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 BPVTW 200MHz and 800MHz

Flanges

SPS transverse impedance model

3Peaks 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

5Peaks 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 εl

– Slow instability for intermediate intensity and low εl

• Very well reproduced with HEADTAIL simulations– SPS impedance model includes kickers, wall, BPMs and RF cavities– Direct space charge not included

9

H. Bartosik

measurements HEADTAIL simulations

4.5x1011 p/b @ 0.35 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

2014 8 8Post-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 MHzfinger

effeff

Lm.f

c4780

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:Q20measurements 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 = 17. 25 mmd = 78 mm

Broadband impedance of step transitions

Weak dependence on L2

L2

1Im2Im

ZZ

1Im Z

1Im Z

i

N

i

istransition nZZ

1

ImIm

Courtesy of Jose E. Varela

Broadband impedance of step transitionsFlange Type Enamel Bellow Num. of

elementsResistor

BPV-QD Yes Yes 90 No

BPH-QF Yes Yes 39 Long

QF-MBA Yes Yes 83 Short

MBA-MBA Yes Yes 14 Short

QF-QF No Yes 26 Short

QD-QD Yes No 99 No

QF-QF No No 20 No

BPH-QF Yes Yes 39 Long

QD-QD No No 75 No

QD-QD Yes No 99 No

Pumping portsmMZZ effeff yy /1.1320012000 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

1200ppN

Total number of shielded pumping ports

P. Collier et al.: Reducing the SPS Machine Impedance, 2002

SPS Pumping portSPS Pumping port shielding

Pumping ports

2000 Impedance reduction campaign: shielding of the pumping ports, lepton cavities etc.)

mMZZ effeff yy /1.1320012000

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

effeff yy ZZ 20012000

Measured ≈13

Expected ≈11

mM /

Bending magnets

mMNZZZ ppSBMBB

ySAMBA

yppy /11

2

1Im

1200ppN