1. A first glance at the impedance of an SPS collimation system Nicolas Mounet, Benoit Salvant, Carlo Zannini Acknowledgments: collimation team (Daniele, Roderik and Stefano), Hannes Bartosik, Elias Métral and Giovanni Rumolo

2. Parameters for collimation system from Daniele (at 450 GeV) nameAngle [degrees] Planebetax[m]betay[m]halfgap[mm]MaterialLength[m] TCP.SPS0H24.989.62.56CFC0.6 TCSG.SPS.10H88.925.35.64CFC1 TCSG.SPS.290V52.246.84.09CFC1 TCSG.SPS.5138Skew35.167.64.21CFC1 TCSG.SPS.637Skew31.274.34.10CFC1 Q26 Q20 nameAngle [degrees] Planebetax[m]betay[m]Halfgap [mm]MaterialLength[m] TCP.SPS0H36.892.23.11CFC0.6 TCSG.SPS.10H9336.75.77CFC1 TCSG.SPS.290V62.156.84.51CFC1 TCSG.SPS.5138Skew46.874.74.60CFC1 TCSG.SPS.637Skew42.880.64.50CFC1

3. Impedance computations Resistive wall of collimators with ReWall  by N. Mounet Geometric impedance from Stupakov formula for new TCTP type of collimator with buttons (pessimistic)  by N. Mounet Comparison with SPS impedance model  by C. Zannini

4. impedance of individual collimators (N. Mounet) Q26 Q20  Impedance computed in the plane of collimation (resisitive wall only) Contribution seems to be about half for TCP and half for TCS

5. Comparison between 26 GeV and 450 GeV (pessimistic for 26 GeV as should in principle be retracted) Zx Zy 26 GeV 450 GeV Zy Zx Difference is clearly visible!

6. Comparison with impedance model (C. Zannini), contribution to total impedance (N. Mounet) Real part Imaginary part  Geometric impedance small compared to resistive wall impedance  Impedance of collimators in the 10 to 20% range of the full SPS impedance (dipolar) Q26 vertical (dipolar) 26 GeV

7. Comparison with impedance model (C. Zannini), contribution to total impedance (N. Mounet) Q26 horizontal (dipolar) Real part Imaginary part  Geometric impedance small compared to resistive wall impedance  Impedance of collimators in the 10 to 20% range of the full SPS impedance (dipolar) 26 GeV

8.  Geometric impedance small compared to resistive wall impedance  Impedance of collimators in the 5 to 15% range of the full SPS impedance (dipolar) Comparison with impedance model (C. Zannini), contribution to total impedance (N. Mounet) Q20 vertical (dipolar) Real part Imaginary part 450 GeV

9.  Geometric impedance small compared to resistive wall impedance  Impedance of collimators in the 5 to 20% range of the full SPS impedance (dipolar) Comparison with impedance model (C. Zannini), contribution to total impedance (N. Mounet) Q20 horizontal (dipolar) Real part Imaginary part 450 GeV

10. First estimations using DELPHI and Sacherer formula by Nicolas Mounet show an increase of imaginary tune shift and TMCI threshold of the order of 5%.  As presented, this collimation system would not be a brick wall showstopper for the SPS transverse collective effects, but transverse impedance is large enough that we have to be careful in the implementation and be sure that it has clear benefits that offset the impedance increase. Impact on collective effects?

11. Conclusions Many thanks to all colleagues involved for sending relevant information within such a short time Very preliminary results The proposed collimation system configuration would lead to an increase of transverse impedance contributions in the range of 5 to 20% Increasing conductivity of the jaw would also help as in LHC (coating or new carbon jaws)