1. Beam halo and beam losses in IR1 and IR5
R. Assmann, AB
MIBWG
June 15th, 2007
RWA, 31/5/2007

2. The LHC Challenge
Talk at EPAC 2002 in Paris: “Requirements and Design Criteria for the LHC Collimation System”.
High stored energy and stored energy density!
Small collimation gaps!
RWA, 31/5/2007

3. 8.5 W/m Preventing Quenches
Shock beam impact: 2 MJ/mm2 in 200 ns (0.5 kg TNT)
Maximum beam loss at 7 TeV: 1% of beam over 10 s
500 kW
Quench limit of SC LHC magnet:
8.5 W/m
RWA, 31/5/2007

4. System Design “Phase 1” Momentum Cleaning Betatron Cleaning
“Final” system: Layount is 100% frozen!
RWA, 31/5/2007
 Outcome of accelerator physics + energy deposition optimization

5. SC triplet and experiment
Multi-Stage Cleaning
Without beam cleaning (collimators):
Quasi immediate quench of super-conducting magnets (for higher intensities) and stop of physics.
Required cleaning efficiency: always better than 99.9%.
Beam propagation
Core
Unavoidable losses
Primary
halo (p)
Secondary halo p p
Shower p
Tertiary halo
Impact parameter
≤ 1 mm p e p
collimator
Primary
Secondary
collimator
Shower
SC triplet and experiment e
Absorber
TCT
RWA, 31/5/2007

6. The LHC “TCSG” Collimator
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 materials. Some very different with 2 beams!
 For design see TS seminar A. Bertarelli.
RWA, 31/5/2007

7. Functional Description
Two-stage cleaning (robust CFC primary and secondary collimators).
Catching the cleaning-induced showers (Cu/W collimators).
Protecting the warm magnets against heat and radiation (passive absorbers).
Local cleaning and protection at triplets (Cu/W collimators).
Catching the p-p induced showers (Cu collimators).
Intercepting mis-injected beam (TCDI, TDI, TCLI).
Intercepting dumped beam (TCDQ, TCS.TCDQ).
Scraping and halo diagnostics (primary collimators and thin scrapers).
RWA, 31/5/2007

8. Top Level Collimator Controls
S. Redaelli et al
Successful test of LHC collimator control architecture with SPS beam (low, middle, top level)
RWA, 31/5/2007

9.  Multi-turn loss predictions
Cleaning Efficiency
Simulations: 5 million halo protons
200 turns
realistic interactions in all collimator-like objects
LHC aperture model (p losses) and FLUKA
G. Robert-Demolaize & S. Redaelli
 Multi-turn loss predictions
RWA, 31/5/2007

10. Ramp: Efficiency with Collimators Scaled for Constant Beam Tolerances
Efficiency / m
dN/dt = 0.1%/s, N = 3e14 p, ideal
Cleaning efficiency
Quench limit requirement
Beam energy [TeV]
C. Bracco et al
RWA, 31/5/2007

11. Efficiency
Assumption always: Lost protons/ions are hitting the primary collimator (multi-turn diffusion process with 5 nm per turn).
Ideally: Protons/ions just disappear (“black hole” collimator):  100 % efficiency (1 - #protons escaping / total)  0 inefficiency (# protons escaping / total)  zero heat load from halo protons on SC magnets
In reality: A few protons/ions can escape:  efficiency < 100% (we talk about > 99.95%)  inefficiency > 0 (we talk about < 5 × 10-4)
Quenches: Heat load per m. Critical parameter are losses per m of SC magnet, or efficiency per m! No problem if losses are distributed over 27 km…  efficiency (we talk about > % per m)  inefficiency (we talk about < 2 × 10-5 per m)
RWA, 31/5/2007

12. 7 TeV Proton Loss Distribution
p losses ~ inefficiency
G. Robert-Demolaize et al
RWA, 31/5/2007

13. Beam Losses in IR1 and IR5 Betatron halo losses: Momentum halo losses:
No direct losses in IR1 and IR5 triplets or experiments when collimators are correctly set up. Fully protected by tertiary collimators (H and V on each incoming beam).
Load of tertiary beam halo at tertiary collimators about 0.05% of total losses: For example: @ TCP @ TCT Peak loss (0.2h, 4e11 p/s)  < 2e8 p/s (spike) Parasitic losses (20h, 4e9 p/s)  < 2e6 p/s (normal)
Completely uncritical for triplet quench with tertiary collimators in place.
Efficiency will be lower during commissioning and early running. Losses should never be higher than listed above in normal operation.
Experiments will see the showers from the tungsten collimators.
Momentum halo losses:
No detailed loss maps yet. Momentum losses much lower than betatronic.
RWA, 31/5/2007

14. Preparing Commissioning at 7 TeV
0.8 mm at a typical collimator
0.2 mm at a typical collimator
Phase 1
 Commissioning is being prepared: Controls, tools, scenarios, …
RWA, 31/5/2007

