Study on Thermal Deposition in the Interaction Region Magnets

1. Study on Thermal Deposition in the Interaction Region Magnets CARE 06 INFN–LNF 15-17 November 2006 francesco.broggi@mi.infn.it francesco.broggi@cern.ch

2. Outline • Chronology (where this study comes from) • Method of calculations • Cases and results • 2005/06 reprise of the problem • Work done this year • Next CARE 06 INFN–LNF 15-17 November 2006

3. Study of a new Nb3Sn design for the LHC insertion quad started in 1995, suggested by the Milan group (L.Rossi) • Ended in 1998 (1999 final report) Chronology CARE 06 INFN–LNF 15-17 November 2006

4. Purpose of the Study was: • Use of the Nb3Sn technology instead of the "traditional" NbTi, for the construction of the focussing quadrupoles in the interaction region of LHC in order to have : • Higher focussing gradient (higher luminosity), in the same magnet aperture or • The same focussing gradient in a larger aperture, (easier beam dynamics, especially at the injection). CARE 06 INFN–LNF 15-17 November 2006

5. 1300 p-p 7 TeV events Evaluation of the power distribution in the various elements (FLUKA) Tracking of the secondary particles (ad hoc code) Thermal Analysis (2D ANSYS) DTUJET Calculation Procedure This coupling with the thermal analysis was the key and innovative part of this study The thermal analysis is a very important issue in this problem, because a good cooling system in the magnet allow to operate the magnets in very high radiation environment with a good safety margin. CARE 06 INFN–LNF 15-17 November 2006

6. “Old” Cases Studied Version LHC 6.5 with G = 203 T/m and Beam Screens CARE 06 INFN–LNF 15-17 November 2006

7. Modelization and Hypothesis Detailed description of the magnets with the coil layers, insulation, wedges and yokes TRACKING • Beam pipe thickness 1.5 mm • Detector peak field 2 T • Detector radius 1.1 m • Detector length 5.3 m • Crossing angle 200 mrad • Cross section (inel.+ single diff. event) 80 mbarn • Luminosity 1034 cm-2s-1 • FLUKA • Cut off for Hadrons 1 MeV • Cut off for electrons/positron 1.5 MeV • Cut off for photons 0.2 MeV • Cut off for neutrons 0.4 eV THERMAL ANALYSIS MODEL 2D - Steady State Thermal Conductivity Computed from cable-insulation stack Insulation Non isotropic G10 Heat flux Purely longitudinal Heat transfer coefficient 1000 W/m2K at 1.9 K CARE 06 INFN–LNF 15-17 November 2006

8. Total Power into the Quads and the Inner Conductor Layer Note the negative effect of the uniform cylindrical adsorbers (startup of the cascade from particles that would freely travel, deposing their energy in the following, less critical quads). CARE 06 INFN–LNF 15-17 November 2006

9. Summary of the “old” cases • The statistical error has been evaluated from different runs with independent random seeds • 1% for the region binning • 3% medium binning (Bin Volume = 0.5x0.5x50 = 12.5 cm3) • 4% small binning ( " " = 0.25x0.25x50 = 3.1 cm3) • 7% very small binning ( " " = 0.25x0.25x10 = 0.63 cm3) CARE 06 INFN–LNF 15-17 November 2006

10. Indications from the”old” cases I • Negative effect of the cylindrical absorbers • The case with higher gradient (G=300 T/m) is slightly worst than the reference case (G=235 T/m) • Case with lager aperture (F=85 mm) is better for the deposed power but it has a small increment in the peak power. • From the thermal analysis the power released by the radiation does not endanger the operating point of the magnets and guarantee a good stability margin, as a matter of fact the maximum temperature is in the median plane, where the magnetic field is lower enough to guarantee a safe combination of the two parameters. • Conversely in the higher field regions the temperature increment is not too high. • Larger stability margin can be achieved by using the aluminum collars instead of the stainless steel ones (tradeoff with the mechanical properties). • Nb3Sn is a good solution for the second generation low-b quads, either to increase the focussing gradient, or to get the same focussing performance in a larger aperture. CARE 06 INFN–LNF 15-17 November 2006

11. Indications from the”old” cases II • In the “nominal (academic) case” or LHC version 6.5 with beam screens: • quad aperture; 70 mm ; • quad gradient; 235/203 T/m; • trim quad between Q1 and Q2a; 82 T/m The most loaded quad is the second or the last one (Q2a,Q3), absorbing some 25-35 W with a peak power of about 7-10 mW/cm3 (depending on the bin volume) With the actual luminosity value L=1034 cm2s-1 Indication of a positive effect by opening the aperture, this lead to consider large (100 mm) quad aperture for the “new” studies CARE 06 INFN–LNF 15-17 November 2006

12. New Studies What the energy/power deposed in the magnets if moving closer to IP Why moving towards IP ? Approaching the triplet to the IP opens the possibility of an increased focusing and hence of a significantly larger luminosity(J.-P. Koutchouk) Conversely the energy deposition in the magnets becomes a critical point, because of the different secondary beam dynamics and the increased power CARE 06 INFN–LNF 15-17 November 2006

