1. Revised estimates of heat loads and radiation damage in the IT and D1
F. Cerutti, L.S. Esposito
WP3 meeting, 27 March 2014

2. Contents Inner Triplet—CP—D1 beam screen design
recap the effect on energy deposition
of the BS executive design, which is different from the
conceptual one used until now in the FLUKA & MARS
simulations (as already presented at the Technical Meeting on Vacuum for HL-LHC on 5 March 2014)
investigate the reason(s) of the significant peak dose
increase in Q3B
individuate possible mitigation solutions
update total heat load 2

3. D1 CP Q3 FLUKA geometry model for IT—CP—D1 Coils:
Nb3Sn: IT quadrupoles
Nb-Ti: orbit correctors, super-ferric magnets, D1
Apertures:
60 mm TAS
150 mm Inner Triplet + CP + D1
TAS Q3 CP D1
28 February 2014 3 

4. Reference: R. Kersevan, WP3 meeting, 28 January 2014
Conceptual design of the beam screen (BS) for the Q1 and Q2-Q3-CP-D1 areas.
Reference: R. Kersevan, WP3 meeting, 28 January 2014
6 mm W shielding (Q2 and beyond) to be modified to allow for bigger capillaries
(see R. vanWeelderen’s talk, this WS)
1 (left) and 2 (right) mm-thick BS
Baseline design is 2 mm!
Luca Dassa, Rafael Fernandez-Gomez, EN-MME-ES 4

5. Spot the differences between BS designs
old version (BS #1)
new version (BS #2)
16 mm absorbers
cooling capillary (tube) size
absorber shape
INERMET 180
beam screen thickness (2⇒1 mm) thus bringing Q1 aperture to 113 mm elsewhere to 123 mm
[still to be modified]
6 mm absorbers 5

6. Effect on peak dose due to BS design changes
Particular worry has been raised by the increase on Q3B
A possible mitigation for the orbit corrector (to be investigated) is to move it at the end of the CP taking advantage of the more favourable geometry of the high-order correctors. Possible effect on beam performance to be assessed 6

7. BPM with tungsten absorbers
Beneficial in particular for the interconnect Q3—CP
(and Q2A—Q2B and Q2B—Q3)
Obviously no impact inside Q3B 7

8. Φ-z distribution of the dose along IT—CP—D1
Blue rectangles indicate the azimuthal regions shielded by the tungsten absorbers
Black rectangles indicate the azimuthal regions covered by coils
Owing to the IT magnetic configuration,
through Q2 the losses move from the top to the bottom 8

9. Transverse distribution
Coil protection near the poles is not assured by the tungsten absorbers
(anyway hitting the wedges rather than the cable?) 9

10. Criticality of BS geometry (rather than material)
Even taking ideal absorbers totally opaque, the Q3 peak dose remains high
due to the revised shape 10

11. Back to (almost) the original BS geometry
[i.e. BS #1 with INERMET and only 1mm SS]
BS #2
(For Q1 stay with BS #2 as on slide 5) 11

12. Where we end up
(30 MGy over 3000fb-1) 12

13. A clarification on the orbit corrector
Dose peak is located in the insulator.
For horizontal crossing it is located in the coils, but is lower. 13

14. Peak power profile @ 5 × 1034 cm-2 s-1
In any case good margin wrt assumed quench limits
(40 (13) mW/cm3 for Nb3Sn (NbTi)) 14

15. Total heat load (vertical crossing)
BS#2, 50 cm gap in ICs
BS#2, 10 cm gap in ICs
BS#3, 50 cm gap in ICs
Power [W]
Magnet
cold mass
Beam
screen
Q1A + Q1B
110
150
Q2A + corr
105 50 55
Q2B + corr
130 70 65
Q3A + Q3B
160 60 CP 45 D1
100 95 90
Interconnects 25 85
Total
700
510
690
515
675
535
Estimation with BS#1
630
615
@ 5 × 1034 cm-2 s-1
Total values for horizontal crossing are about 10% lower 15

16. aim to cover as much as possible the coil part close to the poles
Summary
Impact of the executive beam screen design has been evaluated and the reasons of the sizeable increment in the Q3B have been disentangled
Mitigation measures:
aim to cover as much as possible the coil part close to the poles
shield Q3—CP interconnect to protect the orbit corrector
the IT-CP-D1 cold mass (beam screen) is expected to absorb ~700 (~550) W from collision debris at 5 × 1034 cm-2 s-1 16