly wide field: Accelerator physics, nuclear physics, material science, precision engineering, production technology, radiation physics. • A staged collimation approach is being implemented for the LHC, relying on the available expertise in-house and in other labs. • The collaboration and exchange with other labs is very important to design and build the best possible system (achieve our design goals)! • Bid for support from European Community (FP 7). We hope to have GSI as major partner in the domain of understanding and controlling beam losses. RWA, GSI 11/07 54

The Collimation Team… Collimation team: About 60 CERN technicians, engineers and physicists… in various The Collimation Team… Collimation team: About 60 CERN technicians, engineers and physicists… in various groups and departments. + many friends in connected areas (BLM’s, MP, …) + collaborators in various laboratories (SLAC, FNAL, BNL, Kurchatov, …) RWA, GSI 11/07 55