13. Hypothesis TRACKING • Beam pipe aperture 58.0 - 34.0 mm (TAS) - 95.5 mm (Beam screens after the TAS are taken into account) • Detector Solenoid Field with its fringing field (theoretical) • Detector peak field 2 T (ATLAS) • “ radius 1.1 m • “ length 5.3 m • Hard edge approx. for the quadrupole field Cross section = 80 mbarn (inel.+ single diff. event) • FLUKA • Quad aperture 100.0 mm • Accurate definition of the quadrupole structure (current, insulation, wedges, collars, yokes) • Magnetic field in the quad material (ROXIE) • Cut off for Hadrons 1 MeV • Cut off for electrons/positron 1.5 MeV • Cut off for photons 0.2 MeV • Cut off for neutrons 0.4 eV CARE 06 INFN–LNF 15-17 November 2006

14. Geometry and materials G10 Insulation (0.2, 0.7, 0.5 mm) S.S. Beam pipe (1.75 mm) S.S. Beam screen with cooling tubes Nb3Sn Current shells (15 mm, 60°) S.S. Pole wedges S.S. Collar (20 mm) Fe Yoke (18 cm) CARE 06 INFN–LNF 15-17 November 2006

15. Cases studied Distance IP – Q1 = 23 m ; L = 8.64 1034 cm2s-1 Quad Gradient = 193 T/m ;qcr = 512 mrad Distance IP – Q1 = 19 m ; L = 8.67 1034 cm2s-1 Quad Gradient = 204 T/m ;qcr = 514 mrad Distance IP – Q1 = 16 m ; L = 8.72 1034 cm2s-1 Quad Gradient = 208 T/m ;qcr = 507 mrad Distance IP – Q1 = 13 m ; L = 8.77 1034 cm2s-1 Quad Gradient = 213 T/m ;qcr = 500 mrad (As from J.-P. K. computations) CARE 06 INFN–LNF 15-17 November 2006

16. ResultsI (mean values) The study is a parametric one, so it is should be used to check the effects of the insertion moving. Cut-offs values and biasing option in order to have “reasonable” CPU Time (~ 60 hours on Intel Centrino 2 GHz for each configuration) More accurate absolute values can be obtained with different calculation option and higher CPU times. Pcharged ~ 60% Pneutral ~ 40% PTAS~ 1 kW 15 % Hadron 73 % em showers The power is increased of about one order of magnitude, respect to the actual case, because of the corresponding increase of the Luminosity CARE 06 INFN–LNF 15-17 November 2006

17. Results II(mean values) CARE 06 INFN–LNF 15-17 November 2006

18. Results III(peak values) The maximum peak power deposition occurs in the second quadrupole (Q2a) CARE 06 INFN–LNF 15-17 November 2006

19. Results IV(peak values) CARE 06 INFN–LNF 15-17 November 2006

20. Results V(peak values) The asymmetric distribution is due to the crossing angle (in these cases it is higher than the actual LHC parameter of 200 mrad) CARE 06 INFN–LNF 15-17 November 2006

21. What indications ? The power deposed in the TAS is almost constant for all the cases The total power deposed into the quads increases, approaching the IP The power deposition in Q1 and in its first shells increase almost linearly, approaching the IP The power deposition in Q3 increase too, but the behaviour is less “linear” The “hottest” quads is Q2a for IP-Q1 = 23 m while in the other cases the hottest one is Q3 The peak power is almost constant for all the situations examined The highest peak power deposition is in Q2a and it is almost constant for all the cases studied The power distribution in the last quad is more spreaded CARE 06 INFN–LNF 15-17 November 2006

22. What’s Next ? Complete this study with a thermal analysis of the quad behaviour • Get values as accurate as possible by “playing” with the cut-off and biasing parameters • Update the event generator from DTUJET to DPMJET (not big changes expected) Carefully evaluate the actual LHC insertion (LHC 6.5 layout) with : • Very detailed description of the layout with NbTi coils (valves, flanges etc..) • Take into account the tile calorimeter and the engineering of the detector • Effect of the detector field (2 Tesla ATLAS, IP1; 4 Tesla CMS, IP5) • Compare (if some difference is evident) between NbTi and Nb3Sn (academic/FLUKA exercise?) CARE 06 INFN–LNF 15-17 November 2006

23. New Options/Solutions • Dipole first • Small Dipole first • Light quads The power in the TAS is almost constant for all the positions Every solution or possibility can/should be checked CARE 06 INFN–LNF 15-17 November 2006

24. Thanks • G.Battistoni(INFN), A. Ferrari and the CERN FLUKA Group • J.-P. Koutchouk (parameters for the study) • C. Vollinger (ROXIE quad field map) • C.Hoa, E. Wildner, G. Sterbini for the fruitful discussions and help in developing the study CARE 06 INFN–LNF 15-17 November 2006