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Update on the TDI impedance simulations and RF heating for HL-LHC beams

Update on the TDI impedance simulations and RF heating for HL-LHC beams. Alexej Grudiev on behalf of the impedance team TDI re-design meeting 30/10/2012. outline. Geometry of TDI and the source of impedances Simulation of the trapped modes

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Update on the TDI impedance simulations and RF heating for HL-LHC beams

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  1. Update on the TDI impedance simulations and RF heating for HL-LHC beams Alexej Grudiev on behalf of the impedance team TDI re-design meeting 30/10/2012

  2. outline • Geometry of TDI and the source of impedances • Simulation of the trapped modes • Calculation of the impedance of the absorber blocks • Summary

  3. Geometry of TDI in HFSS. Horizontal plane of symmetry is used Half gap = 8 mm • Big size and complex shape results in a huge number of the trapped modes with sharp narrow band impedance • Proximity of the absorber blocks to the beam results in the broad band impedance, i.e. resistive wall impedance

  4. R/Q estimated from longitudinal impedance calculated in CST, hBN, b0, σz = 50 mm 4(Zl-Zl0)*df/πf is plotted where Zl0 = 71 Ohm to make the real part positive BUT the Q-factor cannot be found in time-domain CST simulations

  5. R/Q estimated from longitudinal impedance, hBN, b0, σz = 100 mm, and HFSS eigenmode results 4(Zl-Zl0)*df/πf is plotted where Zl0 = 71 Ohm to make the real part positive

  6. Table of longitudinal mode parameters calculated in HFSS, hBN, 4S60@500MHzaccelerator definition of R/Q: P=I2*R/Q*Q -? -?

  7. Low frequency mode at 31 MHzElectric field distribution in horizontal and vertical planes (log scale) All volume filled with EM fields Inside and outside of beam screen f = 31 MHz; Q = 164; RT = 80 Ohm; Ploss for Ib=0.36A: ~10W

  8. Low frequency mode at 58.6 MHzElectric field distribution in horizontal plane All volume filled with EM fields Inside and outside of beam screen f = 58.6 MHz; Q = 195; RT = 150 Ohm; Ploss for Ib=0.36A: ~19W power loss distribution: 50% -> Al keeper 43% -> Cu beam screen 2 x 2% -> Cu flexible contacts 2% -> SS jaw support 1% -> SS vacuum tank

  9. High frequency mode at 1224 MHz Electric field distribution in horizontal plane Localized field distribution f = 1224 MHz; Q = 755; RT = 14 kOhm power loss distribution: 49% -> Al keeper 38% -> Cu beam screen 1.5% -> Cu flexible contact 4% -> SS jaw support 7.5% -> SS vacuum tank

  10. Power loss for 50 and 25 ns HL-LHC beamsGaussian bunches: sigma_z = 85 mm

  11. Power loss for 50 and 25 ns HL-LHC beamscos^2 bunch: total bunch 1.336 ns

  12. A way to estimate shunt impedance for other gaps and boundary conditions w/o lengthy HFSS simulations

  13. Comparison of the power estimate from CST and HFSS calculations Shunt impedance for other gaps and boundary conditions (BC) can be estimated using CST R/Q estimate calculated for specific gap and BC and assuming HFSS Q estimate calculated for gap=16mm is valid for other gaps and BC, then the power loss estimate can be done without long HFSS simulations

  14. Power estimated from ReZl, hBN, hgap=8mm, σz = 85 mm, same HWHH: b0,b1,b2

  15. Power estimated from ReZl, hBN, hgap=8->20->55mm, cos^2 bunch, HL-LHC 25 ns beam : b0,b1,b2 The impedance of the higher frequency modes (> 1 GHz) depends on the gap, roughly linear with the gap. Power dissipation is reduced from a few kilowatts down to the level of 100 Watts. hgap=8mm hgap=20mm hgap=55mm The impedance of the low frequency modes (<200MHz) weakly (far from linear) depends on the gap! At fully open jaws position a few 100s of Watts can be dissipated mainly on the block keepers and beam screen.

  16. Coating simulations This is preliminary results of the on-going work. At this moment we can not simulate the coating s directly in 3D simulation codes. Some model have to be used. OR analytical formalism for parallel plate geometry . Reasonable agreement in Real part, less good in imaginary. Convergence ???

  17. Re. Wall Power loss for HL-LHC beam 50 ns1404, 3.5e11 N. Mounet

  18. Re. Wall Power loss for HL-LHC beam 25 ns2808, 2.2e11 N. Mounet

  19. RF heating of the hBN blocks coated with 5 um of Ti flash coating ~1 kW power is dissipated in 5 um coating over a surface of ~Lx4b = 2.8m x 20mm The surface power deposition density: 18 kW/m2 The volume power deposition density: 3.6 GW/m3 Is it an issue??? 2b 2b

  20. Summary • Trapped modes can results in few 100s of Watt RF heating even for fully open TDI position. Deposited ~ 50/50 on the jaws and beam screen. The power loss could be much (x10) higher for closed position. • Broad band resistive impedance results in higher RF heating for small gap ~1kW and much smaller (x10) for fully open. Power deposition in very thin coating could be an issue especially if the beam passes close to one jaw.

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