Experience in Beam Collimation Dating back to my work as PL LHC Collimation, Machine Coordinator LHC and EIC for LEP2 SuperKEKB: Challenges for the High Luminosity Frontier 30 - 31 January 2020, KEK, Japan Ralph W. Aßmann Leading Scientist Accelerator R&D DESY
Experience Mainly from the LHC Luminosity Frontier for p-p Colliders Higgs Sem. 4.7. 2012 First beam 10.9. 2008 Page 2 Experience in Beam Collimation | Ralph Assmann | KEK 2020
High Luminosity Frontier Fixed tunnel length Beam-beam: Luminosity is increased via bunch charge ! stored energy (and stored energy density!) constant 1 N p = L 4 ⇤ m 0 c 2 · f rev · F · · E stored � ∗ ⇥ n β * = IP beta function ( β x = β y ) Normalized = norm. transv. emittance ε n emittance N p = protons per bunch Beta* pushed f rev = revolution frequency pushed down F = geometrical correction down m 0 = rest mass, e.g. of proton c = velocity of light 3 Ralph Assmann HB2010
Stored Energy Density (~ Luminosity, Damage) LHC Reaching New Territory – Note Advance of KEKB versus LEP-2 SuperKEKB Page 4 Experience in Beam Collimation | Ralph Assmann | KEK 2020
Examples of Beam Damage Tungsten collimator in the SPS Entry and exit holes of an electron beam Lead block impacting on a spoiler accidentally put into a p beam (courtesy P. Tenenbaum) Damage of coating of a SLC collimator (courtesy G. Stevenson) Page 5 Experience in Beam Collimation | Ralph Assmann | KEK 2020
Stored Energy (~ Heating, Background) LHC Reaching New Territory – Note Advance of KEKB versus LEP-2 Page 6 Experience in Beam Collimation | Ralph Assmann | KEK 2020
LEP: Conventional Collimator Concept LEP collimator (courtesy R. Jung) LEP was a big system (200 blocks) without major problems (but not easy to operate) … Page 7 Experience in Beam Collimation | Ralph Assmann | KEK 2020
From KEKb to SuperKEKb Design for factor 40 in Luminosity Page 8 Experience in Beam Collimation | Ralph Assmann | KEK 2020
Stored Energy and Energy Density LHC Reaching New Territory – Note Advance of KEKB versus LEP-2 Page 9 Experience in Beam Collimation | Ralph Assmann | KEK 2020
From KEKb to SuperKEKb Design for factor 40 in Luminosity Page 10 Experience in Beam Collimation | Ralph Assmann | KEK 2020
From KEKb to SuperKEKb Design for factor 40 in Luminosity Collimators at strategic locations with (always) well controlled settings can guarantee machine protection and background control! à Probably two stage system powerful enough for e+e- collider: primary collimators far from experiments (beta and off-momentum) + local protection collimators against irregular beam loss and background control? Page 11 Experience in Beam Collimation | Ralph Assmann | KEK 2020
LHC Hardware: Water Cooled Jaw è Up to 500 kW impacting on a jaw (7 kW absorbed in jaw) … Advanced material: Fiber-reinforced graphite (CFC) RWA, SLAC 8/07 12
The LHC “TCSG” Collimator 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, SLAC 8/07 13
Collimator General Layout (vertical and skew shown) Water Vacuum pumping Connections Modules Collimator Tank (water cooled) Quick connection flanges BLM Beam 2 A. Bertarelli RWA, SLAC 8/07 14
Collimators as „First Wall“ Collimators are Beam propagation our 7 TeV fixed Core target experiment. Diffusion CERN 2003 Primary processes halo (p) π Secondary halo p Scattering processes p Impact e parameter Sensitive ≤ 1 µ m equipment Collimator Shower Strongly advancing field: One-stage to two-stage to three-stage cleaning … Improving models of halo scattering and tracking … Knowledge of material behavior, advanced materials … 15 Experience in Beam Collimation | Ralph Assmann | KEK 2020
Collimation Design Principle Clear Design Logic Used Successfully at the LHC 1. Establish aperture model of the full ring and normalize with nominal beam size. 2. Establish margins for operation (maximum orbit, injection oscillations, ...) à reduces available aperture 3. Describe loss scenarios: a) Irregular losses (injection error, dump, failures, ...) à determine loss locations around ring à design local protection collimators and their required settings b) Regular local losses (beam-gas scattering, synchrotron radiation fans, ...) à determine loss locations around ring à design local protection collimators and their required settings c) Regular global losses (diffusion processes, energy losses, ...) à will be lost at smallest overall aperture (on/off momentum) à design global collimation system (on/ off momentum) that safely catches those losses d) Assign average and peak loss rates for expected loss locations (shock heating, damage, heating, deformations, cooling requirements, ..). 4. Design an appropriate collimation system (phase advances, azimuthal angle) that intercepts all losses safely. Determine materials and settings . 5. Check impedance of the system (also trapped modes) and iterate settings if required. Page 16 Experience in Beam Collimation | Ralph Assmann | KEK 2020
