From:	Elias Metral
Sent:	Wednesday, August 11, 2010 6:04 PM
To:	William Andreazza
Cc:	Benoit Salvant; Fritz Caspers; Alexej Grudiev; Federico Roncarolo; Rama 
Calaga
Subject:	New PS wire scanner

Dear William,
As promised, we send you our recommendation after all the electromagnetic 
simulations performed by Benoit and the discussions we had this morning at our 
ICE (Impedance and Collective Effects) meeting. You can find the talk given by 
Benoit at: https://emetral.web.cern.ch/emetral/ICEsection/Meeting_11-08-
10/CST%20simulations%20wire%20scanners.pptx. Benoit's summary (slide 30) is 
the following:

1) Need to check the new wire scanner design for the PS.
2) From these simulations, new design seems to create more longitudinal 
impedance and more losses (than the current one).
3) From the figures obtained, this increase does not appear huge.
4) What should we do?
- Recommendation for short term => Build like this and be ready to install 
ferrites if needed. 
- Recommendation for longer term => Compare these figures with simulation of 
the SPS wire that broke. Perform wire measurements when the tank is built. 
Optimise the position, shape and material of the ferrites

It should be noted that the power loss has been computed in one of the worst 
cases (LHC25 beam) where the short bunch length achieved only at the very end 
of the cycle, after a bunch rotation (meaning that the bunch length is always 
much longer than the value we considered, except for few tens of turns, which 
lead to much lower power losses).
Therefore, we are not yet convinced that ferrite is really necessary (but we 
still have also to look at all the transverse modes). However, ferrite seems 
to help (as expected) and if it is not installed too close to the beam (as it 
is the case on Benoit's slides) and not too close to a PS magnet (a distance 
of ~ 50 cm is safe) and if it does not break (with time...) its presence 
should only help.

After the phone call we just had we said that, if we decide not to install the 
ferrite now and if later we think it is better to install it, then we need to 
break the vacuum and install the 2 plates of ferrite but we said that it is an 
easy operation. A similar (easy) operation is needed if we install now the two 
plates of ferrite and we realize afterwards that we need to remove them.

Finally, taking into account the fact that the ferrite is already available 
and that, in the case we do not install the ferrite now, we need however 1) to 
identify exactly where we could add it, 2) to be sure that all the pieces of 
equipment are foreseen and ready to receive the 2 ferrite plates, and 3) to 
perform some further studies (transverse modes + comparison with the SPS 
case), we could be tempted to ask to install the ferrite now and ask to remove 
it afterwards in case of problem (quite unlikely). However, we must admit that 
in the present case we do not have a strong recommendation for one scenario or 
the other.

As a result, I would recommend to build the new tank with the 2 plates of 
ferrite installed (see positions on Benoit's slides), and it would be great if 
you could give us the new tank (once built) for few days to perform our usual 
impedance measurements. Would this be possible? We could then decide to remove 
the ferrite or not just before the PS installation.
Please tell me what you think.
Kind regards, Elias.