Update of the SPS transverse impedance model C. Zannini, G. Rumolo, B. Salvant Acknowledgments: H. Bartosik, O.Berrig, F. Caspers, E. Chapochnikova, G. Iadarola, E. Métral, N. Mounet, V.G. Vaccaro, J. E. Varela

SPS transverse impedance model Elements included in the database: – 106 BPHs (CST 3D simulations) – 96 BPVs (CST 3D simulations) – 200 MHz cavities without couplers (CST 3D simulations) – 800 MHz cavities without couplers (CST 3D simulations) – Wall impedance that takes into account the different SPS vacuum chambers (analytical calculations) – 19 kickers (CST 3D simulation) – Broadband impedance of the flanges (CST 3D simulations) KickersBeam pipe BPH BPV TW 200MHz and 800MHz Flanges

SPS transverse impedance model 3 Peaks due to the serigraphy of the extraction kickers

SPS transverse impedance model 4 Broadband impedance from kickers, flanges and resistive wall

SPS transverse impedance model 5 Peaks due to the RF system and BPMs

SPS transverse impedance model Benchmark with beam measurements – Tune shift – Instability behavior

Benchmark of the SPS impedance model: tune shift measurements 100 % 20 % 40 % 60 % 80 % The SPS impedance model explains more than 90% of the measured vertical coherent tune shift Vertical coherent tune shift: Measurements performed in September 2012

The SPS impedance model predicts a very small horizontal tune shift (almost flat) in agreement with the measurements Horizontal coherent tune shift: Measurements performed in February 2013 Benchmark of the SPS impedance model: tune shift measurements

Benchmark of the SPS impedance model: instability behavior Two regimes of instability in measurements – Fast instability threshold with linear dependence on ε l – Slow instability for intermediate intensity and low ε l Very well reproduced with HEADTAIL simulations – SPS impedance model includes kickers, wall, BPMs and RF cavities – Direct space charge not included 9 H. Bartosik measurementsHEADTAIL simulations 4.5x eVs nominal Island of slow instability

New elements to be added in the model Simulations are ongoing or must be finalized – Septa – Wire scanner – Non standard elements (special transitions, valves) Update due to future installations and modifications – New wire scanner – New kicker for high bandwidth feedback system – New MSI-V septum – Serigraphy of the last MKE (7/8 were already serigraphed in the 2012)

Thank you for your attention

Evolution of the extraction kickers in the SPS Post-LS1

F. Caspers, T. Kroyer, M. Barnes, E. Gaxiola et al. 13 Serigraphy Seven out of eight SPS extraction kickers have been serigraphed Realistic models: SPS extraction kicker (MKE-L)

Realistic models: MKE kicker with serigraphy

f=44 MHz Comparing MKE with and without serigraphy

The peak observed in the MKE with serigraphy is a quarter-wavelength resonance on the finger length Comparing MKE with and without serigraphy

The trend of the vertical effective impedance along the last 10 years is in good agreement with the expected changing of the kicker impedance model Kickers play a major role in the SPS total impedance Evolution of the extraction kickers in the SPS: vertical tune shift

The trend of the horizontal effective impedance along the last 10 years is in good agreement with the expected changing of the kicker impedance model Kickers play a major role in the SPS total impedance Evolution of the extraction kickers in the SPS: horizontal tune shift

Intra-bunch motion:Q20 measurements HEADTAIL simulations Example for slow instability Example for fast TMC instability H. Bartosik Excellent agreement between measurements and simulation

Broadband impedance of step transitions L2 The imaginary part of the transverse impedance is weakly dependent on the cavity length below 1 GHz For the main SPS cavity like structures the first resonating mode is above 1 GHz (r<80 mm) b = mm d = 78 mm

Broadband impedance of step transitions Weak dependence on L2 L2

Courtesy of Jose E. Varela Broadband impedance of step transitions Flange Type EnamelBellow N um. of elements Resistor BPV-QDYes 90No BPH-QFYes 39Long QF-MBAYes 83Short MBA-MBAYes 14Short QF-QFNoYes26Short QD-QDYesNo99No QF-QFNo 20No BPH-QFYes 39Long QD-QDNo 75No QD-QDYesNo99No

Pumping ports 2000 Impedance reduction campaign: shielding of the pumping ports, lepton cavities etc.) H. Burkhardt, G.Rumolo, F. Zimmermann: Measurements of SPS Single- Bunch coherent Tune Shifts and Head-Tail Growth Rates in the Year 2001 The broadband impedance due to step transitions can give significant contribution to the coherent tune shift Total number of shielded pumping ports P. Collier et al.: Reducing the SPS Machine Impedance, 2002

SPS Pumping port SPS Pumping port shielding Pumping ports 2000 Impedance reduction campaign: shielding of the pumping ports, lepton cavities etc.) The picture does not include pumping holes

Estimation of the broadband impedance of unshielded transitions between magnets and straight sections 744 step-in step-out transitions: – 377 MBA-Straight A – 377 MBB-Straight B Measured≈13 Expected≈11 Bending magnets