1. HL-LHC Meeting, November 2013D2 Status and Plans – G. Sabbi 1 D2 Conceptual Design Status and Next Steps G. Sabbi, X. Wang High Luminosity LHC Annual Meeting Daresbury, UK, November 11-14, 2013

2. HL-LHC Meeting, November 2013D2 Status and Plans – G. Sabbi 2 Target Parameters/Specs Key specifications and optimization targets for D2 design study: Aperture 105 mm Inter-beam distance 186 mm Integrated field 35 Tm Iron yoke OD 560 mm Cryostat/magnetic shield: 10 mm thickness, 1 m outer diameter Target operating point on load-line: 70% Magnetic length below 10 m (shorter magnet, e.g., ~ 8 m, is also interesting) Fringe field <20 mT Cable: consider RHIC and LHC cables as possible options

3. HL-LHC Meeting, November 2013D2 Status and Plans – G. Sabbi 3 Magnetic design strategies 1.Correct both geometric and saturation through iron yoke design Coil is optimized for single aperture (left-right symmetric) Traditional approach, but difficult for HL-LHC parameters Reflected in error table v1.2 (June 2013) and v1.3 (July 2013) 2.Proposed to design iron yoke for small saturation and correct the geometric component using at the coil level (requires asymmetric coil) A demonstration case was developed using simple yoke design Compares favorably with v1.4 (October 2013) Further improvements possible

4. HL-LHC Meeting, November 2013D2 Status and Plans – G. Sabbi 4 Error Tables Current version (1.4, October 2013): Previous version (1.3, July 2013):

5. HL-LHC Meeting, November 2013D2 Status and Plans – G. Sabbi 5 Reference Iron Yoke Design Center frame size: Half width: 185 mm Provides 25 mm collar thickness) Half height: 115 mm Selected as a compromise between low saturation (variation of harmonics with current) and cross- talk (“absolute” values of the harmonics, using nominal field as the reference point)

6. HL-LHC Meeting, November 2013D2 Status and Plans – G. Sabbi 6 Saturation vs. frame size Δb2Δb2 Δb3Δb3 x = half width; y = half height Full circle: positive; empty for negative Area proportional to saturation effect NOTE: results are not independent from on the coil design

7. HL-LHC Meeting, November 2013D2 Status and Plans – G. Sabbi 7 Cross-talk vs. frame size b2b2 b4b4 b3b3 b5b5

8. HL-LHC Meeting, November 2013D2 Status and Plans – G. Sabbi 8 Saturation effect

9. HL-LHC Meeting, November 2013D2 Status and Plans – G. Sabbi 9 Fringe Field Questions: How critical is the 20 mT target? Can we increase thickness of outer magnetic shield? Trade-offs between fringe field and other targets, esp. field (besides machine performance improvement, magnet cost could be reduced)

10. HL-LHC Meeting, November 2013D2 Status and Plans – G. Sabbi 10 Coil Design LHC cable Single layer (15 mm coil width) 5 block, 29 cables per quadrant At most a difference of 1 turn between corresponding blocks Results in operating point at 55% along the load line 70% initial target would give ~4.5 T Or, could reconsider RHIC cable Top-bottom symmetry (same for iron yoke) Left-right symmetry with respect to the center line (x = 0)

11. HL-LHC Meeting, November 2013D2 Status and Plans – G. Sabbi 11 Comparison with v1.4 (low order) Still to be analyzed, expect similar Persistent current effect: asymmetric coil results in different values for odd terms and generates even terms – preliminary estimates are provided in the next slide (*) Still to be analyzed, expect similar

12. HL-LHC Meeting, November 2013D2 Status and Plans – G. Sabbi 12 Persistent Current Harmonics

13. HL-LHC Meeting, November 2013D2 Status and Plans – G. Sabbi 13 Comparison with v1.4 (high order) Error tables assumptions: high order systematic can be fully controlled at the design level, small/no saturation, uncertainty/random from previous fabrication experience Preliminary design was optimized within a few units and we can expect that after full optimization high orders will be dominated by uncertainty/random components Still to be analyzed, expect similar Still to be analyzed, expect similar

14. HL-LHC Meeting, November 2013D2 Status and Plans – G. Sabbi 14 Summary Simple window-frame inner yoke profile provides saturation within v1.4 targets Currently using LHC cable for added margin over RHIC (55% SSL at operating point) Improvements in the yoke design are clearly possible to decrease saturation and fringe field, and increase contribution to main field No absolute constraints on aperture, operating field, field quality – trade-offs are possible We demonstrated (to our satisfaction) that this design approach has the needed flexibility, but it is not efficient to further optimize before reviewing key targets/priorities Full optimization should start from iron yoke, then coil

15. HL-LHC Meeting, November 2013D2 Status and Plans – G. Sabbi 15 Next steps & Discussion Points Confirm choices of key parameters: aperture, field, yoke OD, cryostat/magnetic shield thickness, max. fringe field & radius Revise error tables. Some proposals: Set all high field systematics to zero Set saturation harmonics at 1/3 the current values, but: Include compensation of persistent currents? Final design optimization - a few notes: Yoke optimization needs to be pursued iteratively with asymmetric coil optimization, otherwise it is difficult to converge At this stage, should also incorporate mechanical considerations, such as desired thickness of collar for given operating field, etc. CERN+LARP CERN+INFN