Experience in Beam Collimation Dating back to my work as PL LHC - - PowerPoint PPT Presentation
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. Amann Leading Scientist
Ralph W. Aßmann Leading Scientist Accelerator R&D DESY
SuperKEKB: Challenges for the High Luminosity Frontier 30 - 31 January 2020, KEK, Japan Dating back to my work as PL LHC Collimation, Machine Coordinator LHC and EIC for LEP2
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Experience in Beam Collimation | Ralph Assmann | KEK 2020
Luminosity Frontier for p-p Colliders First beam 10.9. 2008 Higgs Sem. 4.7. 2012
Ralph Assmann HB2010
β* = IP beta function (βx=βy) εn = norm. transv. emittance Np = protons per bunch frev = revolution frequency F = geometrical correction m0 = rest mass, e.g. of proton c = velocity of light
constant Fixed tunnel length Beam-beam: bunch charge! Beta* pushed down Normalized emittance pushed down
Luminosity is increased via stored energy (and stored energy density!)
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Experience in Beam Collimation | Ralph Assmann | KEK 2020
LHC Reaching New Territory – Note Advance of KEKB versus LEP-2
SuperKEKB
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Tungsten collimator in the SPS Lead block accidentally put into a p beam (courtesy G. Stevenson) Damage of coating of a SLC collimator Entry and exit holes of an electron beam impacting on a spoiler (courtesy P. Tenenbaum)
Experience in Beam Collimation | Ralph Assmann | KEK 2020
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Experience in Beam Collimation | Ralph Assmann | KEK 2020
LHC Reaching New Territory – Note Advance of KEKB versus LEP-2
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LEP collimator
(courtesy R. Jung)
LEP was a big system (200 blocks) without major problems (but not easy to operate)…
Experience in Beam Collimation | Ralph Assmann | KEK 2020
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Experience in Beam Collimation | Ralph Assmann | KEK 2020
Design for factor 40 in Luminosity
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Experience in Beam Collimation | Ralph Assmann | KEK 2020
LHC Reaching New Territory – Note Advance of KEKB versus LEP-2
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Experience in Beam Collimation | Ralph Assmann | KEK 2020
Design for factor 40 in Luminosity
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Experience in Beam Collimation | Ralph Assmann | KEK 2020
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?
RWA, SLAC 8/07
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è Up to 500 kW impacting on a jaw (7 kW absorbed in jaw)… Advanced material: Fiber-reinforced graphite (CFC)
RWA, SLAC 8/07
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360 MJ proton beam
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
beams!
RWA, SLAC 8/07
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Collimator Tank (water cooled) Water Connections Vacuum pumping Modules BLM Beam 2 Quick connection flanges
(vertical and skew shown)
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Primary halo (p) Secondary halo p p e π Collimator Core
Diffusion processes Scattering processes
Shower
Beam propagation
Impact parameter ≤ 1 µm
Sensitive equipment
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…
Collimators are
target experiment.
Experience in Beam Collimation | Ralph Assmann | KEK 2020
CERN 2003
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Experience in Beam Collimation | Ralph Assmann | KEK 2020
Clear Design Logic Used Successfully at the LHC
available aperture
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/
d) Assign average and peak loss rates for expected loss locations (shock heating, damage, heating, deformations, cooling requirements, ..).
intercepts all losses safely. Determine materials and settings.
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Experience in Beam Collimation | Ralph Assmann | KEK 2020
Developed further the theory, modeling and hardware for collimation
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Experience in Beam Collimation | Ralph Assmann | KEK 2020
Normalization is crucial for success
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Experience in Beam Collimation | Ralph Assmann | KEK 2020
Protecting the sensitive aperture Collimators must sit at certain phase advance locations (depending on n1, n2, n3) to cover the phase space correctly and
Secondary collimator not 90 deg downstream
RWA, SLAC 8/07
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Momentum Collimation Betatron Collimation
“Phase 1” “Final” system: Layount is 100% frozen!
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Phase 1b: Push performance in collision
Phase 1 (pushed): Still operating at impedance limit (7/10.5/10.5σ). Smaller β* by using tertiary collimators as secondary coll. Profit from thin metallic coating (cannot be guaranteed).
Experience in Beam Collimation | Ralph Assmann | KEK 2020
CERN 2003
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)!
Beam 1 Beam 2
Triplet Triplet D1 D1 H&V tertiary collimators H&V tertiary collimators IP
Work for TCLP first done by I. Baishev/J.B. Jeanneret and checked by N. Mokhov:
propagate towards outside machine.
