1. The HiLumi LHC Design Study is included in the High Luminosity LHC project and is partly funded by the European Commission within the Framework Programme 7 Capacities Specific Programme, Grant Agreement 284404. Optics and TAXN HL-LHC G. Arduini, R. Bruce, O. Brüning, F. Cerutti, R. De Maria, L. Esposito, S. Fartoukh, M. Fitterer, M. Giovannozzi.

2. For any optics: 1.HL-LHC is designed for 10x LHC integrated luminosity -> more radiation 2.HL-LHC optics needs larger crossing angle -> more neutral debries in the 2-in-1 region for horizontal crossing. 3.HL-LHC optics needs larger beam size in the 2-in-1 region because of beta* but also to enhance crab cavity kick.  TAXN needs to protect from more radiation, while allowing more aperture. In addition: Round optics (needs crab cavities) have the largest crossing angle: needs more protection. Flat optics (alternative with or without crab cavities) have largest beam size and smaller crossing angle: needs less protection but more aperture. Design strategy: Despite of the challenges find a solution that accommodates both round and flat optics.  Fixed TAXN cannot be optimal for both optics. 2 TAXN challenge in HL-LHC

3. 3 TAN – Present design criteria Round optics: H crossing Flat optics: H crossing Flat optics: V crossing HL-LHC layout compatible with 3 collision optics for IR1 and IR5: β * =15/15 cm, Round HV crossing, β * =7.5/30 cm, Flat V crossing, β * =30/7.5 cm, Flat H crossing, Energy deposition critical for H crossing, TAN aperture determined by Flat optics. If TAN H apertures change, protection would be optimized for all optics. Beam 1, Beam 2, Neutral Debris (400 µrad cone)

4. 4 TAN – Movable option The TAN could be split in two parts: A fixed TAN to shield all radiation for vertical crossing and most of radiation for horizontal (e.g. closer to the IP by 4 m, larger aperture ~82mm, smaller separation ~140 mm). A second TAN with movable jaws in the H plane (+- 10 mm) only that protects only what is left by the first TAN (no material needed in the central part) and adjust at every change of optics (e.g. during a technical stop, if not every year). The movable TAN would need massive jaws (no like a TCL, it is not required to be moved with beam like a TCDQ). Beam 1, Beam 2, Neutral Debris (400 µrad cone)

5. 5 Backup for present TAXN

6. HL-LHCV1.0: TAN TCT TCL active absorber were copied verbatim from the LHC from the end of the magnetic length of D2. WP8 proposed to insert a mask in front of D2 to enhance protection. Magnetic to mechanical end increased from the LHC. Vacuum reclaimed the area of the mask for sector valves. TAXN and MASK would have to moved towards the IP compromising their effectiveness, but: For HL-LHCV1.1, it was agreed to build an mechanically unfeasible layout by not reserving sufficient longitudinal space for TCT and TCL support structures. This was done following the request to keep continuity between collimation and energy deposition simulations in the hope that either the mask or TCTs could leave the area. 6 TAXN – D2 area layout (debatable) evolution

7. TAXN Aperture: round optics 14σ, flat 12.0σ. Mitigation measures for increasing aperture in the TAXN for flat optics and crabs: 1.relocate/eliminate TCT.4, move TAXN towards D2; 2.Increase beta* in the non crossing plane; 3.decrease beta in the crab cavities (requiring more voltage); 4.Move TAXN-D2-Crabs towards the arc (requiring more voltage and maybe increasing neutrals in the apertures); 5.increase strength in D2 orbit correctors strength (to be checked). Open questions to WP5: What is the minimum protected aperture for the TAXN? What is the minimum protected aperture for Triplets, TAXN, D2, Q4, Q5 if TCT.4 are: in between TAXN and TCL; in between Crab and Q4; eliminated. 7 TAXN State for HL-LHCV1.1