# Presentation: 804601

## Energy Deposition Issues in LHC IR Upgrades

- LHC IR Upgrades Workshop
-  Pheasant Run, St. Charles, IL
- October 3-4, 2005

***Fermilab***

_**LHC IR 2005**_

- Nikolai Mokhov, Fermilab

## OUTLINE

- Radiation Constraints
- Quench Limits
- Protecting LHC IR from pp-products
- Upgrading LHC IR
- Protecting IR from beam loss
- Summary

## RADIATION CONSTRAINTS AT COLLIDERS

- Sustain favorable background conditions in experiments.
- Maintain operational reliability in stores: quench stability and dynamic heat loads on cryogenics.
- Prevent quenching SC magnets and damage of machine and detector components at unsynchronized beam aborts.
-  Minimize radiation damage to components, maximize their lifetime.
- Minimize impact of radiation on personnel and environment: prompt and residual radiation (hands-on maintenance).

## SLOW AND FAST QUENCH LEVELS IN TEVATRON SC MAGNETS

## QUENCH LIMITS

_**Tevatron:**_ Based on measurements and analyses by H. Edwards et al (1977-1978), 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)        8 mW/g ( ~2 mW/g w/cryo)
-  Fast loss (1 ms)      1 mJ/g
-  Fast loss (20 s)  0.5 mJ/g
_**LHC IR quads:**_ 1.6 mW/g DC (see next slide)

## 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 max, 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.

## LHC IR1/IR5 PROTECTION SYSTEM

- At the LHC, after thorough optimization of the IR layout, an IR protection system was designed to protect SC magnets against debris generated in pp-collisions and in near beam elements. The optimization study 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 (liners) and between the low-beta quadrupoles (TASB), inside the cryostats, in front of the D2 separation dipole (TAN) and between the outer triplet quadrupoles. Their parameters were optimized over years via MARS runs to provide better protection and to meet practical requirements.
- Fermilab FN-732, LHC Project Report 633 (2003).

## IR1/IR5 INNER TRIPLET PROTECTION

- Copper
- 1.8-m long
- 34-mm ID, 0.5-m OD

- SS
- 53-mm ID
- 66-mm OD

- 3-mm SS

- TASB: SS/Cu
- 1.2-m long
- 60-mm ID
- 120-mm OD

## TAS AND LINER OPTIMIZATION

- 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

- Chosen: 6.5 mm in Q1
- and 3 mm in Q2-Q3

- Beam screen together with cold bore

## MARS MODELING IN IP1/IP5 

## POWER DENSITY (DOSE) ISOCONTOURS IN IP1/IP5 INNER TRIPLET 

## PEAK POWER DENSITY AND DYNAMIC HEAT LOAD

- max =  0.45 mW/g

- 113.8 W per 4 quads, 20.5 W per four correctors and feedbox: 134.3 W total and about 115 W at 1.9 K.
- Tom Peterson (and Ranko after him) multiplied this by two to get load at “ultimate” luminosity.

## SUMMARY FOR IP1/IP5 (nominal luminosity)

- 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 max <  0.45 mW/g, Q < 10 W/m, and lifetime in the hottest spot of about 7 years. Note that the power density and dose in the SC coils always peaks in the horizontal or vertical planes at the coil inner-most radius.
- Dynamic heat loads at cryo temperatures are about 30 W in each quad (114 W total), 20.5 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 and thick beam tube to below 0.1 mSv/hr on outer vessel.

## LHC UPGRADE SCENARIOS

- “Modest” upgrade to the luminosity of 2.5x1034 cm-2 s-1: traditional quadrupole-first design (large bore Nb3Sn); energy problems are manageable!
- Upgrade to 1035 cm-2 s-1: double-bore inner triplet with separation dipoles placed in front of quads (reduced # of long-range beam-beam collisions, beam on-axis in quads, local corrections for each beam), but severe radiation problems with about 3.5 kW dynamic heat load on the first dipole, and 100 times higher peak power density compared to nominal!

## “MODEST” UPGRADE: 90-mm Nb3Sn quads (1)

- Inner-layer midplane turns
- at Top = 1.95 K

- 200 T/m gradient

- Targetmax = 0.5 mW/g,
- consistent with reasonable
- lifetime, remains

## “MODEST” UPGRADE: 90-mm Nb3Sn quads (2)

- max =  0.84 mW/g, 87% up
- compared to nominal (no
- linear scale with luminosity)

- Heat load is up by about
- a factor of 2.5 (i.e. scales
- with luminosity)

- 0.212 mrad half-crossing angle, 42-mm ID TAS

- EPAC-2003 papers

## DIPOLE-FIRST IR LAYOUT

## DIPOLE-FIRST: COS-THETA vs BLOCK COILS

- Cos-theta: max=50 mW/g (probably
- can be reduced to 13 mW/g with
- low-Z spacers), i.e. well above
- the quench limit.
- Open mid-plane block coil design
- with tungsten rods at LN temper:
- peak max < 1 mW/g, significant
- fraction of heat load is dissipated
- in tungsten roads. But substantial
- R&D is needed.

- MARS15 power density in open-midplane block coil dipole at maximum (non-IP end)

- PAC-2003, PAC-2005

## DIPOLE-FIRST: 2005 DESIGN (1)

- In realistic optimized design, max at non-IP end was above the quench limit with very high heat loads. Solution: split D1 in two sections D1A (1.5 m, 20 T-m) and D1B
- (8.5 m), with 1.5-m TAS2 absorber (54-mm ID) in between.

## DIPOLE-FIRST: 2005 DESIGN (2)

- max =  0.4 mW/g (central coils in D1A and coils close
- to tungsten rods in D1B) at
- luminosity of 1035.
- _Heat loads (W)_
- D1A: 3.6 (SC), 26.6 (collar),
- 4.6 (yoke), 1.6 (rods)
- D1B: 24.1 (SC), 177.2 (collar),
- 15 (yoke), 52.2 (rods), 7 (pipes)
- 1.83 kW in TAS
- 0.27 kW in TAS2
- 5.65 kW in TAN and downstream

## PROTECTING INNER TRIPLETS AND DETECTORS FROM BEAM LOSS

- IP3/IP7 collimators do the main job here, but inner triplet can potentially absorb
- tertiary beam halo and misbehaved beam from 8.4 to 30 : add TCT collimators!

## SUMMARY

- Quench levels in the LHC IR quads are well understood, more work is needed on other magnets.
- All energy deposition issues have been addressed in IR in detailed modeling at nominal and upgraded luminosities.
- IP1 and IP5 SC magnets and CMS and ATLAS detectors are adequately protected at normal operation and accidental conditions with the local (TAS, liners etc) protection systems, main collimation system in IP3/IP7, IP6 collimators (TCDQ etc), and tertiary collimators TCT.
- LHC upgrade scenarios are quite challenging from energy deposition standpoint, simulation results are encouraging, but more work is needed.