1. Beam-Induced Energy Deposition Studies in IR Magnets
LHC SC Magnet Design Studies
Fermilab
Beam-Induced Energy Deposition Studies in IR Magnets
Nikolai Mokhov
Fermilab
WAMDO Workshop on Accelerator Magnet Design and Optimization
CERN
April 3-6, 2006

2. Energy Deposition with MARS - N. Mokhov
OUTLINE
Quench Limits and Design Constraints
Protecting LHC IR from pp-products
Upgrading and Extending IR Model
LARP Design Study Developments
Summary
WAMDO – CERN, Apr. 3-6, 2006
Energy Deposition with MARS - N. Mokhov

3. Energy Deposition with MARS - N. Mokhov
QUENCH LIMITS
Tevatron: Based on measurements and analyses by H. Edwards et al ( ), the following energy deposition design limits for the Tevatron SC dipole magnets (4.4 T, I/Ic=0.9, 4.6 K) have been chosen in Tevatron design report (1979):
Slow loss (DC) mW/g ( ~2 mW/g w/cryo)
Fast loss (1 ms) mJ/g
Fast loss (20 ms) 0.5 mJ/g
LHC IR quads: 1.6 mW/g (12 mJ/cm3) DC (design goal 0.5 mW/g)
Nb3Sn IR quads: ~5 mW/g DC (design goal 1.7 mW/g)
WAMDO – CERN, Apr. 3-6, 2006
Energy Deposition with MARS - N. Mokhov

4. LHC IR PROTECTION: DESIGN CONSTRAINTS
Use nominal design luminosity of 1034 cm-2 s-1, and 1035 cm-2 s-1 for upgrade scenarios.
Geometrical aperture: keep it larger than “n1 = 7” for injection and collision optics, including closed orbit and mechanical tolerances.
Quench stability: keep peak power density emax, which can be as much as an order of magnitude larger than the azimuthal average, below the quench limit with a safety margin of a factor of 3.
Radiation damage: with the above levels, the estimated lifetime exceeds 7 years even in the hottest spots.
Quench limit: tests of porous cable insulation systems and recent calculations concerning the insulation system to be used in the Fermilab-built LHC IR quadrupoles (MQXB) have shown that up to about 1.6 mW/g can be removed while keeping the coil below the magnet quench temperature. 1.2 mW/g was used as a limit in ’90s in these studies.
Dynamic heat load: keep it below 10 W/m.
Hands-on maintenance: keep residual dose rates on the component outer surfaces below 0.1 mSv/hr.
Engineering constraints must always be obeyed.
WAMDO – CERN, Apr. 3-6, 2006
Energy Deposition with MARS - N. Mokhov

5. IR1/IR5 INNER TRIPLET PROTECTION
3-mm SS SS
53-mm ID
66-mm OD
TASB: SS/Cu
1.2-m long
60-mm ID
120-mm OD
Copper
1.8-m long
34-mm ID, 0.5-m OD
WAMDO – CERN, Apr. 3-6, 2006
Energy Deposition with MARS - N. Mokhov

6. LHC IR1/IR5 PROTECTION SYSTEM
As a result of thorough optimization of the IP1/IP5 layouts and low-b quad design, the system was designed (and built) to protect IR SC magnets against debris generated in the pp-collisions, and magnets and detectors against beam halo and a misbehaved beam coming to the IP. This was based on detailed energy deposition calculations with the MARS code at Fermilab.
The system includes a set of absorbers in front of the inner triplet (TAS), inside the triplet aperture and between the low-beta quadrupoles, inside the cryostats, in front of the D2 separation dipole (TAN) and between the outer triplet quads as well as a complex system in IP6 and tertiary TCT collimators for the incoming beam. Their parameters were optimized over the years to provide better protection with engineering constraints in mind.
WAMDO – CERN, Apr. 3-6, 2006
Energy Deposition with MARS - N. Mokhov

7. TAS AND LINER OPTIMIZATION
Beam screen together with cold bore
Chosen: 6.5 mm in Q1
and 3 mm in Q2-Q3
Reduces power density at IP-end of Q1
300 times and dynamic heat load to inner
triplet by 185 Watts. 5% of incoming energy
punch through 1.8-m copper TAS body
WAMDO – CERN, Apr. 3-6, 2006
Energy Deposition with MARS - N. Mokhov

8. TAS AND INNER ABSORBERS
WAMDO – CERN, Apr. 3-6, 2006
Energy Deposition with MARS - N. Mokhov

9. POWER DENSITY AND HEAT LOADS
emax = mW/g W per 4 quads, 20.5 W per four correctors and feedbox: W total and about 115 W at 1.9 K.
WAMDO – CERN, Apr. 3-6, 2006
Energy Deposition with MARS - N. Mokhov