Book Chapter on Theory and Design Developed further the theory, modeling and hardware for collimation Page 17 Experience in Beam Collimation | Ralph Assmann | KEK 2020
Collimation Works in Phase Space Normalization is crucial for success Page 18 Experience in Beam Collimation | Ralph Assmann | KEK 2020
Defining Collimator Hierarchy vs Aperture Protecting the sensitive aperture Collimators must sit at certain phase advance locations (depending on n1, n2, n3) to cover the phase space correctly and optimally à optics design for collimation ! Secondary collimator not 90 deg downstream of primary collimator à two sec. coll. per prim. coll. for improved system! Page 19 Experience in Beam Collimation | Ralph Assmann | KEK 2020
“ Phase 1 ” System Design Momentum Collimation Betatron Collimation “ Final ” system: Layount is 100% C. Bracco frozen! RWA, SLAC 8/07 20
Phase 1b: Push performance in collision Phase 1 (pushed): Still operating at impedance limit (7/10.5/10.5 σ ). Smaller β * by using tertiary collimators as secondary coll. CERN 2003 Profit from thin metallic coating (cannot be guaranteed). 21 Experience in Beam Collimation | Ralph Assmann | KEK 2020
Tertiary Collimators H&V tertiary collimators Beam 2 IP Beam 1 Triplet D1 Triplet D1 H&V tertiary collimators At small β * we also have small phase advance to triplet! Shadow against incoming beam halo on triplet aperture! Two collimators (H+V) for each incoming beam at each IP! è 16 additional collimators (Cu/W jaws)! Replace in case of beam hit (better than triplets)! R. Assmann
(V) Catching the p-p Induced Showers Work for TCLP first done by I. Baishev/J.B. Jeanneret and checked by N. Mokhov: • Showers from p-p interaction in high luminosity points (IR1/IR5) propagate towards outside machine. IP TCLP SC magnet • Showers can quench magnets. • Absorbers at Q5 and D2 to intercept debris (complement the TAN). • Quality of absorption can directly limit the luminosity! No change: In total 8 TCLP ’ s for nominal luminosity! R. Assmann
Collimating with small gaps ~ 0.6 ~ 0.15 Collimator gap must be 10 times smaller than available triplet aperture for nominal luminosity! Collimator settings usually defined in sigma with nominal emittance! LHC beam will be physically quite close to collimator material and collimators are long (up to 1.2 m)! CERN 2003 24 Experience in Beam Collimation | Ralph Assmann | KEK 2020
The Impedance Challenge Machine impedance increases while closing collimators (Carbon curve). LHC will operate at the impedance limit with collimators closed! L. Vos Transverse impedance ~ 1 / (half gap) 3 CERN 2003 25 Experience in Beam Collimation | Ralph Assmann | KEK 2020
2006 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, SLAC 8/07 26
Impedance Limit from IR3/IR7 Collimators » Increase from collimators (nominal settings) for the imaginary part of the effective vertical impedance : – 8 kHz: factor 3 for injection factor 69 for 7 TeV – 20 kHz: factor 3 for injection factor 145 for 7 TeV » Large increase in impedance must be actively counteracted by transverse feedback and octupoles! » Phase 2 collimators to overcome impedance and improve efficiency!
Luminosity optimized in phase 1b with trade-off impedance - background Maximum LUMINOSITY Decrease β * Increase beam current Lower impedance Require better Smaller triplet aperture l imit cleaning efficiency Require better shadow from collimators Close secondary collimators Close tertiary collimators (use as secondary collimators) Increased impedance Increased background IMPEDANCE limitation BACKGROUND limitation Large flexibility crucial in order for maximizing chances to avoid limitations … CERN 2003 28 Experience in Beam Collimation | Ralph Assmann | KEK 2020
Irregular Beam Impact ➔ A. Ferrari,V. Vlachoudis CERN 2003 29 Experience in Beam Collimation | Ralph Assmann | KEK 2020
Recommend
More recommend