No change: In total 8 TCLP’s for nominal luminosity!
IP
TCLP SC magnet
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LHC beam will be physically quite close to collimator material and collimators are long (up to 1.2 m)!
~ 0.15 ~ 0.6
Collimator gap must be 10 times smaller than available triplet aperture for nominal luminosity!
Collimator settings usually defined in sigma with nominal emittance!
Experience in Beam Collimation | Ralph Assmann | KEK 2020
CERN 2003
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Machine impedance increases while closing collimators (Carbon curve). LHC will operate at the impedance limit with collimators closed!
Experience in Beam Collimation | Ralph Assmann | KEK 2020
CERN 2003
RWA, SLAC 8/07
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Improved controls in 2006:
scan in collimator position.
and complete data set in 2006 than in 2004!
» 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
» Phase 2 collimators to
and improve efficiency!
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Luminosity optimized in phase 1b with trade-off impedance - background
Large flexibility crucial in order for maximizing chances to avoid limitations…
Close secondary collimators Close tertiary collimators
(use as secondary collimators)
Maximum LUMINOSITY Decrease β* Smaller triplet aperture Require better shadow from collimators Increased impedance Increased background Increase beam current Lower impedance
limit
IMPEDANCE limitation BACKGROUND limitation Require better cleaning efficiency
Experience in Beam Collimation | Ralph Assmann | KEK 2020
CERN 2003
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Experience in Beam Collimation | Ralph Assmann | KEK 2020
CERN 2003
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Experience in Beam Collimation | Ralph Assmann | KEK 2020
CERN 2003
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(a) Injection (b) 7 TeV
Experience in Beam Collimation | Ralph Assmann | KEK 2020
CERN 2003
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Cooling is essential: T < 50 ˚C (for outgassing) Heat load up to 7 kW on a small area… ➔ Fix carbon-based collimator onto metallic cooling support (advanced technologies exist but expensive and long lead times: clamping?)
Experience in Beam Collimation | Ralph Assmann | KEK 2020
CERN 2003
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J-P. BOJON, J.M. JIMENEZ,
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. The magnitude of a local electron cloud and its possible effects are studied.
Experience in Beam Collimation | Ralph Assmann | KEK 2020
CERN 2003
Momentum Cleaning Betatron Cleaning
108 collimators and absorbers in phase I (only
movable shown in sketch)
Gaps: ± 6/7 σ
2-3 mm
Settings in nominal beam sigma at 3.5 TeV Settings in mm at 3.5 TeV for tightest collimator settings achieved (beam 1)
factor 5,000
cleaning to SC arc magnets IR2 IR5 Dump IR8 IR1 Off-momentum coll. Betatron coll. Highest SC losses all around the LHC ring: Predicted years ago!
(beam1, vertical beam loss, intermediate settings)
Leakage or Inefficiency
better worse
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99.995 %
worse better
MD 99.960 %
3.5 TeV operational collimator settings (not best possible)
No quench of any magnet!
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Experience in Beam Collimation | Ralph Assmann | KEK 2020
Clear Design Logic Used Successfully at the LHC
available aperture
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/
d) Assign average and peak loss rates for expected loss locations (shock heating, damage, heating, deformations, cooling requirements, ..).
intercepts all losses safely. Determine materials and settings.
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Experience in Beam Collimation | Ralph Assmann | KEK 2020
system à LHC did well with this approach
and other sensitive equipment)
minimize detector background)
losses at safe locations far from collision points).
collimation but easier to catch than at LHC with p.
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Experience in Beam Collimation | Ralph Assmann | KEK 2020
– Packet of particles, confined in transverse x longitudinal volume.
– Number of protons per bunch.
– Measure of beam energy: E = γ mc2
– Increase of beam energy after end of beam injection
– Mode of data production for physics: Beams after end of squeeze, put into collision, every IP optimized for luminosity.
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– Transverse normalized emittance (γε): Invariant phase space area, ideally conserved with energy. Unit: m-rad or m. – Transverse emittance (ε): Phase space area, is reduced with energy (“adiabatic energy damping”). Unit: m-rad or m. – Both terms are a beam property: everywhere in the ring the same!
– Function to describe beam envelope. Describes focusing from
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– Beta function at the interaction point à used to reduce beam size in the IP and to increase lumiosity.
production.
γε = 3.75 µm ε = 0.5 nm (@7 TeV) β* = 0.55 m σ* = (β* ε)½ = 17 µm
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* =
*