Particle Studio simulations of the SPS BPH (suite)

1. Particle Studio simulations of the SPS BPH (suite) 24/04/2009

2. agenda • Crosscheck of the low frequency impedance • Issue with PS DFT? • Trapped mode parameters for PEC and lossy materials • Procedure to get the wake function for Headtail • Advantages and drawbacks of Particle Studio/Microwave studio.

3. From time domain (Bruno) From frequency domain Z/n=0.8 mOhm No truncation issue on the matched simulation (decay) However, truncation affects the unmatched simulation

4. agenda • Crosscheck of the low frequency impedance • Issue with PS DFT? • Trapped mode parameters for PEC and lossy materials • Procedure to get the wake function for Headtail • Advantages and drawbacks of Particle Studio/Microwave studio.

5. Issue with the DFT of Particle Studio? Homemade FFT: For details see https://sps-impedance.web.cern.ch/sps-impedance/BrunoYongHoWakeFFTc.ppt • The oscillations observed on the particle studio DFT disappear when a homemade DFT is applied.  To be checked with CST. • The sampling rate of the CST DFT (f~17 MHz) does not correspond to the sampling rate expected from the total wake length (f=1/(Nt)=1/T=c/L~60 MHz). It is as if the wake were 3.3 times longer…  To be checked with CST.

6. Monika Balk (CST) said they have had many remarks from users about this DFT, and they will change it in the next version.

7. Old geometry (PAC paper) Microwave studio Frequency domain: eigenmode AKS solver Federico found 300 Ohm with HFSS Particle studio Time domain: Wakefield solver

8. Try with “slotline pickup” beam

9. slotline geometry Microwave studio Frequency domain: eigenmode JDM solver Particle studio Time domain: Wakefield solver

10. Further remarks • Alexej advised to measure R/Q on the time domain, and not in frequency domain. • Also, I should calculate the R/Q on the magnitude and not the real part.

11. agenda • Crosscheck of the low frequency impedance • Issue with PS DFT? • Trapped mode parameters for PEC and lossy materials • Procedure to get the wake function for Headtail • Advantages and drawbacks of Particle Studio/Microwave studio.

12. Improving the model Old structure Newer structure

13. Longitudinal (PEC)

14. Longitudinal (with losses) Electrodes + pipe  Stainless Steel Casing  Anticorodal

15. Dipolar vertical impedance (PEC)

16. agenda • Crosscheck of the low frequency impedance • Issue with PS DFT? • Trapped mode parameters for PEC and lossy materials • Procedure to get the wake function for Headtail • Advantages and drawbacks of Particle Studio/Microwave studio.

17. Obtaining the wake function for Headtail? Impedance For f = k*f (position k=0 corresponds to f=0, careful with Matlab…) Normalizing by transverse offset Performed by Matlab fft Time 0 at position j=1 Delay correction Amplitude correction This – sign convention in Particle Studio leads to negative inductive impedances Wake function For t = j*t (position j=0 corresponds to t=0)

18. Obtaining the wake function for Headtail? Wake function For t = j*t (position j=0 corresponds to t=0) Check: Recovering the wake potential with a convolution with the gaussian bunch With the normalised bunch charge distribution

19. Let’s check…

20. 1) Outputs from Particle Studio Calculations for the dipolar vertical wake (vertical displacement at first positive vertical mesh line 0.9 mm) source bunch rms = 5 mm Vertical dipolar Wake (time domain PS simulation) Vertical dipolar impedance obtained by PS DFT Note: our transverse sign convention Inductive transverse is positive

21. 2) Outputs from Matlab DFT and PS DFT(inspired from ABCI) Real dipolar impedance Imaginary dipolar impedance Note: PS transverse sign convention Inductive transverse is negative

22. 3) Trivial check on the wake potential Zoom on SPS bunch length • As expected: • No loss of information • correct x and y axes units Wake potential = FFT-1(FFT(Wake potential))

23. 4) Wake function? Imaginary dipolar impedance Real dipolar impedance Exponentially diverging at high frequencies  Truncation around 15 GHz

24. 5) Truncation of the impedance:First check on getting back the wake potential Wake potential = FFT-1(FFT(Wake potential)) ? Wake potential = FFT-1(Truncation(FFT(Wake potential))) Here, the impedance is cut at 15 GHz Wake potential = FFT-1(Truncation(FFT(Wake potential)))

25. 5) Truncation of the impedance:getting the wake function Wake potential = FFT-1(FFT(Wake potential)) Wake potential = FFT-1(Truncation(FFT(Wake potential))) ? Wake function = FFT-1(Truncation(deconvolution(FFT(Wake potential)))) Here, the impedance is cut at 15 GHz

26. Bunch length rms= 10mm Bunch length rms= 5mm

27. BPH dipolar and quadrupolar wake functions for Headtail

28. BPV dipolar and quadrupolar wake functions for Headtail

29. Kickers + BPHs + BPVs

30. Kickers + BPHs + BPVs

31. Kickers + BPHs + BPVs+Beam pipe

32. Kickers + BPHs + BPVs + Beam pipe

33. Importing into headtail • Input wakes expected by Headtail are in V/pCmm • Distance is in m • Need to interpolate to be able to sum all contributions • Take into account the beta function at the BPM location: • At time=0, we assume the transverse wake function should be 0, and W(t=0)=0 before importing into Headtail.

34. Wake functions to be imported

35. Headtail simulations kickers only kickers+BPMs kickers+BPMs+beam pipe kickers only kickers+BPMs kickers+BPMs+beam pipe

36. Headtail simulations Vertical plane Horizontal plane

37. agenda • Crosscheck of the low frequency impedance • Issue with PS DFT? • Trapped mode parameters for PEC and lossy materials • Procedure to get the wake function for Headtail • Advantages and drawbacks of Particle Studio/Microwave studio.

38. Advantages and drawbacks of Particle Studio/Microwave studio. • Advantages • Easy and efficient postprocessing • Convenient to use the exact same models between frequency domain and time domain • Efficient helpdesk • Issues • Hexahedral mesh is not suited for circular shapes • DFT should be taken with care • Black box