# Presentation: 694078

## Tracking Studies of LHC Collimation System at SLAC

- Yunhai Cai
- Stanford Linear Accelerator Center

- October 20, 2004

*US HLC Accelerator Research Program meeting, *
*Napa Valley, California,  October 19-21, 2004*

## Impedance of the phase I collimators (C) is over the budget for the nominal design current. This means that we most likely to select mental as collimator material for the phase II collimators.
But, due to the high energy and high intensity of the LHC beam to metallic collimator is easily melted in an accidental beam loss. Hence, we consider to use consumable collimators based on the design for linear collider for the phase II system.
Efficiency of the secondary collimators has to be to be improved to the level of 1x10-4. That means that the number of escaped protons from the secondary collimators relative to the number of impacted protons on the primary collimators is below 0.01%.
Needs to reduce the background in the particle detectors to a tolerable level.  Collimators are an important part of the machine protection system.

- But, due to the high energy and high intensity of the LHC beam to metallic collimator is easily melted in an accidental beam loss. Hence, we consider to use consumable collimators based on the design for linear collider for the phase II system.
- Efficiency of the secondary collimators has to be to be improved to the level of 1x10-4. That means that the number of escaped protons from the secondary collimators relative to the number of impacted protons on the primary collimators is below 0.01%.
- Needs to reduce the background in the particle detectors to a tolerable level.  Collimators are an important part of the machine protection system.

- Motivations for Phase II Collimation System

## Purposes of Multi-Turn Tracking Study of Collimation System

- Optimize the collimator system: functionality, location, material, geometry, and operating procedure.
- Provide the loss map to study the energy deposition. Support the engineering design of the collimator, over heating? What kind of cooling system?
- Understand and predict the beam halo, beam loss and the background in the detector

## Planned Collimators for LHC

- IR7 betatron cleaning (warm section) :
- 		4 primary collimators (3+1)
- 		3 scraper (3)
- 		32 secondary collimators (11+11+10)
- IR3 energy cleaning (warm section):
- 		1 primary collimator (1)
- 		1 scraper (1)
- 		8 secondary collimators (4+4)
- It is not clear to me if this system could satisfy all design requirements.

- SLAC

## Phase II Collimators in IR7(betatron collimators: 11)

| Name | A [degree] | S[m] |
| --- | --- | --- |
| TCSM.A6L7.B1 | 142.5 | 45.495 |
| TCSM.B5L7.B1 | 141.6 | 104.722 |
| TCSM.A5L7.B1 | 42.7 | 108.722 |
| TCSM.D4L7.B1 | 90.0 | 130.052 |
| TCSM.B4L7.B1 | 0.0 | 199.978 |
| TCSM.A4L7.B1 | 135.7 | 203.978 |
| TCSM.A4R7.B1 | 45.2 | 207.978 |
| TCSM.B5R7.B1 | 139.6 | 299.234 |
| TCSM.D5R7.B1 | 53.3 | 315.234 |
| TCSM.E5R7.B1 | 128.5 | 319.234 |
| TCSM.6R7.B1 | 0.5 | 353.839 |

## Simulation of Collimation System Using Sixtrack+K2(CERN)

- Nonlinear but ideal lattices: injection and collision
- Thin-lens approximation is used in Sixtrack to speed up the simulation
- A run of 200 turns with 64x1000 protons takes eight hours on a Linux PC
- Primary collimators at 6 and secondary ones at 7It is in the linear region and matrix approximation is quite adequate)
- Initial beam distribution: center: 6.003 and spread 0.0015. (h,v,r)

## Proton Scattering inside Collimators (K2)

- Electromagnetic: ionization and Coulomb scattering
- Bremsstrahlung and lepton pair production
- Nuclear: elastic and inelastic scattering
- Including edge effects
- Benchmarked against (FLUKA and Struct)
- Save coordinates of inelastic scattered protons as absorbed and used as FLUKA simulation of energy deposition

## Code Comparison: K2/STRUCT/FLUKA by M. Brugger

- x

- y

- Em

- px

- py

- Collision energy: 7Tev, 0.5m long CU, 40 (m, rad)

## Benchmark to Ralph’s Simulation of Phase I Collimation System 

- Injection energy: 450 Gev

- # impacts

- # absorbed

- <impact parameter>

- spread of impact
- parameter

## Efficiency vs. Length

- Ralph’s phase II              Yunhai’s phase I

- Injection energy: 450 Gev?

## Efficiency vs. Length at Collision Energy (7 Tev)

**only phase I collimators are used in simulation**

## Design Issues and Boundary Conditions

- Can we change the primary collimators?
- Can we use more collimators? Phase 4
- Can we replace the phase I collimators?
- What material? Length?
- Setting of the collimators? Gaps and orientation?
- Where the escaped protons go? Triplets?
- Change location or optics?

## Issues to be Discussed

- Apertures of entire machine
- Who should implement it?
- Local beam loss and protection near the superconducting magnets
- Near detector cleaning and background?
- Should we benchmark the code?
- Direct simulation of halo generation?
- Plan to measure the background during the commissioning?

## Conclusion

- The sixtrack+K2 has been ported to SLAC successfully and we are ready to use it to do the design work
- Near-term goal is to finalize the phase II design before April 2005. To achieve that, we should define a few milestones along the way and clarify the requirements.
- Many thanks to our CERN colleagues!!!