Status of the SPS impedance model
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Transcript of Status of the SPS impedance model
Status of the SPS impedance model
C. Zannini, G. Rumolo, B. Salvant
Acknowledgments: H. Bartosik, O.Berrig, G. Iadarola, E. Métral, N. Mounet, V.G. Vaccaro, Jose E. Varela
Overview
• Present SPS transverse impedance model• Broadband impedance of step transitions• Future update of the model• SPS Longitudinal impedance model• Summary
Present SPS transverse impedance model• Elements included in the database:
– Realistic model that takes into account the different SPS vacuum chambers weighted by the respective length and beta function. Also the iron in the magnet is taken into account
– 19 kickers (CST 3D simulation)– 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)– Enamel flanges (CST 3D simulations)
KickersBeam pipe
BPH BPV
TW 200MHz and 800MHz
Enamel flanges
Evolution of the extraction kickers in the SPS
SPS vertical impedance model
5
SPS horizontal impedance model
6
Vertical coherent tune shift
100 %
20 %
40 %
60 %
80 %
Present SPS impedance model reproduces about 70% of the vertical tune measured in the Q20
Present impedance model reproduces the instability behavior (H. Bartosik, Talk at the SPSU, 12 December 2013)
Measurements performed in September 2012
Stability diagram: Q20o Two regimes of instability in measurements
• Fast instability threshold with linear dependence on εl
• Slow instability for intermediate intensity and low εl
o Excellent qualitative agreement with HEADTAIL simulations • Slightly lower threshold in simulation (amplitude detuning or space charge?)
LIU SPS-BD, 12. December 2013 8
measurements HEADTAIL simulations
4.5x1011 p/b @ 0.35 eVs
nominal Island of slow instability
H. Bartosik
Intra-bunch motion: Q20 (I)o Example for slow instability
• Clear indication for mode 1 in measurement• Good agreement with HEADTAIL simulation
LIU SPS-BD, 12. December 2013 9
measurements HEADTAIL simulations
H. Bartosik
Intra-bunch motion: Q20 (II)o Example for fast TMC instability
• Excellent agreement between measurements and simulation• Travelling wave pattern clearly visible
LIU SPS-BD, 12. December 2013 10
measurements HEADTAIL simulations
H. Bartosik
Horizontal coherent tune shift
The kicker impedance model predicts a negative horizontal effective impedance (positive slope of the coherent tune shift) in agreement with the measurements
Measurements performed in February 2013
Overview
• Present SPS transverse impedance model• Broadband impedance of step transitions• Future update of the model• SPS Longitudinal impedance model• Summary
Broadband impedance of a step transition
• Based on the results of 3D EM simulations, the broadband impedance contribution due to an abrupt transition is independent of the relativistic beta. Therefore, based on the aperture model, the generalized broadband impedance of the PSB transitions has been calculated as:
C. Zannini, Electromagnetic simulations of CERN accelerator components and experimental applications. PhD thesis, Lausanne, EPFL, 2013. CERN-THESIS-2013-076.
Transverse Impedance
Broadband impedance of step transitions
Weak dependence on L
L
i
N
i
istransition nZZ
1
ImIm
1Im Z
1Im2Im
ZZ
1Im Z
22
11bd
Z i
Broadband impedance of step transitions
Weak dependence on L2
L2
1Im2Im
ZZ
1Im Z
1Im Z
22
11bd
Z i
i
N
i
istransition nZZ
1
ImIm
Broadband impedance of step transitions
L2
mm
The imaginary part of the transverse impedance is weakly dependent on the cavity length below 1 GHz
For all the SPS cavity like structures the first resonating mode is well above 1 GHz (r<80 mm)
Broadband impedance of step transitions
L2
0 fZZ eff
mz 25.0
Courtesy of Jose E. Varela
Broadband impedance of step transitionsFlange Type Enamel Bellow Num. of
elements Resistor
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
Vertical coherent tune shift
100 %
20 %
40 %
60 %
80 %
Step transitions seem to explain almost the totality of the missed tune shift
SPS Pumping portSPS Pumping port shielding
Pumping ports
effeff yy ZZ 20012000 2000 Impedance reduction campaign: shielding of the pumping ports, lepton cavities etc.)
Estimation of the broadband impedance of unshielded transitions between bending magnets and straight sections
• 744 step transitions:– 377 MBA-Straight A– 377 MBB-Straight B
Imag [ Zy(f=0) ]= 11.8 MΩ/m
effeff yy ZZ 20012000
Measured 13.1
Expected (only from transitions in the magnets)
11.8
mM /
Overview
• Present SPS transverse impedance model• Broadband impedance of step transitions• Future update of the model• SPS Longitudinal impedance model• Summary
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– New wire scanner– New kicker for high bandwidth feedback system– New MSI-V septum
Overview
• Present SPS transverse impedance model• Broadband impedance of step transitions• Future update of the model• SPS Longitudinal impedance model• Summary
Status of the SPS longitudinal impedance model• Elements included in the database:
– Realistic model that takes into account the different SPS vacuum chambers weighted by the respective length and beta function. Also the iron in the magnet is taken into account
– 19 kickers (CST 3D simulation)
KickersWall impedance
Longitudinal wall impedance
Calculation performed with ImpedanceWake2D
Longitudinal impedance
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SPS impedance in total
LIU-SPS BD Meeting, 24th October 2013
fr (GHz) Rsh (MOhm) Q R/Q (kOhm)0.629 0.388 500 0.780.885 0.0146 482 0.0300.892 0.0198 493 0.0401.052 0.1597 773 0.2071.062 0.1903 773 0.2461.069 0.0454 654 0.0691.092 0.0570 667 0.0851.185 0.0116 610 0.0191.215 0.0012 624 0.0021.598 0.0426 672 0.0631.613 0.5975 686 0.8711.859 0.2951 896 0.3291.960 0.0721 1993 0.0360.550 0.2275 1000 0.2281.050 0.2275 1250 0.1821.41 1.871 210 8.91
BPMs
Zs (?)
200 MHz HOM
Flanges• + cavity & kicker impedance
Courtesy H. Timko
Overview
• Present SPS transverse impedance model• Broadband impedance of step transitions• Future update of the model• SPS Longitudinal impedance model• Summary
Summary and next steps
• The SPS impedance model (kicker, wall, cavities, BPMs) explains about 70% of the measured vertical coherent tune shift
• Transition pieces seem to be able to explain the remaining 30%
• More realistic model of transition pieces• Update of the model including septa and wire scanner• Continuously update of the model according to new
installations and modifications
Thank you for your attention
F. Caspers, T. Kroyer, M. Barnes, E. Gaxiola et al.
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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
c 4780
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