Agenda Lessons from TU Darmstadt New total wakes with CST 2010 Strip line pickups

Lessons from TU Darmstadt

ECHO Code (Igor Zagorodnov (DESY) could be used for very short bunches in collimators  interest for CLIC collimators PAC’06 (Zagorodnov and Bane) However, according to Wolfgang Mueller, the code is in a development state that does not allow for users at the moment. A. Tsakanian (also DESY) is also working on wakes of short XFEL bunches with conducting and ceramic pipes Maybe interesting to get in touch with them. As a follow-up of one of Bruno Spataro’s comments, Wolfgang also mentioned we should keep at least 3 mesh cells between the beam location and the integration path. The pencil beam is not so pencil in the neighboring mesh cell. Wolfgang advised to be careful with indirect integration techniques as they may be less noisy, but they may hide some issues by averaging. Ferrite materials are difficult to use in simulations (even non lossy ferrites). Without B. Doliwa’s routines, it is not recommended to try simulating in frequency domain. Time domain is OK, but one should be very careful with the mesh size inside the ferrite (thorough stability studies). Wolgang mentioned 100 times more mesh cells are likely needed in the ferrite than in the vacuum. Oliver Boine-Frankenheim mentioned that a new PhD student at GSI is working on kicker impedance. This could be an interesting collaboration as we share the same needs. Lukas is also planning to work on kickers simulations very soon. Thomas Weiland mentioned that using a stainless steel pipe surrounded by vacuum was not very realistic as most of the pipe length is surrounded by magnets… It may not matter for the frequency range of interest for the SPS, but it is very true! Thomas Weiland also mentioned over a beer that these multilayer impedances have already been derived for a long time.

Following the CST 2010 version New total wakes with CST for the BPM Following the CST 2010 version

Check with theoretical predictions Theoretical wake from Palumbo, Vaccaro, Zobov, INFN, 1994 Indirect integration Theoretical wake CST 2010 CST simulated wake CST 2009 Many thanks to Monika and Ulrich for having found quickly the issue! Factor 4.4 between theory and simulations!

With the 2010 CST version Larger impact of the BPMs

Headtail simulations with only the wake function from the BPMs (all BPVs and BPHs)  unstable between 2 1012 and 3 1012 p Nb= 2 1012 Nb= 3 1012

Remark on SPS striplines Oscillation builds up turn after turn. This oscillation seem to follow the bunch. Is that signal?

Data from SPS Headtail Monitor (long stripline) From R. Steinhagen Ripple following the bunch Bunch

From the directional coupler (40 cm exponential stripline)

Simulations on SPS Stripline pickups to understand the signals Signal measured at this port Initial generic stripline model from Clara Palau and Christian Boccard (BI) 20 cm rms bunch length 10 cm rms bunch length

No transition With elliptic/round transition Does this ripple also builds up with the number of bunches and/or the number of turns?

Simulations on SPS Stripline pickups to understand the signals Headtail monitor (60 cm long stripline) Directional coupler (40 cm exponential stripline) Ripples following the bunch building up were observed in the SPS measurements  as predicted by , likely due to the transition between the magnet elliptic chamber and round chamber

Exponential pickup in the wrong direction Exponential pickup in the right direction

Striplines seem to have a very small wake, but to be checked more thoroughly for the transverse plane. Also Wolfgang advised to check the simulated ripple for numerical error through mesh scans.