10. ABSORBED AND RESIDUAL DOSE
Annual dose up to 30 MGy in coils.
30-day/1-day residual contact dose up to 45 mSv/hr
WAMDO – CERN, Apr. 3-6, 2006
Energy Deposition with MARS - N. Mokhov

11. Residual Dose on Outer Vessel and in SC Coils vs Time
WAMDO – CERN, Apr. 3-6, 2006
Energy Deposition with MARS - N. Mokhov

12. PROTECTION SYSTEM PERFORMANCE AT 1034
As a result of optimization of the protection system, it became possible to meet design constraints for the LHC IR at luminosity of 1034 cm-2 s-1, with emax < mW/g, Q < 10 W/m, and lifetime in the hottest spot of about 7 years.
Dynamic heat loads at cryo temperatures are about 30 W in each quad (114 W total), 20 W in correctors and feedbox, 2 W in D2 dipole, and 0.5 to 2 W in outer triplet quads. At room temperature, the main players are TAS (184 W), D1 dipole (50 W), and TAN (189 W).
Residual dose from several hundred mSv/hr in TAS, TAN and inner absorbers to below mSv/hr on outer vessel.
WAMDO – CERN, Apr. 3-6, 2006
Energy Deposition with MARS - N. Mokhov

13. IR AND QUAD MARS MODEL DEVELOPMENTS
Convert to a more consistent LHC lattice version 6.5 (layout, dimensions, fields)
Realistic beam screen in Q1
Nb3Sn coil design with 80 to 110-mm apertures
A possibility for user-friendly variation of quad apertures and internal absorber thickness
High-Z materials for liner; low-Z spacers in coils
Upgrade of detector & machine-detector interface
Extension of the model into arcs (outer triplet, matching section, dispersion suppressor and arcs)
Substantial developments of the MARS15 code
WAMDO – CERN, Apr. 3-6, 2006
Energy Deposition with MARS - N. Mokhov

14. IP1/IP5 MARS15 Model with TAN, LHCf, ZDC and TOTEM
WAMDO – CERN, Apr. 3-6, 2006
Energy Deposition with MARS - N. Mokhov

15. ENERGY DEPOSITION STUDIES FOR LARP IR MAGNETS
Mission:
Provide full support to superconducting magnet design studies in the area of beam-induced energy deposition effects in the IR quadrupoles and dipoles.
2. Continuously develop simulation tools and IR region models to keep physics modules at state-of-the-art level and geometry and lattice descriptions up-to-date.
3.With engineering constraints in mind, develop and optimize mitigation measures to reduce power density, accumulated dose and dynamic heat loads below the corresponding limits (with a safety margin of a factor of 3 for quench-related peak power density) for the luminosity up to 1035 cm-2 s-1.
WAMDO – CERN, Apr. 3-6, 2006
Energy Deposition with MARS - N. Mokhov

16. Open Mid-Plane Dipole-First
WAMDO – CERN, Apr. 3-6, 2006
Energy Deposition with MARS - N. Mokhov

17. MARS15 Nb3Sn QUAD MODEL AND RESULTS
A lot of work here done by I. Rakhno
WAMDO – CERN, Apr. 3-6, 2006
Energy Deposition with MARS - N. Mokhov

18. ED in 90-mm Nb3Sn Quad and Coil ID Dependence
At peak, Q2B is above the design goal of 1.7 mW/g
Lifetime is about 1.5 years with current materials:
need to reduce peak ED and use other materials
WAMDO – CERN, Apr. 3-6, 2006
Energy Deposition with MARS - N. Mokhov

19. Energy Spectra in Coils and Thicker Liner
WAMDO – CERN, Apr. 3-6, 2006
Energy Deposition with MARS - N. Mokhov

20. Energy Deposition with MARS - N. Mokhov
High-Z Inner Absorber
Dynamic heat load scales with luminosity
while peak ED is lower in LARP magnets
per pp-collision
WAMDO – CERN, Apr. 3-6, 2006
Energy Deposition with MARS - N. Mokhov

21. Energy Deposition with MARS - N. Mokhov
SUMMARY
Quench levels in the LHC IR quads are well understood, more work is needed on new magnets.
All energy deposition issues have been addressed in IR in detailed modeling at nominal & upgrade luminosities.
IP1 and IP5 SC magnets are adequately protected with local protection systems, main collimation system in IP3/IP7, IP6 collimators (TCDQ etc), and tertiary collimators TCT.
LHC upgrade scenarios are challenging from energy deposition standpoint.
Feasibility studies performed both for quad- and dipole-first schemes; simulation results for splitted open-midplane dipole, and thicker inner absorber and high-Z absorbers in quads are quite encouraging.
Quench and material beam tests are needed.
WAMDO – CERN, Apr. 3-6, 2006
Energy Deposition with MARS - N. Mokhov