15. IP1/IP5 MARS15 Extended Model
Machine, interface and related detector elements
in  550 m from IP1 and IP5: 3-D geometry,
materials, magnetic fields, tunnel and rock outside
(up to 12 m laterally).
Tungsten tertiary collimators TCTV and TCTH at
and m from IP, respectively,
aligned wrt BEAM2 coming to IP5 and BEAM1
coming to IP1.
First source: tails from betatron cleaning in IP7 –
files of proton hits in TCTs for BEAM1 and BEAM2
from Tom Weiler.
Second source: beam-gas interactions of BEAM2 at
0 to 550-m from IP5 using gas pressure map from
CERN colleagues.
MARS15 calculations: power density and dynamic
heat loads in inner triplet quads, absorbed and
residual doses in the entire region, and particle
fluxes at CMS and ATLAS.
Most calculations completed for IP5; started for IP1.
CERN/LARP Collimation, Aug. 23, 2006
IP1/IP5 TCT Collimators - N.V. Mokhov

16. IP1/IP5 TCT Collimators - N.V. Mokhov
TCTV and TCTH Models
Aspect ratio V:H = 1:12
CERN/LARP Collimation, Aug. 23, 2006
IP1/IP5 TCT Collimators - N.V. Mokhov

17. Betatron Cleaning: Hadron Fluxes in IR5
Total in TCT – TAN region
Charged hadrons at 0 to 150 m
CERN/LARP Collimation, Aug. 23, 2006
IP1/IP5 TCT Collimators - N.V. Mokhov

18. Betatron Cleaning: Radiation Loads in IR5
Peak power density in Q3 SC coils: 6.e-5 mW/g
Peak absorbed dose: a few kGy/yr
Peak residual dose: 7 mSv/hr
CERN/LARP Collimation, Aug. 23, 2006
IP1/IP5 TCT Collimators - N.V. Mokhov

19. Betatron Cleaning: Radiation Loads in TCT-TAN Region
Peak absorbed dose: 12 MGy/yr in jaws, 20 kGy/yr outside jaws
Peak residual dose: 8 mSv/hr on jaws, 0.1 mSv/hr around TCTs
CERN/LARP Collimation, Aug. 23, 2006
IP1/IP5 TCT Collimators - N.V. Mokhov

20. Beam1 and Beam 2 Asymmetry
Beam1, 7 TeV
Betatron cleaning
Ideal performance
TCDQ
Quench limit (nominal I, t=0.2h)
Local inefficiency [1/m]
Beam2, 7 TeV
Betatron cleaning
Ideal performance
TCDQ
Quench limit (nominal I, t=0.2h)
Local inefficiency: #p lost in bin over total #p lost over length of aperture bin!
RWA, 31/5/2007

21. Asymmetry IR1/IR5 Beam 1 betatron halo losses on TCT left sides of IP:
IR1: 5e-4 of total halo loss
IR5: 5e-6 of total halo loss
Beam 2 betatron halo losses on TCT right sides of IP:
IR1: 2e-5 of total halo loss
IR5: 3e-4 of total halo loss
Halo losses in experimental insertions are asymmetric. Detailed losses depend on collimator settings, phase advance and halo phase space properties.
Above settings assume IR2 and IR8 collimators present and at same setting as IR1/IR5 teriary collimators. We might open them and losses in IR1/IR5 will increase (small gaps not needed in IR2/8 & trapped mode issues with higher b*, small gaps in IR2/8).  In worst case increase losses by a factor ~2.
RWA, 31/5/2007

22. Summary
Tertiary collimators are in place and shield IR1/IR5 well against halo losses.
Triplet quenches from beam halo now uncritical. Showering studies done.
Betatron halo losses at tertiary collimators should be as follows (nominal intensity, nominal cleaning efficiency, nominal optics, IR2/8 retracted):
Below ~4e6 p/s in stable physics conditions (20h beam lifetime)
Below ~4e8 p/s for “long spikes” (0.2h beam lifetime for up to 10s)
Never higher than this but likely quite a bit lower in early years.
Accidential losses at 7 TeV can put 1 nominal bunch into the edge of the horizontal TCT (will not happen with correct collimator set-up, will damage TCT: scratch of surface, unlikely is a water leak).
Momentum halo loss maps to be produced, but losses will be lower.
Team in place to support studies: C. Bracco, T. Weiler, S. Redaelli, R. Assmann
RWA, 31/5/2007

23. Acronyms TC… = Target Collimator TCL… = Target Collimator Long
TCP = Primary collimator
TCSG = Secondary collimator Graphite
TCSM = Secondary collimator Metal
TCHS = Halo Scraper
TCL… = Target Collimator Long
TCLI = Injection protection (types A and B)
TCLP = Physics debris
TCLA = Absorber
TCD… = Target Collimator Dump
TCDQ = Q4
TCDS = Septum
TCDI = Injection transfer lines
TD… = Target Dump
TDI = Injection
RWA, 31/5/2007