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13th HiLumi WP2 Task Leader Meeting
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Europe/Zurich
6/R-018 (CERN)
Minutes of the 13th WP2 Task Leader Meeting held on 13/08/2013
Present: R. Alemany-Fernandez, G. Arduini, R. Bruce, O. Brüning, H. Burkhardt, F. Cerutti, B. De Girolamo, R. De Maria, L. Esposito, P. Fessia, R. Kersevan, E. Métral, S. Redaelli, E. Todesco, A. Wolski
Minutes of the last meeting and follow-up of actions
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The minutes have been approved without changes
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Gianluigi has contacted D. Missiaen and H. Mainaud-Durand concerning ground motion in the triplet/D1 area.
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The presentation by Sasha/Tatiana on the benchmarking of the Lifetrack/SixTrack for the cases identified in the meeting held on 8/7 is tentatively scheduled for 10/9/2013.
Collimator requirements for the IR1/5 layouts (Roderik)
Roderik presented a schematic collimation layout for HL-LHC IR1-5. The baseline elements are indicated in blue in slide 5 and additional collimator locations are under study (in green in slide 5). Not indicated in the layout are vertical TCLs to protect D2 (under study) and TCLs in the matching section in front of Q5, Q6 and Q7.
The integration of the BBLRs in the collimators needs to be studied in detail.
In the present LHC layout energy deposition simulations indicate only TCL5 needed, but this is incompatible with forward physics program until HL-LHC. TCL4 will be added in LS1. We might add TCL6 as well. No more changes will be then required until LS3. It is not expected to be necessary to install collimators in the dispersion suppressors for proton operation.
Simulations of the effect of an asynchronous dump have evidenced that for the HL-LHC optics HL-LHCv1.0 the phase advance between the dump kicker and the TCTH in point 5 are such to expose these elements to the losses resulting from an asynchronous dump. Riccardo mentioned that the phase advance might be optimized by acting on the optics in LSS6. This is not changing during the squeeze. Action: Riccardo to verify whether a more favourable phase advance can be obtained.
If the aperture at the level of the Q4/5 becomes comparable to that of the triplet the Q5 might shadow the TCTs and a TCL in front of Q5 is required
The level of protection depends critically on the tolerances assumed, on the layout and optics:
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The tolerances assumed for the n1 calculations must be reviewed in light of the Run I experience
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Three layouts will be considered for the collimations studies:
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Layout 1: TCT only for triplet + standard TCL’s (used so far!)
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Layout 2: additional TCTH for Q5
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Layout 3: TCTH + TCTV for Q5
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The possible optics options for Performance Improvement Consolidation (PIC), Upgrade Scenario 1 (US1) and Upgrade Scenario 2 (US2) should be identified and the worst scenarios addressed. Action: Oliver, Gianluigi to summarized the optics configurations used so far for the estimations together with the beam parameters.
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Based on the above collimation settings will be defined and impedance estimates will be provided. Action: Stefano, Elias.
First energy deposition studies for the Matching Section of the HL-LHC IR1 and 5 (Luigi)
Luigi presented the first estimates of energy deposition in the matching section for the HL-LHC scenario. The aperture for the TAN has been estimated to be in the shadow of the triplet in terms of number of sigma (14) with no tolerances (the worst case scenario has been considered among three round and flat beam optics). This could be an optimistic method in particular for objects with smaller aperture than the triplet like the TAN because not all tolerances are scaling with the beam size, however having the triplet at 13.1 sigma (round) and 12.8 sigma (flat) introduces margins with respect to the triplet. A D2 aperture of 105 mm (diameter) has been considered and with this aperture Luigi noted that a clearance of 4.5 mm (radius) is considered between Beam Screen and Cold Bore at D2. (After the meeting, it is was clarified that the additional clearance is due to the specific cooling system of present D2 magnet).
Gianluigi noted that the estimates on the field quality given by Ezio in the past WP2 Task Leader meetings were rather frightening and that a reduction of the D2 aperture to 95 mm was considered. Ezio replied that he is confident that the field quality can be improved significantly and that 105 mm aperture can be kept.
The worst case scenario is represented by point 5 with a horizontal crossing angle. The losses at the TAN and in the matching section are dominated by neutrals (neutrons and gamma) originating at the IP. Differently from the nominal LHC scenario in the HL-LHC case the TAN aperture accepts a larger fraction of the cone of neutrals going through the triplet because of larger overlap between the beam and the cone of neutrals as a result of the triplet larger aperture and because of the larger crossing angle.
Riccardo suggested the option of a dogleg in that area to increase the separation among the beams at the TAN/Q4 and bring back the beams at the nominal separation at Q5 by increasing the force of D1 and D2, designing the new D2 and Q4 with larger separations and using the present D2 as a "D3" to bring the orbit parallel again.
Even installing additional TCLs to protect the elements of the matching section a power deposition in the coils of ~10 mW/cm3 @ 5×1034 cm-2s-1 and an a radiation dose of ~100 MGy/3000 fb-1 are reached.
During the discussion the following points were mentioned:
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The clearance available between the D2 beam screen and cold bore could be used to insert some tungsten shielding (3 mm thickness) to reduce the dose downstream;
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The possibility of adding shielding in Q5 and Q6 should be considered. Ezio mentioned that the new Q4 large aperture magnet could be installed to replace Q5 (in that case two Q4 magnets would be required to replace the Q5 magnet) too.
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The tolerances for the n1 calculations should be reviewed in light of LHC Run 1 experience.
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The possibility of having a remotely controllable TAN should be considered as a mean of reducing the tolerances at the TAN position
Action (Massimo, Stefano): We need urgently to review the n1 definition based on the Run I experience to proceed with the optics scenarios definition.
Actions (Francesco, Luigi):
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Estimate energy deposition for vertical crossing angle as a reference for the power deposition in the best case.
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Estimate energy deposition for horizontal crossing angle with tungsten shielding (3 mm) in D2.
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Estimate the sensitivity of the energy deposition in the matching section to the TAN aperture (e.g. for a reduction by 10% of the aperture)
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Estimate energy deposition for horizontal crossing angle with tungsten shielding in D2 (3 mm) and Q5.
Reported by: Gianluigi and Riccardo
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